Load a preview of Sketch 43 files

Sketch 43 files are technically a zip file, so the JavaScript opens the
zip file & locates a preview.png which is just a quick preview of the
last sketch page edited. After that is loaded it simply places the image
into the DOM

2 files changed, 81 insertions, 0 deletions

diff --git a/app/assets/javascripts/blob/sketch/index.js b/app/assets/javascripts/blob/sketch/index.js
new file mode 100644
index 00000000000..0799991aa40
--- /dev/null
+++ b/app/assets/javascripts/blob/sketch/index.js
@@ -0,0 +1,73 @@
+import JSZip from 'jszip';
+import JSZipUtils from 'jszip-utils';
+
+export default class SketchLoader {
+  constructor(container) {
+    this.container = container;
+    this.loadingIcon = this.container.querySelector('.js-loading-icon');
+
+    this.load();
+  }
+
+  load() {
+    return this.getZipFile()
+      .then(data => JSZip.loadAsync(data))
+      .then(asyncResult => asyncResult.files['previews/preview.png'].async('uint8array'))
+      .then((content) => {
+        const url = window.URL || window.webkitURL;
+        const blob = new Blob([new Uint8Array(content)], {
+          type: 'image/png',
+        });
+        const previewUrl = url.createObjectURL(blob);
+
+        this.render(previewUrl);
+      })
+      .catch(this.error.bind(this));
+  }
+
+  getZipFile() {
+    return new JSZip.external.Promise((resolve, reject) => {
+      JSZipUtils.getBinaryContent(this.container.dataset.endpoint, (err, data) => {
+        if (err) {
+          reject(err);
+        } else {
+          resolve(data);
+        }
+      });
+    });
+  }
+
+  render(previewUrl) {
+    const previewLink = document.createElement('a');
+    const previewImage = document.createElement('img');
+
+    previewLink.href = previewUrl;
+    previewLink.target = '_blank';
+    previewImage.src = previewUrl;
+    previewImage.className = 'img-responsive';
+
+    previewLink.appendChild(previewImage);
+    this.container.appendChild(previewLink);
+
+    this.removeLoadingIcon();
+  }
+
+  error() {
+    const errorMsg = document.createElement('p');
+
+    errorMsg.className = 'prepend-top-default append-bottom-default text-center';
+    errorMsg.textContent = `
+      Cannot show preview. For previews on sketch files, they must have the file format
+      introduced by Sketch version 43 and above.
+    `;
+    this.container.appendChild(errorMsg);
+
+    this.removeLoadingIcon();
+  }
+
+  removeLoadingIcon() {
+    if (this.loadingIcon) {
+      this.loadingIcon.remove();
+    }
+  }
+}
diff --git a/app/assets/javascripts/blob/sketch_viewer.js b/app/assets/javascripts/blob/sketch_viewer.js
new file mode 100644
index 00000000000..0640dd26855
--- /dev/null
+++ b/app/assets/javascripts/blob/sketch_viewer.js
@@ -0,0 +1,8 @@
+/* eslint-disable no-new */
+import SketchLoader from './sketch';
+
+document.addEventListener('DOMContentLoaded', () => {
+  const el = document.getElementById('js-sketch-viewer');
+
+  new SketchLoader(el);
+});