"use strict";

const Promise = require("bluebird");
const bl = require("bl");
const through2 = require("through2");
const path = require("path");

const isCss = require("./is-css");
const createFilePreprocessor = require("./postcss/preprocess");
const loaderShimPath = require("./loader-shim-path");

module.exports = function createTransform(file, options) {
	// TODO: Reuse instance?
	let preprocessFile = createFilePreprocessor(options);

	if (isCss({ file: file })) {
		let buffer = new bl.BufferList();

		function chunkHandler(chunk, encoding, callback) {
			if (encoding === "buffer") {
				buffer.append(chunk);
				callback();
			} else {
				throw new Error(`Expected Buffer, got ${encoding} string instead`);
			}
		}

		function endHandler(callback) {
			return Promise.try(() => {
				return preprocessFile({ file: file, source: buffer.toString() });
			}).then((result) => {
				let imports = result.messages
					.filter((message) => {
						return (
							message.pluginName === "postcss-icss-find-imports"
							&& message.type === "import"
						);
					})
					.map((message) => message.url);

				imports.forEach((importUrl) => {
					this.emit("dep", importUrl);
				});
				
				// This ensures that whenever *any* CSS file is processed, the global loader file gets included as well (which is the file that eventually inserts the concatenated CSS)
				let relativeLoaderPath = path.relative(path.dirname(file), loaderShimPath);
				this.emit("dep", relativeLoaderPath);

				this.push(result.css);
				callback();
			}).catch((error) => {
				callback(error);
			});
		}

		return through2.obj(chunkHandler, endHandler);
	} else {
		return through2.obj();
	}
};