# -*- ruby -*-
#
# This library is used to create a child process and pipes
# send and receive data. We can send ruby codes and receive
# results using an instance of PRuby.
#
# ex)
# PRuby.new{|r|
#   r.send("somecode")    # "somecode" is executed in the child process.
#   timeout(5){ r.recv }
# }
#
# r = PRuby.new
# r.send("somecode")
# result = r.recv
# 

class PRuby
  CRLF = "\r\n"

  def initialize
    if( block_given? )
      begin
	init_io
	yield(self)
      ensure
	terminate
      end
    else
      init_io
    end
  end

  def init_io
    @p2c_in,@p2c_out = IO.pipe()
    @c2p_in,@c2p_out = IO.pipe()
    @pid = fork{
      @p2c_out.close
      @c2p_in.close
      child_loop()
      }
    @p2c_in.close
    @c2p_out.close
    at_exit{
      if( !@p2c_out.closed? )
	@p2c_out.print("killed", CRLF)
	@p2c_out.flush
      end
    }
  end

  def kill(sig)
    Process.kill(sig, @pid)
  end

  def wait
    Process.waitpid(@pid)
  end

  def closed?
    return @c2p_in.closed?
  end

  def close
    @c2p_in.close
    @p2c_out.close
  end

  def terminate
    close
    kill("SIGTERM")
    wait
  end

  def recv()
    if( num = @c2p_in.gets )
      case num
      when /\d+/
	num = num.chop.to_i
      else
	@p2c_out.close
	@c2p_in.close
	num = nil
      end
      if( num )
	mval = @c2p_in.read(num)
	val = Marshal.load(mval)
      else
	val = nil
      end
    else
      val = nil
    end
    return val
  end

  def send(line)
    @p2c_out.print(line.size, CRLF)
    @p2c_out.print(line)
    @p2c_out.flush
  end

  def eval(line)
    send(line)
    return recv()
  end

  def child_loop
    at_exit{
      if( !@c2p_out.closed? )
	@c2p_out.print("killed", CRLF)
	@c2p_out.flush
      end
    }
    while( !@p2c_in.closed? && (num = @p2c_in.gets) )
      case num
      when /\d+/
	num = num.chop.to_i
      else
	num = nil
      end
      if( num )
	script = @p2c_in.read(num)
	val = Kernel.module_eval(script)
	mval = Marshal.dump(val)
	@c2p_out.print(mval.size, CRLF)
	@c2p_out.print(mval)
	@c2p_out.flush
      else
	@c2p_out.close
	@p2c_in.close
      end
    end
  end
end