From ba46af16e693fa86f9270d5e9135a2381a8a62f9 Mon Sep 17 00:00:00 2001
From: Clement Lefebvre <clement.lefebvre@linuxmint.com>
Date: Tue, 20 Jun 2017 15:20:08 +0200
Subject: Add support for validating session names (and proper fallback for
 uninstalled sessions). Ported from slick-greeter.

---
 src/arctica-greeter.vala | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 src/greeter-list.vala    |  2 +-
 src/user-list.vala       |  2 +-
 3 files changed, 48 insertions(+), 2 deletions(-)

diff --git a/src/arctica-greeter.vala b/src/arctica-greeter.vala
index 9b5d279..eb42306 100644
--- a/src/arctica-greeter.vala
+++ b/src/arctica-greeter.vala
@@ -181,6 +181,52 @@ public class ArcticaGreeter
         ctx.add_class ("lightdm");
     }
 
+    public static string? get_default_session ()
+    {
+        var sessions = new List<string> ();
+        sessions.append ("lightdm-xsession");
+
+        // FIXME: this list should be obtained from AGSettings, ideally...
+        sessions.append ("mate");
+        sessions.append ("xfce");
+        sessions.append ("kde-plasma");
+        sessions.append ("kde");
+        sessions.append ("gnome");
+        sessions.append ("cinnamon");
+
+        foreach (string session in sessions) {
+            var path = Path.build_filename  ("/usr/share/xsessions/", session.concat(".desktop"), null);
+            if (FileUtils.test (path, FileTest.EXISTS)) {
+                return session;
+            }
+        }
+
+        warning ("Could not find a default session.");
+        return null;
+    }
+
+    public static string validate_session (string? session)
+    {
+        /* Make sure the given session actually exists. Return it if it does.
+         * otherwise, return the default session.
+         */
+        if (session != null) {
+            var path = Path.build_filename  ("/usr/share/xsessions/", session.concat(".desktop"), null);
+            if (!FileUtils.test (path, FileTest.EXISTS) ) {
+                debug ("Invalid session: '%s'", session);
+                session = null;
+            }
+        }
+
+        if (session == null) {
+            var default_session = ArcticaGreeter.get_default_session ();
+            debug ("Invalid session: '%s'. Using session '%s' instead.", session, default_session);
+            return default_session;
+        }
+
+        return session;
+    }
+
     public bool start_session (string? session, Background bg)
     {
         /* Explicitly set the right scale before closing window */
diff --git a/src/greeter-list.vala b/src/greeter-list.vala
index 17d80a8..8e25602 100644
--- a/src/greeter-list.vala
+++ b/src/greeter-list.vala
@@ -947,7 +947,7 @@ public abstract class GreeterList : FadableBox
 
     protected virtual string get_lightdm_session ()
     {
-        return "ubuntu";
+        return ArcticaGreeter.get_default_session ();
     }
 
     /* Testing code below this */
diff --git a/src/user-list.vala b/src/user-list.vala
index ad68a17..319e833 100644
--- a/src/user-list.vala
+++ b/src/user-list.vala
@@ -859,7 +859,7 @@ public class UserList : GreeterList
         }
         e.background = background;
         e.is_active = is_active;
-        e.session = session;
+        e.session = ArcticaGreeter.validate_session(session);
         e.label = label;
         e.set_show_message_icon (has_messages);
         e.set_is_active (is_active);
-- 
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