<?php // $Id: datalib.php,v 1.298.2.11 2006/10/08 19:44:34 skodak Exp $

/**
 * Library of functions for database manipulation.
 * 
 * Other main libraries:
 * - weblib.php - functions that produce web output
 * - moodlelib.php - general-purpose Moodle functions
 * @author Martin Dougiamas and many others
 * @version $Id: datalib.php,v 1.298.2.11 2006/10/08 19:44:34 skodak Exp $
 * @license http://www.gnu.org/copyleft/gpl.html GNU Public License
 * @package moodlecore
 */


/// GLOBAL CONSTANTS /////////////////////////////////////////////////////////


$empty_rs_cache = array();   // Keeps copies of the recordsets used in one invocation


/// FUNCTIONS FOR DATABASE HANDLING  ////////////////////////////////

/**
 * Execute a given sql command string
 *
 * Completely general function - it just runs some SQL and reports success.
 *
 * @uses $db
 * @param string $command The sql string you wish to be executed.
 * @param bool $feedback Set this argument to true if the results generated should be printed. Default is true.
 * @return string
 */
function execute_sql($command, $feedback=true) {
/// Completely general function - it just runs some SQL and reports success.

    global $db, $CFG;

    $olddebug = $db->debug;

    if (!$feedback) {
        $db->debug = false;
    }

    $empty_rs_cache = array();  // Clear out the cache, just in case changes were made to table structures

    if (defined('MDL_PERFDB')) { global $PERF ; $PERF->dbqueries++; };

    $result = $db->Execute($command);

    $db->debug = $olddebug;

    if ($result) {
        if ($feedback) {
            notify(get_string('success'), 'notifysuccess');
        }
        return true;
    } else {
        if ($feedback) {
            echo '<p><font color="red"><strong>'. get_string('error') .'</strong></font></p>';
        }
        if (!empty($CFG->dblogerror)) {
            $debug=array_shift(debug_backtrace());
            error_log("SQL ".$db->ErrorMsg()." in {$debug['file']} on line {$debug['line']}. STATEMENT:  $command");
        }
        return false;
    }
}
/**
* on DBs that support it, switch to transaction mode and begin a transaction
* you'll need to ensure you call commit_sql() or your changes *will* be lost
* this is _very_ useful for massive updates
*/
function begin_sql() {
/// Completely general function - it just runs some SQL and reports success.

    global $CFG;
    if ($CFG->dbtype === 'postgres7') {
        return execute_sql('BEGIN', false);
    }
    return true;
}
/**
* on DBs that support it, commit the transaction 
*/
function rollback_sql() {
/// Completely general function - it just runs some SQL and reports success.

    global $CFG;
    if ($CFG->dbtype === 'postgres7') {
        return execute_sql('ROLLBACK', false);
    }
    return true;
}



/**
 * returns db specific uppercase function
 */
function db_uppercase() {
    global $CFG;
    switch (strtolower($CFG->dbtype)) {

    case "postgres7":
        return "upper";

    case "mysql":
    default:
        return "ucase";

    }
}

/**
 * returns db specific lowercase function
 */
function db_lowercase() {
    global $CFG;
    switch (strtolower($CFG->dbtype)) {

    case "postgres7":
        return "lower";

    case "mysql":
    default:
        return "lcase";

    }
}

/**
* on DBs that support it, commit the transaction 
*/
function commit_sql() {
/// Completely general function - it just runs some SQL and reports success.

    global $CFG;
    if ($CFG->dbtype === 'postgres7') {
        return execute_sql('COMMIT', false);
    }
    return true;
}

/**
 * Run an arbitrary sequence of semicolon-delimited SQL commands
 *
 * Assumes that the input text (file or string) consists of
 * a number of SQL statements ENDING WITH SEMICOLONS.  The
 * semicolons MUST be the last character in a line.
 * Lines that are blank or that start with "#" or "--" (postgres) are ignored.
 * Only tested with mysql dump files (mysqldump -p -d moodle)
 *
 * @uses $CFG
 * @param string $sqlfile The path where a file with sql commands can be found on the server.
 * @param string $sqlstring If no path is supplied then a string with semicolon delimited sql 
 * commands can be supplied in this argument.
 * @return bool Returns true if databse was modified successfully.
 */
function modify_database($sqlfile='', $sqlstring='') {

    global $CFG;

    $success = true;  // Let's be optimistic

    if (!empty($sqlfile)) {
        if (!is_readable($sqlfile)) {
            $success = false;
            echo '<p>Tried to modify database, but "'. $sqlfile .'" doesn\'t exist!</p>';
            return $success;
        } else {
            $lines = file($sqlfile);
        }
    } else {
        $sqlstring = trim($sqlstring);
        if ($sqlstring{strlen($sqlstring)-1} != ";") {
            $sqlstring .= ";"; // add it in if it's not there.
        }
        $lines[] = $sqlstring;
    }

    $command = '';

    foreach ($lines as $line) {
        $line = rtrim($line);
        $length = strlen($line);

        if ($length and $line[0] <> '#' and $line[0].$line[1] <> '--') {
            if (substr($line, $length-1, 1) == ';') {
                $line = substr($line, 0, $length-1);   // strip ;
                $command .= $line;
                $command = str_replace('prefix_', $CFG->prefix, $command); // Table prefixes
                if (! execute_sql($command)) {
                    $success = false;
                }
                $command = '';
            } else {
                $command .= $line;
            }
        }
    }

    return $success;

}

/// FUNCTIONS TO MODIFY TABLES ////////////////////////////////////////////

/**
 * Add a new field to a table, or modify an existing one (if oldfield is defined).
 * Warning: Please be careful on primary keys, as this function will eat auto_increments
 * @uses $CFG
 * @uses $db
 * @param string $table ?
 * @param string $oldfield ?
 * @param string $field ?
 * @param string $type ?
 * @param string $size ?
 * @param string $signed ?
 * @param string $default ?
 * @param string $null ?
 * @todo Finish documenting this function
 */

function table_column($table, $oldfield, $field, $type='integer', $size='10',
                      $signed='unsigned', $default='0', $null='not null', $after='') {
    global $CFG, $db, $empty_rs_cache;

    if (!empty($empty_rs_cache[$table])) {  // Clear the recordset cache because it's out of date
        unset($empty_rs_cache[$table]);
    }

    switch (strtolower($CFG->dbtype)) {

        case 'mysql':
        case 'mysqlt':

            switch (strtolower($type)) {
                case 'text':
                    $type = 'TEXT';
                    $signed = '';
                    break;
                case 'integer':
                    $type = 'INTEGER('. $size .')';
                    break;
                case 'varchar':
                    $type = 'VARCHAR('. $size .')';
                    $signed = '';
                    break;
                case 'char':
                    $type = 'CHAR('. $size .')';
                    $signed = '';
                    break;
            }

            if (!empty($oldfield)) {
                $operation = 'CHANGE '. $oldfield .' '. $field;
            } else {
                $operation = 'ADD '. $field;
            }

            $default = 'DEFAULT \''. $default .'\'';

            if (!empty($after)) {
                $after = 'AFTER `'. $after .'`';
            }

            return execute_sql('ALTER TABLE '. $CFG->prefix . $table .' '. $operation .' '. $type .' '. $signed .' '. $default .' '. $null .' '. $after);

        case 'postgres7':        // From Petri Asikainen
            //Check db-version
            $dbinfo = $db->ServerInfo();
            $dbver = substr($dbinfo['version'],0,3);

            //to prevent conflicts with reserved words
            $realfield = '"'. $field .'"';
            $field = '"'. $field .'_alter_column_tmp"';
            $oldfield = '"'. $oldfield .'"';

            switch (strtolower($type)) {
                case 'tinyint':
                case 'integer':
                    if ($size <= 4) {
                        $type = 'INT2';
                    }
                    if ($size <= 10) {
                        $type = 'INT';
                    }
                    if  ($size > 10) {
                        $type = 'INT8';
                    }
                    break;
                case 'varchar':
                    $type = 'VARCHAR('. $size .')';
                    break;
                case 'char':
                    $type = 'CHAR('. $size .')';
                    $signed = '';
                    break;
            }

            $default = '\''. $default .'\'';

            //After is not implemented in postgesql
            //if (!empty($after)) {
            //    $after = "AFTER '$after'";
            //}

            //Use transactions
            execute_sql('BEGIN');

            //Always use temporary column
            execute_sql('ALTER TABLE '. $CFG->prefix . $table .' ADD COLUMN '. $field .' '. $type);
            //Add default values
            execute_sql('UPDATE '. $CFG->prefix . $table .' SET '. $field .'='. $default);


            if ($dbver >= '7.3') {
                // modifying 'not null' is posible before 7.3
                //update default values to table
                if (strtoupper($null) == 'NOT NULL') {
                    execute_sql('UPDATE '. $CFG->prefix . $table .' SET '. $field .'='. $default .' WHERE '. $field .' IS NULL');
                    execute_sql('ALTER TABLE '. $CFG->prefix . $table .' ALTER COLUMN '. $field .' SET '. $null);
                } else {
                    execute_sql('ALTER TABLE '. $CFG->prefix . $table .' ALTER COLUMN '. $field .' DROP NOT NULL');
                }
            }

            execute_sql('ALTER TABLE '. $CFG->prefix . $table .' ALTER COLUMN '. $field .' SET DEFAULT '. $default);

            if ( $oldfield != '""' ) {

                // We are changing the type of a column. This may require doing some casts...
                $casting = '';
                $oldtype = column_type($table, $oldfield);
                $newtype = column_type($table, $field);

                // Do we need a cast?
                if($newtype == 'N' && $oldtype == 'C') {
                    $casting = 'CAST(CAST('.$oldfield.' AS TEXT) AS REAL)';
                }
                else if($newtype == 'I' && $oldtype == 'C') {
                    $casting = 'CAST(CAST('.$oldfield.' AS TEXT) AS INTEGER)';
                }
                else {
                    $casting = $oldfield;
                }

                // Run the update query, casting as necessary
                execute_sql('UPDATE '. $CFG->prefix . $table .' SET '. $field .' = '. $casting);
                execute_sql('ALTER TABLE  '. $CFG->prefix . $table .' DROP COLUMN '. $oldfield);
            }

            execute_sql('ALTER TABLE '. $CFG->prefix . $table .' RENAME COLUMN '. $field .' TO '. $realfield);

            return execute_sql('COMMIT');

        default:
            switch (strtolower($type)) {
                case 'integer':
                    $type = 'INTEGER';
                    break;
                case 'varchar':
                    $type = 'VARCHAR';
                    break;
            }

            $default = 'DEFAULT \''. $default .'\'';

            if (!empty($after)) {
                $after = 'AFTER '. $after;
            }

            if (!empty($oldfield)) {
                execute_sql('ALTER TABLE '. $CFG->prefix . $table .' RENAME COLUMN '. $oldfield .' '. $field);
            } else {
                execute_sql('ALTER TABLE '. $CFG->prefix . $table .' ADD COLUMN '. $field .' '. $type);
            }

            execute_sql('ALTER TABLE '. $CFG->prefix . $table .' ALTER COLUMN '. $field .' SET '. $null);
            return execute_sql('ALTER TABLE '. $CFG->prefix . $table .' ALTER COLUMN '. $field .' SET '. $default);
    }
}

/**
 * Get the data type of a table column, using an ADOdb MetaType() call.
 *
 * @uses $CFG
 * @uses $db
 * @param string $table The name of the database table
 * @param string $column The name of the field in the table
 * @return string Field type or false if error
 */

function column_type($table, $column) {
    global $CFG, $db;

    if (defined('MDL_PERFDB')) { global $PERF ; $PERF->dbqueries++; };

    if(!$rs = $db->Execute('SELECT '.$column.' FROM '.$CFG->prefix.$table.' LIMIT 0')) {
        return false;
    }
    
    $field = $rs->FetchField(0);
    return $rs->MetaType($field->type);
}


/// GENERIC FUNCTIONS TO CHECK AND COUNT RECORDS ////////////////////////////////////////

/**
 * Test whether a record exists in a table where all the given fields match the given values.
 *
 * The record to test is specified by giving up to three fields that must
 * equal the corresponding values.
 *
 * @uses $CFG
 * @param string $table The table to check.
 * @param string $field1 the first field to check (optional).
 * @param string $value1 the value field1 must have (requred if field1 is given, else optional).
 * @param string $field2 the second field to check (optional).
 * @param string $value2 the value field2 must have (requred if field2 is given, else optional).
 * @param string $field3 the third field to check (optional).
 * @param string $value3 the value field3 must have (requred if field3 is given, else optional).
 * @return bool true if a matching record exists, else false.
 */
function record_exists($table, $field1='', $value1='', $field2='', $value2='', $field3='', $value3='') {

    global $CFG;

