✨ Koenig - Keep cursor on screen when typing or moving via keyboard

refs TryGhost/Ghost#9505
- when cursor changes through the normal `cursorDidChange` or through certain programmatic changes we trigger a check to see if the cursor is out of the viewport and scroll it into view if necessary
- disable our scroll-into-view routine if the mouse button or shift key is down so that we don't interfere with default browser behaviour which works well in that situation
- for scroll-into-view at the bottom there are two slightly different methods
    - if the cursor is near the bottom of the document we scroll so that the bottom padding of the editor is visible
    - if the cursor is mid-document then we scroll just enough to bring the cursor into the viewport

app/templates/components/gh-koenig-editor.hbs

@@ -21,5 +21,8 @@
         onChange=(action "onBodyChange")
         didCreateEditor=(action "onEditorCreated")
         cursorDidExitAtTop=(action "focusTitle")
+        scrollContainerSelector=scrollContainerSelector
+        scrollOffsetTopSelector=scrollOffsetTopSelector
+        scrollOffsetBottomSelector=scrollOffsetBottomSelector
     }}
 </div>

app/templates/editor.hbs

@@ -71,6 +71,9 @@
                 bodyAutofocus=shouldFocusEditor
                 onBodyChange=(action "updateScratch")
                 headerOffset=editor.headerHeight
+                scrollContainerSelector=".gh-koenig-editor"
+                scrollOffsetTopSelector=".gh-editor-header-small"
+                scrollOffsetBottomSelector=".gh-mobile-nav-bar"
             }}
 
         {{else}}
@@ -205,4 +208,4 @@
     {{/liquid-wormhole}}
 {{/if}}
 
-{{outlet}}
+{{outlet}}

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

@@ -117,7 +117,6 @@ export default Component.extend({
     autofocus: false,
     spellcheck: true,
     options: null,
-    scrollContainer: '',
     headerOffset: 0,
 
     // internal properties
@@ -146,8 +145,7 @@ export default Component.extend({
 
     /* computed properties -------------------------------------------------- */
 
-    // merge in named options with the `options` property data-bag
-    // TODO: what is the `options` property data-bag and when/where does it get set?
+    // merge in named options with any passed in `options` property data-bag
     editorOptions: computed(function () {
         let options = this.options || {};
         let atoms = this.atoms || [];
@@ -190,6 +188,16 @@ export default Component.extend({
             ctrl: false
         };
 
+        // track mousedown/mouseup on the window rather than the ember component
+        // so that we're sure to get the events even when they start outside of
+        // this component or end outside the window.
+        // Mouse events are used to track when a mousebutton is down so that we
+        // can disable automatic cursor-in-viewport scrolling
+        this._onMousedownHandler = run.bind(this, this.handleMousedown);
+        window.addEventListener('mousedown', this._onMousedownHandler);
+        this._onMouseupHandler = run.bind(this, this.handleMouseup);
+        window.addEventListener('mouseup', this._onMouseupHandler);
+
         this._startedRunLoop = false;
     },
 
@@ -346,6 +354,10 @@ export default Component.extend({
 
         this._pasteHandler = run.bind(this, this.handlePaste);
         editorElement.addEventListener('paste', this._pasteHandler);
+
+        if (this.scrollContainerSelector) {
+            this._scrollContainer = document.querySelector(this.scrollContainerSelector);
+        }
     },
 
     // our ember component has rendered, now we need to render the mobiledoc
@@ -538,6 +550,7 @@ export default Component.extend({
         if (this._skipCursorChange) {
             this._skipCursorChange = false;
             this.set('selectedRange', editor.range);
+            this._scrollCursorIntoView();
             return;
         }
 
@@ -584,6 +597,7 @@ export default Component.extend({
 
         // pass the selected range through to the toolbar + menu components
         this.set('selectedRange', editor.range);
+        this._scrollCursorIntoView();
     },
 
     // fired when the active section(s) or markup(s) at the current cursor
@@ -711,6 +725,19 @@ export default Component.extend({
         }
     },
 
