#! /usr/bin/env bash
# Copyright (C) 2011 Sebastian Pipping <sebastian@pipping.org>
# Licensed under GPL v3 or later
#
# 2011-04-01

GIT='git --no-pager'

# Require Git repository in reach
${GIT} show --oneline >/dev/null || exit 1

# Command line parameters
[[ $# == 0 ]] && tags=$(git tag -l) || tags=$@

abbrev() {
	sha1=$1
	${GIT} show -s --format=%h "${sha1}"
}

is_tag_object() {
	tag=$1
	[ $(${GIT} cat-file -t "${tag}") == tag ] && echo true || echo false
}

main() {
	for tag in ${tags}; do
		tag_ref=refs/tags/"${tag}"

		# Valid tag?
		${GIT} rev-parse "${tag_ref}" &>/dev/null || {
			echo "Tag '${tag}' not found, skipping" 1>&2
			continue
		}

		# Plain tag or tag object?
		tag_object=$(is_tag_object "${tag_ref}")
		if ${tag_object}; then
			cat_file_output=$(${GIT} cat-file tag "${tag}")
			commit_sha1=$(head -n 1 <<<"${cat_file_output}")
			commit_sha1=${commit_sha1##object }
			original_commit=${commit_sha1}
		else
			original_commit=$(${GIT} rev-parse ${tag_ref})
		fi

		# Get contained tree SHA1
		tree_sha1=$(${GIT} show -s '--format=%T' "${original_commit}")

		# Get earliest commit with same tree SHA1
		earliest_commit=$(${GIT} rev-list --all --topo-order \
			'--format=%H	%T' \
			| fgrep "${tree_sha1}" | tail -n 1 | cut -f 1)

		if [[ -z "${earliest_commit}" ]]; then
			echo "Sanity check failed, internal error" 1>&2
			exit 1
		fi

		# Work to do?
		if [[ "${earliest_commit}" == "${original_commit}" ]]; then
			printf "Tag '%s' (%s) already at earliest commit (%s), skipping\n" \
				"${tag}" \
				$(${tag_object} && echo object || echo plain) \
				$(abbrev "${original_commit}")
			continue
		fi

		if ${tag_object}; then
			tagger_line=$(tail -n +4 <<<"${cat_file_output}" | head -n 1)
			tagger_line=${tagger_line##tagger }

			tag_message=$(tail -n +6 <<<"${cat_file_output}")
			committer_name=$(sed  's/^\(.\+\) <\([^>]\+\)\+> \([0-9]\+ [+-][0-9]\{4\}\)$/\1/' <<<"${tagger_line}")
			committer_email=$(sed 's/^\(.\+\) <\([^>]\+\)\+> \([0-9]\+ [+-][0-9]\{4\}\)$/\2/' <<<"${tagger_line}")
			committer_date=$(sed  's/^\(.\+\) <\([^>]\+\)\+> \([0-9]\+ [+-][0-9]\{4\}\)$/\3/' <<<"${tagger_line}")

			GIT_COMMITTER_NAME="${committer_name}" \
				GIT_COMMITTER_EMAIL="${committer_email}" \
				GIT_COMMITTER_DATE="${committer_date}" \
				${GIT} tag -f -a -m "${tag_message}" "${tag}" "${earliest_commit}"
		else
			${GIT} tag -f "${tag}" "${earliest_commit}"
		fi
	done
}

main