feat: apply template instead of creating base availabilities

packages/flutter_availability/lib/src/service/availability_service.dart

@@ -62,6 +62,20 @@ class AvailabilityService {
     }
   }
 
+  /// Creates a set of availabilities for the given [range] by applying the
+  /// [template] to each day in the range
+  Future<void> applyTemplate({
+    required AvailabilityTemplateModel template,
+    required DateTimeRange range,
+  }) async {
+    await dataInterface.applyTemplateForUser(
+      userId,
+      template,
+      range.start,
+      range.end,
+    );
+  }
+
   /// Returns a stream where data from availabilities and templates are merged
   Stream<List<AvailabilityWithTemplate>> getOverviewDataForMonth(
     DateTime dayInMonth,

packages/flutter_availability/lib/src/ui/screens/availability_modification.dart

@@ -72,16 +72,17 @@ class _AvailabilitiesModificationScreenState
         widget.onExit();
         return;
       }
-      if (widget.initialAvailabilities.isNotEmpty) {
+      if (_availabilityViewModel.templateSelected) {
-        await service.clearAvailabilities(
+        await service.applyTemplate(
-          widget.initialAvailabilities.getAvailabilities(),
+          template: _availabilityViewModel.templates.first,
+          range: widget.dateRange,
+        );
+      } else {
+        await service.createAvailability(
+          availability: _availabilityViewModel.toModel(),
+          range: widget.dateRange,
         );
       }
-
-      await service.createAvailability(
-        availability: _availabilityViewModel.toModel(),
-        range: widget.dateRange,
-      );
       widget.onExit();
     }
 
@@ -135,6 +136,7 @@ class _AvailabilitiesModificationScreenState
       setState(() {
         _availabilityViewModel = _availabilityViewModel.copyWith(
           startTime: start,
+          templateSelected: false,
         );
       });
     }
@@ -143,6 +145,7 @@ class _AvailabilitiesModificationScreenState
       setState(() {
         _availabilityViewModel = _availabilityViewModel.copyWith(
           endTime: end,
+          templateSelected: false,
         );
       });
     }
@@ -151,6 +154,7 @@ class _AvailabilitiesModificationScreenState
       setState(() {
         _availabilityViewModel = _availabilityViewModel.copyWith(
           breaks: breaks,
+          templateSelected: false,
         );
       });
     }