# -*- encoding: utf-8 -*-

# A failover client that wraps multiple {OnStomp::Client clients} and maintains
# a connection to one of these clients. Frames are sent to the currently
# connected client. If the connection is lost, a failover client will
# automatically reconnect to another client in the pool, re-transmit any
# necessary frames and resume operation.
class OnStomp::Failover::Client
  include OnStomp::Failover::FailoverConfigurable
  include OnStomp::Failover::FailoverEvents
  include OnStomp::Interfaces::FrameMethods
  
  # The class to use when instantiating a new {#client_pool}.
  # Defaults to {OnStomp::Failover::Pools::RoundRobin}
  # @return [Class]
  attr_configurable_pool :pool
  # The class to use when instantiating a new frame buffer.
  # Defaults to {OnStomp::Failover::Buffers::Written}
  # @return [Class]
  attr_configurable_buffer :buffer
  # The delay in seconds to wait between connection retries.
  # Defaults to `10`
  # @return [Fixnum]
  attr_configurable_int :retry_delay, :default => 10
  # The maximum number of times to retry connecting during a reconnect
  # loop. A non-positive number will force the failover client to try to
  # reconnect indefinitely. Defaults to `0`
  # @return [Fixnum]
  attr_configurable_int :retry_attempts, :default => 0
  # Whether or not to randomize the {#client_pool} before connecting through
  # any of its {OnStomp::Client clients}. Defaults to `false`
  # @return [true,false]
  attr_configurable_bool :randomize, :default => false
  
  attr_reader :uri, :hosts,
    :client_pool, :active_client, :frame_buffer, :connection
  
  def initialize(uris, options={})
    if uris.is_a? Array
      @uri = OnStomp::Failover::URI::FAILOVER.new [], nil
      @hosts = uris
    else
      @uri = OnStomp::Failover::URI::FAILOVER.parse uris
      @hosts = @uri.failover_uris
    end
    @client_mutex = Mutex.new
    configure_configurable options
    create_client_pool hosts
    @active_client = nil
    @connection = nil
    @frame_buffer = buffer.new self
    @disconnecting = false
    retry_ready = false
    @retry_thread = Thread.new do
      until @disconnecting
        retry_ready = true
        Thread.stop
        @client_mutex.synchronize {
          reconnect unless @disconnecting
        }
      end
    end
    Thread.pass until retry_ready && @retry_thread.stop?
  end
  
  # Returns true if there is an {#active_client} and it is
  # {OnStomp::Client#connected? connected}.
  # @return [true,false,nil]
  def connected?
    active_client && active_client.connected?
  end

  # Transmits a frame to the {#active_client} if one exists.
  # @return [OnStomp::Components::Frame,nil]
  def transmit frame, cbs={}
    active_client && active_client.transmit(frame, cbs)
  end
  
  # Connects to one of the clients in the {#client_pool}
  # @return [self]
  def connect
    @disconnecting = false
    unless @client_mutex.synchronize { reconnect }
      raise OnStomp::Failover::MaximumRetriesExceededError
    end
    self
  end
  
  # Ensures that a connection is properly established, then invokes
  # {OnStomp::Client#disconnect disconnect} on the {#active_client}
  def disconnect *args, &block
    if active_client
      Thread.pass until connected? || @failed
      @client_mutex.synchronize do
        @disconnecting = true
        active_client.disconnect *args, &block if connected?
      end
    end
  end
  
  private
  def reconnect
    @failed = false
    attempt = 1
    until connected? || retry_exceeded?(attempt)
      sleep_for_retry attempt
      begin
        trigger_failover_retry :before, attempt
        @active_client = client_pool.next_client
        # `reconnect` could be called again within the marked range.
        active_client.connect # <--- From here
        @connection = active_client.connection
      rescue Exception
        trigger_failover_event :connect_failure, :on, active_client, $!.message
      end
      trigger_failover_retry :after, attempt
      attempt += 1
    end
    @failed = !connected?
    trigger_failover_event(:connected, :on, active_client) unless @failed
    !@failed
  end
  
  def retry_exceeded? attempt
    retry_attempts > 0 && attempt > retry_attempts
  end
  
  def sleep_for_retry attempt
    sleep(retry_delay) if retry_delay > 0 && attempt > 1
  end
    
  def create_client_pool hosts
    @client_pool = pool.new hosts
    on_connection_closed do |client, *_|
      if client == active_client
        unless @disconnecting
          trigger_failover_event(:lost, :on, active_client)
          # Wake up the reconnect thread. This ensures that subsequent
          # connections are all spawned from the same source.
          # Previously, we re-spawned here and that was rather problematic.
          @retry_thread.run
        end
      end
    end
  end
end