defmodule CobblemonUiWeb.Plugs.SpriteStatic do
  @moduledoc """
  Serves cached Pokémon sprite images from the sprites cache directory.

  Matches requests to `/sprites/<name>.png` and serves the corresponding
  file from `CobblemonUi.SpriteCache.sprites_dir()`. If the file doesn't
  exist locally, triggers an on-demand download before responding.
  """

  import Plug.Conn

  def init(opts), do: opts

  def call(%Plug.Conn{request_path: "/sprites/" <> filename} = conn, _opts) do
    if String.ends_with?(filename, ".png") do
      species = String.trim_trailing(filename, ".png")
      CobblemonUi.SpriteCache.ensure_sprite(species)
      path = CobblemonUi.SpriteCache.sprite_path(species)

      if File.exists?(path) do
        conn
        |> put_resp_content_type("image/png")
        |> put_resp_header("cache-control", "public, max-age=604800, immutable")
        |> send_file(200, path)
        |> halt()
      else
        conn
        |> send_resp(404, "Not found")
        |> halt()
      end
    else
      conn
    end
  end

  def call(conn, _opts), do: conn
end