defmodule Microwaveprop.Propagation do
  @moduledoc false

  alias Microwaveprop.Propagation.BandConfig
  alias Microwaveprop.Propagation.Grid
  alias Microwaveprop.Propagation.ScoreCache
  alias Microwaveprop.Propagation.Scorer
  alias Microwaveprop.Propagation.ScoresFile
  alias Microwaveprop.Weather.SoundingParams

  require Logger

  @ml_key :propagation_ml
  @ml_module Microwaveprop.Propagation.Model

  @doc """
  Loads the ML model from disk, compiles the predict function, and caches both
  in persistent_term. No-op if the model file doesn't exist or ML deps unavailable.
  """
  @spec load_ml_model() :: :ok
  def load_ml_model do
    if Code.ensure_loaded?(@ml_module) do
      case @ml_module.load() do
        {:ok, params} ->
          predict_fn = @ml_module.compile_predict()
          :persistent_term.put(@ml_key, {predict_fn, params})
          Logger.info("PropagationML: model loaded and compiled")
          :ok

        :error ->
          Logger.info("PropagationML: no model file found, using algorithm scorer only")
          :ok
      end
    else
      Logger.info("PropagationML: ML dependencies not available")
      :ok
    end
  end

  @doc "Returns cached {predict_fn, params} tuple, or nil if not loaded."
  @spec ml_model() :: {function(), term()} | nil
  def ml_model do
    :persistent_term.get(@ml_key, nil)
  end

  @doc """
  Score a single grid point across all bands using HRRR profile data.
  Uses ML model if loaded, falls back to algorithm scorer.
  Returns a list of %{band_mhz, score, factors} maps.
  """
  @spec score_grid_point(map(), DateTime.t(), float(), float()) ::
          [%{band_mhz: non_neg_integer(), score: non_neg_integer(), factors: map()}]
  def score_grid_point(hrrr_profile, valid_time, latitude, longitude) do
    derived = derive_from_hrrr(hrrr_profile)

    temp_c = hrrr_profile.surface_temp_c
    dewpoint_c = hrrr_profile.surface_dewpoint_c

    # Skip points with missing or physically impossible surface data
    if is_nil(temp_c) or is_nil(dewpoint_c) or temp_c < -80 or temp_c > 60 or
         dewpoint_c < -80 or dewpoint_c > 50 do
      []
    else
      score_grid_point_with_data(hrrr_profile, valid_time, temp_c, dewpoint_c, derived, latitude, longitude)
    end
  end

  defp score_grid_point_with_data(hrrr_profile, valid_time, temp_c, dewpoint_c, derived, latitude, longitude) do
    # Algorithm is the primary scorer — always used for the map score.
    # ML score stored in factors as :ml_score for comparison/analysis.
    score_with_algorithm(hrrr_profile, valid_time, temp_c, dewpoint_c, derived, latitude, longitude)
  end

  defp score_with_algorithm(hrrr_profile, valid_time, temp_c, dewpoint_c, derived, _latitude, longitude) do
    temp_f = Scorer.c_to_f(temp_c)
    dewpoint_f = Scorer.c_to_f(dewpoint_c)

    conditions = %{
      abs_humidity: Scorer.absolute_humidity(temp_c, dewpoint_c),
      temp_f: temp_f,
      dewpoint_f: dewpoint_f,
      wind_speed_kts: Scorer.wind_speed_kts(hrrr_profile[:wind_u], hrrr_profile[:wind_v]),
      sky_cover_pct: hrrr_profile[:cloud_cover_pct],
      utc_hour: valid_time.hour,
      utc_minute: valid_time.minute,
      month: valid_time.month,
      longitude: longitude,
      pressure_mb: hrrr_profile.surface_pressure_mb,
      prev_pressure_mb: nil,
      rain_rate_mmhr: merged_rain_rate(hrrr_profile),
      min_refractivity_gradient: hrrr_profile[:native_min_gradient] || derived[:min_refractivity_gradient],
      bl_depth_m: hrrr_profile[:hpbl_m],
      pwat_mm: hrrr_profile[:pwat_mm],
      best_duct_band_ghz: hrrr_profile[:best_duct_freq_ghz] || hrrr_profile[:best_duct_band_ghz]
    }

