=========================
Users, Chats and Channels
=========================


Introduction
************

The library widely uses the concept of "entities". An entity will refer
to any ``User``, ``Chat`` or ``Channel`` object that the API may return
in response to certain methods, such as ``GetUsersRequest``.

Getting entities
****************

Through the use of the :ref:`sessions`, the library will automatically
remember the ID and hash pair, along with some extra information, so
you're able to just do this:

    .. code-block:: python

        # Dialogs are the "conversations you have open".
        # This method returns a list of Dialog, which
        # has the .entity attribute and other information.
        dialogs = client.get_dialogs(limit=200)

        # All of these work and do the same.
        lonami = client.get_entity('lonami')
        lonami = client.get_entity('t.me/lonami')
        lonami = client.get_entity('https://telegram.dog/lonami')

        # Other kind of entities.
        channel = client.get_entity('telegram.me/joinchat/AAAAAEkk2WdoDrB4-Q8-gg')
        contact = client.get_entity('+34xxxxxxxxx')
        friend  = client.get_entity(friend_id)

        # Using Peer/InputPeer (note that the API may return these)
        # users, chats and channels may all have the same ID, so it's
        # necessary to wrap (at least) chat and channels inside Peer.
        #
        # NOTICE how the IDs *must* be wrapped inside a Peer() so the
        # library knows their type.
        from telethon.tl.types import PeerUser, PeerChat, PeerChannel
        my_user    = client.get_entity(PeerUser(some_id))
        my_chat    = client.get_entity(PeerChat(some_id))
        my_channel = client.get_entity(PeerChannel(some_id))


.. warning::

    As it has been mentioned already, getting the entity of a channel
    through e.g. ``client.get_entity(channel id)`` will **not** work.
    You would use ``client.get_entity(types.PeerChannel(channel id))``.
    Remember that supergroups are channels and normal groups are chats.
    This is a common mistake!


All methods in the :ref:`telegram-client` call ``.get_input_entity()`` prior
to sending the requst to save you from the hassle of doing so manually.
That way, convenience calls such as ``client.send_message('lonami', 'hi!')``
become possible.

Every entity the library encounters (in any response to any call) will by
default be cached in the ``.session`` file (an SQLite database), to avoid
performing unnecessary API calls. If the entity cannot be found, additonal
calls like ``ResolveUsernameRequest`` or ``GetContactsRequest`` may be
made to obtain the required information.


Entities vs. Input Entities
***************************

.. note::

    Don't worry if you don't understand this section, just remember some
    of the details listed here are important. When you're calling a method,
    don't call ``.get_entity()`` beforehand, just use the username or phone,
    or the entity retrieved by other means like ``.get_dialogs()``.


On top of the normal types, the API also make use of what they call their
``Input*`` versions of objects. The input version of an entity (e.g.
``InputPeerUser``, ``InputChat``, etc.) only contains the minimum
information that's required from Telegram to be able to identify
who you're referring to: a ``Peer``'s **ID** and **hash**.

This ID/hash pair is unique per user, so if you use the pair given by another
user **or bot** it will **not** work.

To save *even more* bandwidth, the API also makes use of the ``Peer``
versions, which just have an ID. This serves to identify them, but
peers alone are not enough to use them. You need to know their hash
before you can "use them".

As we just mentioned, API calls don't need to know the whole information
about the entities, only their ID and hash. For this reason, another method,
``.get_input_entity()`` is available. This will always use the cache while
possible, making zero API calls most of the time. When a request is made,
if you provided the full entity, e.g. an ``User``, the library will convert
it to the required ``InputPeer`` automatically for you.

**You should always favour** ``.get_input_entity()`` **over** ``.get_entity()``
for this reason! Calling the latter will always make an API call to get
the most recent information about said entity, but invoking requests don't
need this information, just the ``InputPeer``. Only use ``.get_entity()``
if you need to get actual information, like the username, name, title, etc.
of the entity.

To further simplify the workflow, since the version ``0.16.2`` of the
library, the raw requests you make to the API are also able to call
``.get_input_entity`` wherever needed, so you can even do things like:

    .. code-block:: python

        client(SendMessageRequest('username', 'hello'))

The library will call the ``.resolve()`` method of the request, which will
resolve ``'username'`` with the appropriated ``InputPeer``. Don't worry if
you don't get this yet, but remember some of the details here are important.