index.js

'use strict';
var got = require('got');
var cheerio = require('cheerio');
var uncss = require('uncss');

function getCss(cb) {
	got('https://github.com', function (err, data) {
		if (err) {
			cb(err);
			return;
		}

		var ret = [];
		var $ = cheerio.load(data);

		$('link[href*="assets/github"]').each(function (i, el) {
			ret.push(el.attribs.href);
		});

		if (ret.length === 0) {
			cb(new Error('Could not find GitHub stylesheets'));
			return;
		}

		cb(null, ret);
	});
}

function getRenderedFixture(cb) {
	var url = 'https://github.com/sindresorhus/github-markdown-css/blob/gh-pages/fixture.md';

	got(url, function (err, data) {
		if (err) {
			cb(err);
			return;
		}

		var $ = cheerio.load(data);
		var html = $('.markdown-body').parent().html();

		cb(null, html);
	});
}

function cleanupCss(str) {
	var css = require('css');
	var style = css.parse(str);
	var mdBodyProps = [];

	style.stylesheet.rules = style.stylesheet.rules.filter(function (el) {
		if (el.type === 'keyframes' || el.type === 'comment' || el.type === 'font-face') {
			return false;
		}

		if (el.type ==='rule') {
			if (/::-webkit-validation|:-moz-placeholder|^\.integrations-slide-content|^\.prose-diff|@font-face|^button::|^article$/.test(el.selectors[0])) {
				return false;
			}

			if (el.selectors.length === 1 && /^(?:html|body)$/.test(el.selectors[0])) {
				el.declarations = el.declarations.filter(function (declaration) {
					if (!/^font|^(?:line-height|color)$|text-size-adjust$/.test(declaration.property)) {
						return false;
					}

					return true;
				});
			}

			el.selectors = el.selectors.map(function (selector) {
				if (/^(?:body|html)$/.test(selector)) {
					selector = '.markdown-body';
				}

				if (!/\.markdown-body/.test(selector)) {
					selector = '.markdown-body ' + selector;
				}

				return selector;
			});

			// collect `.markdown-body` rules
			if (el.selectors.length === 1 && el.selectors[0] === '.markdown-body') {
				[].push.apply(mdBodyProps, el.declarations);
				return false;
			}
		}

		if (el.declarations.length === 0) {
			return false;
		}

		return true;
	});

	// merge `.markdown-body` rules
	style.stylesheet.rules.unshift({
		type: 'rule',
		selectors: ['.markdown-body'],
		declarations: mdBodyProps
	});

	var ret = css.stringify(style);

	ret = '@font-face {\n  font-family: octicons-anchor;\n  src: url(data:font/woff;charset=utf-8;base64,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) format(\'woff\');\n}\n\n' + ret;

	return ret;
}

module.exports = function (cb) {
	getRenderedFixture(function (err, html) {
		if (err) {
			cb(err);
			return;
		}

		getCss(function (err, stylesheets) {
			if (err) {
				cb(err);
				return;
			}

			uncss(html, {
				stylesheets: stylesheets,
				ignore: [/^\.highlight/]
			}, function (err, css) {
				if (err) {
					throw err;
				}

				cb(null, cleanupCss(css));
			});
		});
	});
};