defmodule CobblemonUi.TierListScraper do
  use GenServer
  require Logger

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

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

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

  @doc "Returns the current tier list map (%{lowercase_name => tier})."
  def get_tier_list do
    GenServer.call(__MODULE__, :get_tier_list)
  end

  @doc "Triggers a background re-scrape from HTTP."
  def refresh do
    GenServer.cast(__MODULE__, :refresh)
  end

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

  @impl true
  def init(_opts) do
    tier_list = load_from_file()

    if map_size(tier_list) == 0 do
      Logger.info("[TierListScraper] No cached data found, scheduling HTTP fetch")
      send(self(), :fetch)
    else
      Logger.info("[TierListScraper] Loaded #{map_size(tier_list)} pokemon from cache file")
    end

    {:ok, tier_list}
  end

  @impl true
  def handle_call(:get_tier_list, _from, state) do
    {:reply, state, state}
  end

  @impl true
  def handle_cast(:refresh, state) do
    Logger.info("[TierListScraper] Manual refresh requested")
    send(self(), :fetch)
    {:noreply, state}
  end

  @impl true
  def handle_info(:fetch, state) do
    Logger.info("[TierListScraper] Starting scrape from #{@url}")

    case run_scrape() do
      {:ok, tier_list} ->
        Logger.info("[TierListScraper] Updated state with #{map_size(tier_list)} pokemon")
        {:noreply, tier_list}

      {:error, reason} ->
        Logger.error("[TierListScraper] Scrape failed, keeping existing state: #{inspect(reason)}")
        {:noreply, state}
    end
  end

  # ---------------------------------------------------------------------------
  # Private scrape pipeline
  # ---------------------------------------------------------------------------

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

  defp 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

  defp 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

  defp write_json(data) do
    path = output_file()
    Logger.debug("[TierListScraper] Writing cache to #{path}")
    File.mkdir_p!(Path.dirname(path))
    File.write(path, Jason.encode!(data, pretty: true))
  end

  defp load_from_file do
    path = output_file()

    with {:ok, contents} <- File.read(path),
         {:ok, entries} <- Jason.decode(contents) do
      map = to_tier_map(entries)
      Logger.info("[TierListScraper] Loaded #{map_size(map)} pokemon from #{path}")
      map
    else
      {:error, :enoent} ->
        Logger.info("[TierListScraper] Cache file not found at #{path}")
        %{}

      {:error, reason} ->
        Logger.warning("[TierListScraper] Failed to load cache file: #{inspect(reason)}")
        %{}
    end
  end

  defp to_tier_map(entries) do
    Map.new(entries, fn
      %{"name" => name, "tier" => tier} -> {String.downcase(name), tier}
      %{name: name, tier: tier} -> {String.downcase(name), tier}
    end)
  end

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