# This file is part of Radicale - CalDAV and CardDAV server
# Copyright © 2022-2024 Peter Varkoly
# Copyright © 2024-2024 Peter Bieringer <pb@bieringer.de>
# Copyright © 2024-2025 Peter Marschall <peter@adpm.de>
#
# This library is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with Radicale.  If not, see <http://www.gnu.org/licenses/>.
"""
Authentication backend that checks credentials with a LDAP server.
 The following parameters are needed in the configuration:
   ldap_uri               URI to the LDAP server
   ldap_base              Base DN of the LDAP server
   ldap_reader_dn         DN of an LDAP user with read access to get the user accounts
   ldap_secret            Password of the 'ldap_reader_dn'
                          Better: use 'ldap_secret_file'!
   ldap_secret_file       Path of the file containing the password of the 'ldap_reader_dn'
   ldap_filter            Search filter to find the user DN to authenticate
 The following parameters control TLS connections:
   ldap_security          Encryption mode to be used,
                          one of: *none* | tls | starttls
   ldap_ssl_verify_mode   Certificate verification mode for tls and starttls;
                          one of: *REQUIRED* | OPTIONAL | NONE
   ldap_ssl_ca_file       Path to the CA file in PEM format to certify the server certificate
 The following parameters are optional:
   ldap_user_attribute    Attribute to be used as username after authentication, e.g. cn;
                          if not given, the name used to logon is used.
   ldap_groups_attribute  Attribute in the user entry to read the user's group memberships from,
                          e.g. memberof, groupMememberShip. This may even be a non-DN attribute!
   ldap_group_base        Base DN to search for groups;
                          only if it differs from 'ldap_base' and if 'ldap_group_members_attribute' is set
   ldap_group_filter      Search filter to search for groups having the user DN found as member;
                          only if 'ldap_group_members_attribute' is set
   ldap_group_members_attribute    Attribute in the group entries to read the group's members from,
                          e.g. member.
 The following parameters are for LDAP servers with oddities
   ldap_ignore_attribute_create_modify_timestamp
                          Ignore modifyTimestamp and createTimestamp attributes. Needed for Authentik LDAP server

"""
import ssl

from radicale import auth, config
from radicale.log import logger


class Auth(auth.BaseAuth):
    _ldap_uri: str
    _ldap_base: str
    _ldap_reader_dn: str
    _ldap_secret: str
    _ldap_filter: str
    _ldap_attributes: list[str] = []
    _ldap_user_attr: str
    _ldap_groups_attr: str
    _ldap_group_base: str
    _ldap_group_filter: str
    _ldap_group_members_attr: str
    _ldap_module_version: int = 3
    _ldap_security: str = "none"
    _ldap_ssl_verify_mode: str = "REQUIRED"
    _ldap_ssl_ca_file: str = ""

    def __init__(self, configuration: config.Configuration) -> None:
        super().__init__(configuration)
        try:
            import ldap3
            self.ldap3 = ldap3
        except ImportError:
            try:
                import ldap
                import ldap.filter
                self._ldap_module_version = 2
                self.ldap = ldap
            except ImportError as e:
                raise RuntimeError("LDAP authentication requires the ldap3 or ldap module") from e

        self._ldap_ignore_attribute_create_modify_timestamp = configuration.get("auth", "ldap_ignore_attribute_create_modify_timestamp")
        self._ldap_uri = configuration.get("auth", "ldap_uri")
        self._ldap_base = configuration.get("auth", "ldap_base")
        self._ldap_reader_dn = configuration.get("auth", "ldap_reader_dn")
        self._ldap_secret = configuration.get("auth", "ldap_secret")
        self._ldap_filter = configuration.get("auth", "ldap_filter")
        self._ldap_user_attr = configuration.get("auth", "ldap_user_attribute")
        self._ldap_groups_attr = configuration.get("auth", "ldap_groups_attribute")
        self._ldap_group_base = configuration.get("auth", "ldap_group_base")
        self._ldap_group_filter = configuration.get("auth", "ldap_group_filter")
        self._ldap_group_members_attr = configuration.get("auth", "ldap_group_members_attribute")
        ldap_secret_file_path = configuration.get("auth", "ldap_secret_file")
        if ldap_secret_file_path:
            with open(ldap_secret_file_path, 'r') as file:
                self._ldap_secret = file.read().rstrip('\n')
        self._ldap_security = configuration.get("auth", "ldap_security")
        if self._ldap_security not in ("none", "tls", "starttls"):
            raise RuntimeError("Illegal value for config setting ´ldap_security'")
        self._ldap_ssl_ca_file = configuration.get("auth", "ldap_ssl_ca_file")
        self._ldap_ssl_verify_mode = configuration.get("auth", "ldap_ssl_verify_mode")
        if self._ldap_ssl_verify_mode not in ("NONE", "OPTIONAL", "REQUIRED"):
            raise RuntimeError("Illegal value for config setting ´ldap_ssl_verify_mode'")