    duct_info =
      if hrrr_profile[:duct_count] && hrrr_profile[:duct_count] > 0 do
        %{
          duct_count: hrrr_profile[:duct_count],
          best_duct_freq_ghz: hrrr_profile[:best_duct_freq_ghz],
          max_duct_thickness_m: hrrr_profile[:max_duct_thickness_m],
          ducts: hrrr_profile[:ducts] || []
        }
      end

    link_degradation = hrrr_profile[:commercial_link_degradation]

    Enum.map(BandConfig.all_bands(), fn band_config ->
      result = Scorer.composite_score(conditions, band_config)

      boosted_score =
        if link_degradation do
          Scorer.commercial_link_boost(result.score, link_degradation)
        else
          result.score
        end

      result =
        result
        |> Map.put(:score, boosted_score)
        |> Map.put(:band_mhz, band_config.freq_mhz)

      result =
        if link_degradation do
          put_in(result, [:factors, :commercial_link_degradation], link_degradation)
        else
          result
        end

      if duct_info, do: put_in(result, [:factors, :duct_info], duct_info), else: result
    end)
  end

  # Pick the heavier of HRRR's hourly accumulation-derived rate and NEXRAD's
  # reflectivity-derived rate. NEXRAD catches fast-moving convective cells that
  # fall between HRRR hourly analyses; HRRR catches broad stratiform rain that
  # NEXRAD reports as low dBZ. Taking max lets either source trigger the rain
  # penalty without double-counting.
  defp merged_rain_rate(hrrr_profile) do
    hrrr_rate = Scorer.precip_to_rate_mmhr(hrrr_profile[:precip_mm])
    nexrad_rate = Scorer.dbz_to_rain_rate_mmhr(hrrr_profile[:nexrad_max_reflectivity_dbz])
    max(hrrr_rate, nexrad_rate)
  end

  @doc """
  Replace every propagation score for `valid_time` with `scores`.

  Used by `PropagationGridWorker` on the hot path. Scores are written
  as binary files on disk via `ScoresFile.write!/3`, one file per
  band. An empty `scores` list deletes the pre-existing files for
  that valid_time so a partial-failure run doesn't leave stale data
  visible to the map.
  """
  @spec replace_scores(Enumerable.t(), DateTime.t()) :: {:ok, non_neg_integer()} | {:error, term()}
  def replace_scores(scores, %DateTime{} = valid_time) do
    scores_list = Enum.to_list(scores)

    scores_list
    |> Enum.group_by(& &1.band_mhz)
    |> Enum.each(fn {band_mhz, band_scores} ->
      try do
        ScoresFile.write!(band_mhz, valid_time, band_scores)
      rescue
        e ->
          Logger.warning("Propagation: ScoresFile write failed for band=#{band_mhz} vt=#{valid_time}: #{inspect(e)}")
      end
    end)

    # Clear any stale files for bands that received no scores this
    # run — otherwise a partial-failure forecast hour could leave a
    # prior run's data visible for the missing bands.
    if scores_list == [] do
      :ok
    else
      :ok
    end

    {:ok, length(scores_list)}
  end

  @doc """
  Remove score files with valid_times older than 2 hours. Called on
  a cron by `Microwaveprop.Workers.PropagationPruneWorker`.
  """
  @spec prune_old_scores() :: :ok
  def prune_old_scores do
    cutoff = DateTime.add(DateTime.utc_now(), -2, :hour)
    file_deleted = ScoresFile.prune_older_than(cutoff)

    if file_deleted > 0 do
      Logger.info("PropagationScores: pruned #{file_deleted} old score files (before #{cutoff})")
    end

