module Daemonize

def call_as_daemon(block, logfile_name = nil, app_name = nil)
  # we use a pipe to return the PID of the daemon
  rd, wr = IO.pipe
  if tmppid = safefork
    # in the parent
    wr.close
    pid = rd.read.to_i
    rd.close
    Process.waitpid(tmppid)
    return pid
  else
    # in the child
    rd.close
    # Detach from the controlling terminal
    unless Process.setsid
      fail Daemons.RuntimeException.new('cannot detach from controlling terminal')
    end
    # Prevent the possibility of acquiring a controlling terminal
    trap 'SIGHUP', 'IGNORE'
    exit if pid = safefork
    wr.write Process.pid
    wr.close
    $0 = app_name if app_name
    # Release old working directory
    Dir.chdir '/'
    close_io
    redirect_io(logfile_name)
    # Split rand streams between spawning and daemonized process
    srand
    block.call
    exit
  end
end

def close_io
  # Make sure all input/output streams are closed
  # Part I: close all IO objects (except for $stdin/$stdout/$stderr)
  ObjectSpace.each_object(IO) do |io|
    unless [$stdin, $stdout, $stderr].include?(io)
      io.close rescue nil
    end
  end
  # Make sure all input/output streams are closed
  # Part II: close all file decriptors (except for $stdin/$stdout/$stderr)
  3.upto(8192) do |i|
    IO.for_fd(i).close rescue nil
  end
end

def daemonize(logfile_name = nil, app_name = nil)
  # Fork and exit from the parent
  safefork && exit
  # Detach from the controlling terminal
  unless sess_id = Process.setsid
    fail Daemons.RuntimeException.new('cannot detach from controlling terminal')
  end
  # Prevent the possibility of acquiring a controlling terminal
  trap 'SIGHUP', 'IGNORE'
  exit if safefork
  $0 = app_name if app_name
  # Release old working directory
  Dir.chdir '/'
  close_io
  redirect_io(logfile_name)
  # Split rand streams between spawning and daemonized process
  srand
  sess_id
end

def redirect_io(logfile_name)
  begin; $stdin.reopen '/dev/null'; rescue ::Exception; end
  if logfile_name == 'SYSLOG'
    # attempt to use syslog via syslogio
    begin
      require 'syslogio'
      $stdout = ::Daemons::SyslogIO.new($0, :local0, :info, $stdout)
      $stderr = ::Daemons::SyslogIO.new($0, :local0, :err, $stderr)
      # error out early so we can fallback to null
      $stdout.puts "no logfile provided, output redirected to syslog"
    rescue ::Exception
      # on unsupported platforms simply reopen /dev/null
      begin; $stdout.reopen '/dev/null'; rescue ::Exception; end
      begin; $stderr.reopen '/dev/null'; rescue ::Exception; end
    end
  elsif logfile_name
    $stdout.reopen logfile_name, 'a'
    File.chmod(0644, logfile_name)
    $stdout.sync = true
    begin; $stderr.reopen $stdout; rescue ::Exception; end
    $stderr.sync = true
  else
    begin; $stdout.reopen '/dev/null'; rescue ::Exception; end
    begin; $stderr.reopen '/dev/null'; rescue ::Exception; end
  end
end

def safefork
  tryagain = true
  while tryagain
    tryagain = false
    begin
      if pid = fork
        return pid
      end
    rescue Errno::EWOULDBLOCK
      sleep 5
      tryagain = true
    end
  end
end

def simulate(logfile_name = nil, app_name = nil)
  $0 = app_name if app_name
  # Release old working directory
  Dir.chdir '/'
  close_io
  # Free $stdin and point it to somewhere sensible
  begin; $stdin.reopen '/dev/null'; rescue ::Exception; end
  # Split rand streams between spawning and daemonized process
  srand
end