"use strict";

const propagateAbort = require("@promistream/propagate-abort");
const pushBuffer = require("push-buffer");

module.exports = function sequentialize() {
	let lastKnownSource;

	let readBuffer = pushBuffer({
		sequential: true,
		pull: async () => {
			return lastKnownSource.read();
		}
	});

	let peekBuffer = pushBuffer({
		sequential: true,
		pull: async () => {
			return lastKnownSource.peek();
		}
	});

	return {
		_promistreamVersion: 0,
		description: `sequentialize`,
		// FIXME: We don't queue up aborts because once a downstream has encountered an error, it may have stopped trying to read, and we would deadlock. While the Aborted marker reads *do* get queued, the abort itself should probably be immediate. Need to make sure that this doesn't clash with any other part of the spec.
		abort: propagateAbort,
		peek: function peek(source) {
			lastKnownSource = source;
			return peekBuffer.request();
		},
		read: function read(source) {
			lastKnownSource = source;
			return readBuffer.request();
		}
	};
};