import 'package:uuid/uuid.dart';

import 'payment_method.dart';

/// Types of [TabEvent] the server understands.
enum TabEventType {
  lineAdded('line_added'),
  lineRemoved('line_removed'),
  settled('settled');

  final String value;

  const TabEventType(this.value);
}

/// Something that happened on a tab, reported to the server for sales
/// statistics. [payload] is the JSON object that is stored in the outbox and
/// sent as is.
class TabEvent {
  final String id;
  final Map<String, dynamic> payload;

  const TabEvent({required this.id, required this.payload});
}

/// One settled line in a `settled` event.
typedef SettledLine = ({
  String productName,
  int quantity,
  int unitPriceInCents,
});

/// Builds the events, so their JSON shape lives in one place.
class TabEventFactory {
  final _uuid = const Uuid();
  final DateTime Function() _now;

  TabEventFactory({DateTime Function()? now}) : _now = now ?? DateTime.now;

  /// [quantity] is how many pieces were added; always positive.
  TabEvent lineAdded({
    required String tabId,
    required String customerName,
    required String productName,
    required int unitPriceInCents,
    required int quantity,
  }) {
    return _lineEvent(
      TabEventType.lineAdded,
      tabId: tabId,
      customerName: customerName,
      productName: productName,
      unitPriceInCents: unitPriceInCents,
      quantity: quantity,
    );
  }

  /// [quantity] is how many pieces were removed; always positive.
  TabEvent lineRemoved({
    required String tabId,
    required String customerName,
    required String productName,
    required int unitPriceInCents,
    required int quantity,
  }) {
    return _lineEvent(
      TabEventType.lineRemoved,
      tabId: tabId,
      customerName: customerName,
      productName: productName,
      unitPriceInCents: unitPriceInCents,
      quantity: quantity,
    );
  }

  TabEvent settled({
    required String tabId,
    required String customerName,
    required int amountInCents,
    required PaymentMethod paymentMethod,
    required List<SettledLine> items,
    String? commandId,
  }) {
    return _event(
      TabEventType.settled,
      tabId: tabId,
      customerName: customerName,
      fields: {
        'amountInCents': amountInCents,
        'paymentMethod': paymentMethodValue(paymentMethod),
        'commandId': ?commandId,
        'items': [
          for (final item in items)
            {
              'productName': item.productName,
              'quantity': item.quantity,
              'unitPriceInCents': item.unitPriceInCents,
            },
        ],
      },
    );
  }

  /// The server's payment method names: `cash`, `payconiq`,
  /// `payment_pending` or `other`.
  static String paymentMethodValue(PaymentMethod method) {
    return switch (method) {
      PaymentMethod.cash => 'cash',
      PaymentMethod.payconiq => 'payconiq',
      PaymentMethod.paymentPending => 'payment_pending',
    };
  }

  TabEvent _lineEvent(
    TabEventType type, {
    required String tabId,
    required String customerName,
    required String productName,
    required int unitPriceInCents,
    required int quantity,
  }) {
    if (quantity < 1) {
      throw ArgumentError.value(quantity, 'quantity', 'Must be at least 1');
    }

    return _event(
      type,
      tabId: tabId,
      customerName: customerName,
      fields: {
        'productName': productName,
        'unitPriceInCents': unitPriceInCents,
        'quantity': quantity,
      },
    );
  }

  TabEvent _event(
    TabEventType type, {
    required String tabId,
    required String customerName,
    required Map<String, dynamic> fields,
  }) {
    final id = _uuid.v4();

    return TabEvent(
      id: id,
      payload: {
        'id': id,
        'type': type.value,
        'tabId': tabId,
        'customerName': customerName,
        'occurredAt': _now().toUtc().toIso8601String(),
        ...fields,
      },
    );
  }
}