const sass = require('sass');
const fs = require('fs-extra');

// The SASS doc claims that renderSync is twice as fast as render, so if speed
// turns out to be an issue we could use that instead. The advantage of async is
// that we can run complation of each file in parallel (and running other async
// gulp tasks in parallel too).

// sasss.render is old school async, so convert it to a promise here.
async function sassRender(options) {
	return new Promise((resolve, reject) => {
		sass.render(options, ((error, result) => {
			if (error) {
				reject(error);
			} else {
				resolve(result);
			}
		}));
	});
}

module.exports = async function compileSass(inputPaths, outputPath) {
	const promises = [];
	for (const inputPath of inputPaths) {
		console.info(`Compiling ${inputPath}...`);

		promises.push(sassRender({
			file: inputPath,
			sourceMap: true,
			outFile: outputPath,
		}));
	}

	const results = await Promise.all(promises);

	const cssString = results.map(r => r.css.toString()).join('\n');
	const mapString = results.map(r => r.map.toString()).join('\n');

	await Promise.all([
		fs.writeFile(outputPath, cssString, 'utf8'),
		fs.writeFile(`${outputPath}.map`, mapString, 'utf8'),
	]);

	console.info(`Generated ${outputPath}`);
};