class ActionCable::Connection::StreamEventLoop

def attach(io, stream)
  @todo << lambda do
    @map[io] = @nio.register(io, :r)
    @map[io].value = stream
  end
  wakeup
end

def detach(io, stream)
  @todo << lambda do
    @nio.deregister io
    @map.delete io
    io.close
  end
  wakeup
end

def initialize
  @nio = @executor = @thread = nil
  @map = {}
  @stopping = false
  @todo = Queue.new
  @spawn_mutex = Mutex.new
end

def post(task = nil, &block)
  task ||= block
  spawn
  @executor << task
end

def run
  loop do
    if @stopping
      @nio.close
      break
    end
    until @todo.empty?
      @todo.pop(true).call
    end
    next unless monitors = @nio.select
    monitors.each do |monitor|
      io = monitor.io
      stream = monitor.value
      begin
        if monitor.writable?
          if stream.flush_write_buffer
            monitor.interests = :r
          end
          next unless monitor.readable?
        end
        incoming = io.read_nonblock(4096, exception: false)
        case incoming
        when :wait_readable
          next
        when nil
          stream.close
        else
          stream.receive incoming
        end
      rescue
        # We expect one of EOFError or Errno::ECONNRESET in
        # normal operation (when the client goes away). But if
        # anything else goes wrong, this is still the best way
        # to handle it.
        begin
          stream.close
        rescue
          @nio.deregister io
          @map.delete io
        end
      end
    end
  end
end

def spawn
  return if @thread && @thread.status
  @spawn_mutex.synchronize do
    return if @thread && @thread.status
    @nio ||= NIO::Selector.new
    @executor ||= Concurrent::ThreadPoolExecutor.new(
      min_threads: 1,
      max_threads: 10,
      max_queue: 0,
    )
    @thread = Thread.new { run }
    return true
  end
end

def stop
  @stopping = true
  wakeup if @nio
end

def timer(interval, &block)
  Concurrent::TimerTask.new(execution_interval: interval, &block).tap(&:execute)
end

def wakeup
  spawn || @nio.wakeup
end

def writes_pending(io)
  @todo << lambda do
    if monitor = @map[io]
      monitor.interests = :rw
    end
  end
  wakeup
end