Add a history manager

runDialog and lookingGlass both implement a home-made history
manager, each working slightly differently than each other in
behavior and implementation.

Extract the behavior and implementation from runDialog, which
reads and saves to GSettings.

https://bugzilla.gnome.org/show_bug.cgi?id=642237

js/Makefile.am

@@ -7,6 +7,7 @@ nobase_dist_js_DATA = 	\
 	misc/fileUtils.js	\
 	misc/format.js		\
 	misc/gnomeSession.js	\
+	misc/history.js		\
 	misc/params.js		\
 	misc/util.js		\
 	perf/core.js		\

js/misc/history.js

@@ -0,0 +1,72 @@
+/* -*- mode: js2; js2-basic-offset: 4; indent-tabs-mode: nil -*- */
+
+const Lang = imports.lang;
+const Signals = imports.signals;
+
+const DEFAULT_LIMIT = 512;
+
+function HistoryManager(settings_key) {
+    this._init(settings_key);
+}
+
+HistoryManager.prototype = {
+    _init: function(settings_key, limit) {
+        this._limit = limit || DEFAULT_LIMIT;
+        this._key = settings_key;
+        this._history = global.settings.get_strv(settings_key);
+        this._historyIndex = -1;
+
+        global.settings.connect('changed::' + settings_key,
+                                Lang.bind(this, this._historyChanged));
+    },
+
+    _historyChanged: function() {
+        this._history = global.settings.get_strv(this._key);
+        this._historyIndex = this._history.length;
+    },
+
+    prevItem: function(text) {
+        this._setHistory(this._historyIndex--, text);
+        return this._indexChanged();
+    },
+
+    nextItem: function(text) {
+        this._setHistory(this._historyIndex++, text);
+        return this._indexChanged();
+    },
+
+    lastItem: function() {
+        this._historyIndex = this._history.length;
+        return this._indexChanged();
+    },
+
+    addItem: function(input) {
+        if (this._history.length == 0 ||
+            this._history[this._history.length - 1] != input) {
+
+            this._history.push(input);
+            this._save();
+        }   
+    },
+
+    _indexChanged: function() {
+        let current = this._history[this._historyIndex] || '';
+        this.emit('changed', current);
+        return current;
+    },
+
+    _setHistory: function(index, text) {
+        this._historyIndex = Math.max(this._historyIndex, 0);
+        this._historyIndex = Math.min(this._historyIndex, this._history.length);
+
+        if (text)
+            this._history[index] = text;
+    },
+
+    _save: function() {
+        if (this._history.length > this._limit)
+            this._history.splice(0, this._history.length - this._key);
+        global.settings.set_strv(this._key, this._history);
+    }
+};
+Signals.addSignalMethods(HistoryManager.prototype);