    $select = where_clause($field1, $value1, $field2, $value2, $field3, $value3);

    return record_exists_sql('SELECT * FROM '. $CFG->prefix . $table .' '. $select .' LIMIT 1');
}


/**
 * Test whether a SQL SELECT statement returns any records.
 *
 * This function returns true if the SQL statement executes
 * without any errors and returns at least one record.
 *
 * @param string $sql The SQL statement to execute.
 * @return bool true if the SQL executes without errors and returns at least one record.
 */
function record_exists_sql($sql) {
    $rs = get_recordset_sql($sql);

    if ($rs && $rs->RecordCount() > 0) {
        return true;
    } else {
        return false;
    }
}

/**
 * Count the records in a table where all the given fields match the given values.
 *
 * @uses $CFG
 * @param string $table The table to query.
 * @param string $field1 the first field to check (optional).
 * @param string $value1 the value field1 must have (requred if field1 is given, else optional).
 * @param string $field2 the second field to check (optional).
 * @param string $value2 the value field2 must have (requred if field2 is given, else optional).
 * @param string $field3 the third field to check (optional).
 * @param string $value3 the value field3 must have (requred if field3 is given, else optional).
 * @return int The count of records returned from the specified criteria.
 */
function count_records($table, $field1='', $value1='', $field2='', $value2='', $field3='', $value3='') {

    global $CFG;

    $select = where_clause($field1, $value1, $field2, $value2, $field3, $value3);

    return count_records_sql('SELECT COUNT(*) FROM '. $CFG->prefix . $table .' '. $select);
}

/**
 * Count the records in a table which match a particular WHERE clause.
 *
 * @uses $CFG
 * @param string $table The database table to be checked against.
 * @param string $select A fragment of SQL to be used in a WHERE clause in the SQL call.
 * @param string $countitem The count string to be used in the SQL call. Default is COUNT(*).
 * @return int The count of records returned from the specified criteria.
 */
function count_records_select($table, $select='', $countitem='COUNT(*)') {

    global $CFG;

    if ($select) {
        $select = 'WHERE '.$select;
    }

    return count_records_sql('SELECT '. $countitem .' FROM '. $CFG->prefix . $table .' '. $select);
}

/**
 * Get the result of a SQL SELECT COUNT(...) query.
 *
 * Given a query that counts rows, return that count. (In fact,
 * given any query, return the first field of the first record
 * returned. However, this method should only be used for the
 * intended purpose.) If an error occurrs, 0 is returned.
 *
 * @uses $CFG
 * @uses $db
 * @param string $sql The SQL string you wish to be executed.
 * @return int the count. If an error occurrs, 0 is returned.
 */
function count_records_sql($sql) {
    $rs = get_recordset_sql($sql);
    
    if ($rs) {
        return $rs->fields[0];
    } else {
        return 0;   
    }
}

/// GENERIC FUNCTIONS TO GET, INSERT, OR UPDATE DATA  ///////////////////////////////////

/**
 * Get a single record as an object
 *
 * @uses $CFG
 * @param string $table The table to select from.
 * @param string $field1 the first field to check (optional).
 * @param string $value1 the value field1 must have (requred if field1 is given, else optional).
 * @param string $field2 the second field to check (optional).
 * @param string $value2 the value field2 must have (requred if field2 is given, else optional).
 * @param string $field3 the third field to check (optional).
 * @param string $value3 the value field3 must have (requred if field3 is given, else optional).
 * @return mixed a fieldset object containing the first mathcing record, or false if none found.
 */
function get_record($table, $field1, $value1, $field2='', $value2='', $field3='', $value3='', $fields='*') {

    global $CFG;

    $select = where_clause($field1, $value1, $field2, $value2, $field3, $value3);

    return get_record_sql('SELECT '.$fields.' FROM '. $CFG->prefix . $table .' '. $select);
}

/**
 * Get a single record as an object using an SQL statement
 *
 * The SQL statement should normally only return one record. In debug mode
 * you will get a warning if more record is returned (unless you
 * set $expectmultiple to true). In non-debug mode, it just returns
 * the first record. 
 *
 * @uses $CFG
 * @uses $db
 * @param string $sql The SQL string you wish to be executed, should normally only return one record.
 * @param bool $expectmultiple If the SQL cannot be written to conviniently return just one record, 
 *      set this to true to hide the debug message.
 * @param bool $nolimit sometimes appending ' LIMIT 1' to the SQL causes an error. Set this to true
 *      to stop your SQL being modified. This argument should probably be deprecated.
 * @return Found record as object. False if not found or error
 */
function get_record_sql($sql, $expectmultiple=false, $nolimit=false) {

    global $CFG;

    if ($nolimit) {
        $limit = '';
    } else if ($expectmultiple) {
        $limit = ' LIMIT 1';
    } else if (isset($CFG->debug) && $CFG->debug > 7) {
        // Debugging mode - don't use a limit of 1, but do change the SQL, because sometimes that
        // causes errors, and in non-debug mode you don't see the error message and it is 
        // impossible to know what's wrong.
        $limit = ' LIMIT 100';
    } else {
        $limit = ' LIMIT 1';
    }

    if (!$rs = get_recordset_sql($sql . $limit)) {
        return false;   
    }
    
    $recordcount = $rs->RecordCount();

    if ($recordcount == 0) {          // Found no records
        return false; 

    } else if ($recordcount == 1) {    // Found one record
        return (object)$rs->fields;

    } else {                          // Error: found more than one record
        notify('Error:  Turn off debugging to hide this error.');
        notify($sql . $limit);
        if ($records = $rs->GetAssoc(true)) {
            notify('Found more than one record in get_record_sql !');
            print_object($records);
        } else {
            notify('Very strange error in get_record_sql !');
            print_object($rs);
        }
        print_continue("$CFG->wwwroot/$CFG->admin/config.php");
    }
}

/**
 * Gets one record from a table, as an object
 *
 * @uses $CFG
 * @param string $table The database table to be checked against.
 * @param string $select A fragment of SQL to be used in a where clause in the SQL call.
 * @param string $fields A comma separated list of fields to be returned from the chosen table.
 * @return object|false Returns an array of found records (as objects) or false if no records or error occured.
 */
function get_record_select($table, $select='', $fields='*') {

    global $CFG;

    if ($select) {
        $select = 'WHERE '. $select;
    }

    return get_record_sql('SELECT '. $fields .' FROM '. $CFG->prefix . $table .' '. $select);
}

/**
 * Get a number of records as an ADODB RecordSet.
 *
 * Selects records from the table $table.
 * 
 * If specified, only records where the field $field has value $value are retured.
 * 
 * If specified, the results will be sorted as specified by $sort. This
 * is added to the SQL as "ORDER BY $sort". Example values of $sort
 * mightbe "time ASC" or "time DESC".
 * 
 * If $fields is specified, only those fields are returned.
 *
 * This function is internal to datalib, and should NEVER should be called directly 
 * from general Moodle scripts.  Use get_record, get_records etc.
 * 
 * If you only want some of the records, specify $limitfrom and $limitnum.
 * The query will skip the first $limitfrom records (according to the sort
 * order) and then return the next $limitnum records. If either of $limitfrom
 * or $limitnum is specified, both must be present.
 * 
 * The return value is an ADODB RecordSet object
 * @link http://phplens.com/adodb/reference.functions.adorecordset.html
 * if the query succeeds. If an error occurrs, false is returned.
 *
 * @param string $table the table to query.
 * @param string $field a field to check (optional).
 * @param string $value the value the field must have (requred if field1 is given, else optional).
 * @param string $sort an order to sort the results in (optional, a valid SQL ORDER BY parameter).
 * @param string $fields a comma separated list of fields to return (optional, by default all fields are returned).
 * @param int $limitfrom return a subset of records, starting at this point (optional, required if $limitnum is set).
 * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
 * @return mixed an ADODB RecordSet object, or false if an error occured.
 */
function get_recordset($table, $field='', $value='', $sort='', $fields='*', $limitfrom='', $limitnum='') {

    if ($field) {
        $select = "$field = '$value'";
    } else {
        $select = '';
    }
    
    return get_recordset_select($table, $select, $sort, $fields, $limitfrom, $limitnum);
}

/**
 * Get a number of records as an ADODB RecordSet.
 *
 * If given, $select is used as the SELECT parameter in the SQL query,
 * otherwise all records from the table are returned.
 * 
 * Other arguments and the return type as for @see function get_recordset. 
 *
 * @uses $CFG
 * @param string $table the table to query.
 * @param string $select A fragment of SQL to be used in a where clause in the SQL call.
 * @param string $sort an order to sort the results in (optional, a valid SQL ORDER BY parameter).
 * @param string $fields a comma separated list of fields to return (optional, by default all fields are returned).
 * @param int $limitfrom return a subset of records, starting at this point (optional, required if $limitnum is set).
 * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
 * @return mixed an ADODB RecordSet object, or false if an error occured.
 */
function get_recordset_select($table, $select='', $sort='', $fields='*', $limitfrom='', $limitnum='') {

    global $CFG;

    if ($select) {
        $select = ' WHERE '. $select;
    }

    if ($limitfrom !== '') {
        $limit = sql_paging_limit($limitfrom, $limitnum);
    } else {
        $limit = '';
    }

    if ($sort) {
        $sort = ' ORDER BY '. $sort;
    }

    return get_recordset_sql('SELECT '. $fields .' FROM '. $CFG->prefix . $table . $select . $sort .' '. $limit);
}

/**
 * Get a number of records as an ADODB RecordSet.
 *
 * Only records where $field takes one of the values $values are returned.
 * $values should be a comma-separated list of values, for example "4,5,6,10"
 * or "'foo','bar','baz'".
 * 
 * Other arguments and the return type as for @see function get_recordset. 
 *
 * @param string $table the table to query.
 * @param string $field a field to check (optional).
 * @param string $values comma separated list of values the field must have (requred if field is given, else optional).
 * @param string $sort an order to sort the results in (optional, a valid SQL ORDER BY parameter).
 * @param string $fields a comma separated list of fields to return (optional, by default all fields are returned).
 * @param int $limitfrom return a subset of records, starting at this point (optional, required if $limitnum is set).
 * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
 * @return mixed an ADODB RecordSet object, or false if an error occured.
 */
function get_recordset_list($table, $field='', $values='', $sort='', $fields='*', $limitfrom='', $limitnum='') {

    if ($field) {
        $select = "$field IN ($values)";
    } else {
        $select = '';
    }

    return get_recordset_select($table, $select, $sort, $fields, $limitfrom, $limitnum);
}

/**
 * Get a number of records as an ADODB RecordSet.  $sql must be a complete SQL query.
 * This function is internal to datalib, and should NEVER should be called directly 
 * from general Moodle scripts.  Use get_record, get_records etc.
 *  
 * The return type is as for @see function get_recordset. 
 *
 * @uses $CFG
 * @uses $db
 * @param string $sql the SQL select query to execute.
 * @return mixed an ADODB RecordSet object, or false if an error occured.
 */
function get_recordset_sql($sql) {

    global $CFG, $db;

    if (defined('MDL_PERFDB')) { global $PERF ; $PERF->dbqueries++; };

    if (!$rs = $db->Execute($sql)) {
        if (isset($CFG->debug) and $CFG->debug > 7) {
            notify($db->ErrorMsg() .'<br /><br />'. $sql);
        }
        if (!empty($CFG->dblogerror)) {
            $debug=array_shift(debug_backtrace());
            error_log("SQL ".$db->ErrorMsg()." in {$debug['file']} on line {$debug['line']}. STATEMENT:  $sql");
        }
        return false;
    }

    return $rs;
}

/**
 * Utility function used by the following 4 methods.
 * 
 * @param object an ADODB RecordSet object.
 * @return mixed mixed an array of objects, or false if an error occured or the RecordSet was empty.
 */
function recordset_to_array($rs) {
    if ($rs && $rs->RecordCount() > 0) {
        if ($records = $rs->GetAssoc(true)) {
            foreach ($records as $key => $record) {
                $objects[$key] = (object) $record;
            }
            return $objects;
        } else {
            return false;
        }
    } else {
        return false;
    }
}

/**
 * Get a number of records as an array of objects.
 *
 * If the query succeeds and returns at least one record, the
 * return value is an array of objects, one object for each
 * record found. The array key is the value from the first 
 * column of the result set. The object associated with that key
 * has a member variable for each column of the results.
 *
 * @param string $table the table to query.
 * @param string $field a field to check (optional).
 * @param string $value the value the field must have (requred if field1 is given, else optional).
 * @param string $sort an order to sort the results in (optional, a valid SQL ORDER BY parameter).
 * @param string $fields a comma separated list of fields to return (optional, by default all fields are returned).
 * @param int $limitfrom return a subset of records, starting at this point (optional, required if $limitnum is set).
 * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
 * @return mixed an array of objects, or false if no records were found or an error occured.
 */
function get_records($table, $field='', $value='', $sort='', $fields='*', $limitfrom='', $limitnum='') {
    $rs = get_recordset($table, $field, $value, $sort, $fields, $limitfrom, $limitnum);
    return recordset_to_array($rs);
}

