MemoServ: add CANCEL, CHECK, and INFO

CANCEL recalls the sender's most recent unread memo to a target (one the
recipient already read can't be recalled); CHECK reports whether the last
memo you sent someone has been read; INFO summarises your mailbox. Adds
memo_cancel/memo_check store methods and shares MAX_MEMOS from the module
root instead of duplicating it in send.rs.

modules/memoserv/src/cancel.rs

@@ -0,0 +1,19 @@
+use echo_api::{Sender, ServiceCtx, Store};
+
+// CANCEL <nick>: recall the last unread memo you sent to <nick>. A memo the
+// recipient has already read can't be recalled.
+pub fn handle(me: &str, from: &Sender, account: &str, args: &[&str], ctx: &mut ServiceCtx, db: &mut dyn Store) {
+    let Some(&target) = args.get(1) else {
+        ctx.notice(me, from.uid, "Syntax: CANCEL <nick>");
+        return;
+    };
+    let Some(dest) = db.resolve_account(target).map(str::to_string) else {
+        ctx.notice(me, from.uid, format!("\x02{target}\x02 isn't registered."));
+        return;
+    };
+    if db.memo_cancel(&dest, account) {
+        ctx.notice(me, from.uid, format!("Your last unread memo to \x02{target}\x02 has been cancelled."));
+    } else {
+        ctx.notice(me, from.uid, format!("You have no unread memo to \x02{target}\x02 to cancel."));
+    }
+}

modules/memoserv/src/check.rs

@@ -0,0 +1,18 @@
+use echo_api::{human_time, Sender, ServiceCtx, Store};
+
+// CHECK <nick>: has the last memo you sent to <nick> been read yet?
+pub fn handle(me: &str, from: &Sender, account: &str, args: &[&str], ctx: &mut ServiceCtx, db: &mut dyn Store) {
+    let Some(&target) = args.get(1) else {
+        ctx.notice(me, from.uid, "Syntax: CHECK <nick>");
+        return;
+    };
+    let Some(dest) = db.resolve_account(target).map(str::to_string) else {
+        ctx.notice(me, from.uid, format!("\x02{target}\x02 isn't registered."));
+        return;
+    };
+    match db.memo_check(&dest, account) {
+        Some((true, ts)) => ctx.notice(me, from.uid, format!("Your last memo to \x02{target}\x02 (sent {}) has been \x02read\x02.", human_time(ts))),
+        Some((false, ts)) => ctx.notice(me, from.uid, format!("Your last memo to \x02{target}\x02 (sent {}) has \x02not\x02 been read yet.", human_time(ts))),
+        None => ctx.notice(me, from.uid, format!("You have no memo on record to \x02{target}\x02.")),
+    }
+}

modules/memoserv/src/info.rs

@@ -0,0 +1,12 @@
+use echo_api::{Sender, ServiceCtx, Store};
+
+// INFO: a summary of your mailbox (total, unread, capacity).
+pub fn handle(me: &str, from: &Sender, account: &str, ctx: &mut ServiceCtx, db: &mut dyn Store) {
+    let total = db.memo_list(account).len();
+    let unread = db.unread_memos(account);
+    ctx.notice(
+        me,
+        from.uid,
+        format!("You have \x02{total}\x02 memo(s), \x02{unread}\x02 unread, of a maximum \x02{}\x02.", super::MAX_MEMOS),
+    );
+}

modules/memoserv/src/lib.rs

@@ -14,14 +14,26 @@ mod list;
 mod read;
 #[path = "del.rs"]
 mod del;
+#[path = "cancel.rs"]
+mod cancel;
+#[path = "check.rs"]
+mod check;
+#[path = "info.rs"]
+mod info;
 
 const BLURB: &str = "MemoServ delivers messages to registered users, online or not. You must be identified to use it.";
 
+// A full mailbox rejects new memos, so nobody can be flooded.
+pub(crate) const MAX_MEMOS: usize = 30;
+
 const TOPICS: &[HelpEntry] = &[
     HelpEntry { cmd: "SEND", summary: "leave a memo for an account", detail: "Syntax: \x02SEND <nick> <text>\x02\nLeaves a memo on a registered account's mailbox." },
     HelpEntry { cmd: "LIST", summary: "list your memos", detail: "Syntax: \x02LIST\x02\nLists the memos in your mailbox." },
     HelpEntry { cmd: "READ", summary: "read a memo", detail: "Syntax: \x02READ <num>|NEW|ALL\x02\nReads a memo by number, your unread ones, or all of them." },
     HelpEntry { cmd: "DEL", summary: "delete a memo", detail: "Syntax: \x02DEL <num>|ALL\x02\nDeletes a memo by number, or your whole mailbox." },
+    HelpEntry { cmd: "CANCEL", summary: "recall a memo you sent", detail: "Syntax: \x02CANCEL <nick>\x02\nRecalls the last memo you sent them, as long as they haven't read it yet." },
+    HelpEntry { cmd: "CHECK", summary: "see if a memo was read", detail: "Syntax: \x02CHECK <nick>\x02\nReports whether the last memo you sent them has been read." },
+    HelpEntry { cmd: "INFO", summary: "your mailbox summary", detail: "Syntax: \x02INFO\x02\nShows how many memos you have, how many are unread, and your capacity." },
 ];
 
 pub struct MemoServ {
@@ -60,6 +72,9 @@ impl Service for MemoServ {
             Some("LIST") => list::handle(me, from, account, ctx, db),
             Some("READ") => read::handle(me, from, account, args, ctx, db),
             Some("DEL") | Some("DELETE") => del::handle(me, from, account, args, ctx, db),
+            Some("CANCEL") => cancel::handle(me, from, account, args, ctx, db),
+            Some("CHECK") => check::handle(me, from, account, args, ctx, db),
+            Some("INFO") => info::handle(me, from, account, ctx, db),
             Some(other) => ctx.notice(me, from.uid, format!("I don't know the command \x02{other}\x02. Try \x02HELP\x02.")),
             None => {}
         }

modules/memoserv/src/send.rs

@@ -1,7 +1,6 @@
 use echo_api::{Sender, ServiceCtx, Store};
 
-// A full mailbox rejects new memos, so nobody can be flooded.
-const MAX_MEMOS: usize = 30;
+use super::MAX_MEMOS;
 
 // SEND <nick> <text>: leave a memo on a registered account's mailbox.
 pub fn handle(me: &str, from: &Sender, account: &str, args: &[&str], ctx: &mut ServiceCtx, db: &mut dyn Store) {