[polari/wip/fmuellner/tracker: 3/5] logManager: Support running queries in chunks

[Florian Müllner <fmuellner src gnome org>]

commit a6e49dc5b6e7284ab0fa0a4f7898f771647541db
Author: Carlos Garnacho <carlosg gnome org>
Date:   Tue Dec 29 18:14:52 2015 +0100

    logManager: Support running queries in chunks
    
    It is not always desirable to retrieve the full result set at once;
    in particular for the history in the chat log that uses TplLogWalker
    currently, we want to maintain the behavior of only loading the most
    recent history initially and fetch additional logs on demand.
    To support this, extend the previously added GenericQuery class to
    specify an optional limit.

 src/logManager.js |   42 +++++++++++++++++++++++++++++++++++++-----
 1 files changed, 37 insertions(+), 5 deletions(-)
---
diff --git a/src/logManager.js b/src/logManager.js
index 0cdc2e6..845c725 100644
--- a/src/logManager.js
+++ b/src/logManager.js
@@ -13,14 +13,18 @@ function getDefault() {
 const GenericQuery = new Lang.Class({
     Name: 'GenericQuery',
 
-    _init: function(connection) {
+    _init: function(connection, limit = -1) {
         this._connection = connection;
         this._results = [];
+        this._limit = limit;
+        this._count = 0;
+        this._closed = false;
+        this._cursor = null;
         this._task = null;
     },
 
-    run: function(sparql, cancellable, callback) {
-        this._task = Gio.Task.new(this._connection, cancellable, Lang.bind(this,
+    _createTask: function(cancellable, callback) {
+        return Gio.Task.new(this._connection, cancellable, Lang.bind(this,
             function(o, res) {
                 let success = false;
                 try {
@@ -32,6 +36,10 @@ const GenericQuery = new Lang.Class({
                 callback(success ? this._results : []);
                 this._task = null;
             }));
+    },
+
+    run: function(sparql, cancellable, callback) {
+        this._task = this._createTask(cancellable, callback);
 
         this._connection.query_async(sparql, cancellable, Lang.bind(this,
             function(c, res) {
@@ -43,11 +51,28 @@ const GenericQuery = new Lang.Class({
                     return;
                 }
 
+                this._cursor = cursor;
                 cursor.next_async(cancellable,
                                   Lang.bind(this, this._onCursorNext));
             }));
     },
 
+    next: function (limit, cancellable, callback) {
+        if (this._task)
+            return false;
+
+        this._results = [];
+        this._count = 0;
+        this._limit = limit;
+        this._task = this._createTask(cancellable, callback);
+        this._cursor.next_async(cancellable, Lang.bind(this, this._onCursorNext));
+        return true;
+    },
+
+    isClosed: function () {
+        return this._closed;
+    },
+
     _onCursorNext: function(cursor, res) {
         let valid = false;
         try {
@@ -58,12 +83,19 @@ const GenericQuery = new Lang.Class({
 
         if (valid) {
             this._pushResult(cursor);
-            cursor.next_async(this._task.get_cancellable(),
-                              Lang.bind(this, this._onCursorNext));
+            this._count++;
+
+            if (this._limit <= 0 || this._count < this._limit) {
+                cursor.next_async(this._task.get_cancellable(),
+                                  Lang.bind(this, this._onCursorNext));
+            } else {
+                this._task.return_boolean(true);
+            }
         } else {
             cursor.close();
             if (!this._task.had_error())
                 this._task.return_boolean(true);
+            this._closed = true;
         }
     },