[IMP] mail: compute the messageViewList scroll position inside the model

task-2579306

closes odoo/odoo#83042

Signed-off-by: Sébastien Theys (seb) <seb@odoo.com>

addons/mail/static/src/components/message_list/message_list.js

@@ -364,15 +364,17 @@ export class MessageList extends Component {
             thread,
             threadViewer,
         });
+        if (this.messageListView) {
+            this.messageListView.update({
+                clientHeight: this._getScrollableElement().clientHeight,
+                scrollHeight: this._getScrollableElement().scrollHeight,
+                scrollTop: this._getScrollableElement().scrollTop,
+            });
+        }
         if (!this._isLastScrollProgrammatic && threadView && threadView.exists()) {
-            // Margin to compensate for inaccurate scrolling to bottom and height
-            // flicker due height change of composer area.
-            const margin = 30;
             // Automatically scroll to new received messages only when the list is
             // currently fully scrolled.
-            const hasAutoScrollOnMessageReceived = (order === 'asc')
-                ? scrollTop >= this._getScrollableElement().scrollHeight - this._getScrollableElement().clientHeight - margin
-                : scrollTop <= margin;
+            const hasAutoScrollOnMessageReceived = this.messageListView.isAtEnd;
             threadView.update({ hasAutoScrollOnMessageReceived });
         }
         if (threadViewer && threadViewer.exists()) {

addons/mail/static/src/models/message_list_view/message_list_view.js

@@ -6,11 +6,39 @@ import { attr, one } from '@mail/model/model_field';
 registerModel({
     name: 'MessageListView',
     identifyingFields: ['threadViewOwner'],
+    recordMethods: {
+        /***
+         * @private
+         * @returns {boolean}
+         */
+        _computeIsAtEnd() {
+            /**
+             * The margin that we use to detect that the scrollbar is a the end of
+             * the threadView.
+             */
+            const endThreshold = 30;
+            if (this.threadViewOwner.order === 'asc') {
+                return this.scrollTop >= this.scrollHeight - this.clientHeight - endThreshold;
+            }
+            return this.scrollTop <= endThreshold;;
+        },
+    },
     fields: {
+        clientHeight: attr(),
         /**
          * States the OWL component of this message list view
          */
         component: attr(),
+        /**
+         * States whether the message list scroll position is at the end of
+         * the message list. Depending of the message list order, this could be
+         * the top or the bottom.
+         */
+        isAtEnd: attr({
+            compute: '_computeIsAtEnd',
+        }),
+        scrollHeight: attr(),
+        scrollTop: attr(),
         threadViewOwner: one('ThreadView', {
             inverse: 'messageListView',
             readonly: true,