Add support \DateTimeInterface (googleapis#956)

* Add support \DateTimeInterface

* Update PhpUnit and remove unnecessary overhead

* Update refactor

* Update php5.5 compatibility

* Change intval to cast

* Cast expression optimization

.gitignore

@@ -4,6 +4,7 @@ composer.phar
 composer.lock
 docs/json/**/*
 vendor/
+.idea/
 
 # do not delete
 keys/

Firestore/src/ValueMapper.php

@@ -17,16 +17,16 @@
 
 namespace Google\Cloud\Firestore;
 
+use Google\Cloud\Core\ArrayTrait;
 use Google\Cloud\Core\Blob;
-use Google\Cloud\Core\Int64;
-use Google\Protobuf\NullValue;
+use Google\Cloud\Core\DebugInfoTrait;
 use Google\Cloud\Core\GeoPoint;
+use Google\Cloud\Core\Int64;
 use Google\Cloud\Core\Timestamp;
-use Google\Cloud\Core\ArrayTrait;
 use Google\Cloud\Core\ValidateTrait;
-use Google\Cloud\Core\DebugInfoTrait;
 use Google\Cloud\Core\ValueMapperTrait;
 use Google\Cloud\Firestore\Connection\ConnectionInterface;
+use Google\Protobuf\NullValue;
 
 /**
  * Normalizes values between Google Cloud PHP and Cloud Firestore.
@@ -402,6 +402,15 @@ private function encodeObjectValue($value)
             return $this->encodeAssociativeArrayValue((array) $value);
         }
 
+        if ($value instanceof \DateTimeInterface) {
+            return [
+                'timestampValue' => [
+                    'seconds' => $value->format('U'),
+                    'nanos' => (int)($value->format('u') * 1000)
+                ]
+            ];
+        }
+
         if ($value instanceof Blob) {
             return ['bytesValue' => (string) $value];
         }

Firestore/tests/Unit/ValueMapperTest.php

@@ -26,7 +26,6 @@
 use Google\Cloud\Firestore\DocumentReference;
 use Google\Cloud\Firestore\FieldPath;
 use Google\Cloud\Firestore\FieldValue;
-use Google\Cloud\Firestore\FirestoreClient;
 use Google\Cloud\Firestore\ValueMapper;
 use Google\Protobuf\NullValue;
 use PHPUnit\Framework\TestCase;
@@ -192,9 +191,11 @@ public function decodedValues()
         $blobValue = 'hello world';
         $blob = new Blob($blobValue);
 
-        $now = (string) time();
-        $nanos = 10;
-        $timestamp = new Timestamp(\DateTimeImmutable::createFromFormat('U', (string) $now), $nanos);
+        $datetime = \DateTimeImmutable::createFromFormat('U.u', microtime(true));
+        $now = (string) $datetime->format('U');
+        $micros = (int) $datetime->format('u');
+        $nanos = (int) $datetime->format('u') * 1000 + 10;
+        $timestamp = new Timestamp(\DateTimeImmutable::createFromFormat('U', $now), $nanos);
 
         $lat = 100.01;
         $lng = 100.25;
@@ -298,6 +299,14 @@ function ($val) {
                 function ($val) use ($blobValue) {
                     $this->assertEquals($blobValue, $val['bytesValue']);
                 }
+            ], [
+                $datetime,
+                function ($val) use ($now, $micros) {
+                    $this->assertEquals([
+                        'seconds' => $now,
+                        'nanos' => intval($micros * 1000)
+                    ], $val['timestampValue']);
+                }
             ], [
                 $timestamp,
                 function ($val) use ($now, $nanos) {