#!/usr/bin/env bash
# Copyright (c) 2005, Intel Corporation, James Ketrenos

function die()
{
	ret=$1
	shift
	echo $@ >&2
	exit $ret
}

[ ! "$MERGE" ] && 
	die 1 "MERGE must be set to merge program (ie, export MERGE=kdiff3)"

parent=
branch=
function get_parent_and_branch()
{
	[ ! -e .git/refs/parent ] && return 1
	parent=$(cat .git/refs/parent)
	[ ! "$parent" ] && return 1

	if echo ${parent} | egrep -q "#"; then
		branch="refs/heads/"$(echo $parent | sed -ne "s,.*#\(.*\),\1,p")
		parent=$(echo $parent | sed -e "s,\([^#]*\).*,\1,")
	else
		branch="HEAD"
	fi

	echo $parent | grep "/\$" || parent="${parent}/"

	return 0
}

function merge_parent()
{
	[ -e ".git/refs/heads/repository.merge" ] && 
		die 9 "Prior merge failed and not un-done."

	repo=$1
	branch=$2
	echo $repo | grep "/\$" || repo="${repo}/"
#	First verify there are no uncommitted changes, then proceed...
#	(TODO: Add script commands for checking for uncommitted changes)
#
#	Obtain the parent's HEAD and store as .git/refs/heads/parent.tip and
#		.git/refs/heads/parent.merge
	echo "Checking for updates from ${repo}${branch}..."

	rsync ${RSYNC_FLAGS} -vpL ${repo}${branch} .git/refs/heads/parent.tip || return 1

	parent=$(cat .git/refs/heads/parent)
	new_parent=$(cat .git/refs/heads/parent.tip)
	echo $new_parent > .git/refs/heads/parent.merge || return 2

#	Check for an update; if no update, we're done
	[ "$parent" == "$new_parent" ] && return 0

	child=$(cat .git/HEAD)

#	Grab the latest objects from the parent
	echo "Pulling object files"
	rsync ${RSYNC_FLAGS} -avpr ${repo}objects/ .git/objects/ || return 3

#	Copy the current HEAD to .git/refs/heads/repository.merge
	echo "Caching HEAD in repository.merge"
	cp .git/HEAD .git/refs/heads/repository.merge || return 4


#	Update the GIT index
	echo "Setting local repository to mirror parent"
	echo $new_parent > .git/HEAD || return 5
	rm .git/index
	git-read-tree -m HEAD || return 6
#	git-checkout-cache -f -u -a

# 	At this point, our local repository is now a mirror of the 
#	parent repository.  

#	Merge and commit the repository changes back into the current parent
	echo "Merging child back into parent"
	git-merge-heads $new_parent $child || return 7

#	Update parent / repo index links
	mv -f .git/refs/heads/parent.tip .git/refs/heads/parent || return 12

	mv .git/refs/heads/repository.merge .git/refs/heads/pre-merge
	
	echo "Updating ancestors file..."
	url=$(cat .git/refs/parent)
	sed -i -e "s#$url\t$parent#$url\t$new_parent#g" \
		.git/refs/ancestors
	return 0
}

function merge_cleanup()
{
#	If any of the above fails, the repository should be changed back 
#	to its original state:
	
	rm -f .git/refs/heads/{parent,repository}.merge \
		.git/refs/heads/parent.tip || \
		return 1
	ln -sf refs/heads/master .git/HEAD || return 2
	git-read-tree -m HEAD || return 3
	git-checkout-files -q -f -u -a || return 4

	return 0
}

if ! get_parent_and_branch; then
#	merge_cleanup
	exit 1
fi

echo -e "Attempting merging with:\n\t$parent\n..."
merge_parent $parent $branch || 
	die 12 "Error merging parent."

rm -rf .git/merge*

exit 0