Implement imap_thread (#249)

Close #113

src/Mailbox.php

@@ -216,4 +216,20 @@ public function addMessage(string $message): bool
     {
         return \imap_append($this->resource->getStream(), $this->getFullEncodedName(), $message);
     }
+
+    /**
+     * Returns a tree of threaded message for the current Mailbox.
+     *
+     * @return array
+     */
+    public function getThread(): array
+    {
+        \set_error_handler(function () {});
+
+        $tree = \imap_thread($this->resource->getStream());
+
+        \restore_error_handler();
+
+        return false !== $tree ? $tree : [];
+    }
 }

src/MailboxInterface.php

@@ -108,4 +108,11 @@ public function getIterator(): MessageIteratorInterface;
      * @return bool
      */
     public function addMessage(string $message): bool;
+
+    /**
+     * Returns a tree of threaded message for the current Mailbox.
+     *
+     * @return array
+     */
+    public function getThread(): array;
 }

tests/MailboxTest.php

@@ -179,4 +179,30 @@ public function testBulkSetFlagsNumbersParameter()
             $this->assertFalse($message->isSeen());
         }
     }
+
+    public function testThread()
+    {
+        $mailboxOne = $this->createMailbox();
+        $mailboxOne->addMessage($this->getFixture('thread/my_topic'));
+        $mailboxOne->addMessage($this->getFixture('thread/unrelated'));
+        $mailboxOne->addMessage($this->getFixture('thread/re_my_topic'));
+
+        $expected = [
+            '0.num' => 1,
+            '0.next' => 1,
+            '1.num' => 3,
+            '1.next' => 0,
+            '1.branch' => 0,
+            '0.branch' => 2,
+            '2.num' => 2,
+            '2.next' => 0,
+            '2.branch' => 0,
+        ];
+
+        $this->assertSame($expected, $mailboxOne->getThread());
+
+        $emptyMailbox = $this->createMailbox();
+
+        $this->assertEmpty($emptyMailbox->getThread());
+    }
 }

tests/fixtures/thread/my_topic.eml

@@ -0,0 +1,10 @@
+Message-ID: <[email protected]>
+From: [email protected]
+To: [email protected]
+Subject: Nuu
+Date: Wed, 13 Sep 2017 13:05:45 +0200
+Content-Type: text/plain;
+	charset="us-ascii"
+Content-Transfer-Encoding: quoted-printable
+
+Hi

tests/fixtures/thread/re_my_topic.eml

@@ -0,0 +1,11 @@
+Message-ID: <[email protected]>
+In-Reply-To: <[email protected]>
+From: [email protected]
+To: [email protected]
+Subject: Re: Nuu
+Date: Wed, 13 Sep 2017 13:05:45 +0200
+Content-Type: text/plain;
+	charset="us-ascii"
+Content-Transfer-Encoding: quoted-printable
+
+Hi

tests/fixtures/thread/unrelated.eml

@@ -0,0 +1,10 @@
+Message-ID: <[email protected]>
+From: [email protected]
+To: [email protected]
+Subject: Wut
+Date: Wed, 13 Sep 2017 13:05:45 +0200
+Content-Type: text/plain;
+	charset="us-ascii"
+Content-Transfer-Encoding: quoted-printable
+
+Hi