add private /c links to message.links object (#1619)

* add private /c links to message.links object

* fixing ids for basic groups

* fixing ids for non basic chats and the test

* Improve tests for Message.link

* Simplify id_to_link

telegram/message.py

@@ -338,10 +338,20 @@ class Message(TelegramObject):
 
     @property
     def link(self):
-        """:obj:`str`: Convenience property. If the chat of the message is a supergroup or a
-        channel and has a :attr:`Chat.username`, returns a t.me link of the message."""
-        if self.chat.type in (Chat.SUPERGROUP, Chat.CHANNEL) and self.chat.username:
-            return "https://t.me/{}/{}".format(self.chat.username, self.message_id)
+        """:obj:`str`: Convenience property. If the chat of the message is not
+        a private chat, returns a t.me link of the message."""
+        if self.chat.type != Chat.PRIVATE:
+            if self.chat.username:
+                to_link = self.chat.username
+            else:
+                if self.chat.type != Chat.GROUP:
+                    # Get rid of leading -100 for supergroups
+                    id_to_link = str(self.chat.id)[4:]
+                else:
+                    # Get rid of leading minus for regular groups
+                    id_to_link = str(self.chat.id)[1:]
+                to_link = "c/{}".format(id_to_link)
+            return "https://t.me/{}/{}".format(to_link, self.message_id)
         return None
 
     @classmethod

tests/test_message.py

@@ -303,16 +303,30 @@ class TestMessage(object):
     def test_chat_id(self, message):
         assert message.chat_id == message.chat.id
 
-    def test_link(self, message):
-        assert message.link is None
+    @pytest.mark.parametrize('type', argvalues=[Chat.SUPERGROUP, Chat.CHANNEL])
+    def test_link_with_username(self, message, type):
         message.chat.username = 'username'
-        message.chat.type = 'supergroup'
+        message.chat.type = type
         assert message.link == 'https://t.me/{}/{}'.format(message.chat.username,
                                                            message.message_id)
-        message.chat.type = 'channel'
-        assert message.link == 'https://t.me/{}/{}'.format(message.chat.username,
-                                                           message.message_id)
-        message.chat.type = 'private'
+
+    @pytest.mark.parametrize('type, id', argvalues=[
+        (Chat.CHANNEL, -1003), (Chat.SUPERGROUP, -1003), (Chat.GROUP, -3)
+    ])
+    def test_link_with_id(self, message, type, id):
+        message.chat.username = None
+        message.chat.id = id
+        message.chat.type = type
+        # The leading - for group ids/ -100 for supergroup ids isn't supposed to be in the link
+        assert message.link == 'https://t.me/c/{}/{}'.format(3, message.message_id)
+
+    @pytest.mark.parametrize('id, username', argvalues=[
+        (None, 'username'), (-3, None)
+    ])
+    def test_link_private_chats(self, message, id, username):
+        message.chat.type = Chat.PRIVATE
+        message.chat.id = id
+        message.chat.username = username
         assert message.link is None
 
     def test_effective_attachment(self, message_params):