[gnome-shell/wip/carlosg/osk-updates: 23/40] keyboard: Add 'delete' OSK key action

[Carlos Garnacho <carlosg src gnome org>]

commit 69f39e733e19c442cbf682a2a9b5735e533334dd
Author: Carlos Garnacho <carlosg gnome org>
Date:   Wed Apr 20 23:18:27 2022 +0200

    keyboard: Add 'delete' OSK key action
    
    This action will replace CLUTTER_KEY_Backspace emission for
    the OSK backspace key. Following the available mockups, implement
    different modes of operation:
    
    - Single tap deletes a single character
    - Long tap starts deleting characters one by one
    - Longer tap switches to word-by-word deletion
    
    This is made possible via the input method surrounding text,
    inspecting the string to look the previous char/word position
    backwards, and relies on IM focus providing enough context.
    
    Since deleting text and getting surrounding text are both
    async operations, we make one happen after the other, until
    the button is released.

 js/misc/inputMethod.js |  4 +++
 js/ui/keyboard.js      | 98 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 102 insertions(+)
---
diff --git a/js/misc/inputMethod.js b/js/misc/inputMethod.js
index f1607613ee..cac2c65552 100644
--- a/js/misc/inputMethod.js
+++ b/js/misc/inputMethod.js
@@ -303,4 +303,8 @@ var InputMethod = GObject.registerClass({
     getSurroundingText() {
         return [this._surroundingText, this._surroundingTextCursor];
     }
+
+    hasPreedit() {
+        return this._preeditVisible && this._preeditStr !== '' && this._preeditStr !== null;
+    }
 });
diff --git a/js/ui/keyboard.js b/js/ui/keyboard.js
index 040b41a67a..f3d84b6d2c 100644
--- a/js/ui/keyboard.js
+++ b/js/ui/keyboard.js
@@ -26,6 +26,7 @@ const SHOW_KEYBOARD = 'screen-keyboard-enabled';
 const KEY_SIZE = 2;
 
 const KEY_RELEASE_TIMEOUT = 50;
+const BACKSPACE_WORD_DELETE_THRESHOLD = 50;
 
 var AspectContainer = GObject.registerClass(
 class AspectContainer extends St.Widget {
@@ -1525,6 +1526,9 @@ var Keyboard = GObject.registerClass({
                         this._toggleEmoji();
                     } else if (key.action === 'modifier') {
                         this._toggleModifier(key.keyval);
+                    } else if (key.action === 'delete') {
+                        this._toggleDelete(true);
+                        this._toggleDelete(false);
                     } else if (!this._longPressed && key.action === 'levelSwitch') {
                         this._setActiveLayer(key.level);
                         this._setLatched(
@@ -1548,6 +1552,11 @@ var Keyboard = GObject.registerClass({
                 }
             }
 
+            if (key.action === 'delete') {
+                button.connect('long-press',
+                    () => this._toggleDelete(true));
+            }
+
             if (key.action === 'modifier') {
                 let modifierKeys = this._modifierKeys[key.keyval] || [];
                 modifierKeys.push(button);
@@ -1561,6 +1570,95 @@ var Keyboard = GObject.registerClass({
         }
     }
 
+    _previousWordPosition(text, cursor) {
+        /* Skip word prior to cursor */
+        let pos = Math.max(0, text.slice(0, cursor).search(/\s+\S+\s*$/));
+        if (pos < 0)
+            return 0;
+
+        /* Skip contiguous spaces */
+        for (; pos >= 0; pos--) {
+            if (text.charAt(pos) !== ' ')
+                return GLib.utf8_strlen(text.slice(0, pos + 1), -1);
+        }
+
+        return 0;
+    }
+
+    _toggleDelete(enabled) {
+        if (this._deleteEnabled === enabled)
+            return;
+
+        this._deleteEnabled = enabled;
+        this._timesDeleted = 0;
+
+        if (!Main.inputMethod.currentFocus || Main.inputMethod.hasPreedit()) {
+            /* If there is no IM focus or are in the middle of preedit,
+             * fallback to keypresses */
+            if (enabled)
+                this._keyboardController.keyvalPress(Clutter.KEY_BackSpace);
+            else
+                this._keyboardController.keyvalRelease(Clutter.KEY_BackSpace);
+            return;
+        }
+
+        if (enabled) {
+            let func = (text, cursor) => {
+                if (cursor === 0)
+                    return;
+
+                let encoder = new TextEncoder();
+                let decoder = new TextDecoder();
+
+                /* Find cursor/anchor position in characters */
+                const cursorIdx = GLib.utf8_strlen(decoder.decode(encoder.encode(
+                    text).slice(0, cursor)), -1);
+                const anchorIdx = this._timesDeleted < BACKSPACE_WORD_DELETE_THRESHOLD
+                    ? cursorIdx - 1
+                    : this._previousWordPosition(text, cursor);
+                /* Now get offset from cursor */
+                const offset = anchorIdx - cursorIdx;
+
+                this._timesDeleted++;
+                Main.inputMethod.delete_surrounding(offset, Math.abs(offset));
+            };
+
+            this._surroundingUpdateId = Main.inputMethod.connect(
+                'surrounding-text-updated', () => {
+                    let [text, cursor] = Main.inputMethod.getSurroundingText();
+                    if (this._timesDeleted === 0) {
+                        func(text, cursor);
+                    } else {
+                        if (this._surroundingUpdateTimeoutId > 0) {
+                            GLib.source_remove(this._surroundingUpdateTimeoutId);
+                            this._surroundingUpdateTimeoutId = 0;
+                        }
+                        this._surroundingUpdateTimeoutId =
+                            GLib.timeout_add(GLib.PRIORITY_DEFAULT, KEY_RELEASE_TIMEOUT, () => {
+                                func(text, cursor);
+                                this._surroundingUpdateTimeoutId = 0;
+                                return GLib.SOURCE_REMOVE;
+                            });
+                    }
+                });
+
+            let [text, cursor] = Main.inputMethod.getSurroundingText();
+            if (text)
+                func(text, cursor);
+            else
+                Main.inputMethod.request_surrounding();
+        } else {
+            if (this._surroundingUpdateId > 0) {
+                Main.inputMethod.disconnect(this._surroundingUpdateId);
+                this._surroundingUpdateId = 0;
+            }
+            if (this._surroundingUpdateTimeoutId > 0) {
+                GLib.source_remove(this._surroundingUpdateTimeoutId);
+                this._surroundingUpdateTimeoutId = 0;
+            }
+        }
+    }
+
     _setLatched(latched) {
         this._latched = latched;
         this._setCurrentLevelLatched(this._currentPage, this._latched);