[polari] chatView: Fetch more logs when scrolling past the top

[Florian Müllner <fmuellner src gnome org>]

commit 3c281b95ee4a02990070624019ef8da17792d4ee
Author: Florian Müllner <fmuellner gnome org>
Date:   Sun Nov 3 21:24:04 2013 +0100

    chatView: Fetch more logs when scrolling past the top
    
    The backlog we fetch on startup may not be enough, so allow users
    to request more history by scrolling past the top.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=712249

 src/chatView.js |   24 ++++++++++++++++++++++++
 1 files changed, 24 insertions(+), 0 deletions(-)
---
diff --git a/src/chatView.js b/src/chatView.js
index 1b5c39b..5d530ab 100644
--- a/src/chatView.js
+++ b/src/chatView.js
@@ -7,6 +7,7 @@ const Tp = imports.gi.TelepathyGLib;
 const Tpl = imports.gi.TelepathyLogger;
 
 const Lang = imports.lang;
+const Mainloop = imports.mainloop;
 const Notify = imports.notify;
 const Utils = imports.utils;
 
@@ -18,6 +19,7 @@ const TIMESTAMP_INTERVAL = 300; // seconds of inactivity after which to
                                 // insert a timestamp
 
 const NUM_INITIAL_LOG_EVENTS = 50; // number of log events to fetch on start
+const NUM_LOG_EVENTS = 10; // number of log events to fetch when requesting more
 
 const INDICATOR_OFFSET = 5; // TODO: should be based on line spacing
 
@@ -100,6 +102,7 @@ const ChatView = new Lang.Class({
             logManager.walk_filtered_events(account, target,
                                             Tpl.EventTypeMask.TEXT, null);
 
+        this._fetchingBacklog = true;
         this._logWalker.get_events_async(NUM_INITIAL_LOG_EVENTS,
                                          Lang.bind(this, this._onLogEventsReady));
 
@@ -243,6 +246,7 @@ const ChatView = new Lang.Class({
         this.widget.connect('unmap', Lang.bind(this, this._updateActive));
         this.widget.connect('state-flags-changed',
                             Lang.bind(this, this._updateToplevel));
+        this.widget.connect('scroll-event', Lang.bind(this ,this._onScroll));
         this.widget.vadjustment.connect('value-changed',
                                  Lang.bind(this, this._checkMessages));
         this.widget.vadjustment.connect('changed',
@@ -269,6 +273,7 @@ const ChatView = new Lang.Class({
         let [, events] = lw.get_events_finish(res);
         this._pendingLogs = events.concat(this._pendingLogs);
         this._insertPendingLogs();
+        this._fetchingBacklog = false;
     },
 
     _insertPendingLogs: function() {
@@ -356,6 +361,25 @@ const ChatView = new Lang.Class({
         this._scrollBottom = adj.upper - adj.page_size;
     },
 
+    _onScroll: function(w, event) {
+        let [, dir] = event.get_scroll_direction();
+
+        if (this._fetchingBacklog ||
+            this.widget.vadjustment.value != 0 ||
+            dir != Gdk.ScrollDirection.UP ||
+            this._logWalker.is_end())
+            return false;
+
+        this._fetchingBacklog = true;
+        Mainloop.timeout_add(500, Lang.bind(this,
+            function() {
+                this._logWalker.get_events_async(NUM_LOG_EVENTS,
+                                                 Lang.bind(this, this._onLogEventsReady));
+                return false;
+            }));
+        return false;
+    },
+
     _pendingMessageRemoved: function(channel, message) {
         let [id,] = message.get_pending_message_id();
         if (this._pending[id])