        if self._ldap_uri.lower().startswith("ldaps://") and self._ldap_security not in ("tls", "starttls"):
            logger.info("Inferring 'ldap_security' = tls from 'ldap_uri' starting with 'ldaps://'")
            self._ldap_security = "tls"
        if self._ldap_uri.lower().startswith("ldapi://") and self._ldap_ssl_verify_mode != "NONE":
            logger.info("Lowering 'ldap_'ldap_ssl_verify_mode' to NONE for 'ldap_uri' starting with 'ldapi://'")
            self._ldap_ssl_verify_mode = "NONE"

        if self._ldap_ssl_ca_file == "" and self._ldap_ssl_verify_mode != "NONE" and self._ldap_security in ("tls", "starttls"):
            logger.warning("Certificate verification not possible: 'ldap_ssl_ca_file' not set")
        if self._ldap_ssl_ca_file and self._ldap_security not in ("tls", "starttls"):
            logger.warning("Config setting 'ldap_ssl_ca_file' useless without encrypted LDAP connection")

        logger.info("auth.ldap_uri               : %r" % self._ldap_uri)
        logger.info("auth.ldap_base              : %r" % self._ldap_base)
        logger.info("auth.ldap_reader_dn         : %r" % self._ldap_reader_dn)
        logger.info("auth.ldap_filter            : %r" % self._ldap_filter)
        if self._ldap_user_attr:
            logger.info("auth.ldap_user_attribute    : %r" % self._ldap_user_attr)
        else:
            logger.info("auth.ldap_user_attribute    : (not provided)")
        if self._ldap_groups_attr:
            logger.info("auth.ldap_groups_attribute  : %r" % self._ldap_groups_attr)
        else:
            logger.info("auth.ldap_groups_attribute  : (not provided)")
        if self._ldap_group_base:
            logger.info("auth.ldap_group_base        : %r" % self._ldap_group_base)
        else:
            logger.info("auth.ldap_group_base        : (not provided, using ldap_base)")
            self._ldap_group_base = self._ldap_base
        if self._ldap_group_filter:
            logger.info("auth.ldap_group_filter      : %r" % self._ldap_group_filter)
        else:
            logger.info("auth.ldap_group_filter      : (not provided)")
        if self._ldap_group_members_attr:
            logger.info("auth.ldap_group_members_attr: %r" % self._ldap_group_members_attr)
        else:
            logger.info("auth.ldap_group_members_attr: (not provided)")
        if ldap_secret_file_path:
            logger.info("auth.ldap_secret_file_path  : %r" % ldap_secret_file_path)
            if self._ldap_secret:
                logger.info("auth.ldap_secret            : (from file)")
        else:
            logger.info("auth.ldap_secret_file_path  : (not provided)")
            if self._ldap_secret:
                logger.info("auth.ldap_secret            : (from config)")
        if self._ldap_reader_dn and not self._ldap_secret:
            logger.error("auth.ldap_secret           : (not provided)")
            raise RuntimeError("LDAP authentication requires ldap_secret for ldap_reader_dn")
        logger.info("auth.ldap_security          : %s" % self._ldap_security)
        logger.info("auth.ldap_ssl_verify_mode   : %s" % self._ldap_ssl_verify_mode)
        if self._ldap_ssl_ca_file:
            logger.info("auth.ldap_ssl_ca_file       : %r" % self._ldap_ssl_ca_file)
        else:
            logger.info("auth.ldap_ssl_ca_file       : (not provided)")
        if self._ldap_ignore_attribute_create_modify_timestamp:
            logger.info("auth.ldap_ignore_attribute_create_modify_timestamp applied (relevant for ldap3 only)")
        """Extend attributes to to be returned in the user query"""
        if self._ldap_groups_attr:
            self._ldap_attributes.append(self._ldap_groups_attr)
        if self._ldap_user_attr:
            self._ldap_attributes.append(self._ldap_user_attr)
        logger.info("ldap_attributes             : %r" % self._ldap_attributes)

    def _login2(self, login: str, password: str) -> str:
        try:
            """Bind as reader dn"""
            logger.debug(f"_login2 {self._ldap_uri}, {self._ldap_reader_dn}")
            conn = self.ldap.initialize(self._ldap_uri)
            conn.protocol_version = self.ldap.VERSION3
            conn.set_option(self.ldap.OPT_REFERRALS, 0)

