#!/usr/bin/env rackup -s thin
#
#  async_tailer.ru
#  raggi/thin
#
#  Tested with 150 spawned tails on OS X
#
#  Created by James Tucker on 2008-06-18.
#  Copyright 2008 James Tucker <raggi@rubyforge.org>.

# Uncomment if appropriate for you..
# EM.epoll
# EM.kqueue

tail_log_file = ENV["TAIL_LOG_FILE"] or abort "TAIL_LOG_FILE= env must be set"
unless ::File.file?(tail_log_file) && ::File.readable?(tail_log_file)
  abort "#{tail_log_file} must be a readable regular file"
end

class DeferrableBody
  include EventMachine::Deferrable

  def initialize
    @queue = []
    # make sure to flush out the queue before closing the connection
    callback{
      until @queue.empty?
        @queue.shift.each{|chunk| @body_callback.call(chunk) }
      end
    }
  end

  def schedule_dequeue
    return unless @body_callback
    EventMachine::next_tick do
      next unless body = @queue.shift
      body.each do |chunk|
        @body_callback.call(chunk)
      end
      schedule_dequeue unless @queue.empty?
    end
  end

  def call(body)
    @queue << body
    schedule_dequeue
  end

  def each &blk
    @body_callback = blk
    schedule_dequeue
  end

end

module TailRenderer
  attr_accessor :callback

  def receive_data(data)
    @callback.call([data])
  end

  def unbind
    @callback.succeed
  end
end

class AsyncTailer

  AsyncResponse = [-1, {}, []].freeze

  def call(env)

    body = DeferrableBody.new

    EventMachine::next_tick do

      env['async.callback'].call [200, {'Content-Type' => 'text/html'}, body]

      body.call ["<h1>Async Tailer</h1><pre>"]

    end

    EventMachine::popen("tail -f #{ENV["TAIL_LOG_FILE"]}", TailRenderer) do |t|

      t.callback = body

      # If for some reason we 'complete' body, close the tail.
      body.callback do
        t.close_connection
      end

      # If for some reason the client disconnects, close the tail.
      body.errback do
        t.close_connection
      end

    end

    AsyncResponse
  end

end

run AsyncTailer.new