#!/bin/bash

# Zit: the git-based single-file content tracker

abort() {
	echo $1
	exit 1
}

me="$(basename $0)"
if test "$me" = zit ; then
	cmd="$1"
	shift
else
	cmd="$me"
fi

USAGE="usage: zit COMMAND FILE [ARGS...]"

zit_help() {
	cmd="$1"
	shift
	case "$cmd" in
		git)
		git help "$@"
		;;
		list|tracked)
		echo "usage: zit list"
		echo "Show tracked files, with a one-letter prefix indicating their status:"
		echo "   H   cached"
		echo "   M   unmerged"
		echo "   R   removed/deleted"
		echo "   C   modified/changed"
		echo "   K   to be killed"
		echo "   ?   other"
		;;
		import)
		echo "usage: zit import FILE"
		echo "Import history from an RCS-tracked file. Requires rcs-fast-export."
		;;
		view)
		echo "usage: zit view FILE"
		echo "Browse FILE's history with gitk (if possible) or tig."
		;;
		with)
		echo "usage: zit with FILE COMMAND..."
		echo "Run COMMAND after setting up the git environment for FILE."
		;;
		clone)
		echo "usage: zit clone REPO [FILE]"
		echo "Create and track FILE, retrieving its history from repository REPO."
		echo "FILE is guessed by REPO by stripping the '.git' suffix from the last path component"
		;;
		*)
		echo $USAGE
		echo ""
		echo "Set up a git repository under .zit.FILE to track changes for FILE."
		echo "File must be a regular file and in the current directory."
		echo ""
		echo "Zit commands:"
		echo "   clone	Clone and track a remote file"
		echo "   import	Import RCS history for FILE"
		echo "   init		Synonym for track"
		echo "   list		Synonym for tracked"
		echo "   track	Start tracking changes to FILE"
		echo "   tracked	List tracked files in current directory"
		echo "   view		Browse FILE's history with gitk or tig"
		echo "   with		Run a command in FILE's context"
		echo ""
		echo "See 'zit help git' or 'git help' for git commands."
		;;
		zig)
		echo "usage: zig FILE"
		echo "Browse FILE's history with tig."
		;;
		zik)
		echo "usage: zik FILE"
		echo "Browse FILE's history with gitk."
		;;
	esac
}

ZIT_DIR=.zit

zit_setup() {
	ZIT_FILE="$1"
	test $ZIT_FILE || abort "Please specify a file"
	test -f $ZIT_FILE || abort "No such file $ZIT_FILE"
	test $ZIT_FILE = "`basename $ZIT_FILE`" || abort "Sorry, Zit only works on files in the current directory"

	export GIT_WORK_TREE="`pwd`"

	# first, check if a repo exists already, looking for
	# .zit/file.git or .file.git, in that order
	# if neither is found, and .zit exists, set the repo dir
	# to .zit/file.git, otherwise set it to .file.git
	GIT_DIR="$ZIT_DIR/$ZIT_FILE.git"
	if ! test -d "$GIT_DIR"; then
		GIT_DIR=".$ZIT_FILE.git"
		if ! test -d "$GIT_DIR"; then
			test -d "$ZIT_DIR" && GIT_DIR="$ZIT_DIR/$ZIT_FILE.git"
		fi
	fi
	export GIT_DIR
}

# initialize the zitdir, without actually making the first commit
zitdir_init() {
	zit_setup $1
	test -e $GIT_DIR && abort "$GIT_DIR exists, is $ZIT_FILE tracked already?"
	mkdir $GIT_DIR && echo "Initializing Zit repository in $GIT_DIR"
	test -d $GIT_DIR || abort "Failed to create $GIT_DIR"
	git init || abort "Failed to initialize Git repository in $GIT_DIR"
	rm -rf $GIT_DIR/{hooks,info,branches,refs/tags,objects/pack,description}
	if test -d "$ZIT_DIR"; then
		ZIT_EXCLUDE="$ZIT_DIR/exclude"
	else
		ZIT_EXCLUDE="$GIT_DIR/exclude"
	fi
	if ! test -f "$ZIT_EXCLUDE"; then
		touch "$ZIT_EXCLUDE" || abort "Cannot create $ZIT_EXCLUDE file"
		echo "# Ignore patterns used by Zit repositories in the parent worktree." > "$ZIT_EXCLUDE"
		echo "# By default it's the single '*' glob, since we want to ignore all" >> "$ZIT_EXCLUDE"
		echo "# non-tracked files in the work-tree." >> "$ZIT_EXCLUDE"
		echo "# This file is autogenerated and there's usually no need to edit it." >> "$ZIT_EXCLUDE"
		echo "*" >> "$ZIT_EXCLUDE"
	fi
	git config core.excludesfile "$ZIT_EXCLUDE"
}

