#!/usr/bin/env bash
#
#  File    : svndiff
#  Author  : Matthias Hüsken
#  Purpose : A wrapper to call an arbitrary diff-program in a subversion
#            working copy. Reads the environment variable SVN_DIFF which
#            the user can use to specify his/her favourite diff-program
#            (like diff, mgdiff, tkdiff etc.). The current version in the 
#            working copy is compared to the version in the HEAD revision.
#
#            Script will most probably become obsolete as soon as the
#            subversion APIs for external diff'ing are released.
#
#            Requirements for the script to run properly:
#            - bash :-)
#            - mktemp in $PATH
#            - svn in $PATH
#            - write access to /tmp
#            - a diff program that is called via
#                DIFF_PROG file1 file2
#            - probably a subversion repository...
#            

# if the SVN_DIFF environment variable is not set, fall back to the diff
# program specified here
DIFF_PROG=mgdiff
TMPFILE=""

# remove tmp-file and leave program
function cleanup ()
 {
   # remove the tempfile
   if [ -f $TMPFILE ]
   then
     rm -rf $TMPFILE
   fi
   # look for return value
   if [ $# -le 1 ]
   then 
     VAL=1
   else
     VAL=$1
   fi
   # leave program
   exit $1
 }


# if no arg is given, display usage info and exit
if [ $# -ne 1 ]
then
  echo "Usage is: $0 FILE"
  cleanup 1
fi

# create temp file
TMPFILE=`mktemp -q /tmp/svntmp.XXXXXX`
if [ $? -ne 0 -o ! -f $TMPFILE ]
then
  echo "Couldn't create temp file..."
  cleanup 1
fi

# look for diff program
DIFF="unknown"
# first try $SVN_DIFF
if [ ! -z $SVN_DIFF ]
then
  DIFF=`which $SVN_DIFF 2> /dev/null || echo unknown`
  SEARCHED=$SVN_DIFF
fi
# if we found the prog, everything's fine
# otherwise look for prog specified above...
if [ $DIFF == "unknown" ]
then 
  DIFF=`which $DIFF_PROG 2> /dev/null || echo unknown`
  if [ ! ${SEARCHED}x = x ]; then SEARCHED="$SEARCHED or "; fi
  SEARCHED="$SEARCHED$DIFF_PROG"
  # if we still coudn't find a diff, exit
  if [ $DIFF == "unknown" ]
  then 
    echo "Couldn't find $SEARCHED, is it installed and in \$PATH?"
    cleanup 2
  fi
fi
echo "using diff: $DIFF"

# look for svn
SVN=`which svn 2> /dev/null || echo unknown`
# if we can't find it, exit
if [ $SVN == "unknown" ]
then 
  echo "Couldn't find svn, is it installed and in \$PATH?"
  cleanup 3
fi

# test if the desired file exists
if [ ! -r $1 ]
then
  echo "File $1 doesn't exist..."
  cleanup 4
fi

# get file from latest svn HEAD revision
$SVN cat $1 >> $TMPFILE
RETVAL=$?
# if we successfully retrieved the file, do the actual diff
if [ $RETVAL -eq 0 ]
then
  $DIFF $1 $TMPFILE
fi
# if we were not successful retrieving the file from svn, exit
if [ $RETVAL -ne 0 ]
then
  echo "Couldn't retrieve HEAD revision from svn..."
  cleanup 5
fi