defmodule TradeMachine.GMGradeV2.Pillars.ContractHealth do
  @moduledoc """
  Aggregates AVC's four Contract Health metrics over the final roster.

  Contract Value, Long-Term Risk, Contract Mobility, and Contract Optionality
  retain full precision through the fixed 35/30/20/15 weighted sum.
  """

  alias TradeMachine.GMGradeV2.Benchmark
  alias TradeMachine.GMGradeV2.ChallengeSnapshot
  alias TradeMachine.GMGradeV2.Pillars.ContractHealth.ContractMobility
  alias TradeMachine.GMGradeV2.Pillars.ContractHealth.ContractOptionality
  alias TradeMachine.GMGradeV2.Pillars.ContractHealth.ContractValue
  alias TradeMachine.GMGradeV2.Pillars.ContractHealth.LongTermRisk
  alias TradeMachine.GMGradeV2.Result.MetricResult
  alias TradeMachine.GMGradeV2.Result.PillarResult

  @metric_weights %{
    contract_value: 0.35,
    long_term_risk: 0.30,
    contract_mobility: 0.20,
    contract_optionality: 0.15
  }

  @metric_modules [
    ContractValue,
    LongTermRisk,
    ContractMobility,
    ContractOptionality
  ]

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

  @doc "Returns the full-precision Contract Health pillar result."
  @spec score(map(), ChallengeSnapshot.t()) :: PillarResult.t()
  def score(
        scenario_state,
        %ChallengeSnapshot{benchmark: %Benchmark{} = benchmark} = snapshot
      )
      when is_map(scenario_state) do
    metric_results = Enum.map(@metric_modules, & &1.score(scenario_state, snapshot))
    {strongest, weakest} = extrema(metric_results)

    %PillarResult{
      key: :contract_health,
      version: benchmark.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

  defp weighted_score(metric_results) do
    Enum.sum(
      Enum.map(metric_results, fn result ->
        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
    "Contract Health combines four final-roster contract metrics; " <>
      "#{label(strongest_key)} is strongest at #{strongest_score}, while " <>
      "#{label(weakest_key)} is weakest at #{weakest_score}."
  end

  defp label(:contract_value), do: "Contract Value"
  defp label(:long_term_risk), do: "Long-Term Risk"
  defp label(:contract_mobility), do: "Contract Mobility"
  defp label(:contract_optionality), do: "Contract Optionality"
end