add getTime() (#28)

* add `getTime()`

Author: oittaa

README.md

@@ -110,4 +110,10 @@ $cmp3 = UUID::cmp(
     '{C4A760A8-DBCF-5254-A0D9-6A4474BD1B62}'
 );
 var_dump($cmp3 === 0); // bool(true)
+
+// Extract Unix time from versions 6 and 7 as a string.
+$uuid6_time = UUID::getTime(UUID::uuid6());
+var_dump($uuid6_time); // e.g. string(18) "1639860190.2801270"
+$uuid7_time = UUID::getTime(UUID::uuid7());
+var_dump($uuid7_time); // e.g. string(18) "1639860190.2801320"
 ```

src/UUID.php

@@ -208,12 +208,12 @@ public static function uuid6(): string
     public static function uuid7(): string
     {
         [$unixts, $subsec] = self::getUnixTime();
-        $uhex = str_pad(dechex($unixts), 9, '0', \STR_PAD_LEFT);
+        $uhex = substr(str_pad(dechex($unixts), 9, '0', \STR_PAD_LEFT), -9);
         $shex = str_pad(dechex($subsec), 6, '0', \STR_PAD_LEFT);
         $uhex .= sprintf(
             '%03s7%03s',
             substr($shex, 0, 3),
-            substr($shex, -3)
+            substr($shex, 3, 3)
         );
         $uhex .= bin2hex(random_bytes(8));
         return self::uuidFromHex($uhex, 7);
@@ -242,6 +242,28 @@ public static function equals(string $uuid1, string $uuid2): bool
         return self::getBytes($uuid1) === self::getBytes($uuid2);
     }
 
+    /**
+     * Returns Unix time from a UUID.
+     *
+     * @param string $uuid The UUID string
+     * @return string Unix time
+     */
+    public static function getTime(string $uuid): ?string
+    {
+        $uuid = self::stripExtras($uuid);
+        $version = self::getVersion($uuid);
+        $timehex = '0' . substr($uuid, 0, 12) . substr($uuid, 13, 3);
+        $retval = null;
+        if ($version === 6) {
+            $retval = substr_replace(strval(hexdec($timehex) - self::TIME_OFFSET_INT), '.', -7, 0);
+        } elseif ($version === 7) {
+            $unixts = hexdec(substr($timehex, 0, 10));
+            $subsec = str_pad(strval(hexdec(substr($timehex, 10))), 7, '0', \STR_PAD_LEFT);
+            $retval = $unixts . '.' . $subsec;
+        }
+        return $retval;
+    }
+
     /**
      * Returns the UUID version.
      *

tests/UuidTest.php

@@ -180,4 +180,19 @@ public function testCanUseAliases()
             UUID::getVersion(UUID::v7())
         );
     }
+
+    public function testGetTimeValid()
+    {
+        $now = microtime(true);
+        $uuid6 = UUID::uuid6();
+        $uuid7 = UUID::uuid7();
+        $this->assertEqualsWithDelta($now, UUID::getTime($uuid6), 0.001);
+        $this->assertEqualsWithDelta($now, UUID::getTime($uuid7), 0.001);
+    }
+
+    public function testGetTimeNull()
+    {
+        $uuid4_time = UUID::getTime(UUID::uuid4());
+        $this->assertNull($uuid4_time);
+    }
 }