/**
 * Get a number of records as an array of objects.
 *
 * Return value as for @see function get_records.
 *
 * @param string $table the table to query.
 * @param string $select A fragment of SQL to be used in a where clause in the SQL call.
 * @param string $sort an order to sort the results in (optional, a valid SQL ORDER BY parameter).
 * @param string $fields a comma separated list of fields to return (optional, by default all fields are returned).
 * @param int $limitfrom return a subset of records, starting at this point (optional, required if $limitnum is set).
 * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
 * @return mixed an array of objects, or false if no records were found or an error occured.
 */
function get_records_select($table, $select='', $sort='', $fields='*', $limitfrom='', $limitnum='') {
    $rs = get_recordset_select($table, $select, $sort, $fields, $limitfrom, $limitnum);
    return recordset_to_array($rs);
}

/**
 * Get a number of records as an array of objects.
 *
 * Return value as for @see function get_records.
 *
 * @param string $table The database table to be checked against.
 * @param string $field The field to search
 * @param string $values Comma separated list of possible value
 * @param string $sort Sort order (as valid SQL sort parameter)
 * @param string $fields A comma separated list of fields to be returned from the chosen table.
 * @return mixed an array of objects, or false if no records were found or an error occured.
 */
function get_records_list($table, $field='', $values='', $sort='', $fields='*', $limitfrom='', $limitnum='') {
    $rs = get_recordset_list($table, $field, $values, $sort, $fields, $limitfrom, $limitnum);
    return recordset_to_array($rs);
}

/**
 * Get a number of records as an array of objects.
 *
 * Return value as for @see function get_records.
 * 
 * @param string $sql the SQL select query to execute.
 * @return mixed an array of objects, or false if no records were found or an error occured.
 */
function get_records_sql($sql) {
    $rs = get_recordset_sql($sql);
    return recordset_to_array($rs);
}

/**
 * Utility function used by the following 3 methods.
 * 
 * @param object an ADODB RecordSet object with two columns.
 * @return mixed an associative array, or false if an error occured or the RecordSet was empty.
 */
function recordset_to_menu($rs) {
    if ($rs && $rs->RecordCount() > 0) {
        while (!$rs->EOF) {
            $menu[$rs->fields[0]] = $rs->fields[1];
            $rs->MoveNext();
        }
        return $menu;
    } else {
        return false;
    }
}

/**
 * Get the first two columns from a number of records as an associative array.
 *
 * Arguments as for @see function get_recordset.
 * 
 * If no errors occur, and at least one records is found, the return value
 * is an associative whose keys come from the first field of each record,
 * and whose values are the corresponding second fields. If no records are found,
 * or an error occurs, false is returned.
 *
 * @param string $table the table to query.
 * @param string $field a field to check (optional).
 * @param string $value the value the field must have (requred if field1 is given, else optional).
 * @param string $sort an order to sort the results in (optional, a valid SQL ORDER BY parameter).
 * @param string $fields a comma separated list of fields to return (optional, by default all fields are returned).
 * @return mixed an associative array, or false if no records were found or an error occured.
 */
function get_records_menu($table, $field='', $value='', $sort='', $fields='*') {
    $rs = get_recordset($table, $field, $value, $sort, $fields);
    return recordset_to_menu($rs);
}

/**
 * Get the first two columns from a number of records as an associative array.
 *
 * Arguments as for @see function get_recordset_select.
 * Return value as for @see function get_records_menu.
 *
 * @param string $table The database table to be checked against.
 * @param string $select A fragment of SQL to be used in a where clause in the SQL call.
 * @param string $sort Sort order (optional) - a valid SQL order parameter
 * @param string $fields A comma separated list of fields to be returned from the chosen table.
 * @return mixed an associative array, or false if no records were found or an error occured.
 */
function get_records_select_menu($table, $select='', $sort='', $fields='*') {
    $rs = get_recordset_select($table, $select, $sort, $fields);
    return recordset_to_menu($rs);
}

/**
 * Get the first two columns from a number of records as an associative array.
 *
 * Arguments as for @see function get_recordset_sql.
 * Return value as for @see function get_records_menu.
 *
 * @param string $sql The SQL string you wish to be executed.
 * @return mixed an associative array, or false if no records were found or an error occured.
 */
function get_records_sql_menu($sql) {
    $rs = get_recordset_sql($sql);
    return recordset_to_menu($rs);
}

/**
 * Get a single value from a table row where all the given fields match the given values.
 *
 * @param string $table the table to query.
 * @param string $return the field to return the value of.
 * @param string $field1 the first field to check (optional).
 * @param string $value1 the value field1 must have (requred if field1 is given, else optional).
 * @param string $field2 the second field to check (optional).
 * @param string $value2 the value field2 must have (requred if field2 is given, else optional).
 * @param string $field3 the third field to check (optional).
 * @param string $value3 the value field3 must have (requred if field3 is given, else optional).
 * @return mixed the specified value, or false if an error occured.
 */
function get_field($table, $return, $field1, $value1, $field2='', $value2='', $field3='', $value3='') {
   
    global $CFG;
    $select = where_clause($field1, $value1, $field2, $value2, $field3, $value3);

    $rs = get_recordset_sql('SELECT ' . $return . ' FROM ' . $CFG->prefix . $table . ' ' . $select);

    if ($rs && $rs->RecordCount() == 1) {
        return $rs->fields[$return];
    } else {
        return false;
    }
}

/**
 * Get a single value from a table.
 *
 * @param string $sql an SQL statement expected to return a single value.
 * @return mixed the specified value, or false if an error occured.
 */
function get_field_sql($sql) {

    $rs = get_recordset_sql($sql);

    if ($rs && $rs->RecordCount() == 1) {
        return $rs->fields[0];
    } else {
        return false;
    }
}

/**
 * Get an array of data from one or more fields from a database 
 * use to get a column, or a series of distinct values
 *
 * @uses $CFG
 * @uses $db
 * @param string $sql The SQL string you wish to be executed.
 * @return mixed|false Returns the value return from the SQL statment or false if an error occured.
 * @todo Finish documenting this function
 */
function get_fieldset_sql($sql) {

    global $db, $CFG;

    if (defined('MDL_PERFDB')) { global $PERF ; $PERF->dbqueries++; };

    $rs = $db->Execute($sql);
    if (!$rs) {
        if (isset($CFG->debug) and $CFG->debug > 7) {
            notify($db->ErrorMsg() .'<br /><br />'. $sql);
        }
        if (!empty($CFG->dblogerror)) {
            $debug=array_shift(debug_backtrace());
            error_log("SQL ".$db->ErrorMsg()." in {$debug['file']} on line {$debug['line']}. STATEMENT:  $sql");
        }
        return false;
    }

    if ( $rs->RecordCount() > 0 ) {
        $results = array();
        while (!$rs->EOF) {
            array_push($results, $rs->fields[0]);
            $rs->MoveNext();
        }
        return $results;
    } else {
        return false;
    }
}

/**
 * Set a single field in every table row where all the given fields match the given values.
 *
 * @uses $CFG
 * @uses $db
 * @param string $table The database table to be checked against.
 * @param string $newfield the field to set.
 * @param string $newvalue the value to set the field to.
 * @param string $field1 the first field to check (optional).
 * @param string $value1 the value field1 must have (requred if field1 is given, else optional).
 * @param string $field2 the second field to check (optional).
 * @param string $value2 the value field2 must have (requred if field2 is given, else optional).
 * @param string $field3 the third field to check (optional).
 * @param string $value3 the value field3 must have (requred if field3 is given, else optional).
 * @return mixed An ADODB RecordSet object with the results from the SQL call or false.
 */
function set_field($table, $newfield, $newvalue, $field1, $value1, $field2='', $value2='', $field3='', $value3='') {

    global $db, $CFG;

    if (defined('MDL_PERFDB')) { global $PERF ; $PERF->dbqueries++; };

    $select = where_clause($field1, $value1, $field2, $value2, $field3, $value3);

    return $db->Execute('UPDATE '. $CFG->prefix . $table .' SET '. $newfield  .' = \''. $newvalue .'\' '. $select);
}

/**
 * Delete the records from a table where all the given fields match the given values.
 *
 * @uses $CFG
 * @uses $db
 * @param string $table the table to delete from.
 * @param string $field1 the first field to check (optional).
 * @param string $value1 the value field1 must have (requred if field1 is given, else optional).
 * @param string $field2 the second field to check (optional).
 * @param string $value2 the value field2 must have (requred if field2 is given, else optional).
 * @param string $field3 the third field to check (optional).
 * @param string $value3 the value field3 must have (requred if field3 is given, else optional).
 * @return mixed An ADODB RecordSet object with the results from the SQL call or false.
 */
function delete_records($table, $field1='', $value1='', $field2='', $value2='', $field3='', $value3='') {

    global $db, $CFG;

    if (defined('MDL_PERFDB')) { global $PERF ; $PERF->dbqueries++; };

    $select = where_clause($field1, $value1, $field2, $value2, $field3, $value3);

    return $db->Execute('DELETE FROM '. $CFG->prefix . $table .' '. $select);
}

/**
 * Delete one or more records from a table
 *
 * @uses $CFG
 * @uses $db
 * @param string $table The database table to be checked against.
 * @param string $select A fragment of SQL to be used in a where clause in the SQL call (used to define the selection criteria).
 * @return object A PHP standard object with the results from the SQL call.
 * @todo Verify return type.
 */
function delete_records_select($table, $select='') {

    global $CFG, $db;

    if (defined('MDL_PERFDB')) { global $PERF ; $PERF->dbqueries++; };

    if ($select) {
        $select = 'WHERE '.$select;
    }

    return $db->Execute('DELETE FROM '. $CFG->prefix . $table .' '. $select);
}

/**
 * Insert a record into a table and return the "id" field if required
 *
 * If the return ID isn't required, then this just reports success as true/false.
 * $dataobject is an object containing needed data
 *
 * @uses $db
 * @uses $CFG
 * @param string $table The database table to be checked against.
 * @param array $dataobject A data object with values for one or more fields in the record
 * @param bool $returnid Should the id of the newly created record entry be returned? If this option is not requested then true/false is returned.
 * @param string $primarykey The primary key of the table we are inserting into (almost always "id")
 */
function insert_record($table, $dataobject, $returnid=true, $primarykey='id') {

    global $db, $CFG, $empty_rs_cache;

    if (defined('MDL_PERFDB')) { global $PERF ; $PERF->dbqueries++; };

/// In Moodle we always use auto-numbering fields for the primary key
/// so let's unset it now before it causes any trouble later
    unset($dataobject->{$primarykey});

/// Get an empty recordset. Cache for multiple inserts.
    if (empty($empty_rs_cache[$table])) {
        /// Execute a dummy query to get an empty recordset
        if (!$empty_rs_cache[$table] = $db->Execute('SELECT * FROM '. $CFG->prefix . $table .' WHERE '. $primarykey  .' = \'-1\'')) {
            return false;
        }
    }

    $rs = $empty_rs_cache[$table];

/// Postgres doesn't have the concept of primary key built in
/// and will return the OID which isn't what we want.
/// The efficient and transaction-safe strategy is to 
/// move the sequence forward first, and make the insert
/// with an explicit id.
    if ( $CFG->dbtype === 'postgres7' && $returnid == true ) {
        if ($nextval = (int)get_field_sql("SELECT NEXTVAL('{$CFG->prefix}{$table}_{$primarykey}_seq')")) {
            $dataobject->{$primarykey} = $nextval;            
        } 
    }

/// Get the correct SQL from adoDB
    if (!$insertSQL = $db->GetInsertSQL($rs, (array)$dataobject, true)) {
        return false;
    }

/// Run the SQL statement
    if (!$rs = $db->Execute($insertSQL)) {
        if (isset($CFG->debug) and $CFG->debug > 7) {
            notify($db->ErrorMsg() .'<br /><br />'.$insertSQL);
        }
        if (!empty($CFG->dblogerror)) {
            $debug=array_shift(debug_backtrace());
            error_log("SQL ".$db->ErrorMsg()." in {$debug['file']} on line {$debug['line']}. STATEMENT:  $insertSQL");
        }
        return false;
    }

/// If a return ID is not needed then just return true now
    if (!$returnid) {
        return true;
    }

