/**
 * Module to inline styles while loading the existing stylesheets async
 *
 * @author Ben Zörb @bezoerb https://github.com/bezoerb
 * @copyright Copyright (c) 2014 Ben Zörb
 *
 * Licensed under the MIT license.
 * http://bezoerb.mit-license.org/
 * All rights reserved.
 */
'use strict';
const fs = require('fs');
const path = require('path');
const escapeRegExp = require('lodash.escaperegexp');
const get = require('lodash.get');
const filter = require('lodash.filter');
const isRegExp = require('lodash.isregexp');
const isString = require('lodash.isstring');
const UglifyJS = require('uglify-js');
const reaver = require('reaver');
const postcss = require('postcss');
const discard = require('postcss-discard');
const cheerio = require('cheerio');
const render = require('dom-serializer');
const CleanCSS = require('clean-css');
const slash = require('slash');
const normalizeNewline = require('normalize-newline');
const detectIndent = require('detect-indent');

const loadCssMain = require.resolve('fg-loadcss');

/**
 * Get loadcss + cssrelpreload script
 *
 * @returns {string}
 */
function getScript() {
    const loadCSS = read(path.join(path.dirname(loadCssMain), 'cssrelpreload.js'));

    return UglifyJS.minify(loadCSS).code;
}

/**
 * Fixup slashes in file paths for windows
 *
 * @param {string} str
 * @return {string}
 */
function normalizePath(str) {
    return process.platform === 'win32' ? slash(str) : str;
}

/**
 * Read file *
 * @param {string} file
 * @returns {string}
 */
function read(file) {
    return fs.readFileSync(file, 'utf8');
}

/**
 * Get the indentation of the link tags
 * @param html
 * @param $el
 */
function getIndent(html, $el) {
    const regName = new RegExp(escapeRegExp(get($el, 'name')));
    const regHref = new RegExp(escapeRegExp(get($el, 'attribs.href')));
    const regRel = new RegExp(escapeRegExp(get($el, 'attribs.rel')));
    const lines = filter(html.split(/[\r\n]+/), line => {
        return regName.test(line) && regHref.test(line) && regRel.test(line);
    });
    return detectIndent(lines.join('\n')).indent;
}

/**
 * Minify CSS
 * @param {string} styles
 */
function minifyCSS(styles) {
    return new CleanCSS().minify(styles).styles;
}

function extract(css, critical, minify = false) {
    if (minify) {
        css = minifyCSS(css);
        critical = minifyCSS(critical);
    }

    return normalizeNewline(postcss(discard({css: critical})).process(css).css);
}

/**
 * Helper to prevent cheerio from messing with svg contrnt.
 * Should be merged afe´ter https://github.com/fb55/htmlparser2/pull/259
 * @param {array} str
 */
const getSvgs = (str = '') => {
    const indices = [];
    let start = str.indexOf('<svg', 0);
    let end = str.indexOf('</svg>', start) + 6;
    while (start >= 0) {
        indices.push({start, end});
        start = str.indexOf('<svg', end);
        end = str.indexOf('</svg>', end) + 6;
    }

    return indices.map(({start, end}) => str.substring(start, end));
};

module.exports = (html, styles, options) => {
    if (!isString(html)) {
        html = String(html);
    }

    const $ = cheerio.load(html, {
        decodeEntities: false
    });

    const allLinks = $(
        'link[rel="stylesheet"], link[rel="preload"][as="style"]'
    ).filter(function () {
        return !$(this).parents('noscript').length;
    });

    let links = allLinks.filter('[rel="stylesheet"]');

    const o = Object.assign(
        {
            minify: true
        },
        options || {}
    );

    const target = o.selector || allLinks.get(0) || $('head script').get(0);
    const {indent} = detectIndent(html);
    const targetIndent = getIndent(html, target);
    const $target = $(target);

    if (!Array.isArray(o.ignore)) {
        o.ignore = [o.ignore];
    }

    if (o.ignore) {
        links = filter(links, link => {
            const href = $(link).attr('href');
            return (
                o.ignore.findIndex(arg => {
                    return (isRegExp(arg) && arg.test(href)) || arg === href;
                }) === -1
            );
        });
    }

    // Minify if minify option is set
    if (o.minify) {
        styles = minifyCSS(styles);
    }

    if (styles) {
        const elements = [
            '<style>',
            indent +
                styles
                    .replace(/(\r\n|\r|\n)/g, `$1${targetIndent}${indent}`)
                    .replace(/^[\s\t]+$/g, ''),
            '</style>',
            ''
        ]
            .join(`\n${targetIndent}`)
            .replace(/(\r\n|\r|\n)[\s\t]+(\r\n|\r|\n)/g, '$1$2');

        if ($target.length > 0) {
            // Insert inline styles right before first <link rel="stylesheet" /> or other target
            $target.before(elements);
        } else {
            // Just append to the head
            $('head').append(elements);
        }
    }

    if (links.length > 0) {
        // Modify links and ad clones to noscript block
        $(links).each(function (idx, el) {
            if (o.extract && !o.basePath) {
                throw new Error(
                    'Option `basePath` is missing and required when using `extract`!'
                );
            }

            const $el = $(el);
            const elIndent = getIndent(html, el);

            if (o.extract) {
                const href = $el.attr('href');
                const file = path.resolve(path.join(o.basePath, href));
                if (fs.existsSync(file)) {
                    const orig = fs.readFileSync(file);
                    const diff = extract(orig, styles, o.minify);
                    const filename = reaver.rev(file, diff);

                    fs.writeFileSync(filename, diff);
                    $el.attr('href', normalizePath(reaver.rev(href, diff)));
                }
            }

            // Add each fallback right behind the current style to keep source order when ignoring stylesheets
            $el.after(
                `\n${elIndent}<noscript>${render(this)}</noscript>`
            );

            // Add preload atttibutes to actual link element
            $el.attr('rel', 'preload');
            $el.attr('as', 'style');
            $el.attr('onload', 'this.onload=null;this.rel=\'stylesheet\'');
        });

        // Add loadcss + cssrelpreload polyfill
        const scriptAnchor = $('link[rel="stylesheet"], noscript')
            .filter(function () {
                return !$(this).parents('noscript').length;
            })
            .last()
            .get(0);

        $(scriptAnchor).after(
            `\n${targetIndent}<script>${getScript()}</script>`
        );
    }

    const output = $.html();

    // Quickfix until https://github.com/fb55/htmlparser2/pull/259 is merged/fixed
    const svgs = getSvgs(html);
    const quickfixed = getSvgs(output).reduce(
        (str, code, index) => str.replace(code, svgs[index] || code),
        output
    );

    return Buffer.from(quickfixed);
};