defmodule TradeMachine.GMGradeV2.Pillars.CapFlexibility do
  @moduledoc """
  Aggregates AVC's four Cap & Flexibility metrics from a `CapState` snapshot.

  Current Cap Position, Tax & Apron Exposure, Future Flexibility, and
  Transaction Flexibility retain full precision through the fixed 20/30/30/20
  weighted sum.
  """

  alias TradeMachine.GMGradeV2.ModelVersion
  alias TradeMachine.GMGradeV2.Pillars.CapFlexibility.CurrentCapPosition
  alias TradeMachine.GMGradeV2.Pillars.CapFlexibility.FutureFlexibility
  alias TradeMachine.GMGradeV2.Pillars.CapFlexibility.TaxApronExposure
  alias TradeMachine.GMGradeV2.Pillars.CapFlexibility.TransactionFlexibility
  alias TradeMachine.GMGradeV2.Result.MetricResult
  alias TradeMachine.GMGradeV2.Result.PillarResult

  @metric_weights %{
    current_cap_position: 0.20,
    tax_apron_exposure: 0.30,
    future_flexibility: 0.30,
    transaction_flexibility: 0.20
  }

  @metric_modules [
    CurrentCapPosition,
    TaxApronExposure,
    FutureFlexibility,
    TransactionFlexibility
  ]

  if abs(Enum.sum(Map.values(@metric_weights)) - 1.0) > 1.0e-9 do
    raise "Cap & Flexibility metric weights must sum to 1.0"
  end

  @doc "Returns the full-precision Cap & Flexibility pillar result."
  @spec score(map()) :: PillarResult.t()
  def score(cap_state) when is_map(cap_state) do
    metric_results = Enum.map(@metric_modules, & &1.score(cap_state))
    {strongest, weakest} = extrema(metric_results)

    %PillarResult{
      key: :cap_flexibility,
      version: ModelVersion.model_version(),
      score: weighted_score(metric_results),
      metric_results: metric_results,
      metric_weights: @metric_weights,
      explanation: explanation(strongest, weakest),
      strongest: strongest.key,
      weakest: weakest.key
    }
  end

  @doc "Combines Cap & Flexibility metric results at AVC's fixed weights."
  @spec weighted_score([MetricResult.t()]) :: float()
  def weighted_score(metric_results) when is_list(metric_results) do
    # Intentional AVC emphasis: CapState's Effective Committed Salary already
    # includes dead money, and Future Flexibility also applies the separate Dead
    # Money Score. Do not remove this deliberate double-count.
    Enum.reduce(metric_results, 0.0, fn result, total ->
      total + result.score * Map.fetch!(@metric_weights, result.key)
    end)
  end

  defp extrema(metric_results) do
    {
      Enum.max_by(metric_results, & &1.score),
      Enum.min_by(metric_results, & &1.score)
    }
  end

  defp explanation(
         %MetricResult{key: strongest_key, score: strongest_score},
         %MetricResult{key: weakest_key, score: weakest_score}
       ) do
    "Cap & Flexibility combines four cap-state metrics; " <>
      "#{label(strongest_key)} is strongest at #{strongest_score}, while " <>
      "#{label(weakest_key)} is weakest at #{weakest_score}."
  end

  defp label(:current_cap_position), do: "Current Cap Position"
  defp label(:tax_apron_exposure), do: "Tax & Apron Exposure"
  defp label(:future_flexibility), do: "Future Flexibility"
  defp label(:transaction_flexibility), do: "Transaction Flexibility"
end