Irssi's hierarchy is something like this:


         sub1 sub2
            \ /
       xxx  IRC       COMMON ICQ  yyy
        |____|___________|____|____|
                   |
                  GUI (gtk/gnome, qt/kde, text, none)
                   |
         sub1 sub2 |
            \ /    |
       xxx  IRC    |  COMMON ICQ  yyy
        |____|_____|_____|____|____|
                   |
               COMMON UI
                   |
         sub1 sub2 |
            \ /    |
       xxx  IRC    |    ICQ  yyy
        |____|_____|_____|____|
                   |
                 CORE
                 /
        lib-config


 (IRC, ICQ, xxx and yyy are chat protocols ..)
 (sub1 and sub2 are submodules of IRC module, like DCC and flood protect)


 Chat protocols and frontends are kept in separate modules. Common UI
 and GUI modules also have the common parts which don't know anything
 about the chat protocols. This should allow implementing modules to
 whatever chat protocols and with whatever frontends easily.

 ** Signals

 Communication between different modules are done with "signals". They are
 not related to UNIX signals in any way, you could more like think of them
 as "events" - which might be a better name for them, but I don't really
 want to change it anymore :)

 So, you send signal with signal_emit() and it's sent to all modules that
 have grabbed it by calling signal_add() in their init function. For
 example:

   signal_emit("mysignal", 1, "hello");

 Sends a "mysignal" function with one argument "hello" - before that, you
 should have grabbed the signal somewhere else with:

   static void sig_mysignal(const char *arg1)
   {
     /* arg1 contains "hello" */
   }

   signal_add("mysignal", (SIGNAL_FUNC) sig_mysignal);

 There are three different signal_add() functions which you can use to
 specify if you want to grab the signal first, "normally" or last. You can
 also stop the signal from going any further.

 Emitting signal with it's name creates a small overhead since it has to
 look up the signal's numeric ID first, after which it looks up the signal
 structure. This is done because if you call a signal _really_ often,
 it's faster to find it with it's numeric ID instead of the string. You
 can use signal_get_uniq_id() macro to convert the signal name into ID -
 you'll have to do this only once! - and use signal_emit_id() to emit the
 signal. Don't bother to do this unless your signal is sent (or could be
 sent) several times in a second.

 See src/core/signals.h for definition of the signal function, and
 signals.txt for a list of signals.


 ** lib-config

   Irssi depends on this for reading and saving configuration.
   (created by me for irssi)


 ** CORE module

 Provides some functionality that all other modules can use:
   - signal handling
   - keeping list of settings
   - keeping list of /commands
   - keeping track of loaded modules
   - networking functions (with nonblocking connects, IPv6 support)
   - handles connecting to servers
   - raw logging of server's input/output data
   - /EVAL support
   - fgets() like function line_split() without any maximum line limits
   - command line parameter handling
   - miscellaneous useful little functions
   - handles logging


 ** COMMON UI module

   - knows basics about windows and window items (=channels, queries, ..)
   - printtext() - parsing texts and feeding it for GUI to print.
   - themes
   - translation tables
   - text hilighting
   - command history
   - user interface (/commands) for CORE's functionality


 ** GUI modules

   - all the rest of the functionality needed for a working client.


 ** IRC module

   * CORE

     - IRC specific /commands
     - flood protecting commands sent to server
     - creating IRC masks based on nick/address for bans, ignores, etc.
     - keeps list of channels, nicks, channel modes, bans, etc.
     - keeps list of servers, server settings, irc networks,
       server reconnections and irc network splits
     - redirection of commands' replies
     - lag detection
     - ctcp support and flood protection
     - Handles ignoring people

   * DCC

     - DCC chat, send and get

   * FLOOD

     - detects private or channel flooding and sends "flood" signal
     - automatic ignoring when flooding

   * NOTIFYLIST

     - handles notifylist


 ** IRC UI module

   - placing channels and queries in windows
   - nick completion
   - printing infomation of some events