zit_init() {
	if test "$1"; then
		zitdir_init "$1"
		git add -f $ZIT_FILE || abort "Failed to add $ZIT_FILE"
		git commit "$@" || abort "Failed to make first commit for $ZIT_FILE"
	else
		if test -d "$ZIT_DIR"; then
			echo "$ZIT_DIR exists already"
			exit
		fi
		test -e $ZIT_DIR && abort "$ZIT_DIR exists but it's not a directory, cannot continue"
		mkdir $ZIT_DIR
	fi
}

zit_list() {
	export GIT_WORK_TREE="`pwd`"
	GIT_DIR=""
	for file in "$ZIT_DIR"/*.git .*.git; do
		if ! test -e $file; then
			continue
		fi
		export GIT_DIR="$file"
		file="${file#.}"
		file="${file#zit/}"
		file="${file%.git}"
		(git ls-files -m -d -t; git ls-files -t) | uniq -f 1
	done;
	# if $GIT_DIR is empty, no files were found
	test "$GIT_DIR" || echo "(no files tracked by zit)"
}

# import an RCS-tracked file using rcs-fast-export, if found
zit_import() {
	which rcs-fast-export || abort "rcs-fast-export not found, I can't import RCS-tracked files, sorry"
	zitdir_init $1
	# git-fast-import creates a pack file, so (re)build the objects/pack dir
	mkdir -p $GIT_DIR/objects/pack
	rcs-fast-export $1 | git-fast-import
	# for some reason, rcs-fast-export | git-fast-import leaves the original
	# file in 'deleted' state, a situation which is easily fixed by adding
	# it back
	git add -f $1
}

zit_clone() {
	SRC="$1"
	test -n "$SRC" || abort "Where do you want to clone from?"
	if [ -n "$2" ]; then
		ZIT_FILE="$2"
	else
		ZIT_FILE=`basename $SRC .git`
	fi
	test -e "$ZIT_FILE" && abort "File $ZIT_FILE exists already"
	test "$ZIT_FILE" = "`basename $ZIT_FILE`" || abort "Sorry, Zit only works on files in the current directory"
	touch "$ZIT_FILE" # to make zit_setup happy
	zitdir_init "$ZIT_FILE"

	git remote add origin "$SRC"
	git remote update
	rm "$ZIT_FILE"
	git checkout -b master origin/master
}

case "$cmd" in
	"")
	echo $USAGE
	;;
	help|--help|-h|-?)
	zit_help "$@"
	;;
	init|track)
	zit_init $1
	;;
	clone)
	zit_clone "$@"
	;;
	list|tracked)
	zit_list
	;;
	import)
	zit_import $1
	;;
	view)
	zit_setup $1
	shift
	if test -n "$DISPLAY" -a -n "$(which gitk)" ; then
		gitk "$@"
	elif test -n "$(which tig)" ; then
		tig "$@"
	else
		abort "Neither gitk or tig could be launched"
	fi
	;;
	with)
	zit_setup $1
	shift
	"$@"
	;;
	zig)
	zit_setup $1
	shift
	tig "$@"
	;;
	zik)
	zit_setup $1
	shift
	gitk "$@"
	;;
	# Most commands will work with the generic catch-all mechanism used
	# below, but some of them require a more thorough analysis of the
	# parameters to decide whether $ZIT_FILE should be put back into the
	# parameter list or not. For example,
	# $ zit commit somefile
	# wouldn't do what one expects it to do, unless 'add' is run first,
	# (except that
	# $ zit add somefile
	# wouldn't work either), however
	# $ zit commit somefile -a
	# would work correctly. So we handle some commands separately (for the
	# moment just add and commit)
	add|commit)
	zit_setup $1
	shift
	git $cmd "$@" "$ZIT_FILE"
	;;
	# the raw<command> method can be used to not replicate $ZIT_FILE in the
	# parameter list
	raw*)
	zit_setup $1
	shift
	git ${cmd#raw} "$@"
	;;
	*)
	zit_setup $1
	shift
	git $cmd "$@"
	;;
esac