            if self._ldap_security in ("tls", "starttls"):
                """certificate validation mode"""
                verifyMode = {"NONE": self.ldap.OPT_X_TLS_NEVER,
                              "OPTIONAL": self.ldap.OPT_X_TLS_ALLOW,
                              "REQUIRED": self.ldap.OPT_X_TLS_DEMAND}
                conn.set_option(self.ldap.OPT_X_TLS_REQUIRE_CERT, verifyMode[self._ldap_ssl_verify_mode])
                """CA file to validate certificate against"""
                if self._ldap_ssl_ca_file:
                    conn.set_option(self.ldap.OPT_X_TLS_CACERTFILE, self._ldap_ssl_ca_file)
                """create TLS context- this must be the last TLS setting"""
                conn.set_option(self.ldap.OPT_X_TLS_NEWCTX, self.ldap.OPT_ON)

                if self._ldap_security == "starttls":
                    conn.start_tls_s()

            conn.simple_bind_s(self._ldap_reader_dn, self._ldap_secret)
            """Search for the dn of user to authenticate"""
            escaped_login = self.ldap.filter.escape_filter_chars(login)
            logger.debug(f"_login2 login escaped for LDAP filters: {escaped_login}")
            res = conn.search_s(
                self._ldap_base,
                self.ldap.SCOPE_SUBTREE,
                filterstr=self._ldap_filter.format(escaped_login),
                attrlist=self._ldap_attributes
            )
            if len(res) != 1:
                """User could not be found unambiguously"""
                logger.debug(f"_login2 no unique DN found for '{login}'")
                return ""
            user_entry = res[0]
            user_dn = user_entry[0]
            logger.debug(f"_login2 found LDAP user DN {user_dn}")

            """Let's collect the groups of the user."""
            groupDNs = []
            if self._ldap_groups_attr:
                groupDNs = user_entry[1][self._ldap_groups_attr]

            """Search for all groups having the user_dn found as member."""
            if self._ldap_group_members_attr:
                groupDNs = []
                res = conn.search_s(
                    self._ldap_group_base,
                    self.ldap.SCOPE_SUBTREE,
                    filterstr="(&{0}({1}={2}))".format(
                        self._ldap_group_filter,
                        self._ldap_group_members_attr,
                        self.ldap.filter.escape_filter_chars(user_dn)),
                    attrlist=['1.1']
                )
                """Fill groupDNs with DNs of groups found"""
                if len(res) > 0:
                    groupDNs = []
                    for dn, entry in res:
                        groupDNs.append(dn)

        except Exception as e:
            raise RuntimeError(f"Invalid LDAP configuration:{e}")

        try:
            """Bind as user to authenticate"""
            conn.simple_bind_s(user_dn, password)
            if self._ldap_user_attr:
                if user_entry[1][self._ldap_user_attr]:
                    login = user_entry[1][self._ldap_user_attr][0]
                    if isinstance(login, bytes):
                        login = login.decode('utf-8')
                    logger.debug(f"_login2 user set to: '{login}'")

            """Get RDNs of groups' DNs"""
            tmp = []
            for g in groupDNs:
                try:
                    rdns = self.ldap.dn.explode_dn(g, notypes=True)
                    tmp.append(rdns[0])
                except Exception:
                    if isinstance(g, bytes):
                        g = g.decode('utf-8')
                    tmp.append(g)
            self._ldap_groups = set(tmp)
            logger.debug("_login2 LDAP groups of user: %s", ",".join(self._ldap_groups))

            conn.unbind()
            logger.debug(f"_login2 {login} successfully authenticated")
            return login
        except self.ldap.INVALID_CREDENTIALS:
            return ""

    def _login3(self, login: str, password: str) -> str:
        if self._ldap_ignore_attribute_create_modify_timestamp:
            self.ldap3.utils.config._ATTRIBUTES_EXCLUDED_FROM_CHECK.extend(['createTimestamp', 'modifyTimestamp'])

