A whole bunch of changes

lib/services/fuel_report.dart

@@ -1,19 +1,55 @@
 import '../models/fuel_entry.dart';
 import '../models/vehicle.dart';
 
-/// One vehicle's totals within a [FuelReport]'s date range.
+/// One vehicle's totals — and, for the line-items/receipt-images report
+/// sections, its individual entries — within a [FuelReport]'s date range.
+/// [entries] is sorted oldest-first, the natural order for a ledger of
+/// line items building up to a total.
 class VehicleReportRow {
   final Vehicle vehicle;
-  final int entryCount;
+  final List<FuelEntry> entries;
   final double totalGallons;
   final double totalCost;
 
   VehicleReportRow({
     required this.vehicle,
-    required this.entryCount,
+    required this.entries,
     required this.totalGallons,
     required this.totalCost,
   });
+
+  int get entryCount => entries.length;
+}
+
+/// One entry paired with the vehicle it belongs to — [FuelEntry] only knows
+/// [FuelEntry.vehicleId], not the [Vehicle] itself, so anything that needs
+/// to show both together (like [FuelReport.allEntries], for a combined
+/// cross-vehicle list) needs this pairing.
+class ReportEntry {
+  final FuelEntry entry;
+  final Vehicle vehicle;
+
+  ReportEntry({required this.entry, required this.vehicle});
+}
+
+/// Every qualifying entry in a single calendar month, across every vehicle
+/// in the report — the "Gallons by month" breakdown is this, one per
+/// month present in [FuelReport.monthlyTotals].
+class MonthlyTotal {
+  /// The first of the month, e.g. `DateTime(2026, 8)` for August 2026.
+  final DateTime month;
+  final int fillCount;
+  final double totalGallons;
+  final double totalCost;
+
+  MonthlyTotal({
+    required this.month,
+    required this.fillCount,
+    required this.totalGallons,
+    required this.totalCost,
+  });
+
+  double get avgPricePerGallon => totalGallons == 0 ? 0 : totalCost / totalGallons;
 }
 
 /// Per-vehicle fuel totals for entries with a receipt, dated within
@@ -27,6 +63,47 @@ class FuelReport {
 
   double get totalGallons => rows.fold(0.0, (sum, r) => sum + r.totalGallons);
   double get totalCost => rows.fold(0.0, (sum, r) => sum + r.totalCost);
+  int get fillCount => rows.fold(0, (sum, r) => sum + r.entryCount);
+  double get avgPricePerGallon => totalGallons == 0 ? 0 : totalCost / totalGallons;
+
+  /// Every entry across every vehicle, oldest first — the natural order for
+  /// a combined "purchase detail" ledger that isn't grouped by vehicle.
+  List<ReportEntry> get allEntries {
+    final list = [
+      for (final row in rows)
+        for (final entry in row.entries) ReportEntry(entry: entry, vehicle: row.vehicle),
+    ];
+    list.sort((a, b) => a.entry.date.compareTo(b.entry.date));
+    return list;
+  }
+
+  /// [allEntries] grouped by calendar month, in chronological order — the
+  /// "Purchase detail" section's grouping, and the source data for
+  /// [monthlyTotals].
+  Map<DateTime, List<ReportEntry>> get entriesByMonth {
+    final map = <DateTime, List<ReportEntry>>{};
+    for (final reportEntry in allEntries) {
+      final month = DateTime(reportEntry.entry.date.year, reportEntry.entry.date.month);
+      (map[month] ??= []).add(reportEntry);
+    }
+    return map;
+  }
+
+  /// One [MonthlyTotal] per calendar month with qualifying entries, oldest
+  /// first — the "Gallons by month" chart/table's data.
+  List<MonthlyTotal> get monthlyTotals {
+    final byMonth = entriesByMonth;
+    final months = byMonth.keys.toList()..sort();
+    return [
+      for (final month in months)
+        MonthlyTotal(
+          month: month,
+          fillCount: byMonth[month]!.length,
+          totalGallons: byMonth[month]!.fold(0.0, (sum, re) => sum + re.entry.gallons),
+          totalCost: byMonth[month]!.fold(0.0, (sum, re) => sum + re.entry.totalCost),
+        ),
+    ];
+  }
 }
 
 /// Builds a per-vehicle fuel summary for [startDate]–[endDate] (inclusive,
@@ -68,11 +145,12 @@ FuelReport buildFuelReport({
     // No matching (active) vehicle — e.g. deleted since — nothing sane to
     // attribute these entries to.
     if (vehicle == null) continue;
+    final sortedEntries = entry.value.toList()..sort((a, b) => a.date.compareTo(b.date));
     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),
+      entries: sortedEntries,
+      totalGallons: sortedEntries.fold(0.0, (sum, e) => sum + e.gallons),
+      totalCost: sortedEntries.fold(0.0, (sum, e) => sum + e.totalCost),
     ));
   }
   rows.sort((a, b) => a.vehicle.displayLabel.compareTo(b.vehicle.displayLabel));