defmodule CobblemonUi.TierListScraper do
  require Logger

  @url "https://rankedboost.com/pokemon/tier-list/"
  @filename "pokemon_tier_list.json"

  def output_file do
    dir = System.get_env("CACHE_DIR", ".")
    Path.join(dir, @filename)
  end

  def run do
    Logger.info("[TierListScraper] Starting scrape from #{@url}")

    with {:ok, html} <- fetch_page(),
         {:ok, pokemon} <- parse(html),
         :ok <- write_json(pokemon) do
      Logger.info("[TierListScraper] Successfully scraped and saved #{length(pokemon)} pokemon")
      {:ok, pokemon}
    else
      {:error, reason} = err ->
        Logger.error("[TierListScraper] Scrape failed: #{inspect(reason)}")
        err
    end
  end

  def fetch_page do
    Logger.debug("[TierListScraper] Fetching #{@url}")
    case Req.get(@url, headers: [{"user-agent", "Mozilla/5.0 (compatible; CobblemonUI/1.0)"}]) do
      {:ok, %Req.Response{status: 200, body: body}} ->
        Logger.debug("[TierListScraper] Fetch OK, body size: #{byte_size(body)} bytes")
        {:ok, body}
      {:ok, %Req.Response{status: status}} ->
        Logger.warning("[TierListScraper] Unexpected HTTP status: #{status}")
        {:error, {:http_error, status}}
      {:error, err} ->
        Logger.error("[TierListScraper] HTTP request failed: #{inspect(err)}")
        {:error, err}
    end
  end

  def parse(html) do
    nodes = html |> Floki.parse_document!() |> Floki.find(".pokemon-tier")
    Logger.debug("[TierListScraper] Found #{length(nodes)} .pokemon-tier nodes")

    case nodes do
      [] ->
        Logger.warning("[TierListScraper] No .pokemon-tier elements found — page structure may have changed or content is JS-rendered")
        {:error, :no_pokemon_found}
      _ ->
        pokemon = Enum.map(nodes, &extract_pokemon/1)
        valid = Enum.filter(pokemon, fn %{name: n} -> n != "" end)
        Logger.info("[TierListScraper] Parsed #{length(valid)} valid pokemon (#{length(pokemon) - length(valid)} skipped with empty names)")
        {:ok, valid}
    end
  end

  defp extract_pokemon(node) do
    name =
      node
      |> Floki.find(".name")
      |> Floki.text()
      |> String.trim()

    tier =
      node
      |> Floki.find(".tier")
      |> Floki.text()
      |> String.trim()

    %{name: name, tier: tier}
  end

  def write_json(data) do
    json = Jason.encode!(data, pretty: true)
    File.write(output_file(), json)
  end

  # Returns a map of %{lowercase_name => tier} for fast lookup, or an empty map if unavailable.
  def load_tier_list do
    with {:ok, contents} <- File.read(output_file()),
         {:ok, entries} <- Jason.decode(contents) do
      Map.new(entries, fn %{"name" => name, "tier" => tier} ->
        {String.downcase(name), tier}
      end)
    else
      _ -> %{}
    end
  end
end