+    handleMousedown(event) {
+        // we only care about the left mouse button
+        if (event.which === 1) {
+            this._isMouseDown = true;
+        }
+    },
+
+    handleMouseup(event) {
+        if (event.which === 1) {
+            this._isMouseDown = false;
+        }
+    },
+
     /* Ember event handlers ------------------------------------------------- */
 
     // disable dragging
@@ -879,5 +906,73 @@ export default Component.extend({
         if (this.element && config.environment === 'test') {
             this.element[TESTING_EXPANDO_PROPERTY] = editor;
         }
+    },
+
+    _scrollCursorIntoView() {
+        // disable auto-scroll if the mouse or shift key is being used to create
+        // a selection - the browser handles scrolling well in this case
+        if (!this._scrollContainer || this._isMouseDown || this._modifierKeys.shift) {
+            return;
+        }
+
+        let {range} = this.editor;
+        let selection = window.getSelection();
+        let windowRange = selection && selection.getRangeAt(0);
+        let element = range.head && range.head.section && range.head.section.renderNode && range.head.section.renderNode.element;
+
+        if (windowRange) {
+            // cursorTop is relative to the window rather than document or scroll container
+            let {top: cursorTop, height: cursorHeight} = windowRange.getBoundingClientRect();
+            let viewportHeight = window.innerHeight;
+            let offsetTop = 0;
+            let offsetBottom = 0;
+            let scrollTop = this._scrollContainer.scrollTop;
+
+            if (this.scrollOffsetTopSelector) {
+                let topElement = document.querySelector(this.scrollOffsetTopSelector);
+                offsetTop = topElement ? topElement.offsetHeight : 0;
+            }
+
+            if (this.scrollOffsetBottomSelector) {
+                let bottomElement = document.querySelector(this.scrollOffsetBottomSelector);
+                offsetBottom = bottomElement ? bottomElement.offsetHeight : 0;
+            }
+
+            // for empty paragraphs the window selection range will be 0,0,0,0
+            // so grab the element's bounding rect instead
+            if (cursorTop === 0 && cursorHeight === 0) {
+                if (!element) {
+                    return;
+                }
+
+                ({top: cursorTop, height: cursorHeight} = element.getBoundingClientRect());
+            }
+
+            // keep cursor in view at the top
+            if (cursorTop < 0 + offsetTop) {
+                this._scrollContainer.scrollTop = scrollTop - offsetTop + cursorTop - 20;
+                return;
+            }
+
+            let cursorBottom = cursorTop + cursorHeight;
+            let paddingBottom = 0;
+            let distanceFromViewportBottom = cursorBottom - viewportHeight;
+            let atBottom = false;
+
+            // if we're at the bottom of the doc we should keep the bottom
+            // padding in view, otherwise just scroll to keep the cursor in view
+            if (this._scrollContainer.scrollTop + this._scrollContainer.offsetHeight + 200 >= this._scrollContainer.scrollHeight) {
+                atBottom = true;
+                paddingBottom = parseFloat(getComputedStyle(this.element.parentNode).getPropertyValue('padding-bottom'));
+            }
+
+            if (cursorBottom > viewportHeight - offsetBottom - paddingBottom) {
+                if (atBottom) {
+                    this._scrollContainer.scrollTop = this._scrollContainer.scrollHeight;
+                } else {
+                    this._scrollContainer.scrollTop = scrollTop + offsetBottom + distanceFromViewportBottom + 20;
+                }
+            }
+        }
     }
 });

lib/koenig-editor/addon/options/key-commands.js

@@ -10,7 +10,7 @@ import {
 
 export const DEFAULT_KEY_COMMANDS = [{
     str: 'ENTER',
-    run(editor) {
+    run(editor, koenig) {
         let {isCollapsed, head: {offset, section}} = editor.range;
 
         // if cursor is at beginning of a heading, insert a blank paragraph above
@@ -20,6 +20,7 @@ export const DEFAULT_KEY_COMMANDS = [{
                 let collection = section.parent.sections;
                 postEditor.insertSectionBefore(collection, newPara, section);
             });
+            koenig._scrollCursorIntoView();
             return;
         }