Refactor new->edit transition to avoid editor re-renders

closes TryGhost/Ghost#8287
closes TryGhost/Ghost#8750
- moved all editor model functionality into the new `editor` route+controller
- moved editor template from `editor/edit.hbs` to `editor.hbs`
- refactored `editor` controller and the `editor.new`/`editor.edit` routes to work with a persistent editor rather than a teardown/re-render when transitioning from new->edit
- fixed issue in `{{gh-markdown-editor}}` for `autofocus` behaviour when the component isn't re-rendered
- fixed issue in `{{gh-simplemde}}` that was causing multiple updates to the `value` property when a new value is passed in to the component
- added `{{gh-scheduled-post-countdown}}` component to lower the noise in the editor controller
- removed editor route/controller mixins
- removed the `editor.edit` and `editor.new` controllers

app/components/gh-markdown-editor.js

@@ -204,6 +204,13 @@ export default Component.extend(ShortcutsMixin, {
         let markdown = mobiledoc.cards[0][1].markdown;
         this.set('markdown', markdown);
 
+        // focus the editor when the markdown value changes, this is necessary
+        // because both the autofocus and markdown values can change without a
+        // re-render, eg. navigating from edit->new
+        if (this._editor && markdown !== this._editor.value() && this.get('autofocus')) {
+            this.send('focusEditor');
+        }
+
         // use internal values to avoid updating bound values
         if (!isEmpty(this.get('isFullScreen'))) {
             this.set('_isFullScreen', this.get('isFullScreen'));

app/components/gh-scheduled-post-countdown.js

@@ -0,0 +1,28 @@
+import Component from '@ember/component';
+import moment from 'moment';
+import {computed} from '@ember/object';
+import {inject as service} from '@ember/service';
+
+export default Component.extend({
+    clock: service(),
+
+    post: null,
+
+    // countdown timer to show the time left until publish time for a scheduled post
+    // starts 15 minutes before scheduled time
+    countdown: computed('post.{publishedAtUTC,isScheduled}', 'clock.second', function () {
+        let isScheduled = this.get('post.isScheduled');
+        let publishTime = this.get('post.publishedAtUTC') || moment.utc();
+        let timeUntilPublished = publishTime.diff(moment.utc(), 'minutes', true);
+        let isPublishedSoon = timeUntilPublished > 0 && timeUntilPublished < 15;
+
+        // force a recompute
+        this.get('clock.second');
+
+        if (isScheduled && isPublishedSoon) {
+            return moment(publishTime).fromNow();
+        } else {
+            return false;
+        }
+    })
+});

app/components/gh-simplemde.js

@@ -76,8 +76,12 @@ export default TextArea.extend({
         this._editor = new SimpleMDE(editorOptions);
         this._editor.value(this.get('value') || '');
 
-        this._editor.codemirror.on('change', () => {
-            this.onChange(this._editor.value());
+        this._editor.codemirror.on('change', (instance, changeObj) => {
+            // avoid a "modified x twice in a single render" error that occurs
+            // when the underlying value is completely swapped out
+            if (changeObj.origin !== 'setValue') {
+                this.onChange(this._editor.value());
+            }
         });
 
         this._editor.codemirror.on('focus', () => {