#!/bin/sh
#
# hgmerge - default merge helper for Mercurial
#
# This tries to find a way to do three-way merge on the current system.
# The result ought to end up in $1.

set -e # bail out quickly on failure

LOCAL="$1"
BASE="$2"
OTHER="$3"

if [ -z "$EDITOR" ]; then
    EDITOR="vi"
fi

# find decent versions of our utilities, insisting on the GNU versions where we
# need to
MERGE=merge
DIFF3=gdiff3
DIFF=gdiff
PATCH=gpatch

type $MERGE >/dev/null 2>&1 || MERGE=
type $DIFF3 >/dev/null 2>&1 || DIFF3=diff3
type $DIFF  >/dev/null 2>&1 || DIFF=diff
type $PATCH >/dev/null 2>&1 || PATCH=patch
$DIFF3 --version >/dev/null 2>&1 || DIFF3=

# find optional visual utilities
FILEMERGE='/Developer/Applications/Utilities/FileMerge.app/Contents/MacOS/FileMerge'
KDIFF3=kdiff3
TKDIFF=tkdiff

type $FILEMERGE >/dev/null 2>&1 || FILEMERGE=
type $KDIFF3    >/dev/null 2>&1 || KDIFF3=
type $TKDIFF    >/dev/null 2>&1 || TKDIFF=

# random part of names
RAND="$RANDOM.$RANDOM.$RANDOM.$$"

# temporary directory for diff+patch merge
HGTMP="${TMPDIR-/tmp}/hgmerge.$RAND"

# backup file
BACKUP="$LOCAL.orig.$RAND"

# file used to test for file change
CHGTEST="$LOCAL.chg.$RAND"

# put all your required cleanup here
cleanup() {
    rm -f "$BACKUP" "$CHGTEST"
    rm -rf "$HGTMP"
}

# functions concerning program exit
success() {
    cleanup
    exit 0
}

failure() {
    echo "merge failed" 1>&2
    mv "$BACKUP" "$LOCAL"
    cleanup
    exit 1
}

# Clean up when interrupted
trap "failure" 1 2 3 6 15 # HUP INT QUIT ABRT TERM

# Back up our file (and try hard to keep the mtime unchanged)
mv "$LOCAL" "$BACKUP"
cp "$BACKUP" "$LOCAL"

# Attempt to do a non-interactive merge
if [ -n "$MERGE" ]; then
    $MERGE "$LOCAL" "$BASE" "$OTHER" 2> /dev/null && success
    cp "$BACKUP" "$LOCAL"
elif [ -n "$DIFF3" ]; then
    echo $DIFF3 -m "$BACKUP" "$BASE" "$OTHER"
    $DIFF3 -m "$BACKUP" "$BASE" "$OTHER" > "$LOCAL" && success
    if [ $? -eq 2 ]; then
        echo "$DIFF3 failed! Exiting." 1>&2
        cp "$BACKUP" "$LOCAL"
        failure
    fi
    cp "$BACKUP" "$LOCAL"
fi

# on MacOS X try FileMerge.app, shipped with Apple's developer tools
if [ -n "$FILEMERGE" ]; then
    cp "$BACKUP" "$LOCAL"
    cp "$BACKUP" "$CHGTEST"
    # filemerge prefers the right by default
    $FILEMERGE -left "$OTHER" -right "$LOCAL" -ancestor "$BASE" -merge "$LOCAL"
    [ $? -ne 0 ] && echo "FileMerge failed to launch" && failure
    if test "$LOCAL" -nt "$CHGTEST"
    then
        success
    else
        echo "$LOCAL seems unchanged. Was the merge successful?"
        select answer in yes no
        do
            test "$answer" == "yes" && success || failure
        done
    fi
    failure
fi

if [ -n "$DISPLAY" ]; then
    # try using kdiff3, which is fairly nice
    if [ -n "$KDIFF3" ]; then
	$KDIFF3 --auto "$BASE" "$LOCAL" "$OTHER" -o "$LOCAL" || failure
	success
    fi

    # try using tkdiff, which is a bit less sophisticated
    if [ -n "$TKDIFF" ]; then
	$TKDIFF "$LOCAL" "$OTHER" -a "$BASE" -o "$LOCAL" || failure
	success
    fi
fi

# Attempt to do a merge with $EDITOR
if [ -n "$MERGE" ]; then
    echo "conflicts detected in $LOCAL"
    $MERGE "$LOCAL" "$BASE" "$OTHER" 2>/dev/null || $EDITOR "$LOCAL"
    success
fi

if [ -n "$DIFF3" ]; then
    echo "conflicts detected in $LOCAL"
    $DIFF3 -m "$BACKUP" "$BASE" "$OTHER" > "$LOCAL" || {
        case $? in
            1)
                $EDITOR "$LOCAL" ;;
            2)  echo "$DIFF3 failed! Exiting." 1>&2
                cp "$BACKUP" "$LOCAL"
                failure ;;
        esac
        success
    }
fi

# attempt to manually merge with diff and patch
if [ -n "$DIFF" -a -n "$PATCH" ]; then

    (umask 077 && mkdir "$HGTMP") || {
	echo "Could not create temporary directory $HGTMP" 1>&2
	failure
    }

    $DIFF -u "$BASE" "$OTHER" > "$HGTMP/diff" || :
    if $PATCH "$LOCAL" < "$HGTMP/diff"; then
	success
    else
	# If rejects are empty after using the editor, merge was ok
	$EDITOR "$LOCAL" "$LOCAL.rej" && test -s "$LOCAL.rej" || success
    fi
    failure
fi

echo "hgmerge: unable to find merge, tkdiff, kdiff3, or diff+patch!"
failure