nutrition plans list: show weekly delta and total duration, consistent styling

lib/helpers/date.dart

@@ -30,6 +30,51 @@ List<DateTime> daysInRange(DateTime first, DateTime last) {
   );
 }
 
+/// Formats a Duration into a human-readable string with years, months, and days
+String humanDuration(DateTime startDate, DateTime endDate) {
+  var years = endDate.year - startDate.year;
+  var months = endDate.month - startDate.month;
+  var days = endDate.day - startDate.day;
+
+  if (months < 0) {
+    months += 12;
+    years -= 1;
+  }
+
+// if we overcounted the days, it's a bit trickier to solve than overcounting months
+// e.g. consider a start date february 10 and end date june 8
+// -> days = -2
+// -> months = 4
+// the proper answer can be thought of in 3 ways:
+// * count whole months first, then days: from febr 10 to may 10, and then to june 8. that's 3 months + (num_days_in_may - 10 + 8 days)
+// * count days first, then whole months: from febr 10 to march 8, and then to june 8. that's (num_days_in_feb - 10 + 8 days) + 3 months
+// * technically, one can also use any month to adjust the day: e.g.
+//   count months from febr 10 to april 10, count days to may 8, and count months again to june 8.
+// probably no-one uses the last method. The first approach seems most natural.
+// it means we need to know the number of days (aka the last day index) of the month before endDate
+// which we can do by setting the day to 0 and asking for the day
+  if (days < 0) {
+    days += DateTime(endDate.year, endDate.month, 0).day;
+    months -= 1;
+  }
+
+  final parts = <String>[];
+  if (years > 0) {
+    parts.add('$years year${years == 1 ? '' : 's'}');
+  }
+  if (months > 0) {
+    parts.add('$months month${months == 1 ? '' : 's'}');
+  }
+  if (days > 0) {
+    parts.add('$days day${days == 1 ? '' : 's'}');
+  }
+
+  if (parts.isEmpty) {
+    return 'Duration: 0 days';
+  }
+  return 'Duration: ${parts.join(', ')}';
+}
+
 extension DateTimeExtension on DateTime {
   bool isSameDayAs(DateTime other) {
     final thisDay = DateTime(year, month, day);

lib/widgets/nutrition/nutritional_plans_list.dart

@@ -19,6 +19,7 @@
 import 'package:flutter/material.dart';
 import 'package:intl/intl.dart';
 import 'package:provider/provider.dart';
+import 'package:wger/helpers/date.dart';
 import 'package:wger/helpers/measurements.dart';
 import 'package:wger/l10n/generated/app_localizations.dart';
 import 'package:wger/providers/body_weight.dart';
@@ -48,8 +49,14 @@ class NutritionalPlansList extends StatelessWidget {
     final lastWeight = entries7dAvg.last;
     final weightDifference = lastWeight.value - firstWeight.value;
 
+    // Calculate the time period in weeks
+    final timeDifference = lastWeight.date.difference(firstWeight.date);
+    final weeklyRate =
+        weightDifference / (timeDifference.inDays == 0 ? 1 : timeDifference.inDays) * 7;
+
     // Format the weight change text and determine color
     final String weightChangeText;
+    final String weeklyRateText;
     final Color weightChangeColor;
     final profile = context.read<UserProvider>().profile;
 
@@ -57,12 +64,15 @@ class NutritionalPlansList extends StatelessWidget {
 
     if (weightDifference > 0) {
       weightChangeText = '+${weightDifference.toStringAsFixed(1)} $unit';
+      weeklyRateText = '+${weeklyRate.toStringAsFixed(2)} $unit';
       weightChangeColor = Colors.red;
     } else if (weightDifference < 0) {
       weightChangeText = '${weightDifference.toStringAsFixed(1)} $unit';
+      weeklyRateText = '${weeklyRate.toStringAsFixed(2)} $unit';
       weightChangeColor = Colors.green;
     } else {
       weightChangeText = '0 $unit';
+      weeklyRateText = '0 $unit';
       weightChangeColor = Colors.grey;
     }
 
@@ -71,15 +81,11 @@ class NutritionalPlansList extends StatelessWidget {
       child: Row(
         children: [
           Text(
-            '${AppLocalizations.of(context).weight} change: ',
-            style: Theme.of(context).textTheme.bodySmall,
+            '${AppLocalizations.of(context).weight}: ',
           ),
           Text(
-            weightChangeText,
-            style: Theme.of(context).textTheme.bodySmall?.copyWith(
-                  fontWeight: FontWeight.bold,
-                  color: weightChangeColor,
-                ),
+            '$weightChangeText ($weeklyRateText/week)',
+            style: TextStyle(color: weightChangeColor),
           ),
         ],
       ),
@@ -109,14 +115,18 @@ class NutritionalPlansList extends StatelessWidget {
                     subtitle: Column(
                       crossAxisAlignment: CrossAxisAlignment.start,
                       children: [
+                        Text(
+                          humanDuration(
+                              currentPlan.startDate, currentPlan.endDate ?? DateTime.now()),
+                        ),
                         Text(
                           currentPlan.endDate != null
-                              ? 'from ${DateFormat.yMd(
+                              ? 'From: ${DateFormat.yMd(
                                   Localizations.localeOf(context).languageCode,
-                                ).format(currentPlan.startDate)} to ${DateFormat.yMd(
+                                ).format(currentPlan.startDate)} To: ${DateFormat.yMd(
                                   Localizations.localeOf(context).languageCode,
                                 ).format(currentPlan.endDate!)}'
-                              : 'from ${DateFormat.yMd(
+                              : 'From: ${DateFormat.yMd(
                                   Localizations.localeOf(context).languageCode,
                                 ).format(currentPlan.startDate)} (open ended)',
                         ),