git-backup

#!/usr/bin/env bash


set -o errexit


index_file_for_worktree=
trap cleanup EXIT
function cleanup() {
	if [ -n "$index_file_for_worktree" -a -e "$index_file_for_worktree" ]; then
		rm "$index_file_for_worktree"
	fi
}


if [ $# -eq 0 -o $# -eq 1 -a \( "$1" == "--create" -o "$1" == "-c" \) ]; then
	now=$(date +"%s%z")
	export GIT_AUTHOR_DATE="$now"
	export GIT_COMMITTER_DATE="$now"

	index_file_for_worktree=$(mktemp -t temp-git-index)
	rm "$index_file_for_worktree" # git chokes on an index file of zero length
	GIT_INDEX_FILE="$index_file_for_worktree" git add -A
	tree_id_worktree=$(GIT_INDEX_FILE="$index_file_for_worktree" git write-tree)
	echo "Created a tree object for worktree  : $tree_id_worktree"

	commit_id_worktree="$(git commit-tree -p HEAD -m "BACKUP of worktree as of $(date -r "${now%-*}" +"%F %T %z")" "$tree_id_worktree" )"
	echo "Created a commit object for worktree: $commit_id_worktree"

	tag_name_worktree="backups/$now/worktree"
	git tag "$tag_name_worktree" "$commit_id_worktree"
	echo "Created a tag for worktree          : $tag_name_worktree"

	index_file_blob_id="$(git hash-object -t blob -w "$(git rev-parse --git-path index)")"
	echo "Created a blob object for index file: $index_file_blob_id"

	tag_name_index_file_blob="backups/$now/index"
	git tag "$tag_name_index_file_blob" "$index_file_blob_id"
	echo "Created a tag for blob of index file: $tag_name_index_file_blob"

	echo ""
	"$0" --list
elif [ $# -eq 1 -a \( "$1" == "-l" -o "$1" == "--list" \) ]; then
	{
		lfmt='%s\t%s\t%s\t%s\t%s\n'
		printf "$lfmt" "backup name" "backup date" "worktree comit" "worktree tree" "index blob"
		for backup_name in $(git for-each-ref 'refs/tags/backups/*/worktree' --format "%(refname)"); do
			backup_name=${backup_name#refs/tags/backups/}
			backup_name=${backup_name%/worktree}
			test $(git cat-file -t "refs/tags/backups/${backup_name}/worktree") == commit
			test $(git cat-file -t "refs/tags/backups/${backup_name}/index") == blob
			fields=(
				"$backup_name"
				"$(date -r "${backup_name%-*}" +"%F %T")"
				"$(git rev-parse "refs/tags/backups/${backup_name}/worktree")"
				"$(git rev-parse "refs/tags/backups/${backup_name}/worktree:")"
				"$(git rev-parse "refs/tags/backups/${backup_name}/index")"
			)
			printf "$lfmt" "${fields[@]}"
		done
	} | column -t -s $'\t'
elif [ $# -eq 3 -a "$1" == "--restore" ]; then
	backup_name="$2"
	new_worktree_path="$3"
	git worktree add  "$new_worktree_path" --detach "backups/$backup_name/worktree"
	git -C "$new_worktree_path" reset --soft @~
	git cat-file blob "backups/$backup_name/index" >"$(git -C "$new_worktree_path" rev-parse --git-path index)"
elif [ $# -eq 2 -a \( "$1" == "--delete" -o "$1" == "-d" \) ]; then
	backup_name="$2"
	git tag -d "backups/$backup_name/worktree"
	git tag -d "backups/$backup_name/index"
else
	echo "unrecognized parameters"
fi