import 'market_data_db.dart';
import 'trading_config.dart';

/// Why a rule did not fire. `null` means the rule fired.
enum RuleSkipReason {
  unknownType,
  missingMetric,
  staleData,
  aboveThreshold,
  cooldown,
  zeroReferencePrice,
}

/// Result of evaluating a single [TradingRuleConfig] against snapshots.
class RuleEvaluation {
  RuleEvaluation({
    required this.rule,
    required this.fired,
    this.skipReason,
    this.pricePct,
    this.refPrice,
    this.observedPrice,
    this.questionText,
    this.asOf,
  });

  final TradingRuleConfig rule;
  final bool fired;
  final RuleSkipReason? skipReason;

  /// Signed pct change between observed and reference (e.g. -1.6 for a 1.6% dip).
  final num? pricePct;
  final num? refPrice;
  final num? observedPrice;

  /// Template-substituted question text (only when [fired] is true).
  final String? questionText;

  /// Most recent `as_of` across the snapshots used.
  final DateTime? asOf;
}

/// Pure evaluation of trading rules over [MarketDataSnapshot] inputs.
///
/// Inputs are pre-fetched snapshots so this layer never touches the network
/// or DB. The caller (`TradingPipeline`) decides what to do with results.
class RuleEngine {
  RuleEngine({DateTime Function()? clock}) : _clock = clock ?? DateTime.now;

  final DateTime Function() _clock;

  /// Evaluates [rule] against [snapshots] keyed by metric.
  ///
  /// [lastFiredAt] is the last time this rule fired for the user; pass `null`
  /// when the rule has never fired (or in tests). [lastFiredAt] within the
  /// same UTC date as `now` means the rule is on cooldown.
  RuleEvaluation evaluate({
    required TradingRuleConfig rule,
    required Map<String, MarketDataSnapshot> snapshots,
    DateTime? lastFiredAt,
    DateTime? now,
  }) {
    final DateTime evaluatedAt = (now ?? _clock()).toUtc();

    if (rule.type != 'price_below_pct_of_ref') {
      return RuleEvaluation(
        rule: rule,
        fired: false,
        skipReason: RuleSkipReason.unknownType,
      );
    }

    if (_isCooldown(lastFiredAt, evaluatedAt)) {
      return RuleEvaluation(
        rule: rule,
        fired: false,
        skipReason: RuleSkipReason.cooldown,
      );
    }

    final MarketDataSnapshot? observed = snapshots['last_trade'];
    final MarketDataSnapshot? reference = snapshots[rule.refMetric];
    if (observed == null || reference == null ||
        observed.price == null || reference.price == null) {
      return RuleEvaluation(
        rule: rule,
        fired: false,
        skipReason: RuleSkipReason.missingMetric,
      );
    }

    if (reference.price == 0) {
      return RuleEvaluation(
        rule: rule,
        fired: false,
        skipReason: RuleSkipReason.zeroReferencePrice,
      );
    }

    final num refPrice = reference.price!;
    final num observedPrice = observed.price!;
    final Duration age = evaluatedAt.difference(observed.asOf);
    if (age.inSeconds > rule.maxStalenessSeconds ||
        age.isNegative && age.inSeconds.abs() > rule.maxStalenessSeconds) {
      return RuleEvaluation(
        rule: rule,
        fired: false,
        skipReason: RuleSkipReason.staleData,
        refPrice: refPrice,
        observedPrice: observedPrice,
        asOf: observed.asOf,
      );
    }

    final num pricePct = ((observedPrice - refPrice) / refPrice) * 100;
    final bool fires = pricePct <= rule.thresholdPct;
    if (!fires) {
      return RuleEvaluation(
        rule: rule,
        fired: false,
        skipReason: RuleSkipReason.aboveThreshold,
        pricePct: pricePct,
        refPrice: refPrice,
        observedPrice: observedPrice,
        asOf: observed.asOf,
      );
    }

    final String questionText = _renderTemplate(
      rule.questionTemplate,
      symbol: rule.symbol,
      price: observedPrice,
      pct: pricePct,
      refPrice: refPrice,
    );

    return RuleEvaluation(
      rule: rule,
      fired: true,
      pricePct: pricePct,
      refPrice: refPrice,
      observedPrice: observedPrice,
      questionText: questionText,
      asOf: observed.asOf,
    );
  }

  bool _isCooldown(DateTime? lastFiredAt, DateTime now) {
    if (lastFiredAt == null) {
      return false;
    }
    final DateTime last = lastFiredAt.toUtc();
    return last.year == now.year &&
        last.month == now.month &&
        last.day == now.day;
  }

  String _renderTemplate(
    String template, {
    required String symbol,
    required num price,
    required num pct,
    required num refPrice,
  }) {
    return template
        .replaceAll('{{symbol}}', symbol)
        .replaceAll('{{price}}', _formatPrice(price))
        .replaceAll('{{pct}}', _formatPct(pct))
        .replaceAll('{{ref_price}}', _formatPrice(refPrice));
  }

  String _formatPrice(num value) => value.toStringAsFixed(2);

  String _formatPct(num value) {
    final num abs = value.abs();
    return abs.toStringAsFixed(abs < 10 ? 2 : 1);
  }
}