Koenig - HR card with markdown text expansion

refs https://github.com/TryGhost/Ghost/issues/9311
- adds the `koenig-card-hr` card that renders a `<hr>` element
- adds text expansion to convert `---` into the new HR card

app/styles/components/koenig.css

@@ -277,14 +277,14 @@
     max-width: 100%;
 }
 
+.__mobiledoc-editor hr {
+    margin: 0.5em 0;
+}
+
 /**
  * Cards
  */
 
-.__mobiledoc-card {
-    display: inline-block;
-}
-
 /**
  * Tooltips
  */

lib/koenig-editor/addon/components/koenig-card-hr.js

@@ -0,0 +1,7 @@
+import Component from '@ember/component';
+import layout from '../templates/components/koenig-card-hr';
+
+export default Component.extend({
+    tagName: '',
+    layout
+});

lib/koenig-editor/addon/options/cards.js

@@ -1,4 +1,5 @@
 import createComponentCard from '../utils/create-component-card';
 
 export default [
+    createComponentCard('koenig-card-hr')
 ];

lib/koenig-editor/addon/options/text-expansions.js

@@ -64,6 +64,38 @@ export default function (editor) {
         }
     });
 
+    editor.onTextInput({
+        name: 'md_hr',
+        match: /^---$/,
+        run(editor) {
+            let {range: {head, head: {section}}} = editor;
+
+            // Skip if cursor is not at end of section
+            if (!head.isTail()) {
+                return;
+            }
+
+            // Skip if section is a list item
+            if (section.isListItem) {
+                return;
+            }
+
+            editor.run((postEditor) => {
+                let card = postEditor.builder.createCardSection('koenig-card-hr');
+                let needsTrailingParagraph = !section.next;
+
+                postEditor.replaceSection(section, card);
+
+                // add an empty paragraph after if necessary so writing can continue
+                if (needsTrailingParagraph) {
+                    let newSection = postEditor.builder.createMarkupSection('p');
+                    postEditor.insertSectionAtEnd(newSection);
+                    postEditor.setRange(newSection.tailPosition());
+                }
+            });
+        }
+    });
+
     /* inline markdown ------------------------------------------------------ */
 
     function matchStrongStar(editor, text) {

lib/koenig-editor/addon/templates/components/koenig-card-hr.hbs

@@ -0,0 +1 @@
+<hr>

lib/koenig-editor/app/components/koenig-card-hr.js

@@ -0,0 +1 @@
+export {default} from 'koenig-editor/components/koenig-card-hr';