#!/bin/sh
#
# gvimdiff: display highlighted differences between two files side-by-side in
#           gvim
#
# Note: This program uses the Unix trick of using its name to alter behavior.
#       If this file is called gvimdiff, it brings up the differences in gvim.
#       If it is called vimdiff, it brings up the differences in vim.  If it is
#       called anything else, it fails with an error.  If you need vimdiff,
#       create a symbolic or hard link from gvimdiff to vimdiff.
#
# Author: Gautam H. Mudunuri (gmudunuri@informatica.com)
#
# $Revision: 1.2 $
#


# Get my name and verify it and determine whether to use vim/gvim
progname=`basename $0`
case "$progname" in
    vimdiff)
        vim_exe="vim"
        ;;
    gvimdiff)
        vim_exe="gvim"
        ;;
    *)
        echo >&2 "This program has an invalid name \"$progname\""
        exit 1
        ;;
esac

# Display usage and exit
Usage()
{
    # Options common to vimdiff and gvimdiff
    options="[ -s ]"
    options_desc="\
   -s          do not display identical lines
   -w width    width of diff output
               (default is set for diffs of 80 column wide files)"

    # Add gvimdiff specific options
    [ $vim_exe = "gvim" ] && {
        options="$options [ -f font ] [ -n ] [ -w width ]"
        options_desc="\
   -f font     font to use for display
   -n          do not create a wide window
               (useful if your display is not too wide)
$options_desc"
    }

    # Display usage and exit
    echo >&2 "\
$progname: \
display highlighted differences between two files side-by-side in $vim_exe

Usage: $progname $options arg1 arg2

Both the arguments must be file names OR one must be a file name and the
other a directory name.  If one of the arguments is a directory name, it
refers to the file in that directory with the same name as the other
argument.

Options:
$options_desc"
    exit 1
}

# Parse commandline
n_flag="n"
s_flag="n"
width=
font=
while getopts f:nsw: option
do
    case "$option" in
        f)
            [ $vim_exe != "gvim" ] && Usage
            [ "$font" != "" ] && Usage
            font="$OPTARG"
            ;;
        n)
            [ $vim_exe != "gvim" ] && Usage
            n_flag="y"
            ;;
        s)
            s_flag="y"
            ;;
        w)
            [ "$width" != "" ] && Usage
            width="$OPTARG"
            ;;
        *)
            Usage
            ;;
    esac
done
shift `expr $OPTIND - 1`
[ $# -eq 2 ] || Usage

# Arguments must be files or directories
arg1="$1"
[ -f $arg1 -o -d $arg1 ] || {
    echo >&2 "$progname: $arg1 is not a valid file or directory"
    exit 1
}
arg2="$2"
[ -f $arg2 -o -d $arg2 ] || {
    echo >&2 "$progname: $arg2 is not a valid file or directory"
    exit 1
}

# Both arguments cannot be directories
[ -d "$arg1" -a -d "$arg2" ] && {
    echo >&2 "$progname: $arg1 and $arg2 are both directories"
    echo >&2 "Atleast one file must be specified"
    exit 1
}

# If one argument is a directory, convert it to a filename using the other,
# otherwise use it directly
[ -d "$arg1" ] && file1="$arg1/`basename $arg2`" || file1="$arg1"
[ -d "$arg2" ] && file2="$arg2/`basename $arg1`" || file2="$arg2"

# Both files must be readable
[ -r "$file1" ] || {
    echo >&2 "$progname: cannot open $file1 for reading"
    exit 1
}
[ -r "$file2" ] || {
    echo >&2 "$progname: cannot open $file2 for reading"
    exit 1
}

# Width not specified, use default for 80-column wide files and 9 character
# sdiff "gutter".  (169 = 2 * 80 +  9)
[ "$width" = "" ] && width=169

# Validate width
expr "$width" + 0 > /dev/null 2>&1
status="$?"
[ $status -eq 0 -o $status -eq 1 ] || {
    echo >&2 "$progname: invalid width \"$width\""
    exit 1
}
[ $width -gt 0 ] || {
    echo >&2 "$progname: width $width cannot be zero or negative"
    exit 1
}
[ $width -ge 49 ] || {
    echo >&2 "$progname: width $width is too small, should be atleast 29"
    exit 1
}
[ $width -le 209 ] || {
    echo >&2 "$progname: width $width is too large, should be atmost 209"
    exit 1
}

# Compute width per file, allowing 9 characters for the sdiff "gutter"
file_width=`expr '(' $width - 9 ')' / 2`

# Compute the range of the number of characters we can expect before the sdiff
# separators |, < and >.  This is range rather than a specific number because
# the presence of tabs can shorten the length
min_chars=`expr $file_width - 5`
max_chars=`expr $file_width + 2`

# Define Vim commands for manipulating the sdiff buffer
buffercmds="
    set ts=8 et noro
    retab
    set nomod ro nows
"

# Define Vim commands for sdiff syntax highlighting.  We are going to define
# our custom syntax that is not loaded through the standard syntax mechanism.
# But we still need the standard colors to be defined.  So turn syntax on to
# get them and immediately turn it off
syncmds="
    syn on
    syn off
    syn match sdiffRemoved \"^.\{$min_chars,$max_chars}  <\"
    syn match sdiffChanged \"^.\{$min_chars,$max_chars}  |  .*$\"
    syn match sdiffAdded \"^.\{$min_chars,$max_chars}  >  .*$\"
    hi link sdiffRemoved  Comment
    hi link sdiffChanged  PreProc
    hi link sdiffAdded    Identifier
    let b:current_syntax = \"vimdiff\"
"

# Help commands (doesn't always work)
helpcmd_next="\
    echo 'Ctrl-N: Next Difference Line   Ctrl-P: Previous Difference Line'\
"
helpcmd_prev="\
    echo 'Ctrl-P: Previous Difference Line   Ctrl-N: Next Difference Line'\
"

# Define Vim mappings to jump to next/previous difference
mapcmds="
    nmap <c-n> /^.\{$min_chars,$max_chars}  [<>\|]/e<nl>:$helpcmd_next<nl>
    nmap <c-p> ?^.\{$min_chars,$max_chars}  [<>\|]?e<nl>:$helpcmd_prev<nl>
"

# Collect vim commands to be run
vimcmds="
    set titlestring=\\$progname\\ \\$arg1\\ \\$arg2
    set noml nows nowrap go=agrb ch=2
    $buffercmds
    $syncmds
    $mapcmds
    execute \"normal gg0$max_chars|3l\"
    $helpcmd_next
"

# Set sdiff_flags flags
sdiff_flags=
[ "$s_flag" = "y" ] && sdiff_flags="$flags -s"

# Set vim flags
vim_flags="-R -N"
[ "$font" != "" ] && vim_flags="$vim_flags -fn $font"
[ $n_flag != "y" -a $vim_exe = "gvim" ] && {
    vim_flags="$vim_flags -geometry $width"
}

# Run the diff and display the output in gvim
sdiff -w$width $sdiff_flags $file1 $file2 | $vim_exe $vim_flags -c "$vimcmds" -
