module Mixlib::ShellOut::Unix

def child_process_status
  @process_status_pipe[0]
end

def child_stderr
  @stderr_pipe[0]
end

def child_stdout
  @stdout_pipe[0]
end

def close_all_pipes
  child_stdout.close  unless child_stdout.closed?
  child_stderr.close  unless child_stderr.closed?
  child_process_status.close unless child_process_status.closed?
end

def configure_parent_process_file_descriptors
  # Close the sides of the pipes we don't care about
  stdout_pipe.last.close
  stderr_pipe.last.close
  process_status_pipe.last.close
  # Get output as it happens rather than buffered
  child_stdout.sync = true
  child_stderr.sync = true
  true
end

def configure_subprocess_file_descriptors
  process_status_pipe.first.close
  # HACK: for some reason, just STDIN.close isn't good enough when running
  # under ruby 1.9.2, so make it good enough:
  stdin_reader, stdin_writer = IO.pipe
  stdin_writer.close
  STDIN.reopen stdin_reader
  stdin_reader.close
  stdout_pipe.first.close
  STDOUT.reopen stdout_pipe.last
  stdout_pipe.last.close
  stderr_pipe.first.close
  STDERR.reopen stderr_pipe.last
  stderr_pipe.last.close
  STDOUT.sync = STDERR.sync = true
end

def fork_subprocess
  initialize_ipc
  fork do
    configure_subprocess_file_descriptors
    set_group
    set_user
    set_environment
    set_umask
    set_cwd
    begin
      command.kind_of?(Array) ? exec(*command) : exec(command)
      raise 'forty-two' # Should never get here
    rescue Exception => e
      Marshal.dump(e, process_status_pipe.last)
      process_status_pipe.last.flush
    end
    process_status_pipe.last.close unless (process_status_pipe.last.closed?)
    exit!
  end
end

def initialize_ipc
  @stdout_pipe, @stderr_pipe, @process_status_pipe = IO.pipe, IO.pipe, IO.pipe
  @process_status_pipe.last.fcntl(Fcntl::F_SETFD, Fcntl::FD_CLOEXEC)
end

def open_pipes
  @open_pipes ||= [child_stdout, child_stderr]
end

def propagate_pre_exec_failure
  begin
    e = Marshal.load child_process_status
    raise(Exception === e ? e : "unknown failure: #{e.inspect}")
  rescue EOFError # If we get an EOF error, then the exec was successful
    true
  ensure
    child_process_status.close
  end
end

def read_stderr_to_buffer
  while chunk = child_stderr.read_nonblock(READ_SIZE)
    @stderr << chunk
  end
rescue Errno::EAGAIN
rescue EOFError
  open_pipes.delete_at(1)
end

def read_stdout_to_buffer
  while chunk = child_stdout.read_nonblock(READ_SIZE)
    @stdout << chunk
    @live_stream << chunk if @live_stream
  end
rescue Errno::EAGAIN
rescue EOFError
  open_pipes.delete_at(0)
end

def run_command
  @child_pid = fork_subprocess
  configure_parent_process_file_descriptors
  propagate_pre_exec_failure
  @result = nil
  @execution_time = 0
  # Ruby 1.8.7 and 1.8.6 from mid 2009 try to allocate objects during GC
  # when calling IO.select and IO#read. Some OS Vendors are not interested
  # in updating their ruby packages (Apple, *cough*) and we *have to*
  # make it work. So I give you this epic hack:
  GC.disable
  until @status
    ready = IO.select(open_pipes, nil, nil, READ_WAIT_TIME)
    unless ready
      @execution_time += READ_WAIT_TIME
      if @execution_time >= timeout && !@result
        raise CommandTimeout, "command timed out:\n#{format_for_exception}"
      end
    end
    if ready && ready.first.include?(child_stdout)
      read_stdout_to_buffer
    end
    if ready && ready.first.include?(child_stderr)
      read_stderr_to_buffer
    end
    unless @status
      # make one more pass to get the last of the output after the
      # child process dies
      if results = Process.waitpid2(@child_pid, Process::WNOHANG)
        @status = results.last
        redo
      end
    end
  end
  self
rescue Exception
  # do our best to kill zombies
  Process.waitpid2(@child_pid, Process::WNOHANG) rescue nil
  raise
ensure
  # no matter what happens, turn the GC back on, and hope whatever busted
  # version of ruby we're on doesn't allocate some objects during the next
  # GC run.
  GC.enable
  close_all_pipes
end

def set_cwd
  Dir.chdir(cwd) if cwd
end

def set_environment
  environment.each do |env_var,value|
    ENV[env_var] = value
  end
end

def set_group
  if group
    Process.egid = gid
    Process.gid = gid
  end
end

def set_umask
  File.umask(umask) if umask
end

def set_user
  if user
    Process.euid = uid
    Process.uid = uid
  end
end