#!/bin/sh
# git-difftool-helper is a GIT_EXTERNAL_DIFF-compatible diff tool launcher.
# It supports kdiff3, kompare, tkdiff, xxdiff, meld, opendiff,
# emerge, ecmerge, vimdiff, gvimdiff, and custom user-configurable tools.
# This script is typically launched by using the 'git difftool'
# convenience command.
#
# Copyright (c) 2009 David Aguilar

# Set GIT_DIFFTOOL_NO_PROMPT to bypass the per-file prompt.
should_prompt () {
	test -z "$GIT_DIFFTOOL_NO_PROMPT"
}

# This function prepares temporary files and launches the appropriate
# merge tool.
launch_merge_tool () {
	# Merged is the filename as it appears in the work tree
	# Local is the contents of a/filename
	# Remote is the contents of b/filename
	# Custom merge tool commands might use $BASE so we provide it
	MERGED="$1"
	LOCAL="$2"
	REMOTE="$3"
	BASE="$1"

	# $LOCAL and $REMOTE are temporary files so prompt
	# the user with the real $MERGED name before launching $merge_tool.
	if should_prompt; then
		printf "\nViewing: '$MERGED'\n"
		printf "Hit return to launch '%s': " "$merge_tool"
		read ans
	fi

	# Run the appropriate merge tool command
	case "$merge_tool" in
	kdiff3)
		basename=$(basename "$MERGED")
		"$merge_tool_path" --auto \
			--L1 "$basename (A)" \
			--L2 "$basename (B)" \
			"$LOCAL" "$REMOTE" \
			> /dev/null 2>&1
		;;

	kompare)
		"$merge_tool_path" "$LOCAL" "$REMOTE"
		;;

	tkdiff)
		"$merge_tool_path" "$LOCAL" "$REMOTE"
		;;

	meld)
		"$merge_tool_path" "$LOCAL" "$REMOTE"
		;;

	vimdiff)
		"$merge_tool_path" -d -c "wincmd l" "$LOCAL" "$REMOTE"
		;;

	gvimdiff)
		"$merge_tool_path" -d -c "wincmd l" -f "$LOCAL" "$REMOTE"
		;;

	xxdiff)
		"$merge_tool_path" \
			-R 'Accel.Search: "Ctrl+F"' \
			-R 'Accel.SearchForward: "Ctrl-G"' \
			"$LOCAL" "$REMOTE"
		;;

	opendiff)
		"$merge_tool_path" "$LOCAL" "$REMOTE" | cat
		;;

	ecmerge)
		"$merge_tool_path" "$LOCAL" "$REMOTE" \
			--default --mode=merge2 --to="$MERGED"
		;;

	emerge)
		"$merge_tool_path" -f emerge-files-command \
			"$LOCAL" "$REMOTE" "$(basename "$MERGED")"
		;;

	*)
		if test -n "$merge_tool_cmd"; then
			( eval $merge_tool_cmd )
		fi
		;;
	esac
}

# Verifies that (difftool|mergetool).<tool>.cmd exists
valid_custom_tool() {
	merge_tool_cmd="$(git config difftool.$1.cmd)"
	test -z "$merge_tool_cmd" &&
	merge_tool_cmd="$(git config mergetool.$1.cmd)"
	test -n "$merge_tool_cmd"
}

# Verifies that the chosen merge tool is properly setup.
# Built-in merge tools are always valid.
valid_tool() {
	case "$1" in
	kdiff3 | kompare | tkdiff | xxdiff | meld | opendiff | emerge | vimdiff | gvimdiff | ecmerge)
		;; # happy
	*)
		if ! valid_custom_tool "$1"
		then
			return 1
		fi
		;;
	esac
}

# Sets up the merge_tool_path variable.
# This handles the difftool.<tool>.path configuration.
# This also falls back to mergetool defaults.
init_merge_tool_path() {
	merge_tool_path=$(git config difftool."$1".path)
	test -z "$merge_tool_path" &&
	merge_tool_path=$(git config mergetool."$1".path)
	if test -z "$merge_tool_path"; then
		case "$1" in
		vimdiff)
			merge_tool_path=vim
			;;
		gvimdiff)
			merge_tool_path=gvim
			;;
		emerge)
			merge_tool_path=emacs
			;;
		*)
			merge_tool_path="$1"
			;;
		esac
	fi
}

# Allow GIT_DIFF_TOOL and GIT_MERGE_TOOL to provide default values
test -n "$GIT_MERGE_TOOL" && merge_tool="$GIT_MERGE_TOOL"
test -n "$GIT_DIFF_TOOL" && merge_tool="$GIT_DIFF_TOOL"

# If merge tool was not specified then use the diff.tool
# configuration variable.  If that's invalid then reset merge_tool.
# Fallback to merge.tool.
if test -z "$merge_tool"; then
	merge_tool=$(git config diff.tool)
	test -z "$merge_tool" &&
	merge_tool=$(git config merge.tool)
	if test -n "$merge_tool" && ! valid_tool "$merge_tool"; then
		echo >&2 "git config option diff.tool set to unknown tool: $merge_tool"
		echo >&2 "Resetting to default..."
		unset merge_tool
	fi
fi

# Try to guess an appropriate merge tool if no tool has been set.
if test -z "$merge_tool"; then
	# We have a $DISPLAY so try some common UNIX merge tools
	if test -n "$DISPLAY"; then
		# If gnome then prefer meld, otherwise, prefer kdiff3 or kompare
		if test -n "$GNOME_DESKTOP_SESSION_ID" ; then
			merge_tool_candidates="meld kdiff3 kompare tkdiff xxdiff gvimdiff"
		else
			merge_tool_candidates="kdiff3 kompare tkdiff xxdiff meld gvimdiff"
		fi
	fi
	if echo "${VISUAL:-$EDITOR}" | grep 'emacs' > /dev/null 2>&1; then
		# $EDITOR is emacs so add emerge as a candidate
		merge_tool_candidates="$merge_tool_candidates emerge opendiff vimdiff"
	elif echo "${VISUAL:-$EDITOR}" | grep 'vim' > /dev/null 2>&1; then
		# $EDITOR is vim so add vimdiff as a candidate
		merge_tool_candidates="$merge_tool_candidates vimdiff opendiff emerge"
	else
		merge_tool_candidates="$merge_tool_candidates opendiff emerge vimdiff"
	fi
	echo "merge tool candidates: $merge_tool_candidates"

	# Loop over each candidate and stop when a valid merge tool is found.
	for i in $merge_tool_candidates
	do
		init_merge_tool_path $i
		if type "$merge_tool_path" > /dev/null 2>&1; then
			merge_tool=$i
			break
		fi
	done

	if test -z "$merge_tool" ; then
		echo "No known merge resolution program available."
		exit 1
	fi

else
	# A merge tool has been set, so verify that it's valid.
	if ! valid_tool "$merge_tool"; then
		echo >&2 "Unknown merge tool $merge_tool"
		exit 1
	fi

	init_merge_tool_path "$merge_tool"

	if test -z "$merge_tool_cmd" && ! type "$merge_tool_path" > /dev/null 2>&1; then
		echo "The merge tool $merge_tool is not available as '$merge_tool_path'"
		exit 1
	fi
fi


# Launch the merge tool on each path provided by 'git diff'
while test $# -gt 6
do
	launch_merge_tool "$1" "$2" "$5"
	shift 7
done