[gnome-shell/wip/fmuellner/fix-clear-events: 30/30] events: Re-use event messages where possible

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit e7f2e924100495969d62e91574e03fc0e6fc0112
Author: Florian Müllner <fmuellner gnome org>
Date:   Sat Jun 9 13:23:35 2018 +0200

    events: Re-use event messages where possible
    
    Destroying and recreating the entire events list on every change is not only
    wasteful, it also breaks the clear functionality as messages scheduled for
    removal are replaced with "new" messages after the first message has been
    removed.
    
    Address both issues by keeping track of all messages and re-use them
    whenever possible.
    
    https://gitlab.gnome.org/GNOME/gnome-shell/issues/325

 js/ui/calendar.js | 28 +++++++++++++++++++++-------
 1 file changed, 21 insertions(+), 7 deletions(-)
---
diff --git a/js/ui/calendar.js b/js/ui/calendar.js
index a46017ad0..651aac610 100644
--- a/js/ui/calendar.js
+++ b/js/ui/calendar.js
@@ -821,6 +821,8 @@ var EventsSection = new Lang.Class({
         this._desktopSettings.connect('changed', this._reloadEvents.bind(this));
         this._eventSource = new EmptyEventSource();
 
+        this._messageById = new Map();
+
         this.parent();
 
         this._title = new St.Button({ style_class: 'events-section-title',
@@ -875,20 +877,32 @@ var EventsSection = new Lang.Class({
 
         this._reloading = true;
 
-        this._list.destroy_all_children();
-
         let periodBegin = _getBeginningOfDay(this._date);
         let periodEnd = _getEndOfDay(this._date);
         let events = this._eventSource.getEvents(periodBegin, periodEnd);
 
+        let ids = events.map(e => e.id);
+        this._messageById.forEach((message, id) => {
+            if (ids.includes(id))
+                return;
+            this._messageById.delete(id);
+            this.removeMessage(message);
+        });
+
         for (let i = 0; i < events.length; i++) {
             let event = events[i];
 
-            let message = new EventMessage(event, this._date);
-            message.connect('close', () => {
-                this._ignoreEvent(event);
-            });
-            this.addMessage(message, false);
+            let message = this._messageById.get(event.id);
+            if (!message) {
+                message = new EventMessage(event, this._date);
+                message.connect('close', () => {
+                    this._ignoreEvent(event);
+                });
+                this._messageById.set(event.id, message);
+                this.addMessage(message, false);
+            } else {
+                this.moveMessage(message, i, false);
+            }
         }
 
         this._reloading = false;