[Sources] [DatePickerView+Protected] Add `dateForFirstDayInCurrentSec…

…tion`.

#126, #133, #135

RSDayFlow/RSDFDatePickerView+Protected.h

@@ -34,6 +34,11 @@ NS_ASSUME_NONNULL_BEGIN
  */
 @interface RSDFDatePickerView (RSDFDatePickerViewProtectedMethods)
 
+/**
+ The date of the first day of the month that corresponds to the currently visible section in the date picker view.
+ */
+@property (nonatomic, readonly, nullable) NSDate *dateForFirstDayInCurrentSection;
+
 /**
  Returns the date that corresponds to the specified cell in the date picker view.
  

RSDayFlow/RSDFDatePickerView.m

@@ -194,6 +194,32 @@ - (Class)collectionViewLayoutClass
     return [RSDFDatePickerCollectionViewLayout class];
 }
 
+- (NSDate *)dateForFirstDayInCurrentSection
+{
+    CGPoint point = [self.collectionView.superview convertPoint:self.collectionView.center toView:self.collectionView];
+    NSIndexPath *indexPath = [self.collectionView indexPathForItemAtPoint:point];
+    if (indexPath == nil) {
+
+        NSArray<UICollectionViewLayoutAttributes *> *layoutAttributesArray = [self.collectionView.collectionViewLayout layoutAttributesForElementsInRect:self.collectionView.bounds];
+        if (layoutAttributesArray.count == 0) {
+
+            return nil;
+        }
+
+        for (UICollectionViewLayoutAttributes *layoutAttributes in layoutAttributesArray) {
+
+            if (CGRectContainsPoint(layoutAttributes.frame, point) == YES) {
+
+                return [self dateForFirstDayInSection:layoutAttributes.indexPath.section];
+            }
+        }
+
+        return nil;
+    }
+
+    return [self dateForFirstDayInSection:indexPath.section];
+}
+
 - (Class)dayCellClass
 {
     return [RSDFDatePickerDayCell class];