/// We already know the record PK if it's been passed explicitly,
/// or if we've retrieved it from a sequence (Postgres).
    if (!empty($dataobject->{$primarykey})) {
        return $dataobject->{$primarykey};
    }

/// This only gets triggered with non-Postgres databases
/// however we have some postgres fallback in case we failed 
/// to find the sequence.
    $id = $db->Insert_ID();  

    if ($CFG->dbtype === 'postgres7') {
        // try to get the primary key based on id
        if ( ($rs = $db->Execute('SELECT '. $primarykey .' FROM '. $CFG->prefix . $table .' WHERE oid = '. $id))
             && ($rs->RecordCount() == 1) ) {
            trigger_error("Retrieved $primarykey from oid on table $table because we could not find the sequence.");
            return (integer)$rs->fields[0];
        } 
        trigger_error('Failed to retrieve primary key after insert: SELECT '. $primarykey .
                      ' FROM '. $CFG->prefix . $table .' WHERE oid = '. $id);
        return false;
    }

    return (integer)$id;
}

/** 
 * Escape all dangerous characters in a data record
 *
 * $dataobject is an object containing needed data
 * Run over each field exectuting addslashes() function
 * to escape SQL unfriendly characters (e.g. quotes)
 * Handy when writing back data read from the database
 *
 * @param $dataobject Object containing the database record
 * @return object Same object with neccessary characters escaped
 */
function addslashes_object( $dataobject ) {
    $a = get_object_vars( $dataobject);
    foreach ($a as $key=>$value) {
      $a[$key] = addslashes( $value );
    }
    return (object)$a;
}

/**
 * Update a record in a table
 *
 * $dataobject is an object containing needed data
 * Relies on $dataobject having a variable "id" to
 * specify the record to update
 *
 * @uses $CFG
 * @uses $db
 * @param string $table The database table to be checked against.
 * @param array $dataobject An object with contents equal to fieldname=>fieldvalue. Must have an entry for 'id' to map to the table specified.
 * @return bool
 */
function update_record($table, $dataobject) {

    global $db, $CFG;

    if (! isset($dataobject->id) ) {
        return false;
    }

    // Determine all the fields in the table
    if (!$columns = $db->MetaColumns($CFG->prefix . $table)) {
        return false;
    }
    $data = (array)$dataobject;

    if (defined('MDL_PERFDB')) { global $PERF ; $PERF->dbqueries++; };

    // Pull out data matching these fields
    foreach ($columns as $column) {
        if ($column->name <> 'id' and isset($data[$column->name]) ) {
            $ddd[$column->name] = $data[$column->name];
            // PostgreSQL bytea support
            if ($CFG->dbtype == 'postgres7' && $column->type == 'bytea') {
                $ddd[$column->name] = $db->BlobEncode($ddd[$column->name]);
            }
        }
    }

    // Construct SQL queries
    $numddd = count($ddd);
    $count = 0;
    $update = '';

    foreach ($ddd as $key => $value) {
        $count++;
        $update .= $key .' = \''. $value .'\'';   // All incoming data is already quoted
        if ($count < $numddd) {
            $update .= ', ';
        }
    }

    if ($rs = $db->Execute('UPDATE '. $CFG->prefix . $table .' SET '. $update .' WHERE id = \''. $dataobject->id .'\'')) {
        return true;
    } else {
        if (isset($CFG->debug) and $CFG->debug > 7) {
            notify($db->ErrorMsg() .'<br /><br />UPDATE '. $CFG->prefix . $table .' SET '. $update .' WHERE id = \''. $dataobject->id .'\'');
        }
        if (!empty($CFG->dblogerror)) {
            $debug=array_shift(debug_backtrace());
            error_log("SQL ".$db->ErrorMsg()." in {$debug['file']} on line {$debug['line']}. STATEMENT:  UPDATE $CFG->prefix$table SET $update WHERE id = '$dataobject->id'");
        }
        return false;
    }
}




/// USER DATABASE ////////////////////////////////////////////////

/**
 * Get the guest user information from the database
 *
 * @return object(user) An associative array with the details of the guest user account.
 * @todo Is object(user) a correct return type? Or is array the proper return type with a note that the contents include all details for a user.
 */
function get_guest() {
    return get_complete_user_data('username', 'guest');
}


/**
 * Returns $user object of the main admin user
 *
 * @uses $CFG
 * @return object(admin) An associative array representing the admin user.
 * @todo Verify documentation of this function
 */
function get_admin () {

    global $CFG;

    if ( $admins = get_admins() ) {
        foreach ($admins as $admin) {
            return $admin;   // ie the first one
        }
    } else {
        return false;
    }
}

/**
 * Returns list of all admins
 *
 * @uses $CFG
 * @return object
 */
function get_admins() {

    global $CFG;

    return get_records_sql("SELECT u.*, a.id as adminid
                              FROM {$CFG->prefix}user u,
                                   {$CFG->prefix}user_admins a
                             WHERE a.userid = u.id
                             ORDER BY a.id ASC");
}

/**
 * Returns list of all creators
 *
 * @uses $CFG
 * @return object
 */
function get_creators() {

    global $CFG;

    return get_records_sql("SELECT u.*
                              FROM {$CFG->prefix}user u,
                                   {$CFG->prefix}user_coursecreators a
                             WHERE a.userid = u.id
                             ORDER BY u.id ASC");
}

function get_courses_in_metacourse($metacourseid) {
    global $CFG;

    $sql = "SELECT c.id,c.shortname,c.fullname FROM {$CFG->prefix}course c, {$CFG->prefix}course_meta mc WHERE mc.parent_course = $metacourseid
        AND mc.child_course = c.id ORDER BY c.shortname";

    return get_records_sql($sql);
}

function get_courses_notin_metacourse($metacourseid,$count=false) {

    global $CFG;

    if ($count) {
        $sql  = "SELECT COUNT(c.id)";
    } else {
        $sql = "SELECT c.id,c.shortname,c.fullname";
    }

    $alreadycourses = get_courses_in_metacourse($metacourseid);
    
    $sql .= " FROM {$CFG->prefix}course c WHERE ".((!empty($alreadycourses)) ? "c.id NOT IN (".implode(',',array_keys($alreadycourses)).")
    AND " : "")." c.id !=$metacourseid and c.id != ".SITEID." and c.metacourse != 1 ".((empty($count)) ? " ORDER BY c.shortname" : "");
    
    return get_records_sql($sql);
}


/**
 * Returns $user object of the main teacher for a course
 *
 * @uses $CFG
 * @param int $courseid The course in question.
 * @return user|false  A {@link $USER} record of the main teacher for the specified course or false if error.
 * @todo Finish documenting this function
 */
function get_teacher($courseid) {

    global $CFG;

    if ( $teachers = get_course_teachers($courseid, 't.authority ASC')) {
        foreach ($teachers as $teacher) {
            if ($teacher->authority) {
                return $teacher;   // the highest authority teacher
            }
        }
    } else {
        return false;
    }
}

/**
 * Searches logs to find all enrolments since a certain date
 *
 * used to print recent activity
 *
 * @uses $CFG
 * @param int $courseid The course in question.
 * @return object|false  {@link $USER} records or false if error.
 * @todo Finish documenting this function
 */
function get_recent_enrolments($courseid, $timestart) {

    global $CFG;

    return get_records_sql("SELECT DISTINCT u.id, u.firstname, u.lastname, l.time
                            FROM {$CFG->prefix}user u,
                                 {$CFG->prefix}user_students s,
                                 {$CFG->prefix}log l
                            WHERE l.time > '$timestart'
                              AND l.course = '$courseid'
                              AND l.module = 'course'
                              AND l.action = 'enrol'
                              AND l.info = u.id
                              AND u.id = s.userid
                              AND s.course = '$courseid'
                              ORDER BY l.time ASC");
}

/**
 * Returns array of userinfo of all students in this course
 * or on this site if courseid is id of site
 *
 * @uses $CFG
 * @uses SITEID
 * @param int $courseid The course in question.
 * @param string $sort ?
 * @param string $dir ?
 * @param int $page ?
 * @param int $recordsperpage ?
 * @param string $firstinitial ?
 * @param string $lastinitial ?
 * @param ? $group ?
 * @param string $search ?
 * @param string $fields A comma separated list of fields to be returned from the chosen table.
 * @param string $exceptions ?
 * @return object
 * @todo Finish documenting this function
 */
function get_course_students($courseid, $sort='s.timeaccess', $dir='', $page=0, $recordsperpage=99999,
                             $firstinitial='', $lastinitial='', $group=NULL, $search='', $fields='', $exceptions='') {

    global $CFG;

    if ($courseid == SITEID and $CFG->allusersaresitestudents) {
        // return users with confirmed, undeleted accounts who are not site teachers
        // the following is a mess because of different conventions in the different user functions
        $sort = str_replace('s.timeaccess', 'lastaccess', $sort); // site users can't be sorted by timeaccess
        $sort = str_replace('timeaccess', 'lastaccess', $sort); // site users can't be sorted by timeaccess
        $sort = str_replace('u.', '', $sort); // the get_user function doesn't use the u. prefix to fields
        $fields = str_replace('u.', '', $fields);
        if ($sort) {
            $sort = $sort .' '. $dir;
        }
        // Now we have to make sure site teachers are excluded
        if ($teachers = get_records('user_teachers', 'course', SITEID)) {
            foreach ($teachers as $teacher) {
                $exceptions .= ','. $teacher->userid;
            }
            $exceptions = ltrim($exceptions, ',');
        }
        return get_users(true, $search, true, $exceptions, $sort, $firstinitial, $lastinitial,
                          $page, $recordsperpage, $fields ? $fields : '*');
    }

    $limit     = sql_paging_limit($page, $recordsperpage);
    $LIKE      = sql_ilike();
    $fullname  = sql_fullname('u.firstname','u.lastname');

    $groupmembers = '';

    // make sure it works on the site course
    $select = 's.course = \''. $courseid .'\' AND ';
    if ($courseid == SITEID) {
        $select = '';
    }

    $select .= 's.userid = u.id AND u.deleted = \'0\' ';

    if (!$fields) {
        $fields = 'u.id, u.confirmed, u.username, u.firstname, u.lastname, '.
                  'u.maildisplay, u.mailformat, u.maildigest, u.email, u.city, '.
                  'u.country, u.picture, u.idnumber, u.department, u.institution, '.
                  'u.emailstop, u.lang, u.timezone, s.timeaccess as lastaccess';
    }

    if ($search) {
        $search = ' AND ('. $fullname .' '. $LIKE .'\'%'. $search .'%\' OR email '. $LIKE .'\'%'. $search .'%\') ';
    }

    if ($firstinitial) {
        $select .= ' AND u.firstname '. $LIKE .'\''. $firstinitial .'%\' ';
    }

    if ($lastinitial) {
        $select .= ' AND u.lastname '. $LIKE .'\''. $lastinitial .'%\' ';
    }

    if ($group === 0) {   /// Need something here to get all students not in a group
        return array();

    } else if ($group !== NULL) {
        $groupmembers = ', '. $CFG->prefix .'groups_members gm ';
        $select .= ' AND u.id = gm.userid AND gm.groupid = \''. $group .'\'';
    }

    if (!empty($exceptions)) {
        $select .= ' AND u.id NOT IN ('. $exceptions .')';
    }

    if ($sort) {
        $sort = ' ORDER BY '. $sort .' ';
    }

    $students = get_records_sql("SELECT $fields
                            FROM {$CFG->prefix}user u,
                                 {$CFG->prefix}user_students s
                                 $groupmembers
                            WHERE $select $search $sort $dir $limit");

    if ($courseid != SITEID) {
        return $students;
    }

    // We are here because we need the students for the site.
    // These also include teachers on real courses minus those on the site
    if ($teachers = get_records('user_teachers', 'course', SITEID)) {
        foreach ($teachers as $teacher) {
            $exceptions .= ','. $teacher->userid;
        }
        $exceptions = ltrim($exceptions, ',');
        $select .= ' AND u.id NOT IN ('. $exceptions .')';
    }
    if (!$teachers = get_records_sql("SELECT $fields
                            FROM {$CFG->prefix}user u,
                                 {$CFG->prefix}user_teachers s
                                 $groupmembers
                            WHERE $select $search $sort $dir $limit")) {
        return $students;
    }
    if (!$students) {
        return $teachers;
    }
    return $teachers + $students;
}


/**
 * Counts the students in a given course (or site), or a subset of them
 *
 * @param object $course The course in question as a course object.
 * @param string $search ?
 * @param string $firstinitial ? 
 * @param string $lastinitial ?
 * @param ? $group ?
 * @param string $exceptions ? 
 * @return int
 * @todo Finish documenting this function
 */
function count_course_students($course, $search='', $firstinitial='', $lastinitial='', $group=NULL, $exceptions='') {

    if ($students = get_course_students($course->id, '', '', 0, 999999, $firstinitial, $lastinitial, $group, $search, '', $exceptions)) {
        return count($students);
    }
    return 0;
}


