/**
 * Copyright 2018 Google Inc. All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * @author ebidel@ (Eric Bidelman)
 */

 /**
  * Discovers all the pages in site or single page app (SPA) and creates
  * a tree of the result in ./output/<site slug/crawl.json. Optionally
  * takes screenshots of each page as it is visited.
  *
  * Usage:
  *   node crawlsite.js
  *   URL=https://yourspa.com node crawlsite.js
  *   URL=https://yourspa.com node crawlsite.js --screenshots
  *
  * Then open the visualizer in a browser:
  *   http://localhost:8080/html/d3tree.html
  *   http://localhost:8080/html/d3tree.html?url=../output/https___yourspa.com/crawl.json
  *
  *Start Server:
  *   node server.js
  *
  */

const fs = require('fs');
const del = require('del');
const util = require('util');
const puppeteer = require('puppeteer');
const sharp = require('sharp');

const URL = process.env.URL || 'https://news.polymer-project.org/';
const SCREENSHOTS = process.argv.includes('--screenshots');
const DEPTH = parseInt(process.env.DEPTH) || 2;
const VIEWPORT = SCREENSHOTS ? {width: 1028, height: 800, deviceScaleFactor: 2} : null;
const OUT_DIR = process.env.OUTDIR || `output/${slugify(URL)}`;

const crawledPages = new Map();
const maxDepth = DEPTH; // Subpage depth to crawl site.

function slugify(str) {
  return str.replace(/[\/:]/g, '_');
}

function mkdirSync(dirPath) {
  try {
    dirPath.split('/').reduce((parentPath, dirName) => {
      const currentPath = parentPath + dirName;
      if (!fs.existsSync(currentPath)) {
        fs.mkdirSync(currentPath);
      }
      return currentPath + '/';
    }, '');
  } catch (err) {
    if (err.code !== 'EEXIST') {
      throw err;
    }
  }
}

/**
 * Finds all anchors on the page, inclusive of those within shadow roots.
 * Note: Intended to be run in the context of the page.
 * @param {boolean=} sameOrigin When true, only considers links from the same origin as the app.
 * @return {!Array<string>} List of anchor hrefs.
 */
function collectAllSameOriginAnchorsDeep(sameOrigin = true) {
  const allElements = [];

  const findAllElements = function(nodes) {
    for (let i = 0, el; el = nodes[i]; ++i) {
      allElements.push(el);
      // If the element has a shadow root, dig deeper.
      if (el.shadowRoot) {
        findAllElements(el.shadowRoot.querySelectorAll('*'));
      }
    }
  };

  findAllElements(document.querySelectorAll('*'));

  const filtered = allElements
    .filter(el => el.localName === 'a' && el.href) // element is an anchor with an href.
    .filter(el => el.href !== location.href) // link doesn't point to page's own URL.
    .filter(el => {
      if (sameOrigin) {
        return new URL(location).origin === new URL(el.href).origin;
      }
      return true;
    })
    .map(a => a.href);

  return Array.from(new Set(filtered));
}

/**
 * Crawls a URL by visiting an url, then recursively visiting any child subpages.
 * @param {!Browser} browser
 * @param {{url: string, title: string, img?: string, children: !Array<!Object>}} page Current page.
 * @param {number=} depth Current subtree depth of crawl.
 */
async function crawl(browser, page, depth = 0) {
  if (depth > maxDepth) {
    return;
  }

  // If we've already crawled the URL, we know its children.
  if (crawledPages.has(page.url)) {
    console.log(`Reusing route: ${page.url}`);
    const item = crawledPages.get(page.url);
    page.title = item.title;
    page.img = item.img;
    page.children = item.children;
    // Fill in the children with details (if they already exist).
    page.children.forEach(c => {
      const item = crawledPages.get(c.url);
      c.title = item ? item.title : '';
      c.img = item ? item.img : null;
    });
    return;
  } else {
    console.log(`Loading: ${page.url}`);

    const newPage = await browser.newPage();
    await newPage.goto(page.url, {waitUntil: 'networkidle2'});

    let anchors = await newPage.evaluate(collectAllSameOriginAnchorsDeep);
    anchors = anchors.filter(a => a !== URL) // link doesn't point to start url of crawl.

    page.title = await newPage.evaluate('document.title');
    page.children = anchors.map(url => ({url}));

    if (SCREENSHOTS) {
      const path = `./${OUT_DIR}/${slugify(page.url)}.png`;
      let imgBuff = await newPage.screenshot({fullPage: false});
      imgBuff = await sharp(imgBuff).resize(null, 150).toBuffer(); // resize image to 150 x auto.
      util.promisify(fs.writeFile)(path, imgBuff); // async
      page.img = `data:img/png;base64,${imgBuff.toString('base64')}`;
    }

    crawledPages.set(page.url, page); // cache it.

    await newPage.close();
  }

  // Crawl subpages.
  for (const childPage of page.children) {
    await crawl(browser, childPage, depth + 1);
  }
}

(async() => {

mkdirSync(OUT_DIR); // create output dir if it doesn't exist.
await del([`${OUT_DIR}/*`]); // cleanup after last run.

const browser = await puppeteer.launch();
const page = await browser.newPage();
if (VIEWPORT) {
  await page.setViewport(VIEWPORT);
}

const root = {url: URL};
await crawl(browser, root);

await util.promisify(fs.writeFile)(`./${OUT_DIR}/crawl.json`, JSON.stringify(root, null, ' '));

await browser.close();

})();