import 'package:equatable/equatable.dart';
import 'package:uuid/uuid.dart';

import '../../core/constants/app_constants.dart';
import '../../core/utils/extensions.dart';

enum Gender {
  male('Male'),
  female('Female'),
  other('Other'),
  unspecified('Prefer not to say');

  const Gender(this.label);

  final String label;
}

/// Loyalty tier, derived from lifetime spend.
enum MembershipTier {
  bronze('Bronze', 0, 0.0),
  silver('Silver', 10000, 0.02),
  gold('Gold', 50000, 0.05),
  platinum('Platinum', 150000, 0.08);

  const MembershipTier(this.label, this.threshold, this.discountRate);

  final String label;

  /// Lifetime spend in rupees required to reach this tier.
  final double threshold;

  /// Automatic bill discount granted to members of this tier.
  final double discountRate;

  static MembershipTier forSpend(double lifetimeSpend) {
    return MembershipTier.values.lastWhere(
      (t) => lifetimeSpend >= t.threshold,
      orElse: () => MembershipTier.bronze,
    );
  }

  MembershipTier? get next {
    final i = index;
    return i < MembershipTier.values.length - 1
        ? MembershipTier.values[i + 1]
        : null;
  }
}

/// A registered shopper. A `null` customer on a sale means walk-in.
class Customer extends Equatable {
  const Customer({
    required this.id,
    required this.name,
    required this.mobile,
    this.email,
    this.gender = Gender.unspecified,
    this.dateOfBirth,
    this.loyaltyPoints = 0,
    this.lifetimeSpend = 0,
    this.visitCount = 0,
    this.createdAt,
    this.lastVisitAt,
  });

  final String id;
  final String name;
  final String mobile;
  final String? email;
  final Gender gender;
  final DateTime? dateOfBirth;
  final int loyaltyPoints;
  final double lifetimeSpend;
  final int visitCount;
  final DateTime? createdAt;
  final DateTime? lastVisitAt;

  /// Fixed namespace for customer ids. Must never change: it is half the
  /// input to [idForMobile], so a new one renames every shopper in the fleet.
  static const _namespace = '9f2b7c14-3d6e-5a80-b1f7-2c4e8a05d913';

  static const _uuid = Uuid();

  /// The id for the shopper reachable on [mobile].
  ///
  /// Derived from the number rather than minted at random, which is what lets
  /// a hundred terminals agree without talking to each other. A shopper who
  /// registers at counter 2 in Anna Nagar and shops at counter 5 in T Nagar
  /// gets the same id both times, so the back office collapses them on a
  /// primary key instead of guessing at a merge later.
  static String idForMobile(String mobile) =>
      _uuid.v5(_namespace, normaliseMobile(mobile));

  /// Every digit in [mobile], in order. Used for matching what a cashier types
  /// against what is stored, where a partial number should still find a row.
  static String digitsOf(String mobile) => mobile.replaceAll(RegExp(r'\D'), '');

  /// Reduces a number to the ten-digit national one identity is keyed on.
  ///
  /// One cashier types `+91 98400 12345`, another `098400 12345`, a third
  /// `9840012345`. Keyed on raw digits those are three different shoppers,
  /// which is precisely the duplication [idForMobile] exists to prevent — the
  /// country code would fork a customer just as effectively as a random id.
  ///
  /// Only the two prefixes an Indian number actually carries are stripped, and
  /// only at the exact lengths that make them unambiguous. Anything else is
  /// left alone: mangling a number this rule was not written for is worse than
  /// storing it verbatim.
  static String normaliseMobile(String mobile) {
    final digits = digitsOf(mobile);

    // +91 98400 12345
    if (digits.length == 12 && digits.startsWith('91')) {
      return digits.substring(2);
    }
    // 0 98400 12345 — the old STD trunk prefix, still muscle memory for many.
    if (digits.length == 11 && digits.startsWith('0')) {
      return digits.substring(1);
    }
    return digits;
  }

  MembershipTier get tier => MembershipTier.forSpend(lifetimeSpend);

  /// Cash value of the points currently held.
  double get redeemableValue =>
      loyaltyPoints * AppConstants.loyaltyPointValue;

  /// Rupees of additional spend needed to reach the next tier.
  double? get spendToNextTier {
    final next = tier.next;
    if (next == null) return null;
    return (next.threshold - lifetimeSpend).clamp(0, double.infinity);
  }

  bool get isBirthdayToday {
    final dob = dateOfBirth;
    if (dob == null) return false;
    final now = DateTime.now();
    return dob.month == now.month && dob.day == now.day;
  }

  /// The shopper as they stand after a completed sale.
  ///
  /// Pure, so the caller can compute the new row and persist it in the same
  /// transaction as the bill rather than as a separate write that might fail
  /// on its own.
  Customer applySale({
    required double amount,
    required int pointsEarned,
    required int pointsRedeemed,
    DateTime? at,
  }) {
    return copyWith(
      loyaltyPoints:
          (loyaltyPoints - pointsRedeemed + pointsEarned).clamp(0, 1 << 31),
      lifetimeSpend: (lifetimeSpend + amount).asMoney,
      visitCount: visitCount + 1,
      lastVisitAt: at ?? DateTime.now(),
    );
  }

  Customer copyWith({
    String? name,
    String? email,
    Gender? gender,
    DateTime? dateOfBirth,
    int? loyaltyPoints,
    double? lifetimeSpend,
    int? visitCount,
    DateTime? lastVisitAt,
  }) {
    return Customer(
      id: id,
      name: name ?? this.name,
      mobile: mobile,
      email: email ?? this.email,
      gender: gender ?? this.gender,
      dateOfBirth: dateOfBirth ?? this.dateOfBirth,
      loyaltyPoints: loyaltyPoints ?? this.loyaltyPoints,
      lifetimeSpend: lifetimeSpend ?? this.lifetimeSpend,
      visitCount: visitCount ?? this.visitCount,
      createdAt: createdAt,
      lastVisitAt: lastVisitAt ?? this.lastVisitAt,
    );
  }

  @override
  List<Object?> get props => [id, name, mobile, loyaltyPoints, lifetimeSpend];
}