Fix UUIDv6 negative timestamps near Unix Epoch (#37)

Author: oittaa

src/UUID.php

@@ -260,8 +260,13 @@ public static function getTime(string $uuid): ?string
         $timehex = '0' . substr($uuid, 0, 12) . substr($uuid, 13, 3);
         $retval = null;
         if ($version === 6) {
-            $retval = strval(hexdec($timehex) - self::TIME_OFFSET_INT);
-            $retval = substr_replace(str_pad($retval, 8, '0', \STR_PAD_LEFT), '.', -7, 0);
+            $retval = '';
+            $ts = hexdec($timehex) - self::TIME_OFFSET_INT;
+            if ($ts < 0) {
+                $retval = '-';
+                $ts = abs($ts);
+            }
+            $retval .= substr_replace(str_pad(strval($ts), 8, '0', \STR_PAD_LEFT), '.', -7, 0);
         } elseif ($version === 7) {
             $unixts = hexdec(substr($timehex, 0, 10));
             $subsec = str_pad(strval(self::decodeSubsec(hexdec(substr($timehex, 10)))), 7, '0', \STR_PAD_LEFT);

tests/UuidTest.php

@@ -215,7 +215,13 @@ public function testGetTimeNull()
 
     public function testGetTimeNearEpoch()
     {
-        $uuid6_time = UUID::getTime('1b21dd21-3814-6001-76fa-54fb559c5fcd');
+        $uuid6_time = UUID::getTime('1b21dd21-3814-6001-b6fa-54fb559c5fcd');
         $this->assertSame($uuid6_time, '0.0000001');
     }
+
+    public function testGetTimeNegativeNearEpoch()
+    {
+        $uuid6_time = UUID::getTime('1b21dd21-3813-6fff-b678-1556dde9b80e');
+        $this->assertSame($uuid6_time, '-0.0000001');
+    }
 }