From 71ee30014357a2b59fe9848fae7f824aee8f07dd Mon Sep 17 00:00:00 2001
From: Garvin Hicking <blog@garv.in>
Date: Mon, 28 Jan 2013 09:35:34 +0100
Subject: [PATCH] Purge browser cache using a timestamp variable when switching
 templates. This should hopefully fix Ian and my problems.

---
 docs/NEWS                        |  6 +++++-
 include/admin/templates.inc.php  |  1 +
 include/functions_smarty.inc.php |  8 ++++++++
 serendipity_admin.php            | 17 ++++++++++++++++-
 4 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/docs/NEWS b/docs/NEWS
index 9aab78de..2b46d345 100644
--- a/docs/NEWS
+++ b/docs/NEWS
@@ -3,8 +3,12 @@
 Version 2.0 ()
 ------------------------------------------------------------------------
 
+    * When switching templates, both the backend and the frontend
+      will remember the timestamp of the last template change,
+      to make sure that the browser will not cache a mismatching CSS.
+      
     * Use Smarty for backend display output
-
+    
 Version 1.7 ()
 ------------------------------------------------------------------------
 
diff --git a/include/admin/templates.inc.php b/include/admin/templates.inc.php
index e72d27f9..74f567fb 100644
--- a/include/admin/templates.inc.php
+++ b/include/admin/templates.inc.php
@@ -65,6 +65,7 @@ if ($serendipity['GET']['adminAction'] == 'install' ) {
 
     serendipity_set_config_var('template', htmlspecialchars($serendipity['GET']['theme']));
     serendipity_set_config_var('template_engine', isset($themeInfo['engine']) ? $themeInfo['engine'] : 'default');
+    serendipity_set_config_var('last_template_change', time());
 
     $data["adminAction"] = "install";
     $data["install_template"] = htmlspecialchars($serendipity['GET']['theme']);
diff --git a/include/functions_smarty.inc.php b/include/functions_smarty.inc.php
index b984d152..a34ddcbe 100644
--- a/include/functions_smarty.inc.php
+++ b/include/functions_smarty.inc.php
@@ -967,6 +967,14 @@ function serendipity_smarty_init($vars = array()) {
 
         if (!isset($serendipity['smarty_vars']['head_link_stylesheet'])) {
             $serendipity['smarty_vars']['head_link_stylesheet'] = serendipity_rewriteURL('serendipity.css');
+
+            // When templates are switched, append a specific version string to make sure the browser does not cache the CSS
+            if (strstr($serendipity['smarty_vars']['head_link_stylesheet'], '?')) {
+                $serendipity['smarty_vars']['head_link_stylesheet'] .= '&v=' . $serendipity['last_template_change'];
+            } else {
+                $serendipity['smarty_vars']['head_link_stylesheet'] .= '?v=' . $serendipity['last_template_change'];
+            }
+
         }
 
         $serendipity['smarty']->assign(
diff --git a/serendipity_admin.php b/serendipity_admin.php
index b8bf4e99..c6bbb106 100644
--- a/serendipity_admin.php
+++ b/serendipity_admin.php
@@ -14,9 +14,24 @@ if (IS_installed === false) {
     require(S9Y_INCLUDE_PATH . 'include/functions_permalinks.inc.php');
     require(S9Y_INCLUDE_PATH . 'include/functions_installer.inc.php');
     require(S9Y_INCLUDE_PATH . 'include/functions_config.inc.php');
-    $css_file = 'serendipity.css.php?serendipity[css_mode]=serendipity_admin.css';
+    $css_file = 'serendipity.css.php?serendipity[css_mode]=serendipity_admin.css&v=' . time();
 } else {
     $css_file = serendipity_rewriteURL('serendipity_admin.css');
+
+    // This is a bit of an ugly hack, but when switching templates, the HTML head is already emitted,
+    // so we need a way to actually enforce switching/updating the CSS. So we need to do it at
+    // this place.
+    if ($serendipity['GET']['adminAction'] == 'install' && $serendipity['GET']['adminModule'] == 'templates') {
+        $serendipity['last_template_change'] = time();
+    }
+
+    // When templates are switched, append a specific version string to make sure the browser does not cache the CSS
+    if (strstr($css_file, '?')) {
+        $css_file .= '&v=' . $serendipity['last_template_change'];
+    } else {
+        $css_file .= '?v=' . $serendipity['last_template_change'];
+    }
+
     if (defined('IS_up2date') && IS_up2date === true) {
         serendipity_plugin_api::hook_event('backend_configure', $serendipity);
     }