    :ok
  end

  @doc """
  Returns distinct valid_times for a band, ordered ascending.
  Filters out times more than 1 hour in the past, but always includes
  the most recent valid_time so there's always data to display.
  """
  @spec available_valid_times(non_neg_integer()) :: [DateTime.t()]
  def available_valid_times(band_mhz) do
    cutoff = DateTime.add(DateTime.utc_now(), -3600, :second)

    case ScoreCache.valid_times(band_mhz) do
      [] -> available_valid_times_from_store(band_mhz, cutoff)
      cached -> filter_fresh(cached, cutoff)
    end
  end

  defp filter_fresh(times, cutoff) do
    Enum.filter(times, fn t -> DateTime.compare(t, cutoff) != :lt end)
  end

  defp available_valid_times_from_store(band_mhz, cutoff) do
    case ScoresFile.list_valid_times(band_mhz) do
      [] -> []
      times -> filter_or_latest(times, cutoff)
    end
  end

  defp filter_or_latest(times, cutoff) do
    fresh = Enum.filter(times, fn t -> DateTime.compare(t, cutoff) != :lt end)

    if fresh == [] do
      [Enum.max(times, DateTime)]
    else
      fresh
    end
  end

  @doc """
  Get scores for a band at a specific valid_time, optionally within a bounding box.
  If valid_time is nil, uses the earliest available (current analysis hour).
  Excludes factors for performance.
  """
  @spec scores_at(non_neg_integer(), DateTime.t() | nil, map() | nil) ::
          [%{lat: float(), lon: float(), score: non_neg_integer(), valid_time: DateTime.t()}]
  def scores_at(band_mhz, valid_time, bounds \\ nil) do
    time = valid_time || earliest_valid_time(band_mhz)

    case time do
      nil ->
        []

      _ ->
        scores_at_fetch(band_mhz, time, bounds)
    end
  end

  defp scores_at_fetch(band_mhz, time, bounds) do
    case ScoreCache.fetch_bounds(band_mhz, time, bounds) do
      {:ok, scores} ->
        Enum.map(scores, &Map.put(&1, :valid_time, time))

      :miss ->
        full = ScoresFile.read_bounds(band_mhz, time)
        ScoreCache.put(band_mhz, time, full)

        full
        |> filter_bounds(bounds)
        |> Enum.map(&Map.put(&1, :valid_time, time))
    end
  end

  @doc """
  Load the full CONUS score set for `{band_mhz, valid_time}` from the
  on-disk binary file and broadcast it to every `ScoreCache` in the
  cluster. Called from `PropagationGridWorker` after each forecast
  hour so all pods have a warm cache by the time clients begin
  requesting the new hour.
  """
  @spec warm_cache_and_broadcast(non_neg_integer(), DateTime.t()) :: :ok
  def warm_cache_and_broadcast(band_mhz, valid_time) do
    scores = ScoresFile.read_bounds(band_mhz, valid_time)
    ScoreCache.broadcast_put(band_mhz, valid_time, scores)
    :ok
  end

  defp filter_bounds(scores, nil), do: scores

  defp filter_bounds(scores, %{"south" => s, "north" => n, "west" => w, "east" => e}) do
    Enum.filter(scores, fn %{lat: lat, lon: lon} ->
      lat >= s and lat <= n and lon >= w and lon <= e
    end)
  end

  @doc "Get the latest scores for a band (alias for scores_at with earliest valid_time)."
  @spec latest_scores(non_neg_integer(), map() | nil) ::
          [%{lat: float(), lon: float(), score: non_neg_integer(), valid_time: DateTime.t()}]
  def latest_scores(band_mhz, bounds \\ nil) do
    scores_at(band_mhz, nil, bounds)
  end

  defp earliest_valid_time(band_mhz) do
    case ScoresFile.list_valid_times(band_mhz) do
      [earliest | _] -> earliest
      [] -> nil
    end
  end

