(*
 * Copyright (c) 2016 - present Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *)

open! Utils

(** Prints information about a unix error *)
let print_unix_error cmd e =
  match e with
  | Unix.Unix_error(err, _, _) ->
      Logging.err "Cannot execute %s : %s\n%!"
        cmd (Unix.error_message err)
  | _ -> ()

(** Prints an error message to a log file, prints a message saying that the error can be
    found in that file, and exits, with default code 1 or a given code. *)
let print_error_and_exit ?(exit_code=1) f el =
  Logging.do_err f el;
  let log_file = snd (Logging.log_file_names ()) in
  Logging.stderr "@\nAn error occured. Please find details in %s@\n@\n%!" log_file;
  exit exit_code

(** Executes a command and catches a potential exception and prints it. *)
let exec_command cmd args env =
  try Unix.execve cmd args env
  with (Unix.Unix_error _ as e) ->
    print_unix_error cmd e

(** Given a command to be executed, create a process to execute this command, and wait for it to
    terminate. The standard out and error are not redirected.  If the command fails to execute,
    print an error message and exit. *)
let create_process_and_wait cmd =
  let pid = Unix.create_process cmd.(0) cmd Unix.stdin Unix.stdout Unix.stderr in
  let _, status = Unix.waitpid [] pid in
  let exit_code = match status with
    | Unix.WEXITED i -> i
    | _ -> 1 in
  if exit_code <> 0 then
    print_error_and_exit ~exit_code:exit_code
      "Failed to execute: %s\n" (String.concat " " (Array.to_list cmd))

(** Given a process id and a function that describes the command that the process id
    represents, prints a message explaining the command and its status, if in debug or stats mode.
    It also prints a dot to show progress of jobs being finished.  *)
let print_status f pid (status : Unix. process_status) =
  if Config.debug_mode || Config.stats_mode then
    (let program = f pid in
     match status with
     | WEXITED status ->
         if status = 0 then
           Logging.out "%s OK \n%!" program
         else
           Logging.err "%s exited with code %d\n%!" program status
     | WSIGNALED signal ->
         Logging.err "%s killed by signal %d\n%!" program signal
     | WSTOPPED _ ->
         Logging.err "%s stopped \n%!" program);
  Logging.stdout ".%!"

let start_current_jobs_count () = ref 0

let waited_for_jobs = ref 0

(** [wait_for_son pid_child f jobs_count] wait for pid_child
    and all the other children and update the current jobs count.
    Use f to print the job status *)
let rec wait_for_child f current_jobs_count jobs_map =
  let pid, status = Unix.wait () in
  Pervasives.decr current_jobs_count;
  Pervasives.incr waited_for_jobs;
  print_status f pid status;
  jobs_map := IntMap.remove pid !jobs_map;
  if not (IntMap.is_empty !jobs_map) then
    wait_for_child f current_jobs_count jobs_map

let pid_to_program jobsMap pid =
  try
    IntMap.find pid jobsMap
  with Not_found -> ""

(** [run_jobs_in_parallel jobs_stack gen_cmd cmd_to_string] runs the jobs in the given stack, by
    spawning the jobs in batches of n, where n is [Config.jobs]. It then waits for all those jobs
    and starts a new batch and so on. [gen_cmd] should return a tuple [(dir_opt, command, args,
    env)] where [dir_opt] is an optional directory to chdir to before executing the process, and
    [command], [args], [env] are the same as for [exec_command]. [cmd_to_string] is used for
    printing information about the job's status. *)
let run_jobs_in_parallel jobs_stack gen_cmd cmd_to_string =
  let run_job () =
    let jobs_map = ref IntMap.empty in
    let current_jobs_count = start_current_jobs_count () in
    while not (Stack.is_empty jobs_stack) do
      let job_cmd = Stack.pop jobs_stack in
      let (dir_opt, cmd, args, env) = gen_cmd job_cmd in
      Pervasives.incr current_jobs_count;
      match Unix.fork () with
      | 0 ->
          (match dir_opt with
           | Some dir -> Unix.chdir dir
           | None -> ());
          exec_command cmd args env
      | pid_child ->
          jobs_map := IntMap.add pid_child (cmd_to_string job_cmd) !jobs_map;
          if Stack.length jobs_stack = 0 || !current_jobs_count >= Config.jobs then
            wait_for_child (pid_to_program !jobs_map) current_jobs_count jobs_map
    done in
  run_job ();
  Logging.stdout ".\n%!";
  Logging.out "Waited for %d jobs" !waited_for_jobs

let pipeline ~producer_prog ~producer_args ~consumer_prog ~consumer_args =
  let open Core.Std in
  let pipe_in, pipe_out = Unix.pipe () in
  match Unix.fork () with
  | `In_the_child ->
      (* redirect producer's stdout to pipe_out *)
      Unix.dup2 ~src:pipe_out ~dst:Unix.stdout ;
      (* close producer's copy of pipe ends *)
      Unix.close pipe_out ;
      Unix.close pipe_in ;
      (* exec producer *)
      never_returns (Unix.exec ~prog:producer_prog ~args:producer_args ())
  | `In_the_parent producer_pid ->
      match Unix.fork () with
      | `In_the_child ->
          (* redirect consumer's stdin to pipe_in *)
          Unix.dup2 ~src:pipe_in ~dst:Unix.stdin ;
          (* close consumer's copy of pipe ends *)
          Unix.close pipe_out ;
          Unix.close pipe_in ;
          (* exec consumer *)
          never_returns (Unix.exec ~prog:consumer_prog ~args:consumer_args ())
      | `In_the_parent consumer_pid ->
          (* close parent's copy of pipe ends *)
          Unix.close pipe_out ;
          Unix.close pipe_in ;
          (* wait for children *)
          let producer_status = Unix.waitpid producer_pid in
          let consumer_status = Unix.waitpid consumer_pid in
          (producer_status, consumer_status)