import '../models/fuel_entry.dart';
import '../models/vehicle.dart';

/// One vehicle's totals within a [FuelReport]'s date range.
class VehicleReportRow {
  final Vehicle vehicle;
  final int entryCount;
  final double totalGallons;
  final double totalCost;

  VehicleReportRow({
    required this.vehicle,
    required this.entryCount,
    required this.totalGallons,
    required this.totalCost,
  });
}

/// Per-vehicle fuel totals for entries with a receipt, dated within
/// [startDate]–[endDate] inclusive. See [buildFuelReport].
class FuelReport {
  final DateTime startDate;
  final DateTime endDate;
  final List<VehicleReportRow> rows;

  FuelReport({required this.startDate, required this.endDate, required this.rows});

  double get totalGallons => rows.fold(0.0, (sum, r) => sum + r.totalGallons);
  double get totalCost => rows.fold(0.0, (sum, r) => sum + r.totalCost);
}

/// Builds a per-vehicle fuel summary for [startDate]–[endDate] (inclusive,
/// judged by each entry's purchase date, in local time), restricted to
/// entries that actually have a receipt attached — a report meant to
/// substantiate a fuel tax refund claim is only as good as the
/// documentation behind each entry, so an entry logged without a photo
/// isn't something the report should be claiming on your behalf. "Has a
/// receipt" means a local copy or a cloud copy — [FuelEntry.receiptImagePath]
/// or [FuelEntry.receiptDriveFileId] — not specifically an already-synced
/// one, since sync status is a technical detail unrelated to whether the
/// purchase is documented.
///
/// Vehicles with no qualifying entries in range are omitted rather than
/// shown with an all-zero row. Rows are sorted by [Vehicle.displayLabel].
FuelReport buildFuelReport({
  required List<Vehicle> vehicles,
  required List<FuelEntry> fuelEntries,
  required DateTime startDate,
  required DateTime endDate,
}) {
  final rangeStart = DateTime(startDate.year, startDate.month, startDate.day);
  final rangeEndExclusive =
      DateTime(endDate.year, endDate.month, endDate.day).add(const Duration(days: 1));

  final vehiclesById = {for (final v in vehicles) v.id: v};
  final entriesByVehicle = <String, List<FuelEntry>>{};

  for (final entry in fuelEntries) {
    final hasReceipt = entry.receiptImagePath != null || entry.receiptDriveFileId != null;
    if (!hasReceipt) continue;
    if (entry.date.isBefore(rangeStart) || !entry.date.isBefore(rangeEndExclusive)) continue;
    (entriesByVehicle[entry.vehicleId] ??= []).add(entry);
  }

  final rows = <VehicleReportRow>[];
  for (final entry in entriesByVehicle.entries) {
    final vehicle = vehiclesById[entry.key];
    // No matching (active) vehicle — e.g. deleted since — nothing sane to
    // attribute these entries to.
    if (vehicle == null) continue;
    rows.add(VehicleReportRow(
      vehicle: vehicle,
      entryCount: entry.value.length,
      totalGallons: entry.value.fold(0.0, (sum, e) => sum + e.gallons),
      totalCost: entry.value.fold(0.0, (sum, e) => sum + e.totalCost),
    ));
  }
  rows.sort((a, b) => a.vehicle.displayLabel.compareTo(b.vehicle.displayLabel));

  return FuelReport(startDate: rangeStart, endDate: endDate, rows: rows);
}