BotServ: TRIGGER — regex auto-responses

TRIGGER <#channel> ADD <regex>|<response> | DEL <num> | LIST | CLEAR: when
a channel line matches <regex>, the assigned bot says <response> ($nick
becomes the speaker's nick). Only the first matching trigger fires, and a
line the bot just kicked for gets no response.

Same engine machinery as badwords: patterns compile into one RegexSet per
channel (linear-time, ReDoS-safe), cached and rebuilt only on a revision
change. Patterns validated + size-limited at add time.

botserv/src/trigger.rs

@@ -0,0 +1,66 @@
+use fedserv_api::{ChanError, Sender, ServiceCtx, Store};
+
+// TRIGGER <#channel> ADD <regex>|<response> | DEL <num> | LIST | CLEAR: manage
+// the channel's auto-responses. When a line matches <regex>, the assigned bot
+// says <response> ($nick becomes the speaker's nick). Founder-or-admin.
+pub fn handle(me: &str, from: &Sender, args: &[&str], ctx: &mut ServiceCtx, db: &mut dyn Store) {
+    let Some(&chan) = args.get(1) else {
+        ctx.notice(me, from.uid, "Syntax: TRIGGER <#channel> ADD <regex>|<response> | DEL <num> | LIST | CLEAR");
+        return;
+    };
+    if !super::require_channel_admin(me, from, chan, ctx, db) {
+        return;
+    }
+    match args.get(2).map(|s| s.to_ascii_uppercase()).as_deref() {
+        Some("ADD") => {
+            // Everything after ADD is "<regex>|<response>".
+            let rest = args[3..].join(" ");
+            let Some((pattern, response)) = rest.split_once('|') else {
+                ctx.notice(me, from.uid, "Syntax: TRIGGER <#channel> ADD <regex>|<response> (e.g. (?i)hello|Hi $nick!)");
+                return;
+            };
+            let (pattern, response) = (pattern.trim(), response.trim());
+            if pattern.is_empty() || response.is_empty() {
+                ctx.notice(me, from.uid, "Both a pattern and a response are required: ADD <regex>|<response>.");
+                return;
+            }
+            match db.trigger_add(chan, pattern, response) {
+                Ok(true) => ctx.notice(me, from.uid, format!("Added a trigger to \x02{chan}\x02.")),
+                Ok(false) => ctx.notice(me, from.uid, "That pattern already has a trigger."),
+                Err(ChanError::InvalidPattern) => ctx.notice(me, from.uid, format!("\x02{pattern}\x02 isn't a valid regular expression.")),
+                Err(_) => reg_error(me, from, chan, ctx),
+            }
+        }
+        Some("DEL") => {
+            let Some(n) = args.get(3).and_then(|s| s.parse::<usize>().ok()) else {
+                ctx.notice(me, from.uid, "Syntax: TRIGGER <#channel> DEL <num> (see LIST)");
+                return;
+            };
+            match db.trigger_del(chan, n) {
+                Ok(true) => ctx.notice(me, from.uid, format!("Trigger #\x02{n}\x02 removed from \x02{chan}\x02.")),
+                Ok(false) => ctx.notice(me, from.uid, format!("\x02{chan}\x02 has no trigger #\x02{n}\x02.")),
+                Err(_) => reg_error(me, from, chan, ctx),
+            }
+        }
+        Some("CLEAR") => match db.trigger_clear(chan) {
+            Ok(n) => ctx.notice(me, from.uid, format!("Cleared \x02{n}\x02 trigger(s) from \x02{chan}\x02.")),
+            Err(_) => reg_error(me, from, chan, ctx),
+        },
+        None | Some("LIST") => {
+            let triggers = db.triggers(chan);
+            if triggers.is_empty() {
+                ctx.notice(me, from.uid, format!("\x02{chan}\x02 has no triggers."));
+                return;
+            }
+            ctx.notice(me, from.uid, format!("Triggers for \x02{chan}\x02 ({}):", triggers.len()));
+            for (i, t) in triggers.iter().enumerate() {
+                ctx.notice(me, from.uid, format!("  {}. {} \x02→\x02 {}", i + 1, t.pattern, t.response));
+            }
+        }
+        Some(other) => ctx.notice(me, from.uid, format!("Unknown TRIGGER command \x02{other}\x02. Use ADD, DEL, LIST or CLEAR.")),
+    }
+}
+
+fn reg_error(me: &str, from: &Sender, chan: &str, ctx: &mut ServiceCtx) {
+    ctx.notice(me, from.uid, format!("Couldn't update \x02{chan}\x02 — please try again in a moment."));
+}