"use strict";

const debug = require("debug")("promistream:dynamic:stream-pool");
const unreachable = require("@joepie91/unreachable")("@promistream/dynamic");
const valueID = require("./value-id");

// TODO: Separate out into own package + update `unreachable` label accordingly
// TODO: Validation

module.exports = function createStreamPool() {
	let pool = new WeakMap();
	let streamTypes = new Map();

	return {
		acquire: function (streamFactory) {
			if (!pool.has(streamFactory)) {
				pool.set(streamFactory, []);
			}

			let availableStreams = pool.get(streamFactory);
			
			if (availableStreams.length === 0) {
				debug(`Ran out of streams for type ${valueID(streamFactory)}, creating a new one...`);
				let newStream = streamFactory();
				streamTypes.set(newStream, streamFactory);

				// TODO: Periodic cleanup and activity tracking for instances
				availableStreams.push(newStream);
			} else {
				debug(`Reusing stream from pool for type ${valueID(streamFactory)}`);
			}

			let acquiredStream = availableStreams.shift();

			if (acquiredStream.reset != null) {
				acquiredStream.reset();
			}

			return acquiredStream;
		},
		release: function (stream) {
			let streamFactory = streamTypes.get(stream);

			if (streamFactory != null) {
				let availableStreams = pool.get(streamFactory);
				availableStreams.push(stream);
			} else {
				throw unreachable(`Specified stream does not belong to the pool`);
			}
		}
	};
};