"use strict";

const pipe = require("@promistream/pipe");
const propagatePeek = require("@promistream/propagate-peek");
const propagateAbort = require("@promistream/propagate-abort");
const EndOfStream = require("@promistream/end-of-stream");
const unreachable = require("@joepie91/unreachable")("@promistream/dynamic");

module.exports = function singleValueProcessor(processingStream) {
	// NOTE: This is *not* compliant with the Promistream spec! It can only be used with code that is specifically written to handle it.

	let streamEnded = true;

	let gateStream = {
		_promistreamVersion: 0,
		description: `single-value processor gate stream`,
		peek: propagatePeek, // FIXME: Is this correct? Should this not be dependent on whether a peek and/or read has already been done for this iteration?
		abort: propagateAbort,
		read: function produceValue_singleValueGateStream(source) {
			if (streamEnded === false) {
				streamEnded = true;
				return source.read();
			} else {
				throw new EndOfStream;
			}
		},
	};

	let wrappedPipeline = pipe([
		gateStream,
		processingStream
	]);

	return {
		read: function (source) {
			return wrappedPipeline.read(source);
		},
		reset: function () {
			if (streamEnded === true) {
				streamEnded = false;
			} else {
				throw unreachable("Tried to reset a non-ended stream");
			}
		}
	};
};