nickserv: split into one file per command

Mirrors the chanserv layout: nickserv.rs keeps the service and dispatch,
each command (register, identify, logout, cert) lives in its own file
with its subcommands and parameters. Behaviour is unchanged.

modules/nickserv/identify.rs

@@ -0,0 +1,33 @@
+use crate::engine::db::Db;
+use crate::engine::service::{Sender, ServiceCtx};
+
+// IDENTIFY [account] <password>: log in. The account defaults to the current
+// nick, so both the bare-password and account+password forms work.
+pub fn handle(me: &str, from: &Sender, args: &[&str], ctx: &mut ServiceCtx, db: &Db) {
+    let (account_name, password) = match (args.get(1), args.get(2)) {
+        (Some(account), Some(password)) => (*account, *password),
+        (Some(password), None) => (from.nick, *password),
+        _ => {
+            ctx.notice(me, from.uid, "Syntax: IDENTIFY [account] <password>");
+            return;
+        }
+    };
+    // Distinguish an unregistered account from a wrong password.
+    if !db.exists(account_name) {
+        ctx.notice(me, from.uid, format!("\x02{account_name}\x02 isn't registered."));
+        return;
+    }
+    match db.authenticate(account_name, password) {
+        Some(account) => {
+            // Already identified to this account: don't re-fire the login.
+            if from.account == Some(account) {
+                ctx.notice(me, from.uid, format!("You're already identified as \x02{}\x02.", account));
+                return;
+            }
+            let account = account.to_string();
+            ctx.login(from.uid, &account);
+            ctx.notice(me, from.uid, format!("You're now identified as \x02{}\x02. Welcome back!", account));
+        }
+        None => ctx.notice(me, from.uid, "Invalid password. Please try again."),
+    }
+}