Bulk export (#684)

* First pass (working) collection export to zip

* Add export confirmation screen

* 👕

* Refactor

* Job for team export, move to tmp file, settings UI

* Export all collections job

* 👕

* Add specs

* Clarify UI

server/utils/zip.js

@@ -0,0 +1,49 @@
+// @flow
+import fs from 'fs';
+import JSZip from 'jszip';
+import tmp from 'tmp';
+import unescape from '../../shared/utils/unescape';
+import { Collection, Document } from '../models';
+
+async function addToArchive(zip, documents) {
+  for (const doc of documents) {
+    const document = await Document.findById(doc.id);
+
+    zip.file(`${document.title}.md`, unescape(document.text));
+
+    if (doc.children && doc.children.length) {
+      const folder = zip.folder(document.title);
+      await addToArchive(folder, doc.children);
+    }
+  }
+}
+
+async function archiveToPath(zip) {
+  return new Promise((resolve, reject) => {
+    tmp.file({ prefix: 'export-', postfix: '.zip' }, (err, path) => {
+      if (err) return reject(err);
+
+      zip
+        .generateNodeStream({ type: 'nodebuffer', streamFiles: true })
+        .pipe(fs.createWriteStream(path))
+        .on('finish', () => resolve(path))
+        .on('error', reject);
+    });
+  });
+}
+
+export async function archiveCollection(collection: Collection) {
+  const zip = new JSZip();
+  await addToArchive(zip, collection.documentStructure);
+  return archiveToPath(zip);
+}
+
+export async function archiveCollections(collections: Collection[]) {
+  const zip = new JSZip();
+
+  for (const collection of collections) {
+    const folder = zip.folder(collection.name);
+    await addToArchive(folder, collection.documentStructure);
+  }
+  return archiveToPath(zip);
+}