Telethon
========
**Telethon** is Telegram client implementation in Python which uses the latest available API of Telegram.
The project's **core only** is based on TLSharp, a C# Telegram client implementation.

.. contents:: Table of contents

Why Telethon?
=============
.. epigraph::

  Why should I bother with Telethon? There are more mature projects already, such as
  `telegram-cli <https://github.com/vysheng/tg>`_ with even (limited) Python support. And we have the
  `official <https://github.com/telegramdesktop/tdesktop>`_ `clients <https://github.com/DrKLO/Telegram>`_!

With Telethon you don't really need to know anything before using it. Create a client with your settings.
Connect. You're ready to go.

Being written **entirely** on Python, Telethon can run as a script under any environment you wish, (yes,
`Android too <https://f-droid.org/repository/browse/?fdfilter=termux&fdid=com.termux>`_). You can schedule it,
or use it in any other script you have. Want to send a message to someone when you're available? Write a script.
Do you want check for new messages at a given time and find relevant ones? Write a script.

Hungry for more API calls which the :code:`TelegramClient` class doesn't *seem* to have implemented?
Please read [this section](#using-more-than-just-telegramclient).

Obtaining your Telegram :code:`API ID` and :code:`Hash`
=======================================================
In order to use Telethon, you first need to obtain your very own API ID and Hash:

1. Follow `this link <https://my.telegram.org>`_ and login with your phone number.
2. Click under *API Development tools*.
3. A *Create new application* window will appear. Fill in your application details.
   There is no need to enter any *URL*, and only the first two fields (*App title* and *Short name*)
   can be changed later as long as I'm aware.
4. Click on *Create application* at the end.

Now that you know your :code:`API ID` and :code:`Hash`, you can continue installing Telethon.

Installing Telethon
===================
Installing Telethon via :code:`pip`
-----------------------------------
On a terminal, issue the following command:

.. code:: sh

  sudo -H pip install telethon

You're ready to go.

Installing Telethon manually
----------------------------

1. Install the required :code:`pyaes` module: :code:`sudo -H pip install pyaes`
   (`GitHub <https://github.com/ricmoo/pyaes>`_, `package index <https://pypi.python.org/pypi/pyaes>`_)
2. Clone Telethon's GitHub repository: :code:`git clone https://github.com/LonamiWebs/Telethon.git`
3. Enter the cloned repository: :code:`cd Telethon`
4. Run the code generator: :code:`python3 telethon_generator/tl_generator.py`
5. Done!

Running Telethon
================
If you've installed Telethon via pip, launch an interactive python3 session and enter the following:

.. code:: python

  >>> from telethon import InteractiveTelegramClient
  >>> # 'sessionid' can be 'yourname'. It'll be saved as yourname.session
  >>> # Also (obviously) replace the api_id and api_hash with your values
  ...
  >>> client = InteractiveTelegramClient('sessionid', '+34600000000',
  ...     api_id=12345, api_hash='0123456789abcdef0123456789abcdef')

  ┌───────────────────────────────────────────────────────────┐
  │                      Initialization                       │
  └───────────────────────────────────────────────────────────┘
  Initializing interactive example...
  Connecting to Telegram servers...
  >>> client.run()

If, on the other hand, you've installed Telethon manually, head to the :code:`api/` directory and create a
copy of the :code:`settings_example` file, naming it :code:`settings` (lowercase!). Then fill the file with the
corresponding values (your :code:`api_id`, :code:`api_hash` and phone number in international format).

Then, simply run :code:`python3 try_telethon.py` to start the interactive example.

Advanced uses
=============
Using more than just `TelegramClient`
-------------------------------------
The :code:`TelegramClient` class should be used to provide a quick, well-documented and simplified starting point.
It is **not** meant to be a place for _all_ the available Telegram :code:`Request`'s, because there are simply too many.

However, this doesn't mean that you cannot :code:`invoke` all the power of Telegram's API.
Whenever you need to :code:`invoke` a Telegram :code:`Request`, all you need to do is the following:

.. code:: python

  result = client.invoke(SomeRequest(...))

