open Unix
open List
open Str

(* Fork new processes. *)
let shell_exec strs =
  match strs with
    | [] -> print_endline "Error: Bad Input"
    | cmd :: _ ->
	let cmd_args = Array.of_list strs in
	let pid = fork () in
	  match pid with
	    | 0 -> 
		begin
		  try
		    execvp cmd cmd_args
		  with
		    | Unix_error (ENOENT, cmd, cmd_args) -> 
			print_endline "No such program."
		    | Unix_error (ENOEXEC,_,_) ->
			print_endline "Not an exec."
		    | Unix_error (_,_,_) ->
			print_endline "Something is wrong!"
		end; exit 0
	    | _ -> ignore (wait ())

let shell_cd strs =
  if (strs = []) then
    print_string ""
  else
    try
      chdir (hd strs)
    with
	_ -> print_endline "Error changing directory."

(* Dispatch loop *)
let input_dispatch pstr =
  if (pstr <> []) then
    begin
      let cmd = hd pstr in
      let cmd_args = tl pstr in
	match cmd with
	  | "cd"      -> shell_cd cmd_args
	  | "pid"     -> print_endline (string_of_int (getpid ()))
	  | "gc-stat" -> Gc.print_stat Pervasives.stdout
	  | "exit"    -> exit 0
	  | _         -> shell_exec pstr
    end
  else
    print_string ""

(* Parse the users input string, return a list of strings. *)
let parse_string str =
  let pstr = split (regexp " +") str in pstr
	    
let rec shell_loop () =
  begin
    print_string (getcwd ());
    print_string " % ";
    input_dispatch (parse_string (read_line ()));
    shell_loop ()
  end

let main () =
  if Array.length Sys.argv < 2 then
    begin
      print_string "OShell v1.0a on OCaml ";
      print_endline Sys.ocaml_version;
      shell_loop ()
    end
  else
    let lstr = Array.to_list Sys.argv in
    (* Get rid of Sys.argv(0), the program name. *)
    let pstr = tl lstr in
      input_dispatch pstr
      

let _ = main ()