require "active_support/callbacks"
require "active_support/core_ext/module/attribute_accessors_per_thread"
require "concurrent"

module ActionCable
  module Server
    # Worker used by Server.send_async to do connection work in threads.
    class Worker # :nodoc:
      include ActiveSupport::Callbacks

      thread_mattr_accessor :connection
      define_callbacks :work
      include ActiveRecordConnectionManagement

      attr_reader :executor

      def initialize(max_size: 5)
        @executor = Concurrent::ThreadPoolExecutor.new(
          min_threads: 1,
          max_threads: max_size,
          max_queue: 0,
        )
      end

      # Stop processing work: any work that has not already started
      # running will be discarded from the queue
      def halt
        @executor.kill
      end

      def stopping?
        @executor.shuttingdown?
      end

      def work(connection)
        self.connection = connection

        run_callbacks :work do
          yield
        end
      ensure
        self.connection = nil
      end

      def async_exec(receiver, *args, connection:, &block)
        async_invoke receiver, :instance_exec, *args, connection: connection, &block
      end

      def async_invoke(receiver, method, *args, connection: receiver, &block)
        @executor.post do
          invoke(receiver, method, *args, connection: connection, &block)
        end
      end

      def invoke(receiver, method, *args, connection:, &block)
        work(connection) do
          begin
            receiver.send method, *args, &block
          rescue Exception => e
            logger.error "There was an exception - #{e.class}(#{e.message})"
            logger.error e.backtrace.join("\n")

            receiver.handle_exception if receiver.respond_to?(:handle_exception)
          end
        end
      end

      private

        def logger
          ActionCable.server.logger
        end
    end
  end
end