feat #160: implement hour restriction to date time picker

example/lib/main.dart

@@ -100,6 +100,17 @@ class ExampleApp extends StatelessWidget {
               ),
             ),
           ),
+          SizedBox(
+            width: buttonWidth,
+            child: ElevatedButton(
+              onPressed: () {
+                _openDateTimePicker(
+                  context,
+                );
+              },
+              child: Text('Date time Picker', textAlign: TextAlign.center),
+            ),
+          ),
           SizedBox(
             width: buttonWidth,
             child: ElevatedButton(
@@ -599,6 +610,9 @@ class ExampleApp extends StatelessWidget {
     BuildContext context,
   ) {
     BottomPicker.dateTime(
+      hourPredicate: (hour) {
+        return hour > 6;
+      },
       headerBuilder: (context) {
         return Row(
           mainAxisAlignment: MainAxisAlignment.spaceBetween,

lib/bottom_picker.dart

@@ -277,6 +277,7 @@ class BottomPicker extends StatefulWidget {
     this.headerBuilder,
     this.calendarDays = CupertinoDatePickerWidget.fullWeek,
     this.diameterRatio = 1.1,
+    this.hourPredicate,
   }) {
     datePickerMode = CupertinoDatePickerMode.dateAndTime;
     bottomPickerType = BottomPickerType.dateTime;
@@ -811,6 +812,9 @@ class BottomPicker extends StatefulWidget {
   /// The bottom picker selector diameter ratio.
   final double diameterRatio;
 
+  /// A predicate that can be used to select which hours are selectable.
+  SelectableHourPredicate? hourPredicate;
+
   ///display the bottom picker popup
   ///[context] the app context to display the popup
   void show(BuildContext context) {
@@ -1023,6 +1027,7 @@ class BottomPickerState extends State<BottomPicker> {
                                     itemExtent: widget.itemExtent,
                                     showTimeSeparator: widget.showTimeSeparator,
                                     pickerThemeData: widget.pickerThemeData,
+                                    hourPredicate: widget.hourPredicate,
                                   )
                                 : widget.bottomPickerType ==
                                         BottomPickerType.year

lib/cupertino/cupertino_date_picker.dart

@@ -4,7 +4,6 @@
 library;
 
 import 'dart:math' as math;
-
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/scheduler.dart';
 
@@ -47,6 +46,9 @@ const double _kTimerPickerLabelFontSize = 17.0;
 // The width of each column of the countdown time picker.
 const double _kTimerPickerColumnIntrinsicWidth = 106;
 
+/// Signature for predicating hour for enabled hours selections.
+typedef SelectableHourPredicate = bool Function(int hour);
+
 TextStyle _themeTextStyle(BuildContext context, {bool isValid = true}) {
   final TextStyle style =
       CupertinoTheme.of(context).textTheme.dateTimePickerTextStyle;
@@ -284,6 +286,7 @@ class CupertinoDatePickerWidget extends StatefulWidget {
     this.selectionOverlayBuilder,
     this.showTimeSeparator = false,
     this.calendarDays = fullWeek,
+    this.selectableHourPredicate,
   })  : initialDateTime = initialDateTime ?? DateTime.now(),
         assert(
           itemExtent > 0,
@@ -336,6 +339,11 @@ class CupertinoDatePickerWidget extends StatefulWidget {
       this.initialDateTime.minute % minuteInterval == 0,
       'initial minute is not divisible by minute interval',
     );
+    assert(
+      (selectableHourPredicate == null) ||
+          (selectableHourPredicate?.call(this.initialDateTime.hour) == true),
+      'Hour must satisfy the hour predicate',
+    );
   }
 
   /// The mode of the date picker as one of [CupertinoDatePickerMode]. Defaults
@@ -468,6 +476,9 @@ class CupertinoDatePickerWidget extends StatefulWidget {
   /// {@end-tool}
   final SelectionOverlayBuilder? selectionOverlayBuilder;
 