/**
 * Returns list of all teachers in this course
 *
 * If $courseid matches the site id then this function
 * returns a list of all teachers for the site.
 *
 * @uses $CFG
 * @param int $courseid The course in question.
 * @param string $sort ?
 * @param string $exceptions ? 
 * @return object
 * @todo Finish documenting this function
 */
function get_course_teachers($courseid, $sort='t.authority ASC', $exceptions='') {

    global $CFG;

    if (!empty($exceptions)) {
        $exceptions = ' AND u.id NOT IN ('. $exceptions .') ';
    }

    if (!empty($sort)) {
        $sort = ' ORDER by '.$sort;
    }

    return get_records_sql("SELECT u.id, u.username, u.firstname, u.lastname, u.maildisplay, u.mailformat, u.maildigest,
                                   u.email, u.city, u.country, u.lastlogin, u.picture, u.lang, u.timezone,
                                   u.emailstop, t.authority,t.role,t.editall,t.timeaccess as lastaccess
                            FROM {$CFG->prefix}user u,
                                 {$CFG->prefix}user_teachers t
                            WHERE t.course = '$courseid' AND t.userid = u.id
                              AND u.deleted = '0' AND u.confirmed = '1' $exceptions $sort");
}

/**
 * Returns all the users of a course: students and teachers
 *
 * @param int $courseid The course in question.
 * @param string $sort ?
 * @param string $exceptions ?
 * @param string $fields A comma separated list of fields to be returned from the chosen table.
 * @return object
 * @todo Finish documenting this function
 */
function get_course_users($courseid, $sort='timeaccess DESC', $exceptions='', $fields='') {

    /// Using this method because the single SQL is too inefficient
    // Note that this has the effect that teachers and students are
    // sorted individually. Returns first all teachers, then all students

    if (!$teachers = get_course_teachers($courseid, $sort, $exceptions)) {
        $teachers = array();
    }
    if (!$students = get_course_students($courseid, $sort, '', 0, 99999, '', '', NULL, '', $fields, $exceptions)) {
        $students = array();
    }

    return $teachers + $students;

}

/**
 * Search through course users
 *
 * If $coursid specifies the site course then this function searches 
 * through all undeleted and confirmed users
 *
 * @uses $CFG
 * @uses SITEID
 * @param int $courseid The course in question.
 * @param int $groupid The group in question.
 * @param string $searchtext ?
 * @param string $sort ?
 * @param string $exceptions ? 
 * @return object
 * @todo Finish documenting this function
 */
function search_users($courseid, $groupid, $searchtext, $sort='', $exceptions='') {
    global $CFG;

    $LIKE      = sql_ilike();
    $fullname  = sql_fullname('u.firstname', 'u.lastname');

    if (!empty($exceptions)) {
        $except = ' AND u.id NOT IN ('. $exceptions .') ';
    } else {
        $except = '';
    }

    if (!empty($sort)) {
        $order = ' ORDER BY '. $sort;
    } else {
        $order = '';
    }

    $select = 'u.deleted = \'0\' AND u.confirmed = \'1\'';

    if (!$courseid or $courseid == SITEID) {
        return get_records_sql("SELECT u.id, u.firstname, u.lastname, u.email
                      FROM {$CFG->prefix}user u
                      WHERE $select
                          AND ($fullname $LIKE '%$searchtext%' OR u.email $LIKE '%$searchtext%')
                          $except $order");
    } else {

        if ($groupid) {
            return get_records_sql("SELECT u.id, u.firstname, u.lastname, u.email
                          FROM {$CFG->prefix}user u,
                               {$CFG->prefix}groups_members g
                          WHERE $select AND g.groupid = '$groupid' AND g.userid = u.id
                              AND ($fullname $LIKE '%$searchtext%' OR u.email $LIKE '%$searchtext%')
                              $except $order");
        } else {
            if (!$teachers = get_records_sql("SELECT u.id, u.firstname, u.lastname, u.email
                          FROM {$CFG->prefix}user u,
                               {$CFG->prefix}user_teachers s
                          WHERE $select AND s.course = '$courseid' AND s.userid = u.id
                              AND ($fullname $LIKE '%$searchtext%' OR u.email $LIKE '%$searchtext%')
                              $except $order")) {
                $teachers = array();
            }
            if (!$students = get_records_sql("SELECT u.id, u.firstname, u.lastname, u.email
                          FROM {$CFG->prefix}user u,
                               {$CFG->prefix}user_students s
                          WHERE $select AND s.course = '$courseid' AND s.userid = u.id
                              AND ($fullname $LIKE '%$searchtext%' OR u.email $LIKE '%$searchtext%')
                              $except $order")) {
                $students = array();
            }
            return $teachers + $students;
        }
    }
}


/**
 * Returns a list of all site users
 * Obsolete, just calls get_course_users(SITEID)
 *
 * @uses SITEID
 * @deprecated Use {@link get_course_users()} instead.
 * @param string $fields A comma separated list of fields to be returned from the chosen table.
 * @return object|false  {@link $USER} records or false if error.
 * @todo Finish documenting this function. The return type need to be better defined.
 */
function get_site_users($sort='u.lastaccess DESC', $fields='*', $exceptions='') {

    return get_course_users(SITEID, $sort, $exceptions, $fields);
}


/**
 * Returns a subset of users
 *
 * @uses $CFG
 * @param bool $get If false then only a count of the records is returned
 * @param string $search A simple string to search for
 * @param bool $confirmed A switch to allow/disallow unconfirmed users
 * @param array(int) $exceptions A list of IDs to ignore, eg 2,4,5,8,9,10
 * @param string $sort A SQL snippet for the sorting criteria to use
 * @param string $firstinitial ?
 * @param string $lastinitial ?
 * @param string $page ?
 * @param string $recordsperpage ?
 * @param string $fields A comma separated list of fields to be returned from the chosen table.
 * @return object|false|int  {@link $USER} records unless get is false in which case the integer count of the records found is returned. False is returned if an error is encountered.
 * @todo Finish documenting this function. The return type needs to be better defined.
 */
function get_users($get=true, $search='', $confirmed=false, $exceptions='', $sort='firstname ASC',
                   $firstinitial='', $lastinitial='', $page=0, $recordsperpage=99999, $fields='*') {

    global $CFG;

    $limit     = sql_paging_limit($page, $recordsperpage);
    $LIKE      = sql_ilike();
    $fullname  = sql_fullname();

    $select = 'username <> \'guest\' AND username <> \'changeme\' AND deleted = 0';

    if (!empty($search)){
        $search = trim($search);
        $select .= " AND ($fullname $LIKE '%$search%' OR email $LIKE '%$search%') ";
    }

    if ($confirmed) {
        $select .= ' AND confirmed = \'1\' ';
    }

    if ($exceptions) {
        $select .= ' AND id NOT IN ('. $exceptions .') ';
    }

    if ($firstinitial) {
        $select .= ' AND firstname '. $LIKE .' \''. $firstinitial .'%\'';
    }
    if ($lastinitial) {
        $select .= ' AND lastname '. $LIKE .' \''. $lastinitial .'%\'';
    }

    if ($sort and $get) {
        $sort = ' ORDER BY '. $sort .' ';
    } else {
        $sort = '';
    }

    if ($get) {
        return get_records_select('user', $select .' '. $sort .' '. $limit, '', $fields);
    } else {
        return count_records_select('user', $select .' '. $sort .' '. $limit);
    }
}


/**
 * shortdesc (optional)
 *
 * longdesc
 *
 * @uses $CFG
 * @param string $sort ?
 * @param string $dir ?
 * @param int $categoryid ?
 * @param int $categoryid ?
 * @param string $search ?
 * @param string $firstinitial ?
 * @param string $lastinitial ?
 * @returnobject {@link $USER} records
 * @todo Finish documenting this function
 */

function get_users_listing($sort='lastaccess', $dir='ASC', $page=0, $recordsperpage=99999,
                           $search='', $firstinitial='', $lastinitial='') {

    global $CFG;

    $limit     = sql_paging_limit($page, $recordsperpage);
    $LIKE      = sql_ilike();
    $fullname  = sql_fullname();

    $select = "deleted <> '1' AND username <> 'changeme'";

    if (!empty($search)) {
        $search = trim($search);
        $select .= " AND ($fullname $LIKE '%$search%' OR email $LIKE '%$search%') ";
    }

    if ($firstinitial) {
        $select .= ' AND firstname '. $LIKE .' \''. $firstinitial .'%\' ';
    }

    if ($lastinitial) {
        $select .= ' AND lastname '. $LIKE .' \''. $lastinitial .'%\' ';
    }

    if ($sort) {
        $sort = ' ORDER BY '. $sort .' '. $dir;
    }

/// warning: will return UNCONFIRMED USERS
    return get_records_sql("SELECT id, username, email, firstname, lastname, city, country, lastaccess, confirmed
                              FROM {$CFG->prefix}user
                             WHERE $select $sort $limit ");

}


/**
 * Full list of users that have confirmed their accounts.
 *
 * @uses $CFG
 * @return object
 */
function get_users_confirmed() {
    global $CFG;
    return get_records_sql("SELECT *
                              FROM {$CFG->prefix}user
                             WHERE confirmed = 1
                               AND deleted = 0
                               AND username <> 'guest'
                               AND username <> 'changeme'");
}


/**
 * Full list of users that have not yet confirmed their accounts.
 *
 * @uses $CFG
 * @param string $cutofftime ?
 * @return object  {@link $USER} records
 * @todo Finish documenting this function
 */
function get_users_unconfirmed($cutofftime=2000000000) {
    global $CFG;
    return get_records_sql("SELECT *
                             FROM {$CFG->prefix}user
                            WHERE confirmed = 0
                              AND firstaccess > 0
                              AND firstaccess < '$cutofftime'");
}


/**
 * Full list of bogus accounts that are probably not ever going to be used
 *
 * @uses $CFG
 * @param string $cutofftime ?
 * @return object  {@link $USER} records
 * @todo Finish documenting this function
 */

function get_users_not_fully_set_up($cutofftime=2000000000) {
    global $CFG;
    return get_records_sql("SELECT *
                             FROM {$CFG->prefix}user
                            WHERE confirmed = 1
                             AND lastaccess > 0
                             AND lastaccess < '$cutofftime'
                             AND deleted = 0
                             AND (lastname = '' OR firstname = '' OR email = '')");
}


/**
 * shortdesc (optional)
 *
 * longdesc
 *
 * @uses $CFG
 * @param string $cutofftime ?
 * @return object  {@link $USER} records
 * @todo Finish documenting this function
 */
function get_users_longtimenosee($cutofftime) {
    global $CFG;
    return get_records_sql("SELECT DISTINCT *
                              FROM {$CFG->prefix}user_students
                             WHERE timeaccess > '0'
                               AND timeaccess < '$cutofftime' ");
}

/**
 * Returns an array of group objects that the user is a member of
 * in the given course.  If userid isn't specified, then return a
 * list of all groups in the course.
 *
 * @uses $CFG
 * @param int $courseid The id of the course in question.
 * @param int $userid The id of the user in question as found in the 'user' table 'id' field.
 * @return object
 */
function get_groups($courseid, $userid=0) {
    global $CFG;

    if ($userid) {
        $dbselect = ', '. $CFG->prefix .'groups_members m';
        $userselect = 'AND m.groupid = g.id AND m.userid = \''. $userid .'\'';
    } else {
        $dbselect = '';
        $userselect = '';
    }

    return get_records_sql("SELECT DISTINCT g.*
                              FROM {$CFG->prefix}groups g $dbselect
                             WHERE g.courseid = '$courseid' $userselect ");
}


/**
 * Returns an array of user objects
 *
 * @uses $CFG
 * @param int $groupid The group in question.
 * @param string $sort ?
 * @param string $exceptions ?
 * @return object
 * @todo Finish documenting this function
 */
function get_group_users($groupid, $sort='u.lastaccess DESC', $exceptions='', $fields='u.*') {
    global $CFG;
    if (!empty($exceptions)) {
        $except = ' AND u.id NOT IN ('. $exceptions .') ';
    } else {
        $except = '';
    }
    // in postgres, you can't have things in sort that aren't in the select, so...
    $extrafield = str_replace('ASC','',$sort);
    $extrafield = str_replace('DESC','',$extrafield);
    $extrafield = trim($extrafield);
    if (!empty($extrafield)) {
        $extrafield = ','.$extrafield;
    }
    return get_records_sql("SELECT DISTINCT $fields $extrafield
                              FROM {$CFG->prefix}user u,
                                   {$CFG->prefix}groups_members m
                             WHERE m.groupid = '$groupid'
                               AND m.userid = u.id $except
                          ORDER BY $sort");
}

