defmodule XMAVLink.Utils do
  @moduledoc ~s"""
  MAVLink support functions used during code generation and runtime
  Parts of this module are ported from corresponding implementations
  in mavutils.py
  """

  import Bitwise

  import List, only: [flatten: 1]
  import Enum, only: [sort_by: 2, join: 2, map: 2, reverse: 1]

  @doc """
  Sort parsed message fields into wire order according
  to https://mavlink.io/en/guide/serialization.html
  List extension fields separately so that we can
  not include them for MAVLink 1 messages
  """
  @spec wire_order([%{type: String.t(), is_extension: boolean}]) :: [[%{}]]
  def wire_order(fields) do
    type_order_map = %{
      uint64_t: 1,
      int64_t: 1,
      double: 1,
      uint32_t: 2,
      int32_t: 2,
      float: 2,
      uint16_t: 3,
      int16_t: 3,
      uint8_t: 4,
      uint8_t_mavlink_version: 4,
      int8_t: 4,
      char: 4
    }

    [
      sort_by(
        Enum.filter(fields, &(!&1.is_extension)),
        &Map.fetch(type_order_map, String.to_atom(&1.type))
      ),
      Enum.filter(fields, & &1.is_extension)
    ]
  end

  def eight_bit_checksum(value) do
    Bitwise.bxor(value &&& 0xFF, value >>> 8)
  end

  @doc """
  Calculate an x25 checksum of a list or binary based on
  pymavlink mavcrc.x25crc
  """

  @spec x25_crc([] | binary()) :: pos_integer
  def x25_crc(list) when is_list(list) do
    x25_crc(0xFFFF, flatten(list))
  end

  def x25_crc(bin) when is_binary(bin) do
    x25_crc(0xFFFF, bin)
  end

  def x25_crc(crc, []), do: crc

  def x25_crc(crc, <<>>), do: crc

  def x25_crc(crc, [head | tail]) do
    crc |> x25_accumulate(head) |> x25_crc(tail)
  end

  def x25_crc(crc, <<head::size(8), tail::binary>>) do
    crc |> x25_accumulate(head) |> x25_crc(tail)
  end

  defp x25_accumulate(crc, value) do
    tmp = Bitwise.bxor(value, crc &&& 0xFF)
    tmp = Bitwise.bxor(tmp, tmp <<< 4) &&& 0xFF
    crc = Bitwise.bxor(Bitwise.bxor(Bitwise.bxor(crc >>> 8, tmp <<< 8), tmp <<< 3), tmp >>> 4)
    crc &&& 0xFFFF
  end

  @doc "Helper function for messages to pack string fields"
  @spec pack_string(binary, non_neg_integer) :: binary
  def pack_string(s, ordinality) do
    s |> String.pad_trailing(ordinality, <<0>>)
  end

  @doc "Helper function for messages to pack array fields"
  @spec pack_array(list(), integer, (any() -> binary())) :: binary()
  def pack_array(a, ordinality, _) when length(a) > ordinality,
    do: {:error, "Maximum elements allowed is \#{ordinality}"}

  def pack_array(a, ordinality, field_packer) when length(a) < ordinality,
    do: pack_array(a ++ [0], ordinality, field_packer)

  def pack_array(a, _, field_packer), do: a |> map(field_packer) |> join(<<>>)

  @doc "Helper function for decode() to unpack array fields"
  # TODO bitstring generator instead? https://elixir-lang.org/getting-started/comprehensions.html
  @spec unpack_array(binary(), (binary() -> {any(), list()})) :: list()
  def unpack_array(bin, fun), do: unpack_array(bin, fun, [])
  def unpack_array(<<>>, _, lst), do: reverse(lst)

  def unpack_array(bin, fun, lst) do
    {elem, rest} = fun.(bin)
    unpack_array(rest, fun, [elem | lst])
  end

  @doc """
  Resolve an address string to an IP address tuple.

  Accepts both IP addresses (e.g., "192.168.1.1") and DNS hostnames
  (e.g., "service.namespace.svc.cluster.local").

  Uses Erlang's `:inet.getaddr/2` for resolution, which handles both
  IP addresses and DNS lookups.

  Returns `{:ok, ip_tuple}` on success or `{:error, reason}` on failure.

  ## Examples

      iex> resolve_address("127.0.0.1")
      {:ok, {127, 0, 0, 1}}

      iex> resolve_address("localhost")
      {:ok, {127, 0, 0, 1}}
  """
  def resolve_address(address) when is_binary(address) do
    # Convert string to charlist for :inet.getaddr
    charlist_address = String.to_charlist(address)

    case :inet.getaddr(charlist_address, :inet) do
      {:ok, ip_tuple} ->
        {:ok, ip_tuple}

      {:error, reason} ->
        {:error, reason}
    end
  end

  @doc "Parse an ip address string into a tuple"
  def parse_ip_address(address) when is_binary(address) do
    parse_ip_address(String.split(address, "."), [], 0)
  end

  def parse_ip_address([], address, 4) do
    List.to_tuple(reverse(address))
  end

  def parse_ip_address([], _, _) do
    {:error, :invalid_ip_address}
  end

  def parse_ip_address([component | rest], address, count) do
    case Integer.parse(component) do
      :error ->
        {:error, :invalid_ip_address}

      {n, _} ->
        cond do
          n >= 0 and n <= 255 ->
            parse_ip_address(rest, [n | address], count + 1)

          true ->
            {:error, :invalid_ip_address}
        end
    end
  end

  def parse_positive_integer(port) when is_binary(port) do
    case Integer.parse(port) do
      :error ->
        :error

      {n, _} when n > 0 ->
        n

      _ ->
        :error
    end
  end

  def pack_float(f) when is_float(f), do: <<f::little-signed-float-size(32)>>
  # Have received these from QGroundControl
  def pack_float(:nan), do: <<0, 0, 192, 127>>

  def unpack_float(<<f::little-signed-float-size(32)>>), do: f
  def unpack_float(<<0, 0, 192, 127>>), do: :nan

  def pack_double(f) when is_float(f), do: <<f::little-signed-float-size(64)>>
  # Quick test in C gave this for double NaN
  def pack_double(:nan), do: <<0, 0, 0, 0, 0, 0, 248, 127>>

  def unpack_double(<<f::little-signed-float-size(64)>>), do: f
  def unpack_double(<<0, 0, 0, 0, 0, 0, 248, 127>>), do: :nan
end