;;; TCP Chat Server — multi-terminal chat using gen_tcp
;;;
;;; Start the server:
;;;   mix clje.run --no-halt examples/tcp_chat_server.clje
;;;
;;; Then connect clients in separate terminals:
;;;   mix clje.run --no-halt examples/tcp_chat_client.clje -- alice
;;;   mix clje.run --no-halt examples/tcp_chat_client.clje -- bob
;;;
;;; Protocol (line-based):
;;;   Client → Server:  JOIN:<username> | MSG:<text> | QUIT
;;;   Server → Client:  SYS:<text> | MSG:<user>:<text> | JOIN:<user> | QUIT:<user>

(ns TcpChatServer
  (:require [clje.core :refer :all]
            [Map] [String] [gen_tcp] [inet]))

;; ── Room manager ──────────────────────────────────────────────────
;; Holds {username → socket} map, broadcasts messages to all members.

(defn room-loop [members]
  (receive
    [:join username socket handler-pid]
      (do
        (TcpChatServer/broadcast members (str "JOIN:" username "\n"))
        (TcpChatServer/send-line socket (str "SYS:Welcome " username "! " (count members) " user(s) online.\n"))
        (TcpChatServer/room-loop (assoc members username #el[socket handler-pid])))

    [:msg username text]
      (do
        (TcpChatServer/broadcast members (str "MSG:" username ":" text "\n"))
        (TcpChatServer/room-loop members))

    [:quit username]
      (let [new-members (dissoc members username)]
        (TcpChatServer/broadcast new-members (str "QUIT:" username "\n"))
        (TcpChatServer/room-loop new-members))

    [:list reply-pid]
      (do
        (send reply-pid #el[:members (Map/keys members)])
        (TcpChatServer/room-loop members))))

(defn broadcast [members line]
  (doseq [[_name [socket _pid]] members]
    (gen_tcp/send socket line)))

(defn send-line [socket line]
  (gen_tcp/send socket line))

;; ── Per-client handler ────────────────────────────────────────────
;; Receives TCP data via active mode and forwards to room manager.

(defn client-handler [socket room username]
  (receive
    [:tcp _sock data]
      (let [line (String/trim data)]
        (cond
          (String/starts-with? line "MSG:")
            (do
              (send room #el[:msg username (String/slice line 4 (String/length line))])
              (TcpChatServer/client-handler socket room username))

          (== line "QUIT")
            (do
              (send room #el[:quit username])
              (gen_tcp/close socket)
              (println (str "  [" username " quit]")))

          :else
            (do
              (TcpChatServer/send-line socket (str "SYS:Unknown command. Send MSG:<text> or QUIT\n"))
              (TcpChatServer/client-handler socket room username))))

    [:tcp_closed _sock]
      (do
        (send room #el[:quit username])
        (println (str "  [" username " disconnected]")))

    [:tcp_error _sock _reason]
      (do
        (send room #el[:quit username])
        (println (str "  [" username " error]")))))

;; ── Accept loop ───────────────────────────────────────────────────

(defn accept-loop [listen-socket room]
  (case (gen_tcp/accept listen-socket)
    [:ok client-socket]
      (do
        (TcpChatServer/handle-new-client client-socket room)
        (TcpChatServer/accept-loop listen-socket room))
    [:error reason]
      (println (str "Accept error: " reason))))

(defn handle-new-client [socket room]
  ;; First message must be JOIN:<username>
  ;; Socket starts in passive mode so we can recv synchronously
  (case (gen_tcp/recv socket 0 5000)
    [:ok data]
      (let [line (String/trim data)]
        (if (String/starts-with? line "JOIN:")
          (let [username (String/slice line 5 (String/length line))
                ;; Switch to active mode for the handler
                _ (inet/setopts socket (list #el[:active true]))
                handler (spawn (fn []
                          (TcpChatServer/client-handler socket room username)))]
            (gen_tcp/controlling-process socket handler)
            (send room #el[:join username socket handler])
            (println (str "  [" username " connected]")))
          (do
            (TcpChatServer/send-line socket "SYS:First message must be JOIN:<username>\n")
            (gen_tcp/close socket))))
    [:error _reason]
      (gen_tcp/close socket)))

;; ── Start ─────────────────────────────────────────────────────────

(defn start [port]
  (case (gen_tcp/listen port (list :binary #el[:active false] #el[:packet :line] #el[:reuseaddr true]))
    [:ok listen-socket]
      (do
        (println (str "TCP Chat Server listening on port " port))
        (println "Connect with: mix clje.run --no-halt examples/tcp_chat_client.clje -- <username>")
        (let [room (spawn (fn [] (TcpChatServer/room-loop {})))]
          (TcpChatServer/accept-loop listen-socket room)))
    [:error reason]
      (println (str "Failed to listen on port " port ": " reason))))

;; Start the server on port 4040
(TcpChatServer/start 4040)