/**
 * An efficient way of finding all the users who aren't in groups yet
 *
 * Currently unimplemented.
 * @uses $CFG
 * @param int $courseid The course in question.
 * @return object
 */
function get_users_not_in_group($courseid) {
    global $CFG;

    return array();     /// XXX TO BE DONE
}

/**
 * Returns an array of user objects
 *
 * @uses $CFG
 * @param int $groupid The group(s) in question.
 * @param string $sort How to sort the results
 * @return object (changed to groupids)
 */
function get_group_students($groupids, $sort='u.lastaccess DESC') {

    global $CFG;

    if (is_array($groupids)){
        $groups = $groupids;
        $groupstr = '(m.groupid = '.array_shift($groups);
        foreach ($groups as $index => $value){
            $groupstr .= ' OR m.groupid = '.$value;
        }
        $groupstr .= ')';
    }
    else {
        $groupstr = 'm.groupid = '.$groupids;
    }

    return get_records_sql("SELECT DISTINCT u.*
                              FROM {$CFG->prefix}user u,
                                   {$CFG->prefix}groups_members m,
                                   {$CFG->prefix}groups g,
                                   {$CFG->prefix}user_students s
                             WHERE $groupstr
                               AND m.userid = u.id
                               AND m.groupid = g.id
                               AND g.courseid = s.course
                               AND s.userid = u.id
                          ORDER BY $sort");
}

/**
 * Returns list of all the teachers who can access a group
 *
 * @uses $CFG
 * @param int $courseid The course in question.
 * @param int $groupid The group in question.
 * @return object
 */
function get_group_teachers($courseid, $groupid) {
/// Returns a list of all the teachers who can access a group
    if ($teachers = get_course_teachers($courseid)) {
        foreach ($teachers as $key => $teacher) {
            if ($teacher->editall) {             // These can access anything
                continue;
            }
            if (($teacher->authority > 0) and ismember($groupid, $teacher->id)) {  // Specific group teachers
                continue;
            }
            unset($teachers[$key]);
        }
    }
    return $teachers;
}


/**
 * Returns the user's group in a particular course
 *
 * @uses $CFG
 * @param int $courseid The course in question.
 * @param int $userid The id of the user as found in the 'user' table.
 * @param int $groupid The id of the group the user is in.
 * @return object
 * @todo Finish documenting this function
 */
function user_group($courseid, $userid) {
    global $CFG;

    return get_records_sql("SELECT g.*
                             FROM {$CFG->prefix}groups g,
                                  {$CFG->prefix}groups_members m
                             WHERE g.courseid = '$courseid'
                               AND g.id = m.groupid
                               AND m.userid = '$userid'
                               ORDER BY name ASC");
}




/// OTHER SITE AND COURSE FUNCTIONS /////////////////////////////////////////////


/**
 * Returns $course object of the top-level site.
 *
 * @return course  A {@link $COURSE} object for the site
 * @todo Finish documenting this function.
 */
function get_site() {

    global $SITE;

    if (!empty($SITE->id)) {   // We already have a global to use, so return that
        return $SITE;
    }

    if ($course = get_record('course', 'category', 0)) {
        return $course;
    } else {
        return false;
    }
}

/**
* Returns list of courses, for whole site, or category
*
* Returns list of courses, for whole site, or category
*
* @param    type description
*
* Important: Using c.* for fields is extremely expensive because 
*            we are using distinct. You almost _NEVER_ need all the fields
*            in such a large SELECT
*/
function get_courses($categoryid="all", $sort="c.sortorder ASC", $fields="c.*") {

    global $USER, $CFG;
    
    $categoryselect = "";
    if ($categoryid != "all" && is_numeric($categoryid)) {
        $categoryselect = "c.category = '$categoryid'";
    }

    $teachertable = "";
    $visiblecourses = "";
    $sqland = "";
    if (!empty($categoryselect)) {
        $sqland = "AND ";
    }
    if (!empty($USER->id)) {  // May need to check they are a teacher
        if (!iscreator()) {
            $visiblecourses = "$sqland ((c.visible > 0) OR t.userid = '$USER->id')";
            $teachertable = "LEFT JOIN {$CFG->prefix}user_teachers t ON t.course = c.id";
        }
    } else {
        $visiblecourses = "$sqland c.visible > 0";
    }

    if ($categoryselect or $visiblecourses) {
        $selectsql = "{$CFG->prefix}course c $teachertable WHERE $categoryselect $visiblecourses";
    } else {
        $selectsql = "{$CFG->prefix}course c $teachertable";
    }

    $extrafield = str_replace('ASC','',$sort);
    $extrafield = str_replace('DESC','',$extrafield);
    $extrafield = trim($extrafield);
    if (!empty($extrafield)) {
        $extrafield = ','.$extrafield;
    }
    return get_records_sql("SELECT ".((!empty($teachertable)) ? " DISTINCT " : "")." $fields $extrafield FROM $selectsql ".((!empty($sort)) ? "ORDER BY $sort" : ""));
}


/**
* Returns list of courses, for whole site, or category
*
* Similar to get_courses, but allows paging
*
* @param    type description
*
* Important: Using c.* for fields is extremely expensive because 
*            we are using distinct. You almost _NEVER_ need all the fields
*            in such a large SELECT
*/
function get_courses_page($categoryid="all", $sort="c.sortorder ASC", $fields="c.*",
                          &$totalcount, $limitfrom="", $limitnum="") {

    global $USER, $CFG;

    $categoryselect = "";
    if ($categoryid != "all" && is_numeric($categoryid)) {
        $categoryselect = "c.category = '$categoryid'";
    }

    $teachertable = "";
    $visiblecourses = "";
    $sqland = "";
    if (!empty($categoryselect)) {
        $sqland = "AND ";
    }
    if (!empty($USER) and !empty($USER->id)) {  // May need to check they are a teacher
        if (!iscreator()) {
            $visiblecourses = "$sqland ((c.visible > 0) OR t.userid = '$USER->id')";
            $teachertable = "LEFT JOIN {$CFG->prefix}user_teachers t ON t.course=c.id";
        }
    } else {
        $visiblecourses = "$sqland c.visible > 0";
    }

    if ($limitfrom !== "") {
        $limit = sql_paging_limit($limitfrom, $limitnum);
    } else {
        $limit = "";
    }

    $selectsql = "{$CFG->prefix}course c $teachertable WHERE $categoryselect $visiblecourses";

    $totalcount = count_records_sql("SELECT COUNT(DISTINCT c.id) FROM $selectsql");

    return get_records_sql("SELECT $fields FROM $selectsql ".((!empty($sort)) ? "ORDER BY $sort" : "")." $limit");
}


/**
 * List of courses that a user is a member of.
 *
 * @uses $CFG
 * @param int $userid The user of interest
 * @param string $sort ?
 * @return object {@link $COURSE} records
 */
function get_my_courses($userid, $sort='visible DESC,sortorder ASC') {

    global $CFG, $USER;

    $course = array();

    if ($students = get_records('user_students', 'userid', $userid, '', 'id, course')) {
        foreach ($students as $student) {
            $course[$student->course] = $student->course;
        }
    }
    if (count($course) > 0 && empty($USER->admin)) {
        if ($courses = get_records_list('course', 'id', implode(',', $course), '', 'id,visible')) {
            foreach ($courses as $k => $c) {
                if (!$c->visible) {
                    unset($course[$c->id]);
                }
            }
        }
    }

    if ($teachers = get_records('user_teachers', 'userid', $userid, '', 'id, course')) {
        foreach ($teachers as $teacher) {
            $course[$teacher->course] = $teacher->course;
        }
    }

    if (empty($course)) {
        return $course;
    }

    $courseids = implode(',', $course);

    return get_records_list('course', 'id', $courseids, $sort);

//  The following is correct but VERY slow with large datasets
//
//    return get_records_sql("SELECT c.*
//                              FROM {$CFG->prefix}course c,
//                                   {$CFG->prefix}user_students s,
//                                   {$CFG->prefix}user_teachers t
//                             WHERE (s.userid = '$userid' AND s.course = c.id)
//                                OR (t.userid = '$userid' AND t.course = c.id)
//                             GROUP BY c.id
//                             ORDER BY $sort");
}


/**
 * A list of courses that match a search
 *
 * @uses $CFG
 * @param array $searchterms ?
 * @param string $sort ?
 * @param int $page ?
 * @param int $recordsperpage ?
 * @param int $totalcount Passed in by reference. ?
 * @return object {@link $COURSE} records
 * @todo Finish documenting this function
 */
function get_courses_search($searchterms, $sort='fullname ASC', $page=0, $recordsperpage=50, &$totalcount) {

    global $CFG;

    $limit = sql_paging_limit($page, $recordsperpage);

    //to allow case-insensitive search for postgesql
    if ($CFG->dbtype == 'postgres7') {
        $LIKE = 'ILIKE';
        $NOTLIKE = 'NOT ILIKE';   // case-insensitive
        $REGEXP = '~*';
        $NOTREGEXP = '!~*';
    } else {
        $LIKE = 'LIKE';
        $NOTLIKE = 'NOT LIKE';
        $REGEXP = 'REGEXP';
        $NOTREGEXP = 'NOT REGEXP';
    }

    $fullnamesearch = '';
    $summarysearch = '';

    foreach ($searchterms as $searchterm) {
        if ($fullnamesearch) {
            $fullnamesearch .= ' AND ';
        }
        if ($summarysearch) {
            $summarysearch .= ' AND ';
        }

        if (substr($searchterm,0,1) == '+') {
            $searchterm = substr($searchterm,1);
            $summarysearch .= " summary $REGEXP '(^|[^a-zA-Z0-9])$searchterm([^a-zA-Z0-9]|$)' ";
            $fullnamesearch .= " fullname $REGEXP '(^|[^a-zA-Z0-9])$searchterm([^a-zA-Z0-9]|$)' ";
        } else if (substr($searchterm,0,1) == "-") {
            $searchterm = substr($searchterm,1);
            $summarysearch .= " summary $NOTREGEXP '(^|[^a-zA-Z0-9])$searchterm([^a-zA-Z0-9]|$)' ";
            $fullnamesearch .= " fullname $NOTREGEXP '(^|[^a-zA-Z0-9])$searchterm([^a-zA-Z0-9]|$)' ";
        } else {
            $summarysearch .= ' summary '. $LIKE .'\'%'. $searchterm .'%\' ';
            $fullnamesearch .= ' fullname '. $LIKE .'\'%'. $searchterm .'%\' ';
        }

    }

    $selectsql = $CFG->prefix .'course WHERE ('. $fullnamesearch .' OR '. $summarysearch .') AND category > \'0\'';

    $totalcount = count_records_sql('SELECT COUNT(*) FROM '. $selectsql);

    $courses = get_records_sql('SELECT * FROM '. $selectsql .' ORDER BY '. $sort .' '. $limit);

    if ($courses) {  /// Remove unavailable courses from the list
        foreach ($courses as $key => $course) {
            if (!$course->visible) {
                if (!isteacher($course->id)) {
                    unset($courses[$key]);
                    $totalcount--;
                }
            }
        }
    }

    return $courses;
}


/**
 * Returns a sorted list of categories
 *
 * @param string $parent ?
 * @param string $sort ?
 * @return ?
 * @todo Finish documenting this function
 */
function get_categories($parent='none', $sort='sortorder ASC') {

    if ($parent === 'none') {
        $categories = get_records('course_categories', '', '', $sort);
    } else {
        $categories = get_records('course_categories', 'parent', $parent, $sort);
    }
    if ($categories) {  /// Remove unavailable categories from the list
        $creator = iscreator();
        foreach ($categories as $key => $category) {
            if (!$category->visible) {
                if (!$creator) {
                    unset($categories[$key]);
                }
            }
        }
    }
    return $categories;
}


/**
* This recursive function makes sure that the courseorder is consecutive
*
* @param    type description
*
* $n is the starting point, offered only for compatilibity -- will be ignored!
* $safe (bool) prevents it from assuming category-sortorder is unique, used to upgrade
*       safely from 1.4 to 1.5
*/
function fix_course_sortorder($categoryid=0, $n=0, $safe=0, $depth=0, $path='') {
    
    global $CFG;

    $count = 0;
    
