module Rdkafka
  # A consumer of Kafka messages. It uses the high-level consumer approach where the Kafka
  # brokers automatically assign partitions and load balance partitions over consumers that
  # have the same `:"group.id"` set in their configuration.
  #
  # To create a consumer set up a {Config} and call {Config#consumer consumer} on that. It is
  # mandatory to set `:"group.id"` in the configuration.
  class Consumer
    include Enumerable

    # @private
    def initialize(native_kafka)
      @native_kafka = native_kafka
    end

    # Close this consumer
    # @return [nil]
    def close
      Rdkafka::Bindings.rd_kafka_consumer_close(@native_kafka)
    end

    # Subscribe to one or more topics letting Kafka handle partition assignments.
    #
    # @param topics [Array<String>] One or more topic names
    #
    # @raise [RdkafkaError] When subscribing fails
    #
    # @return [nil]
    def subscribe(*topics)
      # Create topic partition list with topics and no partition set
      tpl = Rdkafka::Bindings.rd_kafka_topic_partition_list_new(topics.length)
      topics.each do |topic|
        Rdkafka::Bindings.rd_kafka_topic_partition_list_add(
          tpl,
          topic,
          -1
        )
      end
      # Subscribe to topic partition list and check this was successful
      response = Rdkafka::Bindings.rd_kafka_subscribe(@native_kafka, tpl)
      if response != 0
        raise Rdkafka::RdkafkaError.new(response)
      end
    ensure
      # Clean up the topic partition list
      Rdkafka::Bindings.rd_kafka_topic_partition_list_destroy(tpl)
    end

    # Unsubscribe from all subscribed topics.
    #
    # @raise [RdkafkaError] When unsubscribing fails
    #
    # @return [nil]
    def unsubscribe
      response = Rdkafka::Bindings.rd_kafka_unsubscribe(@native_kafka)
      if response != 0
        raise Rdkafka::RdkafkaError.new(response)
      end
    end

    # Return the current subscription to topics and partitions
    #
    # @raise [RdkafkaError] When getting the subscription fails.
    #
    # @return [TopicPartitionList]
    def subscription
      tpl = FFI::MemoryPointer.new(:pointer)
      response = Rdkafka::Bindings.rd_kafka_subscription(@native_kafka, tpl)
      if response != 0
        raise Rdkafka::RdkafkaError.new(response)
      end
      Rdkafka::Consumer::TopicPartitionList.new(tpl.get_pointer(0))
    end

    # Return the current committed offset per partition for this consumer group.
    # The offset field of each requested partition will either be set to stored offset or to -1001 in case there was no stored offset for that partition.
    #
    # @param list [TopicPartitionList] The topic with partitions to get the offsets for.
    # @param timeout_ms [Integer] The timeout for fetching this information.
    #
    # @raise [RdkafkaError] When getting the committed positions fails.
    #
    # @return [TopicPartitionList]
    def committed(list, timeout_ms=200)
      unless list.is_a?(TopicPartitionList)
        raise TypeError.new("list has to be a TopicPartitionList")
      end
      tpl = list.copy_tpl
      response = Rdkafka::Bindings.rd_kafka_committed(@native_kafka, tpl, timeout_ms)
      if response != 0
        raise Rdkafka::RdkafkaError.new(response)
      end
      Rdkafka::Consumer::TopicPartitionList.new(tpl)
    end

    # Query broker for low (oldest/beginning) and high (newest/end) offsets for a partition.
    #
    # @param topic [String] The topic to query
    # @param partition [Integer] The partition to query
    # @param timeout_ms [Integer] The timeout for querying the broker
    #
    # @raise [RdkafkaError] When querying the broker fails.
    #
    # @return [Integer] The low and high watermark
    def query_watermark_offsets(topic, partition, timeout_ms=200)
      low = FFI::MemoryPointer.new(:int64, 1)
      high = FFI::MemoryPointer.new(:int64, 1)

      response = Rdkafka::Bindings.rd_kafka_query_watermark_offsets(
        @native_kafka,
        topic,
        partition,
        low,
        high,
        timeout_ms
      )
      if response != 0
        raise Rdkafka::RdkafkaError.new(response)
      end

      return low.read_int, high.read_int
    end

    # Commit the current offsets of this consumer
    #
    # @param async [Boolean] Whether to commit async or wait for the commit to finish
    #
    # @raise [RdkafkaError] When comitting fails
    #
    # @return [nil]
    def commit(async=false)
      response = Rdkafka::Bindings.rd_kafka_commit(@native_kafka, nil, async)
      if response != 0
        raise Rdkafka::RdkafkaError.new(response)
      end
    end

    # Poll for the next message on one of the subscribed topics
    #
    # @param timeout_ms [Integer] Timeout of this poll
    #
    # @raise [RdkafkaError] When polling fails
    #
    # @return [Message, nil] A message or nil if there was no new message within the timeout
    def poll(timeout_ms)
      message_ptr = Rdkafka::Bindings.rd_kafka_consumer_poll(@native_kafka, timeout_ms)
      if message_ptr.null?
        nil
      else
        # Create struct wrapper
        native_message = Rdkafka::Bindings::Message.new(message_ptr)
        # Raise error if needed
        if native_message[:err] != 0
          raise Rdkafka::RdkafkaError.new(native_message[:err])
        end
        # Create a message to pass out
        Rdkafka::Consumer::Message.new(native_message)
      end
    ensure
      # Clean up rdkafka message if there is one
      unless message_ptr.null?
        Rdkafka::Bindings.rd_kafka_message_destroy(message_ptr)
      end
    end

    # Poll for new messages and yield for each received one
    #
    # @raise [RdkafkaError] When polling fails
    #
    # @yieldparam message [Message] Received message
    #
    # @return [nil]
    def each(&block)
      loop do
        message = poll(250)
        if message
          block.call(message)
        else
          next
        end
      end
    end
  end
end