You have just :code:`invoke`'d :code:`SomeRequest` and retrieved its :code:`result`! That wasn't hard at all, was it?
Now you may wonder, what's the deal with *all the power of Telegram's API*? Have a look under :code:`tl/functions/`.
That is *everything* you can do. You have **over 200 API `Request`'s** at your disposal.

However, we don't pretty know *how* that :code:`result` looks like. Easy. :code:`print(str(result))` should
give you a quick overview. Nevertheless, there may be more than a single :code:`result`! Let's have a look at
this seemingly innocent :code:`TL` definition:

`messages.getWebPagePreview#25223e24 message:string = MessageMedia;`

Focusing on the end, we can see that the `result` of invoking `GetWebPagePreviewRequest` is `MessageMedia`. But how
can `MessageMedia` exactly look like? It's time to have another look, but this time under `tl/types/`:

.. code:: sh

  $ tree -P "message_media_*"
  .
  ├── tl
  │   └── types
  │       ├── message_media_contact.py
  │       ├── message_media_document.py
  │       ├── message_media_empty.py
  │       ├── message_media_geo.py
  │       ├── message_media_photo.py
  │       ├── message_media_unsupported.py
  │       ├── message_media_venue.py
  │       └── message_media_web_page.py

Those are *eight* different types! How do we know what exact type it is to determine its properties? A simple
:code:`if type(result) == MessageMediaContact:` or similar will do. Now you're ready to take advantage of
Telegram's polymorphism.

Tips for porting Telethon
-------------------------
First of all, you need to understand how the :code:`scheme.tl` (:code:`TL` language) works. Every object
definition is written as follows:

:code:`name#id argument_name:argument_type = CommonType`

This means that in a single line you know what the :code:`TLObject` name is. You know it's unique ID, and you
know what arguments it has. It really isn't that hard to write a generator for generating code to any platform!

The generated code should also be able to *encode* the :code:`Request` into bytes, so they can be sent over
the network. This isn't a big deal either, because you know how the :code:`TLObject`'s are made.

Once you have your own [code generator](telethon_generator/tl_generator.py), start by looking at the
`first release <https://github.com/LonamiWebs/Telethon/releases/tag/v0.1>`_ of Telethon.
The code there is simple to understand, easy to read and hence easy to port. No extra useless features.
Only the bare bones. Perfect for starting a *new implementation*.

P.S.: I may have lied a bit. The :code:`TL` language is not that easy. But it's not that hard either.
You're free to sniff the :code:`parser/` files and learn how to parse other more complex lines.
Or simply use that code and change the [SourceBuilder](telethon_generator/parser/source_builder.py)!

Code generator limitations
--------------------------
The current code generator is not complete, yet adding the missing features would only over-complicate an
already hard-to-read code. Some parts of the :code:`.tl` file *should* be omitted, because they're "built-in"
in the generated code (such as writing booleans, etc.).

In order to make sure that all the generated files will work, please make sure to **always** comment out these
lines in :code:`scheme.tl` (the latest version can always be found
`here <https://github.com/telegramdesktop/tdesktop/blob/master/Telegram/SourceFiles/mtproto/scheme.tl>`_):

.. code:: c

  // boolFalse#bc799737 = Bool;
  // boolTrue#997275b5 = Bool;
  // true#3fedd339 = True;
  // vector#1cb5c415 {t:Type} # [ t ] = Vector t;

Also please make sure to rename :code:`updates#74ae4240 ...` to :code:`updates_tg#74ae4240 ...` or similar to
avoid confusion between the :code:`updates` folder and the :code:`updates.py` file! Note that depending on the name,
it may break things somewhere else. So please stick with the suggested name or give one which is still descriptive
enough and easy to remember.

Updating the :code:`scheme.tl`
------------------------------
Have you found a more updated version of the :code:`scheme.tl` file? Those are great news! Updating is as simple
as grabbing the
`latest version <https://github.com/telegramdesktop/tdesktop/blob/master/Telegram/SourceFiles/mtproto/scheme.tl>`_
and replacing the one you can find in this same directory by the updated one.
Don't forget to run :code:`python3 tl_generator.py`.

If the changes weren't too big, everything should still work the same way as it did before; but with extra features.