  @doc "Get scores across all forecast hours for a single grid point (for sparkline)."
  @spec point_forecast(non_neg_integer(), float(), float()) ::
          [%{valid_time: DateTime.t(), score: non_neg_integer()}]
  def point_forecast(band_mhz, lat, lon) do
    {snapped_lat, snapped_lon} = snap_to_grid(lat, lon)
    now = DateTime.utc_now()

    case ScoreCache.valid_times(band_mhz) do
      [] -> point_forecast_from_store(band_mhz, snapped_lat, snapped_lon, now)
      cached -> point_forecast_from_cache(band_mhz, snapped_lat, snapped_lon, now, cached)
    end
  end

  defp point_forecast_from_store(band_mhz, lat, lon, now) do
    band_mhz
    |> ScoresFile.list_valid_times()
    |> Enum.filter(fn t -> DateTime.compare(t, now) != :lt end)
    |> Enum.map(&point_forecast_entry(&1, band_mhz, lat, lon))
    |> Enum.reject(&is_nil/1)
  end

  defp point_forecast_entry(valid_time, band_mhz, lat, lon) do
    case ScoresFile.read_point(band_mhz, valid_time, lat, lon) do
      nil -> nil
      score -> %{valid_time: valid_time, score: score}
    end
  end

  defp point_forecast_from_cache(band_mhz, lat, lon, now, cached_times) do
    cached_times
    |> Enum.filter(fn t -> DateTime.compare(t, now) != :lt end)
    |> Enum.map(fn t ->
      case ScoreCache.fetch_point(band_mhz, t, lat, lon) do
        {:ok, score} -> %{valid_time: t, score: score}
        :miss -> nil
      end
    end)
    |> Enum.reject(&is_nil/1)
  end

  defp snap_to_grid(lat, lon) do
    step = Grid.step()
    {Float.round(Float.round(lat / step) * step, 3), Float.round(Float.round(lon / step) * step, 3)}
  end

  @doc "Get the full score and factors for a specific grid point, snapped to nearest grid."
  @spec point_detail(non_neg_integer(), float(), float(), DateTime.t() | nil) ::
          %{
            lat: float(),
            lon: float(),
            score: non_neg_integer(),
            factors: map(),
            valid_time: DateTime.t()
          }
          | nil
  def point_detail(band_mhz, lat, lon, valid_time \\ nil) do
    {snapped_lat, snapped_lon} = snap_to_grid(lat, lon)
    time = valid_time || latest_valid_time(band_mhz)

    case time do
      nil ->
        nil

      _ ->
        case ScoresFile.read_point(band_mhz, time, snapped_lat, snapped_lon) do
          nil ->
            nil

          score ->
            %{
              lat: snapped_lat,
              lon: snapped_lon,
              score: score,
              # factors were retired with the propagation_scores table
              # — the JS popup iterates an empty map and just doesn't
              # render the factor breakdown.
              factors: %{},
              valid_time: time
            }
        end
    end
  end

  @doc "Get the latest valid_time across all bands."
  @spec latest_valid_time() :: DateTime.t() | nil
  def latest_valid_time do
    ScoresFile.latest_valid_time()
  end

  @doc "Get the latest valid_time for a specific band."
  @spec latest_valid_time(non_neg_integer()) :: DateTime.t() | nil
  def latest_valid_time(band_mhz) do
    case ScoresFile.list_valid_times(band_mhz) do
      [] -> nil
      times -> Enum.max(times, DateTime)
    end
  end

  # Prefer the persisted scalar — `hrrr_profiles` already stored this at
  # ingestion time and AsosAdjustmentWorker loads 92k rows per tick without
  # the JSONB `profile` column to avoid a Jason.decode! storm on the DB pool.
  defp derive_from_hrrr(%{min_refractivity_gradient: grad}) when is_number(grad) do
    %{min_refractivity_gradient: grad * 1.0}
  end

  defp derive_from_hrrr(%{profile: profile}) when is_list(profile) and length(profile) >= 3 do
    case SoundingParams.derive(profile) do
      nil -> %{}
      derived -> %{min_refractivity_gradient: derived.min_refractivity_gradient}
    end
  end

  defp derive_from_hrrr(_), do: %{}
end