greetd: save and restore previously started session

This commit adds the ability to save the session ID into a file every
time a session is successfully started. This file is read on startup so
this session can be selected by default.

Requirement: a `/var/lib/phog` folder must exist and be writeable by
whatever user `greetd` runs as.

src/greetd.c

@@ -29,6 +29,8 @@
 #define WAYLAND_SESSION_FOLDER  "/usr/share/wayland-sessions"
 #define X11_SESSION_FOLDER      "/usr/share/xsessions"
 
+#define LAST_SESSION_FILE       "/var/lib/phog/last-session"
+
 /**
  * SECTION:lockscreen
  * @short_description: The main lock screen
@@ -57,6 +59,8 @@ typedef struct _PhogGreetd
 
   GListStore *available_sessions;
   GHashTable *available_users;
+
+  gchar      *last_session;
 } PhogGreetd;
 
 G_DEFINE_TYPE (PhogGreetd, phog_greetd, G_TYPE_OBJECT)
@@ -156,6 +160,9 @@ greetd_init_sessions_list (PhogGreetd *self)
     
     greetd_list_sessions_in_folder (self, WAYLAND_SESSION_FOLDER, "wayland");
     greetd_list_sessions_in_folder (self, X11_SESSION_FOLDER, "x11");
+
+    if (g_file_get_contents(LAST_SESSION_FILE, &self->last_session, NULL, NULL))
+        self->last_session = g_strstrip(self->last_session);
 }
 
 static void
@@ -371,6 +378,15 @@ phog_greetd_get_available_sessions (PhogGreetd *self)
     return self->available_sessions;
 }
 
+guint
+phog_greetd_get_last_session_idx (PhogGreetd *self)
+{
+    g_return_val_if_fail(PHOG_IS_GREETD (self), G_MAXUINT);
+    g_return_val_if_fail(self->last_session, G_MAXUINT);
+
+    return session_get_position(self, self->last_session);
+}
+
 gboolean
 phog_greetd_create_session (PhogGreetd *self, const gchar * user, GError **error)
 {
@@ -393,12 +409,13 @@ phog_greetd_authenticate (PhogGreetd *self, const gchar *password, GError **erro
 }
 
 gboolean
-phog_greetd_start_session (PhogGreetd *self, gint session_id, GError **error)
+phog_greetd_start_session (PhogGreetd *self, gint session_pos, GError **error)
 {
     g_autoptr(JsonBuilder) builder = greetd_json_builder_new ("start_session");
     PhogGreetdSession *session =
             PHOG_GREETD_SESSION (g_list_model_get_object (G_LIST_MODEL (self->available_sessions),
-                                                                        session_id));
+                                                                        session_pos));
+    const gchar *session_id = phog_greetd_session_get_id (session);
     gchar *str;
 
     json_builder_set_member_name (builder, "cmd");
@@ -418,17 +435,22 @@ phog_greetd_start_session (PhogGreetd *self, gint session_id, GError **error)
                            phog_greetd_session_get_desktop_names (session));
     json_builder_add_string_value (builder, str);
     g_free (str);
-    str = g_strdup_printf ("XDG_SESSION_DESKTOP=%s",
-                           phog_greetd_session_get_id (session));
+    str = g_strdup_printf ("XDG_SESSION_DESKTOP=%s", session_id);
     json_builder_add_string_value (builder, str);
     g_free (str);
-    str = g_strdup_printf ("GDMSESSION=%s",
-                          phog_greetd_session_get_id (session));
+    str = g_strdup_printf ("GDMSESSION=%s", session_id);
     json_builder_add_string_value (builder, str);
     g_free (str);
     json_builder_end_array (builder);
 
-    return greetd_json_builder_end (self, builder, error);
+    if (!greetd_json_builder_end (self, builder, error))
+        return FALSE;
+
+    g_free (self->last_session);
+    self->last_session = g_strdup (session_id);
+    g_file_set_contents(LAST_SESSION_FILE, self->last_session, strlen (self->last_session), NULL);
+
+    return TRUE;
 }
 
 gboolean

src/greetd.h

@@ -23,6 +23,7 @@ GObject            *phog_greetd_new (void);
 
 GHashTable         *phog_greetd_get_available_users (PhogGreetd *self);
 GListStore         *phog_greetd_get_available_sessions (PhogGreetd *self);
+guint               phog_greetd_get_last_session_idx (PhogGreetd *self);
 
 gboolean            phog_greetd_create_session (PhogGreetd *self, const gchar * user, GError **error);
 gboolean            phog_greetd_authenticate (PhogGreetd *self, const gchar * password, GError **error);