#!/bin/bash

SELF=$(basename "${0}")

usage() {
	echo "Usage: ${SELF} [srctree]" >&2
	exit 1
}

cd "${1:-.}" || usage

# helper functions
invoked_as() {
	[[ "${SELF}" == *"${1}" ]]
}
print_value_fallback_to_unknown() {
	echo "${1:-unknown}"
}

# git helper functions
git_hash() {
	git rev-parse --verify "$@"
}
git_hash_YYYYMMDD() {
	git log --pretty='format:%cd' --date=format:'%Y%m%d' -1 "$@"
}
git_branch() {
	git rev-parse --abbrev-ref "$@"
}
github_commit_url() {
	local remote_origin_url="$1"
	local commit_id="$2"
	local domain_pattern="github[.]com"
	echo "${remote_origin_url}" \
		| sed -r -e 's,^(git://|http://|https://|ssh://git@|git@)('"${domain_pattern}"')[:/],https://\2/,' \
		| sed -n -r -e 's,^(https://'"${domain_pattern}"'/.+)[.]git$,\1/commit/'"${commit_id}"',p'
}

# check for git and a git repo
if head_id_long=$(git_hash @ 2>/dev/null); then
	local_branch=$(git_branch @)

	# check for uncommitted changes
	#
	# The solution implemented below is based on the following kernel commits (time order, the latest is the most important one):
	#   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=6147b1cf19651c7de297e69108b141fb30aa2349
	#   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=8ef14c2c41d962756d314f1d7dc972b0ea7a180f
	#   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=ff64dd4857303dd5550faed9fd598ac90f0f2238
	# We intentionally do not implement the fallback to
	#   git diff-index --name-only @
	# as it produces unreliable results (false positives for "dirty") when invoked in fakeroot context.
	# Instead we prefer to omit the dirty-flag completely if it could not be determined in a reliable way.
	# Note --no-optional-locks is supported since git-2.15.0
	if git --no-optional-locks status -uno --porcelain 2>/dev/null | read dummy; then
		dirty="-dirty"
	fi

	# check for untracked files (unused so far)
#	if git ls-files --other --directory --exclude-standard | read dummy; then
#		untracked="-untracked"
#	fi

	# HEAD based version
	if invoked_as version; then
		head_id_short=$(git_hash --short @)
		head_YYYYMMDD=$(git_hash_YYYYMMDD @)

		VERSION="${local_branch}-${head_YYYYMMDD}-${head_id_short}${dirty}"
	fi

	# URL of the HEAD based version
	if invoked_as version-url; then
		remote_origin_url=$(git config --get remote.origin.url)
		VERSION_URL=$(github_commit_url "${remote_origin_url}" "${head_id_long}")
	fi

	# "upstream + number of local commits" based version
	if invoked_as version-upstream; then
		upstream_branch=$(git_branch @{upstream} 2>/dev/null || git_branch master@{upstream} 2>/dev/null)
		if [ $? -eq 0 ]; then
			upstream_last_commit_id_long=$(git_hash ${upstream_branch})
			upstream_last_commit_id_short=$(git_hash --short ${upstream_branch})
			upstream_last_commit_YYYYMMDD=$(git_hash_YYYYMMDD ${upstream_last_commit_id_long})

			local_branch_no_of_commits_ahead=$(git rev-list --no-merges --count ${upstream_branch}..@)
			if [ "${local_branch_no_of_commits_ahead}" -gt 0 ]; then
				ahead="+${local_branch_no_of_commits_ahead}"
			fi

			local_branch_no_of_commits_behind=$(git rev-list --no-merges --count @..${upstream_branch})
			if [ "${local_branch_no_of_commits_behind}" -gt 0 ]; then
				behind="-${local_branch_no_of_commits_behind}"
			fi

			VERSION_UPSTREAM="${local_branch}-${upstream_last_commit_YYYYMMDD}-${upstream_last_commit_id_short}${ahead}${behind}${dirty}"
		fi
	fi
elif [ -f .freetz-version ] || [ -f ../.freetz-version ]; then
	# .freetz-version file containing the (fixed) version number
	# this is intended to be used for release tarballs containing no repository information
	VERSION=$(cat .freetz-version 2>/dev/null || cat ../.freetz-version 2>/dev/null)
fi

if invoked_as version; then
	print_value_fallback_to_unknown "${VERSION}"
elif invoked_as version-url; then
	print_value_fallback_to_unknown "${VERSION_URL}"
elif invoked_as version-upstream; then
	print_value_fallback_to_unknown "${VERSION_UPSTREAM}"
fi