    $catgap    = 1000; // "standard" category gap
    $tolerance = 200;  // how "close" categories can get
    
    if ($categoryid > 0){
        // update depth and path
        $cat   = get_record('course_categories', 'id', $categoryid);
        if ($cat->parent == 0) {
            $depth = 0;
            $path  = '';
        } else if ($depth == 0 ) { // doesn't make sense; get from DB
            // this is only called if the $depth parameter looks dodgy
            $parent = get_record('course_categories', 'id', $cat->parent);
            $path  = $parent->path;
            $depth = $parent->depth;
        }
        $path  = $path . '/' . $categoryid;
        $depth = $depth + 1;

        set_field('course_categories', 'path',  addslashes($path),  'id', $categoryid);        
        set_field('course_categories', 'depth', $depth, 'id', $categoryid);        
    }

    // get some basic info about courses in the category
    $info = get_record_sql('SELECT MIN(sortorder) AS min, 
                                   MAX(sortorder) AS max,
                                   COUNT(sortorder)  AS count                                   
                            FROM ' . $CFG->prefix . 'course 
                            WHERE category=' . $categoryid);
    if (is_object($info)) { // no courses?
        $max   = $info->max;
        $count = $info->count;
        $min   = $info->min;
        unset($info);
    }

    if ($categoryid > 0 && $n==0) { // only passed category so don't shift it
        $n = $min;
    }

    // $hasgap flag indicates whether there's a gap in the sequence
    $hasgap    = false; 
    if ($max-$min+1 != $count) {
        $hasgap = true;
    }
    
    // $mustshift indicates whether the sequence must be shifted to
    // meet its range
    $mustshift = false;
    if ($min < $n+$tolerance || $min > $n+$tolerance+$catgap ) {
        $mustshift = true;
    }

    // actually sort only if there are courses,
    // and we meet one ofthe triggers:
    //  - safe flag
    //  - they are not in a continuos block
    //  - they are too close to the 'bottom'
    if ($count && ( $safe || $hasgap || $mustshift ) ) {
        // special, optimized case where all we need is to shift
        if ( $mustshift && !$safe && !$hasgap) {
            $shift = $n + $catgap - $min;
            // UPDATE course SET sortorder=sortorder+$shift
            execute_sql("UPDATE {$CFG->prefix}course 
                         SET sortorder=sortorder+$shift 
                         WHERE category=$categoryid", 0);
            $n = $n + $catgap + $count; 
            
        } else { // do it slowly
            $n = $n + $catgap;             
            // if the new sequence overlaps the current sequence, lack of transactions
            // will stop us -- shift things aside for a moment...
            if ($safe || ($n >= $min && $n+$count+1 < $min && $CFG->dbtype==='mysql')) {
                $shift = $max + $n + 1000;
                execute_sql("UPDATE {$CFG->prefix}course 
                         SET sortorder=sortorder+$shift 
                         WHERE category=$categoryid", 0);
            }

            $courses = get_courses($categoryid, 'c.sortorder ASC', 'c.id,c.sortorder');
            begin_sql();
            foreach ($courses as $course) { 
                if ($course->sortorder != $n ) { // save db traffic
                    set_field('course', 'sortorder', $n, 'id', $course->id);
                }
                $n++;
            }
            commit_sql();
        }    
    }
    set_field('course_categories', 'coursecount', $count, 'id', $categoryid);

    // $n could need updating     
    $max = get_field_sql("SELECT MAX(sortorder) from {$CFG->prefix}course WHERE category=$categoryid");
    if ($max > $n) {
        $n = $max;
    }

    if ($categories = get_categories($categoryid)) {
        foreach ($categories as $category) {
            $n = fix_course_sortorder($category->id, $n, $safe, $depth, $path);
        }
    }

    return $n+1;
}


/**
 * This function creates a default separated/connected scale
 *
 * This function creates a default separated/connected scale
 * so there's something in the database.  The locations of
 * strings and files is a bit odd, but this is because we
 * need to maintain backward compatibility with many different
 * existing language translations and older sites.
 *
 * @uses $CFG
 */
function make_default_scale() {

    global $CFG;

    $defaultscale = NULL;
    $defaultscale->courseid = 0;
    $defaultscale->userid = 0;
    $defaultscale->name  = get_string('separateandconnected');
    $defaultscale->scale = get_string('postrating1', 'forum').','.
                           get_string('postrating2', 'forum').','.
                           get_string('postrating3', 'forum');
    $defaultscale->timemodified = time();

    /// Read in the big description from the file.  Note this is not
    /// HTML (despite the file extension) but Moodle format text.
    $parentlang = get_string('parentlang');
    if (is_readable($CFG->dataroot .'/lang/'. $CFG->lang .'/help/forum/ratings.html')) {
        $file = file($CFG->dataroot .'/lang/'. $CFG->lang .'/help/forum/ratings.html');
    } else if (is_readable($CFG->dirroot .'/lang/'. $CFG->lang .'/help/forum/ratings.html')) {
        $file = file($CFG->dirroot .'/lang/'. $CFG->lang .'/help/forum/ratings.html');
    } else if ($parentlang and is_readable($CFG->dataroot .'/lang/'. $parentlang .'/help/forum/ratings.html')) {
        $file = file($CFG->dataroot .'/lang/'. $parentlang .'/help/forum/ratings.html');
    } else if ($parentlang and is_readable($CFG->dirroot .'/lang/'. $parentlang .'/help/forum/ratings.html')) {
        $file = file($CFG->dirroot .'/lang/'. $parentlang .'/help/forum/ratings.html');
    } else if (is_readable($CFG->dirroot .'/lang/en_utf8/help/forum/ratings.html')) {
        $file = file($CFG->dirroot .'/lang/en_utf8/help/forum/ratings.html');
    } else {
        $file = '';
    }

    $defaultscale->description = addslashes(implode('', $file));

    if ($defaultscale->id = insert_record('scale', $defaultscale)) {
        execute_sql('UPDATE '. $CFG->prefix .'forum SET scale = \''. $defaultscale->id .'\'', false);
    }
}


/**
 * Returns a menu of all available scales from the site as well as the given course
 *
 * @uses $CFG
 * @param int $courseid The id of the course as found in the 'course' table.
 * @return object
 */
function get_scales_menu($courseid=0) {

    global $CFG;

    $sql = "SELECT id, name FROM {$CFG->prefix}scale
             WHERE courseid = '0' or courseid = '$courseid'
          ORDER BY courseid ASC, name ASC";

    if ($scales = get_records_sql_menu($sql)) {
        return $scales;
    }

    make_default_scale();

    return get_records_sql_menu($sql);
}



/**
 * Given a set of timezone records, put them in the database,  replacing what is there
 *
 * @uses $CFG
 * @param array $timezones An array of timezone records
 */
function update_timezone_records($timezones) {
/// Given a set of timezone records, put them in the database

    global $CFG;

/// Clear out all the old stuff
    execute_sql('TRUNCATE TABLE '.$CFG->prefix.'timezone', false);

/// Insert all the new stuff
    foreach ($timezones as $timezone) {
        insert_record('timezone', $timezone);
    }
}


/// MODULE FUNCTIONS /////////////////////////////////////////////////

/**
 * Just gets a raw list of all modules in a course
 *
 * @uses $CFG
 * @param int $courseid The id of the course as found in the 'course' table.
 * @return object
 * @todo Finish documenting this function
 */
function get_course_mods($courseid) {
    global $CFG;

    if (empty($courseid)) {
        return false; // avoid warnings
    }

    return get_records_sql("SELECT cm.*, m.name as modname
                            FROM {$CFG->prefix}modules m,
                                 {$CFG->prefix}course_modules cm
                            WHERE cm.course = '$courseid'
                            AND cm.module = m.id ");
}


/**
 * Given an id of a course module, finds the coursemodule description
 *
 * @param string $modulename name of module type, eg. resource, assignment,...
 * @param int $cmid course module id (id in course_modules table)
 * @param int $courseid optional course id for extra validation
 * @return object course module instance with instance and module name
 */
function get_coursemodule_from_id($modulename, $cmid, $courseid=0) {

    global $CFG;

    $courseselect = ($courseid) ? "cm.course = '$courseid' AND " : '';

    return get_record_sql("SELECT cm.*, m.name, md.name as modname
                           FROM {$CFG->prefix}course_modules cm,
                                {$CFG->prefix}modules md,
                                {$CFG->prefix}$modulename m
                           WHERE $courseselect
                                 cm.id = '$cmid' AND
                                 cm.instance = m.id AND
                                 md.name = '$modulename' AND
                                 md.id = cm.module");
}

/**
 * Given an instance number of a module, finds the coursemodule description
 *
 * @param string $modulename name of module type, eg. resource, assignment,...
 * @param int $instance module instance number (id in resource, assignment etc. table)
 * @param int $courseid optional course id for extra validation
 * @return object course module instance with instance and module name
 */
function get_coursemodule_from_instance($modulename, $instance, $courseid=0) {

    global $CFG;

    $courseselect = ($courseid) ? "cm.course = '$courseid' AND " : '';

    return get_record_sql("SELECT cm.*, m.name, md.name as modname
                           FROM {$CFG->prefix}course_modules cm,
                                {$CFG->prefix}modules md,
                                {$CFG->prefix}$modulename m
                           WHERE $courseselect
                                 cm.instance = m.id AND
                                 md.name = '$modulename' AND
                                 md.id = cm.module AND
                                 m.id = '$instance'");

}

/**
 * Returns an array of all the active instances of a particular module in given courses, sorted in the order they are defined
 *
 * Returns an array of all the active instances of a particular
 * module in given courses, sorted in the order they are defined
 * in the course.   Returns false on any errors.
 *
 * @uses $CFG
 * @param string  $modulename The name of the module to get instances for
 * @param array(courses)  $courses This depends on an accurate $course->modinfo
 * @todo Finish documenting this function. Is a course object to be documented as object(course) or array(course) since a coures object is really just an associative array, not a php object?
 */
function get_all_instances_in_courses($modulename,$courses) {
    global $CFG;
    if (empty($courses) || !is_array($courses) || count($courses) == 0) {
        return array();
    }
    if (!$rawmods = get_records_sql("SELECT cm.id as coursemodule, m.*,cw.section,cm.visible as visible,cm.groupmode, cm.course
                            FROM {$CFG->prefix}course_modules cm,
                                 {$CFG->prefix}course_sections cw,
                                 {$CFG->prefix}modules md,
                                 {$CFG->prefix}$modulename m
                            WHERE cm.course IN (".implode(',',array_keys($courses)).") AND
                                  cm.instance = m.id AND
                                  cm.section = cw.id AND
                                  md.name = '$modulename' AND
                                  md.id = cm.module")) {
        return array();
    }

    $outputarray = array();

    foreach ($courses as $course) {
        // Hide non-visible instances from students
        if (isteacher($course->id)) {
            $invisible = -1;
        } else {
            $invisible = 0;
        }
        
        if (!$modinfo = unserialize($course->modinfo)) {
            continue;
        }
        foreach ($modinfo as $mod) {
            if ($mod->mod == $modulename and $mod->visible > $invisible) {
                $instance = $rawmods[$mod->cm];
                if (!empty($mod->extra)) {
                    $instance->extra = $mod->extra;
                }
                $outputarray[] = $instance;
            }
        }
    }

    return $outputarray;

}

/**
 * Returns an array of all the active instances of a particular module in a given course, sorted in the order they are defined
 *
 * Returns an array of all the active instances of a particular
 * module in a given course, sorted in the order they are defined
 * in the course.   Returns false on any errors.
 *
 * @uses $CFG
 * @param string  $modulename The name of the module to get instances for
 * @param object(course)  $course This depends on an accurate $course->modinfo
 * @todo Finish documenting this function. Is a course object to be documented as object(course) or array(course) since a coures object is really just an associative array, not a php object?
 */
function get_all_instances_in_course($modulename, $course) {

    global $CFG;

    if (!$modinfo = unserialize($course->modinfo)) {
        return array();
    }

    if (!$rawmods = get_records_sql("SELECT cm.id as coursemodule, m.*,cw.section,cm.visible as visible,cm.groupmode
                            FROM {$CFG->prefix}course_modules cm,
                                 {$CFG->prefix}course_sections cw,
                                 {$CFG->prefix}modules md,
                                 {$CFG->prefix}$modulename m
                            WHERE cm.course = '$course->id' AND
                                  cm.instance = m.id AND
                                  cm.section = cw.id AND
                                  md.name = '$modulename' AND
                                  md.id = cm.module")) {
        return array();
    }

    // Hide non-visible instances from students
    if (isteacher($course->id)) {
        $invisible = -1;
    } else {
        $invisible = 0;
    }

    $outputarray = array();

    foreach ($modinfo as $mod) {
        if ($mod->mod == $modulename and $mod->visible > $invisible) {
            $instance = $rawmods[$mod->cm];
            if (!empty($mod->extra)) {
                $instance->extra = $mod->extra;
            }
            $outputarray[] = $instance;
        }
    }

    return $outputarray;

