defmodule KafkaEx.Protocol.Offset do
  alias KafkaEx.Protocol

  @moduledoc """
  Implementation of the Kafka Offset request and response APIs
  """

  defmodule Request do
    @moduledoc false
    defstruct replica_id: -1,
              topic_name: nil,
              partition: nil,
              time: -1,
              max_number_of_offsets: 1

    @type t :: %Request{
            replica_id: integer,
            topic_name: binary,
            partition: integer,
            time: integer,
            max_number_of_offsets: integer
          }
  end

  defmodule Response do
    @moduledoc false
    defstruct topic: nil, partition_offsets: []
    @type t :: %Response{topic: binary, partition_offsets: list}

    def extract_offset([%__MODULE__{partition_offsets: [%{offset: [offset]}]}]),
      do: offset

    def extract_offset([%__MODULE__{partition_offsets: [%{offset: []}]}]), do: 0
  end

  def create_request(correlation_id, client_id, topic, partition, time) do
    KafkaEx.Protocol.create_request(:offset, correlation_id, client_id) <>
      <<-1::32-signed, 1::32-signed, byte_size(topic)::16-signed, topic::binary,
        1::32-signed, partition::32-signed, parse_time(time)::64, 1::32>>
  end

  def parse_response(
        <<_correlation_id::32-signed, num_topics::32-signed, rest::binary>>
      ),
      do: parse_topics(num_topics, rest)

  @spec parse_time(:latest | :earliest | :calendar.datetime()) :: integer
  def parse_time(:latest), do: -1

  def parse_time(:earliest), do: -2

  def parse_time(time) do
    current_time_in_seconds = :calendar.datetime_to_gregorian_seconds(time)

    unix_epoch_in_seconds =
      :calendar.datetime_to_gregorian_seconds({{1970, 1, 1}, {0, 0, 0}})

    (current_time_in_seconds - unix_epoch_in_seconds) * 1000
  end

  defp parse_topics(0, _), do: []

  defp parse_topics(
         topics_size,
         <<topic_size::16-signed, topic::size(topic_size)-binary,
           partitions_size::32-signed, rest::binary>>
       ) do
    {partitions, topics_data} = parse_partitions(partitions_size, rest)

    [
      %Response{topic: topic, partition_offsets: partitions}
      | parse_topics(topics_size - 1, topics_data)
    ]
  end

  defp parse_partitions(partitions_size, rest, partitions \\ [])

  defp parse_partitions(0, rest, partitions), do: {partitions, rest}

  defp parse_partitions(
         partitions_size,
         <<partition::32-signed, error_code::16-signed, offsets_size::32-signed,
           rest::binary>>,
         partitions
       ) do
    {offsets, rest} = parse_offsets(offsets_size, rest)

    parse_partitions(partitions_size - 1, rest, [
      %{
        partition: partition,
        error_code: Protocol.error(error_code),
        offset: offsets
      }
      | partitions
    ])
  end

  defp parse_offsets(offsets_size, rest, offsets \\ [])

  defp parse_offsets(0, rest, offsets), do: {Enum.reverse(offsets), rest}

  defp parse_offsets(offsets_size, <<offset::64-signed, rest::binary>>, offsets) do
    parse_offsets(offsets_size - 1, rest, [offset | offsets])
  end
end