#!/bin/sh

usage () {
	echo "usage:" $@
	exit 127
}

die () {
	echo $@
	exit 128
}

if test $# -lt 2 || test $# -gt 3
then
	usage "$0 <repository> <new_workdir> [<branch>]"
fi

orig_git=$1
new_workdir=$2
branch=$3

# want to make sure that what is pointed to has a .git directory ...
git_dir=$(cd "$orig_git" 2>/dev/null &&
  git rev-parse --git-dir 2>/dev/null) ||
  die "Not a git repository: \"$orig_git\""

case "$git_dir" in
.git)
	git_dir="$orig_git/.git"
	;;
.)
	git_dir=$orig_git
	;;
esac

# don't link to a configured bare repository
isbare=$(git --git-dir="$git_dir" config --bool --get core.bare)
if test ztrue = z$isbare
then
	die "\"$git_dir\" has core.bare set to true," \
		" remove from \"$git_dir/config\" to use $0"
fi

# don't link to a workdir
if test -h "$git_dir/config"
then
	die "\"$orig_git\" is a working directory only, please specify" \
		"a complete repository."
fi

# don't recreate a workdir over an existing repository
if test -e "$new_workdir"
then
	die "destination directory '$new_workdir' already exists."
fi

# create the workdir
mkdir -p "$new_workdir/.git" || die "unable to create \"$new_workdir\"!"

cd "$git_dir"
mkdir -vp logs/refs # required for bare repositories
git_dir=$(pwd) # make sure the links use full paths
orig_list=$(echo * info/*)
cd - >/dev/null
cd "$new_workdir/.git"
ln -s "$git_dir" orig_git

# create the links to the original repo.  explicitly exclude index, HEAD and
# logs/HEAD from the list since they are purely related to the current working
# directory, and should not be shared.
for x in $orig_list packed-refs logs/refs
do
	case "$x" in
	*\**|rebase-*)
		continue ;;
	logs|info)
		mkdir "$x" ;;
	HEAD)
		# copy the HEAD from the original repository as a default branch
		cp "orig_git/$x" . ;;
	*/*|config|packed-refs)
		;;
	*)
		[ -d "orig_git/$x" ] || continue ;;
	esac
	[ -e "$x" -o -L "$x" ] || {
		set $(echo "$x" |sed 's,[^/]\+,..,g')
		ln -s "${1%..}orig_git/$x" "$x"
	}
done

[ "$branch" ] || exit 0

# now setup the workdir
cd ..
# checkout the branch (either the same as HEAD from the original repository, or
# the one that was asked for)
git checkout -f $branch