open Lwt
open Unix

let host = Unix.inet_addr_loopback 
let port = 7524

let create_socket (): Lwt_unix.file_descr t =
  let sock = Lwt_unix.socket PF_INET SOCK_STREAM 0 in
  Lwt_unix.set_close_on_exec sock;
  Lwt_unix.setsockopt sock Unix.SO_REUSEADDR true;
  let () = Lwt_unix.set_blocking sock false in
  Lwt_io.write_line Lwt_io.stdout "🔍 Relational Engine Server Started" >>= fun () ->
  Lwt_unix.bind sock @@ ADDR_INET(host, port) >>= (fun () -> Lwt_unix.listen sock 10; return sock)

let client_read sock maxlen =
  let str = Bytes.create maxlen in
  let rec _read sock acc =
    Lwt_unix.read sock str 0 maxlen
    >>= fun recvlen -> Lwt_io.write_line Lwt_io.stdout (Printf.sprintf "[LOG] Received %d bytes from client" recvlen)
    >>= fun () -> if recvlen <= maxlen
                  then Lwt.return (acc ^ (Bytes.to_string (Bytes.sub str 0 recvlen)))
                  else _read sock (acc ^ (Bytes.to_string (Bytes.sub str 0 recvlen)))
  in _read sock ""

let rec socket_read sock =
  Lwt_unix.accept sock
  >>= fun (client, _) -> client_read client 512
  >>= fun results -> Lwt_io.write_line Lwt_io.stdout results
  >>= fun () -> return results
  >>= fun results -> Lwt_unix.send client (Bytes.of_string results) 0 (String.length results) []
  >>= fun _ -> Lwt_unix.wait_write client
  >>= fun () -> Lwt_unix.close client
  >>= fun () -> socket_read sock

let start() =
  Stdlib.exit
  @@ Lwt_main.run begin
         Lwt_exit.wrap_and_exit (create_socket ()) >>= fun sock ->
         let clean_callback = Lwt_exit.register_clean_up_callback ~loc:__LOC__ (fun _ -> Lwt_io.write_line Lwt_io.stdout "💥 Shutting down" >>= fun () -> Lwt_unix.close sock) in
         Lwt_exit.wrap_and_exit (socket_read sock) >>= fun () ->
         let () = Lwt_exit.unregister_clean_up_callback clean_callback in
         Lwt_exit.exit_and_wait 0
  end