[FIX] web_editor: show a default selection in collaboration

Before this commit, whenever a peer had no selection in the editor, no
selection would appear to the other collaborators. It was therefore
visually impossible to know excaltly to how many people someone is
connected.

Now, we set the default selection to be in the first node of the
document.

Additionnaly, some selection were not displayed because the call to
`getClientRects` did not return any rect. By creating a deep range
through the use of `getDeepestPosition`, we ensure to retrieve the
selection rect.

task-3217719

closes odoo#114481

Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>
Signed-off-by: Nicolas Bayet <nby@odoo.com>

Author: Goaman

addons/web_editor/static/src/js/editor/odoo-editor/src/OdooEditor.js

@@ -72,6 +72,7 @@ import {
     isVoidElement,
     cleanZWS,
     isZWS,
+    getDeepestPosition,
 } from './utils/utils.js';
 import { editorCommands } from './commands/commands.js';
 import { Powerbox } from './powerbox/Powerbox.js';
@@ -1562,26 +1563,34 @@ export class OdooEditor extends EventTarget {
     _multiselectionDisplayClient({ selection, color, clientId, clientAvatarUrl = '', clientName = this.options._t('Anonymous') }) {
         let clientRects;
 
-        const anchorNode = this.idFind(selection.anchorNodeOid);
-        const focusNode = this.idFind(selection.focusNodeOid);
+        let anchorNode = this.idFind(selection.anchorNodeOid);
+        let focusNode = this.idFind(selection.focusNodeOid);
+        let anchorOffset = selection.anchorOffset;
+        let focusOffset = selection.focusOffset;
         if (!anchorNode || !focusNode) {
-            return;
+            anchorNode = this.editable.children[0];
+            focusNode = this.editable.children[0];
+            anchorOffset = 0;
+            focusOffset = 0;
         }
 
+        [anchorNode, anchorOffset] = getDeepestPosition(anchorNode, anchorOffset);
+        [focusNode, focusOffset] = getDeepestPosition(focusNode, focusOffset);
+
         const direction = getCursorDirection(
             anchorNode,
-            selection.anchorOffset,
+            anchorOffset,
             focusNode,
-            selection.focusOffset,
+            focusOffset,
         );
         const range = new Range();
         try {
             if (direction === DIRECTIONS.RIGHT) {
-                range.setStart(anchorNode, selection.anchorOffset);
-                range.setEnd(focusNode, selection.focusOffset);
+                range.setStart(anchorNode, anchorOffset);
+                range.setEnd(focusNode, focusOffset);
             } else {
-                range.setStart(focusNode, selection.focusOffset);
-                range.setEnd(anchorNode, selection.anchorOffset);
+                range.setStart(focusNode, focusOffset);
+                range.setEnd(anchorNode, anchorOffset);
             }
 
             clientRects = Array.from(range.getClientRects());
@@ -3655,13 +3664,17 @@ export class OdooEditor extends EventTarget {
 
     getCurrentCollaborativeSelection() {
         const selection = this._latestComputedSelection || this._computeHistorySelection();
-        if (!selection) return;
-        return Object.assign({
-            selection: serializeSelection(selection),
+        return {
+            selection: selection ? serializeSelection(selection) : {
+                anchorNodeOid: undefined,
+                anchorOffset: undefined,
+                focusNodeOid: undefined,
+                focusOffset: undefined,
+            },
             color: this._collabSelectionColor,
             clientId: this._collabClientId,
             clientAvatarUrl: this._collabClientAvatarUrl,
-        });
+        };
     }
 
     clean() {