add structured IRC event hooks

docs/plugin-api-additions/events.md

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+# Semantic IRC hooks
+
+`on_join`, `on_part`, `on_quit`, `on_nick`, `on_kick`, `on_message`, and
+`on_notice` accept `(callback, userdata=None, priority=PRI_NORM)`. The general
+form is `hook_event(command, callback, userdata=None, priority=PRI_NORM)`.
+Callbacks receive `(event, userdata)`, where the immutable IRCEvent has
+command, prefix, nick, user, host, params, context, connection_id and time.
+`params` preserves the trailing parameter, including spaces; JOIN parameters
+also retain extended-join account/realname data when supplied by the server.
+
+These wrappers use existing server hooks, before core command processing;
+return the ordinary EAT_* constants. EAT_ZOITECHAT suppresses the entire IRC
+command (including client state updates), not just its text. Use EAT_NONE for
+observation. Other plugins' priority and eating rules remain unchanged.
+The context is the core-selected context, which can be the server tab when a
+query/channel does not yet exist. QUIT is one event per incoming command,
+not one callback per affected channel. `event.time` is the existing server-time
+attribute (zero when unavailable); other message tags are not exposed here.
+
+```python
+def joined(event, userdata):
+    event.context.prnt('{} joined {}'.format(event.nick, event.params[0]))
+    return zoitechat.EAT_NONE
+
+zoitechat.on_join(joined)
+```

plugins/python/_zoitechat_events.py

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+"""Structured, opt-in hooks before the IRC command's core processing."""
+from collections import namedtuple
+import _zoitechat as api
+
+__all__ = ['IRCEvent', 'hook_event', 'on_join', 'on_part', 'on_quit',
+           'on_nick', 'on_kick', 'on_message', 'on_notice']
+IRCEvent = namedtuple('IRCEvent', 'command prefix nick user host params context connection_id time')
+_SUPPORTED = frozenset(('JOIN', 'PART', 'QUIT', 'NICK', 'KICK', 'PRIVMSG', 'NOTICE'))
+
+
+def _parse(line):
+    prefix = ''
+    if line.startswith(':'):
+        prefix, separator, line = line[1:].partition(' ')
+        if not separator:
+            return None
+    command, separator, rest = line.partition(' ')
+    params = []
+    while rest:
+        rest = rest.lstrip(' ')
+        if rest.startswith(':'):
+            params.append(rest[1:])
+            break
+        param, separator, rest = rest.partition(' ')
+        if param:
+            params.append(param)
+    nick, marker, userhost = prefix.partition('!')
+    user, marker, host = userhost.partition('@')
+    return command.upper(), prefix, nick, user, host, tuple(params)
+
+
+def hook_event(command, callback, userdata=None, priority=api.PRI_NORM):
+    """callback(event, userdata) returns existing EAT_* constants."""
+    command = command.upper()
+    if command not in _SUPPORTED:
+        raise ValueError('unsupported semantic event: ' + command)
+    if not callable(callback):
+        raise TypeError('callback must be callable')
+
+    def dispatch(word, word_eol, data, attrs):
+        if not word_eol:
+            return api.EAT_NONE
+        parsed = _parse(word_eol[0])
+        if parsed is None or parsed[0] != command:
+            return api.EAT_NONE
+        event = IRCEvent(*(parsed + (api.get_context(), api.get_prefs('id'), attrs.time)))
+        return callback(event, data)
+
+    return api.hook_server_attrs(command, dispatch, userdata, priority)
+
+
+def on_join(callback, userdata=None, priority=api.PRI_NORM):
+    return hook_event('JOIN', callback, userdata, priority)
+
+
+def on_part(callback, userdata=None, priority=api.PRI_NORM):
+    return hook_event('PART', callback, userdata, priority)
+
+
+def on_quit(callback, userdata=None, priority=api.PRI_NORM):
+    return hook_event('QUIT', callback, userdata, priority)
+
+
+def on_nick(callback, userdata=None, priority=api.PRI_NORM):
+    return hook_event('NICK', callback, userdata, priority)
+
+
+def on_kick(callback, userdata=None, priority=api.PRI_NORM):
+    return hook_event('KICK', callback, userdata, priority)
+
+
+def on_message(callback, userdata=None, priority=api.PRI_NORM):
+    return hook_event('PRIVMSG', callback, userdata, priority)
+
+
+def on_notice(callback, userdata=None, priority=api.PRI_NORM):
+    return hook_event('NOTICE', callback, userdata, priority)