From d10930ddfb880d9d50cde5bfbb36a16c09674c27 Mon Sep 17 00:00:00 2001
From: Ken Hawkins <khawkins98@gmail.com>
Date: Mon, 27 Jan 2020 13:25:05 +0100
Subject: [PATCH] Create gulp-prerender.js

---
 gulp-tasks/gulp-prerender.js | 96 ++++++++++++++++++++++++++++++++++++
 1 file changed, 96 insertions(+)
 create mode 100644 gulp-tasks/gulp-prerender.js

diff --git a/gulp-tasks/gulp-prerender.js b/gulp-tasks/gulp-prerender.js
new file mode 100644
index 0000000..e6253cd
--- /dev/null
+++ b/gulp-tasks/gulp-prerender.js
@@ -0,0 +1,96 @@
++'use strict';
+
+/**
+ * Pre-render generated pages.
+ * You need to also
+ * yarn add fs-path puppeteer serve --save
+ * @todo: move this to vf-extensions
+ * @todo: update hardcoded `build` path to use vfConfig.vfBuildDestination
+ */
+
+module.exports = function(gulp, path, buildDestionation) {
+
+  const glob = require("glob")
+  const puppeteer = require('puppeteer');
+  const fsPath = require('fs-path');
+  const handler = require('serve-handler');
+  const http = require('http');
+
+  async function crawler({ url }) {
+    const browser = await puppeteer.launch({ args: ["--no-sandbox"] });
+
+    let page = null;
+    let html = false;
+
+    // console.log(url)
+
+    try {
+      page = await browser.newPage();
+      //networkidle0: consider navigation to be finished when
+      //there are no more than 2 network connections for at least 500 ms.
+      //(https://github.com/GoogleChrome/puppeteer/blob/master/docs/api.md#pagegobackoptions)
+      await page.goto(url, { waitUntil: "networkidle0" });
+      // await page.evaluate();
+      html = await page.content();
+    } catch (e) {
+      debug.warn(`Not able to fetch ${url}`);
+    } finally {
+      // if (page) {
+      //   await page.close();
+      // }
+      await browser.close();
+      return html;
+    }
+  }
+
+  const saveUrlToFile = function(html, pathName, output) {
+    const savePath = output + '/build/' + pathName;
+
+    fsPath.writeFile(savePath, html, function(err) {
+      if (err) {
+        throw err;
+      } else {
+        // console.log('Page pre-rendered and written.');
+      }
+    });
+  };
+
+  async function fetchAllPages() {
+    const domain = "http://localhost:3010/";
+
+    // for our approach, we only generate index.html files
+    let pages = glob.sync("**/index.html", {cwd: 'build'})
+
+    const browser = await puppeteer.launch({ args: ["--no-sandbox"] });
+    
+    for(let i = 0; i < pages.length; i++) {
+      console.log(`Pre-rendering: ${pages[i]}, ${i+1} of ${pages.length}`);
+      const html = await crawler({
+        url: `${domain}${pages[i]}`,
+        browser
+      });
+      saveUrlToFile(html, pages[i], __dirname);
+    }
+    await browser.close();
+  }
+
+  gulp.task('prerender', async() => {
+    const server = http.createServer((request, response) => {
+      // You pass two more arguments for config and middleware
+      // More details here: https://github.com/zeit/serve-handler#options
+      return handler(request, response, {
+        "public": "build"
+      });
+    })
+
+    server.listen(3010, () => {
+      console.log('Listening at http://localhost:3010');
+    });
+
+    await fetchAllPages();
+    server.close(function () { console.log('Server closed.'); })
+    return "success";
+  });
+ 
+  return gulp;
+};
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