# A JsonStore can save and load json data from file system.
class JsonStore

	# Directory where data are stored.
	#
	# Directory is created lazilly at the first write.
	var store_dir: String

	# Delete all stored data.
	#
	# Warning: all `JsonStore` instances sharing the same `store_dir` will
	# be cleared.
	fun clear do
		if not store_dir.file_exists then return
		store_dir.rmdir
	end

	# Is there data are stored under `key`.
	fun has_key(key: String): Bool do
		return ("{store_dir}/{key}.json".simplify_path).file_exists
	end

	# Save `json` object under `key`.
	fun store_object(key: String, json: JsonObject) do
		store_json(key, json)
	end

	# Save `json` array under `key`.
	fun store_array(key: String, json: JsonArray) do
		store_json(key, json)
	end

	# Save `json` data under `key`.
	#
	# Only `JsonObject` and `JsonArray` are allowed in a json file.
	# Use `store_object` or `store_array` instead.
	private fun store_json(key: String, json: Serializable) do
		var path = "{store_dir}/{key}.json".simplify_path
		path.dirname.mkdir
		var file = new FileWriter.open(path)
		file.write(json.to_json)
		file.close
	end

	# Load a JsonObject associated to `key` from store.
	fun load_object(key: String): JsonObject do
		return load_json(key).as(JsonObject)
	end

	# Load a JsonArray associated to `key` from store.
	fun load_array(key: String): JsonArray do
		return load_json(key).as(JsonArray)
	end

	# Load a JsonObject associated to `key` from store.
	#
	# Ensure `has_data(key)`
	private fun load_json(key: String): nullable Serializable do
		assert has_key(key)
		var path = "{store_dir}/{key}.json".simplify_path
		var file = new FileReader.open(path)
		var text = file.read_all
		file.close
		return text.parse_json
	end

	# Get the list of keys stored under the collection `key`.
	fun list_collection(key: String): JsonArray do
		var res = new JsonArray
		var coll = ("{store_dir}/{key}".simplify_path).to_path
		if not coll.exists or not coll.stat.is_dir then return res
		for file in coll.files do
			if file.to_s.has_suffix(".json") then
				res.add(file.to_s.basename(".json"))
			end
		end
		return res
	end

	# Does `key` matches a collection?
	fun has_collection(key: String): Bool do
		var path = ("{store_dir}/{key}".simplify_path).to_path
		return path.exists and path.stat.is_dir
	end
end