module MultiProcess
  #
  # Store and run a group of processes.
  #
  class Group
    #
    # Return list of processes.
    attr_reader :processes

    # Receiver all processes in group should use.
    #
    # If changed only affect new added processes.
    #
    attr_accessor :receiver

    # Partition size.
    attr_reader :partition

    # Create new process group.
    #
    # @param opts [ Hash ] Options
    # @option otps [ Receiver ] :receiver Receiver to use for new added
    #   processes. Defaults to `MultiProcess::Logger.global`.
    #
    def initialize(receiver: nil, partition: nil)
      @processes = []
      @receiver  = receiver ? receiver : MultiProcess::Logger.global
      @partition = partition ? partition.to_i : 0
      @mutex     = Mutex.new
    end

    # Add new process or list of processes.
    #
    # If group was already started added processes will also be started.
    #
    # @param process [Process, Array<Process>] New process or processes.
    #
    def <<(processes)
      Array(processes).flatten.each do |process|
        processes << process
        process.receiver = receiver

        start process if started?
      end
    end

    # Start all process in group.
    #
    # Call blocks until all processes are started.
    #
    # @option delay [Integer] Delay in seconds between starting processes.
    #
    def start(delay: nil)
      processes.each do |process|
        next if process.started?

        process.start
        sleep delay if delay
      end
    end

    # Check if group was already started.
    #
    # @return [ Boolean ] True if group was already started.
    #
    def started?
      processes.any?(&:started?)
    end

    # Stop all processes.
    #
    def stop
      processes.each(&:stop)
    end

    # Wait until all process terminated.
    #
    # @param opts [ Hash ] Options.
    # @option opts [ Integer ] :timeout Timeout in seconds to wait before
    #   raising {Timeout::Error}.
    #
    def wait(timeout: nil)
      if timeout
        ::Timeout.timeout(timeout) { wait }
      else
        processes.each(&:wait)
      end
    end

    # Start all process and wait for them to terminate.
    #
    # Given options will be passed to {#start} and {#wait}.
    # {#start} will only be called if partition is zero.
    #
    # If timeout is given process will be terminated using {#stop}
    # when timeout error is raised.
    #
    def run(**kwargs)
      if partition > 0
        partition.times.map do
          Thread.new do
            while (process = next_process)
              process.run
            end
          end
        end.each(&:join)
      else
        start(**kwargs)
        wait(**kwargs)
      end
    ensure
      stop
    end

    # Check if group is alive e.g. if at least on process is alive.
    #
    # @return [ Boolean ] True if group is alive.
    #
    def alive?
      processes.any?(&:alive?)
    end

    # Check if group is available. The group is available if all
    # processes are available.
    #
    def available?
      processes.all?(:available?)
    end

    # Wait until group is available. This implies waiting until
    # all processes in group are available.
    #
    # Processes will not be stopped if timeout occurs.
    #
    # @param opts [ Hash ] Options.
    # @option opts [ Integer ] :timeout Timeout in seconds to wait for processes
    #   to become available. Defaults to {MultiProcess::DEFAULT_TIMEOUT}.
    #
    def available!(timeout: MultiProcess::DEFAULT_TIMEOUT)
      Timeout.timeout timeout do
        processes.each(&:available!)
      end
    end

    private

    def next_process
      @mutex.synchronize do
        @index ||= 0
        @index += 1
        processes[@index - 1]
      end
    end
  end
end