feat(graphs): work on category pie chart

lib/util/graphs.dart

@@ -4,6 +4,8 @@ import 'package:fl_chart/fl_chart.dart';
 import 'package:flutter/material.dart';
 import 'package:intl/intl.dart';
 import 'package:flutter_gen/gen_l10n/app_localizations.dart';
+import 'package:prasule/api/category.dart';
+import 'package:prasule/api/walletentry.dart';
 
 /// Monthly/Yearly expense/income [LineChart]
 class ExpensesLineChart extends StatelessWidget {
@@ -295,3 +297,30 @@ class ExpensesBarChart extends StatelessWidget {
         ),
       );
 }
+
+class CategoriesPieChart extends StatelessWidget {
+  const CategoriesPieChart(
+      {super.key, required this.entries, required this.categories});
+
+  final List<WalletSingleEntry> entries;
+  final List<WalletCategory> categories;
+
+  @override
+  Widget build(BuildContext context) => PieChart(
+        PieChartData(
+          sections: List<PieChartSectionData>.generate(
+            categories.length,
+            (index) => PieChartSectionData(
+              value: entries
+                  .where(
+                      (element) => element.category.id == categories[index].id)
+                  .fold<double>(
+                    0,
+                    (previousValue, element) =>
+                        previousValue + element.data.amount,
+                  ),
+            ),
+          ),
+        ),
+      );
+}