+  //TODO add docs
+  final SelectableHourPredicate? selectableHourPredicate;
+
   static const List<int> fullWeek = <int>[
     DateTime.monday,
     DateTime.tuesday,
@@ -853,6 +864,8 @@ class _CupertinoDatePickerDateTimeState
 
     if (isDateInvalid) {
       return;
+    } else if (widget.selectableHourPredicate?.call(selected.hour) == false) {
+      return;
     }
 
     widget.onDateTimeChanged(selected);
@@ -939,18 +952,23 @@ class _CupertinoDatePickerDateTimeState
   // `hourIndex`, is it possible to change the value of the minute picker, so
   // that the resulting date stays in the valid range.
   bool _isValidHour(int meridiemIndex, int hourIndex) {
+    int selectedHour = _selectedHour(meridiemIndex, hourIndex);
     final DateTime rangeStart = DateTime(
       initialDateTime.year,
       initialDateTime.month,
       initialDateTime.day + selectedDayFromInitial,
-      _selectedHour(meridiemIndex, hourIndex),
+      selectedHour,
     );
 
     // The end value of the range is exclusive, i.e. [rangeStart, rangeEnd).
     final DateTime rangeEnd = rangeStart.add(const Duration(hours: 1));
 
+    bool hourInIntevalPredicate =
+        widget.selectableHourPredicate?.call(selectedHour) ?? true;
+
     return (widget.minimumDate?.isBefore(rangeEnd) ?? true) &&
-        !(widget.maximumDate?.isBefore(rangeStart) ?? false);
+        !(widget.maximumDate?.isBefore(rangeStart) ?? false) &&
+        hourInIntevalPredicate;
   }
 
   Widget _buildHourPicker(
@@ -1176,6 +1194,24 @@ class _CupertinoDatePickerDateTimeState
     }
   }
 
+  void _checkOnHourDisplay() {
+    final DateTime selectedDate = selectedDateTime;
+    final bool minCheck = widget.minimumDate?.isAfter(selectedDate) ?? false;
+
+    if (widget.selectableHourPredicate?.call(selectedDate.hour) == false) {
+      const int daysThreshold = 1;
+      final DateTime targetDate =
+          selectedDate.add(const Duration(hours: daysThreshold));
+
+      _scrollToDate(
+        targetDate,
+        selectedDate,
+        minCheck,
+        newItemIndex: dateController.selectedItem + daysThreshold,
+      );
+    }
+  }
+
   // One or more pickers have just stopped scrolling.
   void _pickerDidStopScrolling() {
     // Call setState to update the greyed out date/hour/minute/meridiem.
@@ -1193,6 +1229,7 @@ class _CupertinoDatePickerDateTimeState
     final bool maxCheck = widget.maximumDate?.isBefore(selectedDate) ?? false;
 
     _checkOnCustomDaysDisplay();
+    _checkOnHourDisplay();
     if (minCheck || maxCheck) {
       // We have minCheck === !maxCheck.
       final DateTime targetDate =

lib/widgets/date_picker.dart

@@ -15,6 +15,7 @@ class DatePicker extends StatelessWidget {
   final bool showTimeSeparator;
   final List<int> calendarDays;
   final CupertinoTextThemeData? pickerThemeData;
+  final SelectableHourPredicate? hourPredicate;
 
   const DatePicker({
     super.key,
@@ -31,6 +32,7 @@ class DatePicker extends StatelessWidget {
     this.showTimeSeparator = false,
     this.calendarDays = CupertinoDatePickerWidget.fullWeek,
     this.pickerThemeData,
+    this.hourPredicate,
   });
 
   @override
@@ -46,6 +48,7 @@ class DatePicker extends StatelessWidget {
         itemExtent: itemExtent ?? 0,
         showTimeSeparator: showTimeSeparator,
         mode: mode,
+        selectableHourPredicate: hourPredicate,
         onDateTimeChanged: onDateChanged,
         initialDateTime: initialDateTime,
         minuteInterval: minuteInterval,