from-lazy-value/index.js

"use strict";

const { validateArguments } = require("@validatem/core");
const required = require("@validatem/required");
const isFunction = require("@validatem/is-function");

const EndOfStream = require("@promistream/end-of-stream");
const simpleSource = require("@promistream/simple-source");

module.exports = function createStreamFromLazyValue(_valueGenerator) {
	let [ valueGenerator ] = validateArguments(arguments, {
		valueGenerator: [ required, isFunction ]
	});

	let wasValueRead = false;

	return simpleSource(() => {
		if (wasValueRead === false) {
			wasValueRead = true;
			return valueGenerator();
		} else {
			throw new EndOfStream("Value was read");
		}
	});
};