poezio/doc/source/dev/overview.rst

.. _overview:

Overview
========

.. note:: This is not an introduction to XMPP, but to how poezio works.


Global overview
---------------

Poezio is an application that has three main layers, mostly separated in three
different python modules: ``core``, ``tabs``, and ``windows``. An UML diagram of
Poezio would be inneficient, cluttered, or incomplete, so there is none, if
that bugs you.

.. figure:: ../images/layers.png
    :alt: Layers

**Core** is mostly a “global” object containing the state of the application at
any time, it contains the global commands, the xmpp event handlers, the list
of open tabs, etc. Most objects in poezio have a self.core attribute
referencing the **Core** (it’s a singleton, so there is never more than one
instance). **Core** also contains the main loop of the application, which then
dispatchs the I/O events (keypress) to the appropriate methods.

But the main loop is not the most important thing in poezio; because it is an
IM client, it is essentially event-driven. The event part is handled by
SleekXMPP, which is the library we chose after moving away from xmpppy.


**Tabs** are the second layer of poezio, but the first dealing with the UI: each
**Tab** is a layout of several **windows**, it contains tab-specific commands,
tab-specific keybinds, and it has methods in order for core to
interact with it, and some methods are only proxies for the methods of a
**window**.

Example scenario: If someone presses the key PageUp, then Core will call the
appropriate method on the current _Tab_, which will in turn, if it implements the
method (inherited empty from the Tab class), call a scrolling method from the
appropriate **window**.

All tabs types inherit from the class **Tab**, and the tabs featuring
chat functionnality will inherit from **ChatTab** (which inherits from **Tab**).

Examples of **tabs**: MUCTab, XMLTab, RosterTab, MUCListTab, etc…

Event handlers
--------------

The events handlers are registered right at the start of poezio, and then
when a matching stanza is received, the handler is called in a separate thread
from the main loop. The handlers are in **Core**, and then they call the
appropriate methods in the corresponding **tabs**.

Example scenario: if a message is received from a MUC, then the **Core** handler
will identify the **Tab**, and call the relevant handler from this **Tab**, this tab
will in turn, add the message to the buffer, which will then add it to the
relevant **windows**.

.. note:: All the _windows_ that deal with received or generated text are linked
    to a **text_buffer**, in order to rebuild all the display lines from the
    sources if necessary. This also enables us to have several **windows**
    presenting the same text, even if they are not of the same size and layout.

Commands and completion
-----------------------

Commands are quite straightforward: those are methods that take a string as a
parameter, and they do stuff.

From an user point of view, the methods are entered like that:

.. code-block:: none

    /command arg1 arg2

or

.. code-block:: none

    /command "arg1 with spaces" arg2

However, when creating a command, you wil deal with _one_ str, no matter what.
There are utilities to deal with it (common.shell_split), but it is not always
necessary. Commands are registered in the **commands** dictionnary of a tab
structured as key (command name) -> tuple(command function, help string, completion).


Completions are a bit tricky, but it’s easy once you get used to it:

They take an **Input** (a _windows_ class) as a parameter, named the_input
everywhere in the sources. To effectively have a completion, you have to call
**the_input.auto_completion()** or **the_input.new_completion()** at the end
of the function.


.. code-block:: python

    class Input(Win):
        # …
        def auto_completion(completion_list, after='', quotify=True):
            # …

        def new_completion(completion_list, argument_position, after='', quotify=True):
            # …

Set the input to iterate over _completion_list_ when the user hits tab, insert
**after** after the completed item, and surround the item with double quotes or
not.

To find the current completed argument, use the **input.get_argument_position()**
method. You can then use new_completion() to select the argument to be completed.

You can look for examples in the sources, all the possible cases are
covered (single-argument, complex arguments with spaces, several arguments,
etc…).