From 58b9ce5946c5fea9b6f1a9f1c0c9641c5104d769 Mon Sep 17 00:00:00 2001
From: Stephen Paul Weber <singpolyma@singpolyma.net>
Date: Thu, 16 Apr 2009 10:57:35 -0400
Subject: [PATCH] Better license check.

Tokenise CC license parts and check for compatability.
Fallback is old directly-equal test.
---
 lib/util.php | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/lib/util.php b/lib/util.php
index b6e89f0bd9..00696583ee 100644
--- a/lib/util.php
+++ b/lib/util.php
@@ -1360,9 +1360,28 @@ function common_memcache()
     }
 }
 
+function common_license_terms($uri)
+{
+    if(preg_match('/creativecommons.org\/licenses\/([^\/]+)/', $uri, $matches)) {
+        return explode('-',$matches[1]);
+    }
+    return array($uri);
+}
+
 function common_compatible_license($from, $to)
 {
+    $from_terms = common_license_terms($from);
+    // public domain and cc-by are compatible with everything
+    if(count($from_terms) == 1 && ($from_terms[0] == 'publicdomain' || $from_terms[0] == 'by')) {
+        return true;
+    }
+    $to_terms = common_license_terms($to);
+    // sa is compatible across versions. IANAL
+    if(in_array('sa',$from_terms) || in_array('sa',$to_terms)) {
+        return count(array_diff($from_terms, $to_terms)) == 0;
+    }
     // XXX: better compatibility check needed here!
+    // Should at least normalise URIs
     return ($from == $to);
 }
 
-- 
2.39.5