import 'dart:math' as math;

import 'user_trading_state_db.dart';

/// Runtime scoring mode for prospective / guess-the-move answers.
///
/// Set from [ServerEnv.prospectiveAnswerClosenessEnabled] at server startup.
class ProspectiveAnswerScoring {
  ProspectiveAnswerScoring._();

  /// When false (default): correct sign `+1`, wrong sign `-1`.
  ///
  /// When true: correct sign `+1` plus up to `+1` closeness; wrong sign `-2`.
  static bool closenessExtraPointsEnabled = false;
}

/// Breakdown of one prospective / guess-the-move answer grade.
class ProspectiveAnswerGrade {
  const ProspectiveAnswerGrade({
    required this.directionPoint,
    required this.closenessPoint,
    required this.answerScore,
    required this.absError,
    required this.sameDirection,
  });

  final num directionPoint;
  final num closenessPoint;
  final num answerScore;
  final num absError;
  final bool sameDirection;
}

/// Full credit when absolute error is within this many percentage points.
const num prospectiveAnswerFullCreditTolerance = 1;

/// Grades a slider answer against the expected percent move.
ProspectiveAnswerGrade gradeProspectiveAnswer({
  required num userResponse,
  required num correctAnswer,
}) {
  final bool sameDirection = _sameDirection(
    userResponse: userResponse,
    correctAnswer: correctAnswer,
  );
  final num absError = (userResponse - correctAnswer).abs();

  if (!ProspectiveAnswerScoring.closenessExtraPointsEnabled) {
    final num directionPoint = sameDirection ? 1 : -1;
    return ProspectiveAnswerGrade(
      directionPoint: directionPoint,
      closenessPoint: 0,
      answerScore: directionPoint,
      absError: absError,
      sameDirection: sameDirection,
    );
  }

  final num directionPoint = sameDirection ? 1 : -2;
  final num closenessPoint = sameDirection
      ? _closenessPoint(
          userResponse: userResponse,
          correctAnswer: correctAnswer,
        )
      : 0;
  return ProspectiveAnswerGrade(
    directionPoint: directionPoint,
    closenessPoint: closenessPoint,
    answerScore: directionPoint + closenessPoint,
    absError: absError,
    sameDirection: sameDirection,
  );
}

/// Adds [grade] to cumulative `guess_score` in [user_trading_state].
Future<void> recordProspectiveGuessScore({
  required UserTradingStateDb tradingStateDb,
  required String firebaseUid,
  required ProspectiveAnswerGrade grade,
  required String symbol,
  required DateTime at,
}) async {
  await tradingStateDb.recordGuessScore(
    firebaseUid: firebaseUid,
    scoreDelta: grade.answerScore,
    symbol: symbol,
    at: at,
    directionCorrect: grade.sameDirection,
  );
}

bool _sameDirection({
  required num userResponse,
  required num correctAnswer,
}) {
  return userResponse.compareTo(0) == correctAnswer.compareTo(0);
}

num _closenessPoint({
  required num userResponse,
  required num correctAnswer,
}) {
  final num absError = (userResponse - correctAnswer).abs();
  if (absError <= prospectiveAnswerFullCreditTolerance) {
    return 1;
  }
  final num scale = math.max(1, correctAnswer.abs());
  final num normalizedError =
      (absError - prospectiveAnswerFullCreditTolerance) / scale;
  return math.max(0, 1 - normalizedError);
}