}


/**
 * Determine whether a module instance is visible within a course
 *
 * Given a valid module object with info about the id and course,
 * and the module's type (eg "forum") returns whether the object
 * is visible or not
 *
 * @uses $CFG
 * @param $moduletype ?
 * @param $module ?
 * @return bool
 * @todo Finish documenting this function
 */
function instance_is_visible($moduletype, $module) {

    global $CFG;

    if (!empty($module->id)) {
        if ($records = get_records_sql("SELECT cm.instance, cm.visible
                                        FROM {$CFG->prefix}course_modules cm,
                                             {$CFG->prefix}modules m
                                       WHERE cm.course = '$module->course' AND
                                             cm.module = m.id AND
                                             m.name = '$moduletype' AND
                                             cm.instance = '$module->id'")) {
    
            foreach ($records as $record) { // there should only be one - use the first one
                return $record->visible;
            }
        }
    }
    return true;  // visible by default!
}




/// LOG FUNCTIONS /////////////////////////////////////////////////////


/**
 * Add an entry to the log table.
 *
 * Add an entry to the log table.  These are "action" focussed rather
 * than web server hits, and provide a way to easily reconstruct what
 * any particular student has been doing.
 *
 * @uses $CFG
 * @uses $USER
 * @uses $db
 * @uses $REMOTE_ADDR
 * @uses SITEID
 * @param    int     $courseid  The course id
 * @param    string  $module  The module name - e.g. forum, journal, resource, course, user etc
 * @param    string  $action  'view', 'update', 'add' or 'delete', possibly followed by another word to clarify.
 * @param    string  $url     The file and parameters used to see the results of the action
 * @param    string  $info    Additional description information
 * @param    string  $cm      The course_module->id if there is one
 * @param    string  $user    If log regards $user other than $USER
 */
function add_to_log($courseid, $module, $action, $url='', $info='', $cm=0, $user=0) {
    // Note that this function intentionally does not follow the normal Moodle DB access idioms.
    // This is for a good reason: it is the most frequently used DB update function,
    // so it has been optimised for speed.
    global $db, $CFG, $USER;

    if ($cm === '' || is_null($cm)) { // postgres won't translate empty string to its default
        $cm = 0;
    }

    if ($user) {
        $userid = $user;
    } else {
        if (isset($USER->realuser)) {  // Don't log
            return;
        }
        $userid = empty($USER->id) ? '0' : $USER->id;
    }

    $REMOTE_ADDR = getremoteaddr();

    $timenow = time();
    $info = addslashes($info);
    if (!empty($url)) { // could break doing html_entity_decode on an empty var.
        $url = html_entity_decode($url); // for php < 4.3.0 this is defined in moodlelib.php
    }

    if (defined('MDL_PERFDB')) { global $PERF ; $PERF->dbqueries++; $PERF->logwrites++;};

    $result = $db->Execute('INSERT INTO '. $CFG->prefix .'log (time, userid, course, ip, module, cmid, action, url, info)
        VALUES (' . "'$timenow', '$userid', '$courseid', '$REMOTE_ADDR', '$module', '$cm', '$action', '$url', '$info')");

    if (!$result and ($CFG->debug > 7)) {
        echo '<p>Error: Could not insert a new entry to the Moodle log</p>';  // Don't throw an error
    }
    if ( isset($USER) && (empty($user) || $user==$USER->id) ) {
        $db->Execute('UPDATE '. $CFG->prefix .'user SET lastip=\''. $REMOTE_ADDR .'\', lastaccess=\''. $timenow .'\'
                     WHERE id = \''. $userid .'\' ');
        if ($courseid != SITEID && !empty($courseid)) { // logins etc dont't have a courseid and isteacher will break without it.
            if (defined('MDL_PERFDB')) { global $PERF ; $PERF->dbqueries++;};
            if (isstudent($courseid)) {
                $db->Execute('UPDATE '. $CFG->prefix .'user_students SET timeaccess = \''. $timenow .'\' '.
                             'WHERE course = \''. $courseid .'\' AND userid = \''. $userid .'\'');
            } else if (isteacher($courseid, false, false)) {
                $db->Execute('UPDATE '. $CFG->prefix .'user_teachers SET timeaccess = \''. $timenow .'\' '.
                             'WHERE course = \''. $courseid .'\' AND userid = \''. $userid .'\'');
            }
        }
    }
}


/**
 * Select all log records based on SQL criteria
 *
 * @uses $CFG
 * @param string $select SQL select criteria
 * @param string $order SQL order by clause to sort the records returned
 * @param string $limitfrom ?
 * @param int $limitnum ?
 * @param int $totalcount Passed in by reference.
 * @return object
 * @todo Finish documenting this function
 */
function get_logs($select, $order='l.time DESC', $limitfrom='', $limitnum='', &$totalcount) {
    global $CFG;

    if ($limitfrom !== '') {
        $limit = sql_paging_limit($limitfrom, $limitnum);
    } else {
        $limit = '';
    }

    if ($order) {
        $order = 'ORDER BY '. $order;
    }

    $selectsql = $CFG->prefix .'log l LEFT JOIN '. $CFG->prefix .'user u ON l.userid = u.id '. ((strlen($select) > 0) ? 'WHERE '. $select : '');
    $countsql = $CFG->prefix.'log l '.((strlen($select) > 0) ? ' WHERE '. $select : '');

    $totalcount = count_records_sql("SELECT COUNT(*) FROM $countsql");

    return get_records_sql('SELECT l.*, u.firstname, u.lastname, u.picture
                                FROM '. $selectsql .' '. $order .' '. $limit);
}


/**
 * Select all log records for a given course and user
 *
 * @uses $CFG
 * @uses DAYSECS
 * @param int $userid The id of the user as found in the 'user' table.
 * @param int $courseid The id of the course as found in the 'course' table.
 * @param string $coursestart ?
 * @todo Finish documenting this function
 */
function get_logs_usercourse($userid, $courseid, $coursestart) {
    global $CFG;

    if ($courseid) {
        $courseselect = ' AND course = \''. $courseid .'\' ';
    } else {
        $courseselect = '';
    }

    return get_records_sql("SELECT floor((time - $coursestart)/". DAYSECS .") as day, count(*) as num
                            FROM {$CFG->prefix}log
                           WHERE userid = '$userid'
                             AND time > '$coursestart' $courseselect
                        GROUP BY day ");
}

/**
 * Select all log records for a given course, user, and day
 *
 * @uses $CFG
 * @uses HOURSECS
 * @param int $userid The id of the user as found in the 'user' table.
 * @param int $courseid The id of the course as found in the 'course' table.
 * @param string $daystart ?
 * @return object
 * @todo Finish documenting this function
 */
function get_logs_userday($userid, $courseid, $daystart) {
    global $CFG;

    if ($courseid) {
        $courseselect = ' AND course = \''. $courseid .'\' ';
    } else {
        $courseselect = '';
    }

    return get_records_sql("SELECT floor((time - $daystart)/". HOURSECS .") as hour, count(*) as num
                            FROM {$CFG->prefix}log
                           WHERE userid = '$userid'
                             AND time > '$daystart' $courseselect
                        GROUP BY hour ");
}

/**
 * Returns an object with counts of failed login attempts
 *
 * Returns information about failed login attempts.  If the current user is
 * an admin, then two numbers are returned:  the number of attempts and the
 * number of accounts.  For non-admins, only the attempts on the given user
 * are shown.
 *
 * @param string $mode Either 'admin', 'teacher' or 'everybody'
 * @param string $username The username we are searching for
 * @param string $lastlogin The date from which we are searching
 * @return int
 */
function count_login_failures($mode, $username, $lastlogin) {

    $select = 'module=\'login\' AND action=\'error\' AND time > '. $lastlogin;

    if (isadmin()) {    // Return information about all accounts
        if ($count->attempts = count_records_select('log', $select)) {
            $count->accounts = count_records_select('log', $select, 'COUNT(DISTINCT info)');
            return $count;
        }
    } else if ($mode == 'everybody' or ($mode == 'teacher' and isteacherinanycourse())) {
        if ($count->attempts = count_records_select('log', $select .' AND info = \''. $username .'\'')) {
            return $count;
        }
    }
    return NULL;
}


/// GENERAL HELPFUL THINGS  ///////////////////////////////////

/**
 * Dump a given object's information in a PRE block.
 *
 * Mostly just used for debugging.
 *
 * @param mixed $object The data to be printed
 * @todo add example usage and example output
 */
function print_object($object) {

    echo '<pre>';
    print_r($object);
    echo '</pre>';
}

/**
 * Returns the proper SQL to do paging
 *
 * @uses $CFG
 * @param string $page Offset page number
 * @param string $recordsperpage Number of records per page
 * @return string
 */
function sql_paging_limit($page, $recordsperpage) {
    global $CFG;

    switch ($CFG->dbtype) {
        case 'postgres7':
             return 'LIMIT '. $recordsperpage .' OFFSET '. $page;
        default:
             return 'LIMIT '. $page .','. $recordsperpage;
    }
}

/**
 * Returns the proper SQL to do LIKE in a case-insensitive way
 *
 * @uses $CFG
 * @return string
 */
function sql_ilike() {
    global $CFG;

    switch ($CFG->dbtype) {
        case 'mysql':
             return 'LIKE';
        default:
             return 'ILIKE';
    }
}


/**
 * Returns the proper SQL (for the dbms in use) to concatenate $firstname and $lastname
 *
 * @uses $CFG
 * @param string $firstname User's first name
 * @param string $lastname User's last name
 * @return string
 */
function sql_fullname($firstname='firstname', $lastname='lastname') {
    global $CFG;

    switch ($CFG->dbtype) {
        case 'mysql':
             return ' CONCAT('. $firstname .'," ",'. $lastname .') ';
        case 'postgres7':
             return " ". $firstname ."||' '||". $lastname ." ";
        default:
             return ' '. $firstname .'||" "||'. $lastname .' ';
    }
}

/**
 * Returns the proper SQL to do IS NULL
 * @uses $CFG
 * @param string $fieldname The field to add IS NULL to
 * @return string
 */
function sql_isnull($fieldname) {
    global $CFG;

    switch ($CFG->dbtype) {
        case 'mysql':
             return $fieldname.' IS NULL';
        default:
             return $fieldname.' IS NULL';
    }
}

/** 
 * Prepare a SQL WHERE clause to select records where the given fields match the given values.
 * 
 * Prepares a where clause of the form
 *     WHERE field1 = value1 AND field2 = value2 AND field3 = value3
 * except that you need only specify as many arguments (zero to three) as you need.
 * 
 * @param string $field1 the first field to check (optional).
 * @param string $value1 the value field1 must have (requred if field1 is given, else optional).
 * @param string $field2 the second field to check (optional).
 * @param string $value2 the value field2 must have (requred if field2 is given, else optional).
 * @param string $field3 the third field to check (optional).
 * @param string $value3 the value field3 must have (requred if field3 is given, else optional).
 */
function where_clause($field1='', $value1='', $field2='', $value2='', $field3='', $value3='') {
    if ($field1) {
        $select = "WHERE $field1 = '$value1'";
        if ($field2) {
            $select .= " AND $field2 = '$value2'";
            if ($field3) {
                $select .= " AND $field3 = '$value3'";
            }
        }
    } else {
        $select = '';
    }
    return $select;
}

/**
 * Checks for pg or mysql > 4
 */

function check_db_compat() {
    global $CFG,$db;
    
    if ($CFG->dbtype == 'postgres7') {
        return true;
    }
    
    if (!$rs = $db->Execute("SELECT version();")) {
        return false;
    }

    if (intval($rs->fields[0]) <= 3) {
        return false;
    }

    return true;
}

function course_parent_visible($course = null) {
    global $CFG;

    if (empty($course)) {
        return true;
    }
    if (!empty($CFG->allowvisiblecoursesinhiddencategories)) {
        return true;
    }
    return category_parent_visible($course->category);
}

function category_parent_visible($parent = 0) {
    
    static $visible;

    if (!$parent) {
        return true;
    }
    
    if (empty($visible)) {
        $visible = array(); // initialize
    }

    if (array_key_exists($parent,$visible)) {
        return $visible[$parent];
    }
    
    $category = get_record('course_categories', 'id', $parent);
    $list = explode('/', preg_replace('/^\/(.*)$/', '$1', $category->path));
    $list[] = $parent;
    $parents = get_records_list('course_categories', 'id', implode(',', $list), 'depth DESC');
    $v = true;
    foreach ($parents as $p) {
        if (!$p->visible) {
            $v = false;
        }
    }
    $visible[$parent] = $v; // now cache it
    return $v;
}

// vim:autoindent:expandtab:shiftwidth=4:tabstop=4:tw=140:
?>