"use strict";

const stream = require("../stream");
const isCss = require("../is-css");

module.exports = function createCssDepsStream() {
	let dependents = new Map();
	let depsPhaseItems = [];

	function handleItem(item) {
		Object.values(item.deps).forEach((dependency) => {
			if (!dependents.has(dependency)) {
				dependents.set(dependency, new Set());
			}

			dependents.get(dependency).add(item);
		});

		depsPhaseItems.push(item);
	}

	function flush() {
		return depsPhaseItems.map((item) => {
			let selfIsCss = isCss(item);

			let dependentsForItem = dependents.get(item.id);
			let hasDependents = (dependentsForItem != null);
			let dependentsAreCss = hasDependents && Array.from(dependentsForItem).every((dependent) => isCss(dependent));

			return {
				... item,
				__icssify__discardable: (selfIsCss && dependentsAreCss)
			};
		});
	}

	return stream(handleItem, flush);
};