        """Connect the server"""
        try:
            logger.debug(f"_login3 {self._ldap_uri}, {self._ldap_reader_dn}")
            if self._ldap_security in ("tls", "starttls"):
                logger.debug("_login3 using encryption (reader)")
                verifyMode = {"NONE": ssl.CERT_NONE,
                              "OPTIONAL": ssl.CERT_OPTIONAL,
                              "REQUIRED": ssl.CERT_REQUIRED}
                tls = self.ldap3.Tls(validate=verifyMode[self._ldap_ssl_verify_mode])
                if self._ldap_ssl_ca_file != "":
                    tls = self.ldap3.Tls(validate=verifyMode[self._ldap_ssl_verify_mode], ca_certs_file=self._ldap_ssl_ca_file)
                if self._ldap_security == "tls":
                    logger.debug("_login3 using ssl (reader)")
                    server = self.ldap3.Server(self._ldap_uri, use_ssl=True, tls=tls)
                else:
                    server = self.ldap3.Server(self._ldap_uri, use_ssl=False, tls=tls)
            else:
                logger.debug("_login3 not using encryption (reader)")
                server = self.ldap3.Server(self._ldap_uri)
            try:
                conn = self.ldap3.Connection(server, self._ldap_reader_dn, password=self._ldap_secret, auto_bind=False, raise_exceptions=True)
                if self._ldap_security == "starttls":
                    logger.debug("_login3 using starttls (reader)")
                    conn.start_tls()
            except self.ldap3.core.exceptions.LDAPStartTLSError as e:
                raise RuntimeError(f"_login3 StartTLS Error: {e}")
        except self.ldap3.core.exceptions.LDAPSocketOpenError:
            raise RuntimeError("Unable to reach LDAP server")
        except Exception as e:
            logger.debug(f"_login3 error 1 {e} (reader)")
            pass
        if not conn.bind(read_server_info=False):
            logger.debug("_login3 cannot bind (reader)")
            raise RuntimeError("Unable to read from LDAP server")
        logger.debug(f"_login3 bind as {self._ldap_reader_dn}")
        """Search the user dn"""
        escaped_login = self.ldap3.utils.conv.escape_filter_chars(login)
        logger.debug(f"_login3 login escaped for LDAP filters: {escaped_login}")
        try:
            conn.search(
                search_base=self._ldap_base,
                search_filter=self._ldap_filter.format(escaped_login),
                search_scope=self.ldap3.SUBTREE,
                attributes=self._ldap_attributes
            )
        except Exception as e:
            logger.error(f"_login3 LDAP search for {login} failed: {e}")
            return ""
        if len(conn.entries) != 1:
            """User could not be found unambiguously"""
            logger.debug(f"_login3 no unique DN found for '{login}'")
            return ""

        user_entry = conn.response[0]
        user_dn = user_entry['dn']
        logger.debug(f"_login3 found LDAP user DN {user_dn}")

        """Let's collect the groups of the user."""
        groupDNs = []
        if self._ldap_groups_attr:
            if user_entry['attributes'][self._ldap_groups_attr]:
                if isinstance(user_entry['attributes'][self._ldap_groups_attr], list):
                    groupDNs = user_entry['attributes'][self._ldap_groups_attr]
                else:
                    groupDNs.append(user_entry['attributes'][self._ldap_groups_attr])

        """Search for all groups having the user_dn found as member."""
        if self._ldap_group_members_attr:
            try:
                conn.search(
                    search_base=self._ldap_group_base,
                    search_filter="(&{0}({1}={2}))".format(
                        self._ldap_group_filter,
                        self._ldap_group_members_attr,
                        self.ldap3.utils.conv.escape_filter_chars(user_dn)),
                    search_scope=self.ldap3.SUBTREE,
                    attributes=['1.1']
                )
            except Exception as e:
                """LDAP search failed: consider it as non-fatal - only groups missing"""
                logger.debug(f"_ldap3: LDAP group search failed: {e}")
            else:
                """Fill groupDNs with DNs of groups found"""
                groupDNs = []
                for group in conn.response:
                    groupDNs.append(group['dn'])

        """Close LDAP connection"""
        conn.unbind()

        try:
            """Try to bind as the user itself"""
            try:
                conn = self.ldap3.Connection(server, user_dn, password=password, auto_bind=False)
                if self._ldap_security == "starttls":
                    logger.debug("_login3 using starttls (user)")
                    conn.start_tls()
            except self.ldap3.core.exceptions.LDAPStartTLSError as e:
                raise RuntimeError(f"_login3 StartTLS Error: {e}")
            if not conn.bind(read_server_info=False):
                logger.debug(f"_login3 user '{login}' cannot be found")
                return ""

            """Get RDNs of groups' DNs"""
            tmp = []
            for g in groupDNs:
                try:
                    rdns = self.ldap3.utils.dn.parse_dn(g)
                    tmp.append(rdns[0][1])
                except Exception:
                    tmp.append(g)
            self._ldap_groups = set(tmp)
            logger.debug("_login3 LDAP groups of user: %s", ",".join(self._ldap_groups))

            if self._ldap_user_attr:
                if user_entry['attributes'][self._ldap_user_attr]:
                    if isinstance(user_entry['attributes'][self._ldap_user_attr], list):
                        login = user_entry['attributes'][self._ldap_user_attr][0]
                    else:
                        login = user_entry['attributes'][self._ldap_user_attr]
                    logger.debug(f"_login3 user set to: '{login}'")
            conn.unbind()
            logger.debug(f"_login3 {login} successfully authenticated")
            return login
        except Exception as e:
            logger.debug(f"_login3 error 2 {e}")
            pass
        return ""

    def _login(self, login: str, password: str) -> str:
        """Validate credentials.
        In first step we make a connection to the LDAP server with the ldap_reader_dn credential.
        In next step the DN of the user to authenticate will be searched.
        In the last step the authentication of the user will be proceeded.
        """
        if self._ldap_module_version == 2:
            return self._login2(login, password)
        return self._login3(login, password)
