#!/bin/sh

DEF_VER=0.21.GITGUI

LF='
'

if test "$#" -ne 2
then
	echo >&2 "usage: $0 <SOURCE_DIR> <OUTPUT>"
	exit 1
fi

SOURCE_DIR="$1"
OUTPUT="$2"

# Protect us from reading Git version information outside of the Git directory
# in case it is not a repository itself, but embedded in an unrelated
# repository.
GIT_CEILING_DIRECTORIES="$SOURCE_DIR/.."
export GIT_CEILING_DIRECTORIES

tree_search ()
{
	head=$1
	tree=$2
	for p in $(git -C "$SOURCE_DIR" rev-list --parents --max-count=1 $head 2>/dev/null)
	do
		test $tree = $(git -C "$SOURCE_DIR" rev-parse $p^{tree} 2>/dev/null) &&
		vn=$(git -C "$SOURCE_DIR" describe --abbrev=4 $p 2>/dev/null) &&
		case "$vn" in
		gitgui-[0-9]*) echo $vn; break;;
		esac
	done
}

# Always use the tarball version file if found, just
# in case we are somehow contained in a larger git
# repository that doesn't actually track our state.
# (At least one package manager is doing this.)
#
# We may be a subproject, so try looking for the merge
# commit that supplied this directory content if we are
# not at the toplevel.  We probably will always be the
# second parent in the commit, but we shouldn't rely on
# that fact.
#
# If we are at the toplevel or the merge assumption fails
# try looking for a gitgui-* tag.

if test -f "$SOURCE_DIR"/version &&
   VN=$(cat "$SOURCE_DIR"/version)
then
	: happy
elif prefix="$(git -C "$SOURCE_DIR" rev-parse --show-prefix 2>/dev/null)"
   test -n "$prefix" &&
   head=$(git -C "$SOURCE_DIR" rev-list --max-count=1 HEAD -- . 2>/dev/null) &&
   tree=$(git -C "$SOURCE_DIR" rev-parse --verify "HEAD:$prefix" 2>/dev/null) &&
   VN=$(tree_search $head $tree)
   case "$VN" in
   gitgui-[0-9]*) : happy ;;
   *) (exit 1) ;;
   esac
then
	VN=$(echo "$VN" | sed -e 's/^gitgui-//;s/-/./g');
elif VN=$(git -C "$SOURCE_DIR" describe --abbrev=4 HEAD 2>/dev/null) &&
   case "$VN" in
   gitgui-[0-9]*) : happy ;;
   *) (exit 1) ;;
   esac
then
	VN=$(echo "$VN" | sed -e 's/^gitgui-//;s/-/./g');
else
	VN="$DEF_VER"
fi

dirty=$(git -C "$SOURCE_DIR" diff-index --name-only HEAD 2>/dev/null) || dirty=
case "$dirty" in
'')
	;;
*)
	VN="$VN-dirty" ;;
esac

if test -r "$OUTPUT"
then
	VC=$(sed -e 's/^GITGUI_VERSION=//' <"$OUTPUT")
else
	VC=unset
fi
test "$VN" = "$VC" || {
	echo >&2 "GITGUI_VERSION=$VN"
	echo "GITGUI_VERSION=$VN" >"$OUTPUT"
}