(* Compilieren mit:
   ocamlc -o serverml unix.cma server.ml
   oder
   ocamlopt-o serverml unix.cmxa echoserver.ml
   Starten mit : 
   ./serverml
*)

open Unix
open Printf
open String
  
let err_unknown_cmd = "ERROR unknown command\n"

exception WriteFailure

let readline sd =
  let c = " " in
  let rec loop res =
    if (read sd c 0 1) = 1 then
      if c = "\n"
      then res^c
      else loop (res^c)
    else raise End_of_file
  in
  loop ""
    
let write_safe sd s =
  let len = String.length s in
  if (write sd s 0 len) < len
  then raise WriteFailure

let split_at_space s =
  if (contains s ' ') then
    let space = index s ' ' in
    (sub s 0 space, sub s space (length s - space))
  else (s,"")

let rec ltrim aStr = match aStr with 
  "" -> ""
| (_) ->
    if (aStr.[0] = ' ') then ltrim (sub aStr 1 (length aStr -1))
    else aStr
	
let calculate args op =
  match (split_at_space (ltrim args)) with
    (s, t) -> string_of_int (op (int_of_string (ltrim s)) (int_of_string (ltrim t)))
	
let chop aStr =
  if  ( (aStr.[length aStr -2] = '\r') &&  (aStr.[length aStr -1] = '\n')) 
  then ( sub aStr 0 (length aStr -2))  
  else if (aStr.[length aStr -1] = '\n') then 
    sub aStr 0 (length aStr -1)
  else aStr       
      
let get_ip sock_addr =
  match sock_addr with ADDR_INET
      (inet_addr, port) -> string_of_inet_addr inet_addr
  | _ -> failwith "get_ip"
	
let main =
  let sd = socket PF_INET SOCK_STREAM 0 in
  bind sd (ADDR_INET(inet_addr_any, 9000));
  listen sd 5;
  let rec server_loop () =
    let (csd, client_addr) = accept sd in
    let rec client_loop () =
      match split_at_space(chop(readline csd)) with
	("INFO", _) -> begin 
	  write_safe csd ("YOURIP "^(get_ip client_addr) ^ "\n");
	  client_loop ()
	end
      | ("QUIT", _) -> begin
	  close csd;
	  server_loop ()
      end
      | ("ADD", args) -> begin
	  write_safe csd ((calculate args ( + )) ^ "\n");
	  client_loop ()
      end
      | ("MUL", args) -> begin
	  write_safe csd ((calculate args ( * )) ^ "\n");
	  client_loop ()
      end
      | _ -> begin
	  write_safe csd err_unknown_cmd;
	  client_loop ()
      end
    in
    client_loop ()
  in
  handle_unix_error
    server_loop ()