import 'package:uuid/uuid.dart';

import 'payment_method.dart';

/// Types of [TabEvent] the server understands.
enum TabEventType {
  tabOpened('tab_opened'),
  tabRenamed('tab_renamed'),
  tabDeleted('tab_deleted'),
  lineAdded('line_added'),
  lineRemoved('line_removed'),
  settled('settled'),

  /// A stock count or tracking change made on the tablet. Not about a tab:
  /// it has no `tabId`.
  stockSet('stock_set');

  final String value;

  const TabEventType(this.value);

  static TabEventType? fromValue(String value) {
    for (final type in TabEventType.values) {
      if (type.value == value) return type;
    }
    return null;
  }
}

/// Something that happened on a tab. Together the events form the operation
/// log the server builds the venue's tabs from, and the tablet replays the
/// ones the server hasn't applied yet on top of the server's tabs. [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 productId,
  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;

  TabEvent tabOpened({
    required String tabId,
    required String customerName,
    required DateTime openedAt,
  }) {
    return _event(
      TabEventType.tabOpened,
      tabId: tabId,
      customerName: customerName,
      fields: {'openedAt': openedAt.toUtc().toIso8601String()},
    );
  }

  /// [customerName] is the new name.
  TabEvent tabRenamed({required String tabId, required String customerName}) {
    return _event(
      TabEventType.tabRenamed,
      tabId: tabId,
      customerName: customerName,
      fields: const {},
    );
  }

  /// Written after a `line_removed` for every line still on the tab.
  TabEvent tabDeleted({required String tabId, required String customerName}) {
    return _event(
      TabEventType.tabDeleted,
      tabId: tabId,
      customerName: customerName,
      fields: const {},
    );
  }

  /// [quantity] is how many pieces were added; always positive. [lineId] is
  /// the local line, so the server can keep its id.
  TabEvent lineAdded({
    required String tabId,
    required String customerName,
    required String lineId,
    required String productId,
    required String productName,
    required int unitPriceInCents,
    required int quantity,
  }) {
    return _lineEvent(
      TabEventType.lineAdded,
      tabId: tabId,
      customerName: customerName,
      lineId: lineId,
      productId: productId,
      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 lineId,
    required String productId,
    required String productName,
    required int unitPriceInCents,
    required int quantity,
  }) {
    return _lineEvent(
      TabEventType.lineRemoved,
      tabId: tabId,
      customerName: customerName,
      lineId: lineId,
      productId: productId,
      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)
            {
              'productId': item.productId,
              'productName': item.productName,
              'quantity': item.quantity,
              'unitPriceInCents': item.unitPriceInCents,
            },
        ],
      },
    );
  }

  /// The stock of [productId] was set to [quantity] on this tablet (a count,
  /// or a new product's starting stock); null stops tracking it.
  TabEvent stockSet({required String productId, required int? quantity}) {
    final id = _uuid.v4();

    return TabEvent(
      id: id,
      payload: {
        'id': id,
        'type': TabEventType.stockSet.value,
        'productId': productId,
        'quantity': quantity,
        'occurredAt': _now().toUtc().toIso8601String(),
      },
    );
  }

  /// 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 lineId,
    required String productId,
    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: {
        'lineId': lineId,
        'productId': productId,
        '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,
      },
    );
  }
}