sessionMode: Add support for external mode definitions

Currently adding a new session mode requires patching the sources.
As defining custom modes can be desirable in some circumstances
(for instance for administrators of kiosk setups), load additional
modes from JSON files.

https://bugzilla.gnome.org/show_bug.cgi?id=689304

js/ui/sessionMode.js

@@ -1,5 +1,7 @@
 // -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
 
+const Gio = imports.gi.Gio;
+const GLib = imports.gi.GLib;
 const Lang = imports.lang;
 const Signals = imports.signals;
 
@@ -104,8 +106,65 @@ const _modes = {
     }
 };
 
+function _getModes() {
+    let modes = _modes;
+    let dataDirs = GLib.get_system_data_dirs();
+    for (let i = 0; i < dataDirs.length; i++) {
+        let path = GLib.build_filenamev([dataDirs[i], 'gnome-shell', 'modes']);
+        let dir = Gio.file_new_for_path(path);
+
+        try {
+            dir.query_info('standard:type', Gio.FileQueryInfoFlags.NONE, null);
+        } catch (e) {
+            continue;
+        }
+
+        _getModesFromDir(dir, modes);
+    }
+    return modes;
+}
+
+function _getModesFromDir(dir, modes) {
+    let fileEnum;
+    try {
+        fileEnum = dir.enumerate_children('standard::*',
+                                          Gio.FileQueryInfoFlags.NONE, null);
+    } catch(e) {
+        return;
+    }
+
+    let info;
+    while ((info = fileEnum.next_file(null)) != null) {
+        let name = info.get_name();
+        let suffix = name.indexOf('.json');
+        let modeName = suffix == -1 ? name : name.slice(name, suffix);
+
+        if (modes.hasOwnProperty(modeName))
+            continue;
+
+        let file = dir.get_child(name);
+        let fileContent, success, tag, newMode;
+        try {
+            [success, fileContent, tag] = file.load_contents(null);
+            newMode = JSON.parse(fileContent);
+        } catch(e) {
+            continue;
+        }
+
+        modes[modeName] = {};
+        let propBlacklist = ['unlockDialog'];
+        for (let prop in modes[DEFAULT_MODE]) {
+            if (newMode[prop] !== undefined &&
+                propBlacklist.indexOf(prop) == -1)
+                modes[modeName][prop]= newMode[prop];
+        }
+        modes[modeName]['isPrimary'] = true;
+    }
+    fileEnum.close(null);
+}
+
 function listModes() {
-    let modes = Object.getOwnPropertyNames(_modes);
+    let modes = Object.getOwnPropertyNames(_getModes());
     for (let i = 0; i < modes.length; i++)
         if (_modes[modes[i]].isPrimary)
             print(modes[i]);
@@ -116,8 +175,9 @@ const SessionMode = new Lang.Class({
 
     _init: function() {
         global.connect('notify::session-mode', Lang.bind(this, this._sync));
-        let mode = _modes[global.session_mode].isPrimary ? global.session_mode
-                                                         : 'user';
+        this._modes = _getModes();
+        let mode = this._modes[global.session_mode].isPrimary ? global.session_mode
+                                                              : 'user';
         this._modeStack = [mode];
         this._sync();
     },
@@ -146,8 +206,8 @@ const SessionMode = new Lang.Class({
     },
 
     _sync: function() {
-        let params = _modes[this.currentMode];
-        params = Params.parse(params, _modes[DEFAULT_MODE]);
+        let params = this._modes[this.currentMode];
+        params = Params.parse(params, this._modes[DEFAULT_MODE]);
 
         // A simplified version of Lang.copyProperties, handles
         // undefined as a special case for "no change / inherit from previous mode"