"use strict";

const { StringDecoder } = require("string_decoder");

const pipe = require("@promistream/pipe");
const map = require("@promistream/map");
const buffer = require("@promistream/buffer");
const lastWill = require("@promistream/last-will");

const { validateArguments } = require("@validatem/core");
const required = require("@validatem/required");
const ValidationError = require("@validatem/error");

// FIXME: Move into separate @validatem/* package
function isValidTextEncoding(encoding) {
	if (!Buffer.isEncoding(encoding)) {
		throw new ValidationError(`Must be a valid Buffer text encoding`);
	}
}

module.exports = function decodeString(_encoding) {
	let [ encoding ] = validateArguments(arguments, {
		encoding: [ required, isValidTextEncoding ]
	});

	let decoder = new StringDecoder(encoding);

	return pipe([
		map((inputBuffer) => {
			let decoded = decoder.write(inputBuffer);

			return (decoded.length > 0)
				? [ decoded ]
				: [];
		}),
		buffer(),
		lastWill(() => {
			let lastChunk = decoder.end();

			return (lastChunk.length > 0)
				? lastChunk
				: lastWill.NoValue;
		})
	]);
};