defmodule CobblemonUi.PokeApi do
  @moduledoc """
  Fetches and caches Pokémon type data from PokeAPI.

  Uses an ETS table for fast lookups. Data is fetched once per species
  and cached for the lifetime of the process.
  """

  use GenServer
  require Logger

  @table :poke_api_types_cache

  # ---------------------------------------------------------------------------
  # Client API
  # ---------------------------------------------------------------------------

  def start_link(_opts) do
    GenServer.start_link(__MODULE__, [], name: __MODULE__)
  end

  @doc """
  Returns a list of type names (lowercase strings) for the given species.

  Example: `get_types("bulbasaur")` → `["grass", "poison"]`
  """
  @spec get_types(String.t()) :: [String.t()]
  def get_types(species) when is_binary(species) do
    key = String.downcase(species)

    case :ets.lookup(@table, key) do
      [{^key, types}] ->
        types

      [] ->
        GenServer.call(__MODULE__, {:fetch_types, key}, 15_000)
    end
  end

  # ---------------------------------------------------------------------------
  # Server callbacks
  # ---------------------------------------------------------------------------

  @impl true
  def init(_opts) do
    :ets.new(@table, [:named_table, :set, :public, read_concurrency: true])
    {:ok, %{}}
  end

  @impl true
  def handle_call({:fetch_types, species}, _from, state) do
    result =
      case :ets.lookup(@table, species) do
        [{^species, types}] ->
          types

        [] ->
          types = fetch_types(species)
          :ets.insert(@table, {species, types})
          types
      end

    {:reply, result, state}
  end

  # ---------------------------------------------------------------------------
  # Private helpers
  # ---------------------------------------------------------------------------

  defp fetch_types(species) do
    url = "https://pokeapi.co/api/v2/pokemon/#{species}"

    case Req.get(url) do
      {:ok, %Req.Response{status: 200, body: %{"types" => types}}} ->
        types
        |> Enum.sort_by(fn t -> t["slot"] end)
        |> Enum.map(fn t -> get_in(t, ["type", "name"]) end)
        |> Enum.reject(&is_nil/1)

      {:ok, %Req.Response{status: status}} ->
        Logger.warning("[PokeApi] Type lookup failed for #{species}: HTTP #{status}")
        []

      {:error, reason} ->
        Logger.warning("[PokeApi] Type lookup failed for #{species}: #{inspect(reason)}")
        []
    end
  end
end