#!/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"
$DIFF3 --version >/dev/null 2>&1 || DIFF3=
type "$DIFF"  >/dev/null 2>&1 || DIFF="diff"
type "$DIFF"  >/dev/null 2>&1 || DIFF=
type "$PATCH" >/dev/null 2>&1 || PATCH="patch"
type "$PATCH" >/dev/null 2>&1 || PATCH=

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

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

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

# Ask if the merge was successful
ask_if_merged() {
    while true; do
        echo "$LOCAL seems unchanged."
        echo "Was the merge successful? [y/n]"
        read answer
        case "$answer" in
            y*|Y*) success;;
            n*|N*) failure;;
        esac
    done
}

# 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 "$MERGE" -o -n "$DIFF3" ]; then
    if [ -n "$MERGE" ]; then
        $MERGE "$LOCAL" "$BASE" "$OTHER" 2> /dev/null && success
    elif [ -n "$DIFF3" ]; then
        $DIFF3 -m "$BACKUP" "$BASE" "$OTHER" > "$LOCAL" && success
    fi
    if [ $? -gt 1 ]; then
        echo "automatic merge failed! Exiting." 1>&2
        failure
    fi
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"
    [ $? -ne 0 ] && echo "FileMerge failed to launch" && failure
    test "$LOCAL" -nt "$CHGTEST" && success || ask_if_merged
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

    if [ -n "$MELD" ]; then
        cp "$BACKUP" "$CHGTEST"
        # protect our feet - meld allows us to save to the left file
        cp "$BACKUP" "$LOCAL.tmp.$RAND"
        # Meld doesn't have automatic merging, so to reduce intervention
        # use the file with conflicts
        $MELD "$LOCAL.tmp.$RAND" "$LOCAL" "$OTHER" || failure
        # Also it doesn't return good error code
        test "$LOCAL" -nt "$CHGTEST" && success || ask_if_merged
    fi
fi

# Attempt to do a merge with $EDITOR
if [ -n "$MERGE" -o -n "$DIFF3" ]; then
    echo "conflicts detected in $LOCAL"
    cp "$BACKUP" "$CHGTEST"
    $EDITOR "$LOCAL" || failure
    # Some editors do not return meaningful error codes
    # Do not take any chances
    test "$LOCAL" -nt "$CHGTEST" && success || ask_if_merged
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" "$LOCAL.rej" || failure
        test -s "$LOCAL.rej" || success
    fi
    failure
fi

echo
echo "hgmerge: unable to find any merge utility!"
echo "supported programs:"
echo "merge, FileMerge, tkdiff, kdiff3, meld, diff+patch"
echo
failure