Add content inset support via layout margins

Sources/Internal/FrameProvider.swift

@@ -13,8 +13,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-import CoreGraphics
-import Foundation
+import UIKit
 
 /// Provides frame and size information about all core layout items. The calendar is laid out lazily, starting with an initial known layout
 /// frame (like the frame of an initially visible month header). All subsequent layout calculations are done by laying out items adjacent to
@@ -26,17 +25,19 @@ final class FrameProvider {
   init(
     content: CalendarViewContent,
     size: CGSize,
+    layoutMargins: NSDirectionalEdgeInsets,
     scale: CGFloat,
     monthHeaderHeight: CGFloat)
   {
     self.content = content
     self.size = size
+    self.layoutMargins = layoutMargins
     self.scale = scale
     self.monthHeaderHeight = monthHeaderHeight
 
     switch content.monthsLayout {
     case .vertical:
-      monthWidth = size.width
+      monthWidth = size.width - layoutMargins.leading - layoutMargins.trailing
     case .horizontal(let _monthWidth):
       monthWidth = _monthWidth
     }
@@ -53,6 +54,7 @@ final class FrameProvider {
   // MARK: Internal
 
   let size: CGSize
+  let layoutMargins: NSDirectionalEdgeInsets
   let scale: CGFloat
   let daySize: CGSize
 

Sources/Internal/VisibleItemsProvider.swift

@@ -26,6 +26,7 @@ final class VisibleItemsProvider {
     calendar: Calendar,
     content: CalendarViewContent,
     size: CGSize,
+    layoutMargins: NSDirectionalEdgeInsets,
     scale: CGFloat,
     monthHeaderHeight: CGFloat)
   {
@@ -38,6 +39,7 @@ final class VisibleItemsProvider {
     frameProvider = FrameProvider(
       content: content,
       size: size,
+      layoutMargins: layoutMargins,
       scale: scale,
       monthHeaderHeight: monthHeaderHeight)
   }
@@ -50,6 +52,10 @@ final class VisibleItemsProvider {
     frameProvider.size
   }
 
+  var layoutMargins: NSDirectionalEdgeInsets {
+    frameProvider.layoutMargins
+  }
+
   var scale: CGFloat {
     frameProvider.scale
   }
@@ -701,18 +707,19 @@ final class VisibleItemsProvider {
       switch content.monthsLayout {
       case .vertical(let options):
         minimumScrollOffset = monthFrame.minY -
-          (options.pinDaysOfWeekToTop ? frameProvider.daySize.height : 0)
+          (options.pinDaysOfWeekToTop ? frameProvider.daySize.height : 0) -
+          layoutMargins.top
       case .horizontal:
-        minimumScrollOffset = monthFrame.minX
+        minimumScrollOffset = monthFrame.minX - layoutMargins.leading
       }
     }
 
     if month == content.dayRange.upperBound.month {
       switch content.monthsLayout {
       case .vertical:
-        maximumScrollOffset = monthFrame.maxY
+        maximumScrollOffset = monthFrame.maxY + layoutMargins.bottom
       case .horizontal:
-        maximumScrollOffset = monthFrame.maxX
+        maximumScrollOffset = monthFrame.maxX + layoutMargins.trailing
       }
     }
   }

Sources/Public/CalendarView.swift

@@ -142,6 +142,28 @@ public final class CalendarView: UIView {
     }
   }
 
+  /// `CalendarView` only supports positive values for `layoutMargins`. Negative values will be changed to `0`.
+  public override var layoutMargins: UIEdgeInsets {
+    didSet {
+      super.layoutMargins = UIEdgeInsets(
+        top: max(layoutMargins.top, 0),
+        left: max(layoutMargins.left, 0),
+        bottom: max(layoutMargins.bottom, 0),
+        right: max(layoutMargins.right, 0))
+    }
+  }
+
+  /// `CalendarView` only supports positive values for `directionalLayoutMargins`. Negative values will be changed to `0`.
+  public override var directionalLayoutMargins: NSDirectionalEdgeInsets {
+    didSet {
+      super.directionalLayoutMargins = NSDirectionalEdgeInsets(
+        top: max(directionalLayoutMargins.top, 0),
+        leading: max(directionalLayoutMargins.leading, 0),
+        bottom: max(directionalLayoutMargins.bottom, 0),
+        trailing: max(directionalLayoutMargins.trailing, 0))
+    }
+  }
+
   public override func didMoveToWindow() {
     super.didMoveToWindow()
 
@@ -150,6 +172,10 @@ public final class CalendarView: UIView {
     }
   }
 
+  public override func layoutMarginsDidChange() {
+    setNeedsLayout()
+  }
+
   public override func layoutSubviews() {
     super.layoutSubviews()
 
@@ -388,6 +414,7 @@ public final class CalendarView: UIView {
     if
       let existingVisibleItemsProvider = _visibleItemsProvider,
       existingVisibleItemsProvider.size == bounds.size,
+      existingVisibleItemsProvider.layoutMargins == directionalLayoutMargins,
       existingVisibleItemsProvider.scale == scale
     {
       return existingVisibleItemsProvider
@@ -396,6 +423,7 @@ public final class CalendarView: UIView {
         calendar: calendar,
         content: content,
         size: bounds.size,
+        layoutMargins: directionalLayoutMargins,
         scale: scale,
         monthHeaderHeight: monthHeaderHeight())
       _visibleItemsProvider = visibleItemsProvider
@@ -404,9 +432,12 @@ public final class CalendarView: UIView {
   }
 
   private var initialMonthHeaderAnchorLayoutItem: LayoutItem {
-    visibleItemsProvider.anchorMonthHeaderItem(
+    let offset = CGPoint(
+      x: scrollView.contentOffset.x + directionalLayoutMargins.leading,
+      y: scrollView.contentOffset.y + directionalLayoutMargins.top)
+    return visibleItemsProvider.anchorMonthHeaderItem(
       for: content.monthRange.lowerBound,
-      offset: scrollView.contentOffset,
+      offset: offset,
       scrollPosition: .firstFullyVisiblePosition)
   }
 

Tests/FrameProviderTests.swift

@@ -39,6 +39,7 @@ final class FrameProviderTests: XCTestCase {
         .withVerticalDayMargin(20)
         .withHorizontalDayMargin(10),
       size: size,
+      layoutMargins: .zero,
       scale: 3,
       monthHeaderHeight: monthHeaderHeight)
     verticalPinnedDaysOfWeekFrameProvider = FrameProvider(
@@ -51,6 +52,7 @@ final class FrameProviderTests: XCTestCase {
         .withVerticalDayMargin(20)
         .withHorizontalDayMargin(10),
       size: size,
+      layoutMargins: .zero,
       scale: 3,
       monthHeaderHeight: monthHeaderHeight)
     verticalPartialMonthFrameProvider = FrameProvider(
@@ -64,6 +66,7 @@ final class FrameProviderTests: XCTestCase {
         .withVerticalDayMargin(20)
         .withHorizontalDayMargin(10),
       size: size,
+      layoutMargins: .zero,
       scale: 3,
       monthHeaderHeight: monthHeaderHeight)
     horizontalFrameProvider = FrameProvider(
@@ -76,6 +79,7 @@ final class FrameProviderTests: XCTestCase {
         .withVerticalDayMargin(20)
         .withHorizontalDayMargin(10),
       size: size,
+      layoutMargins: .zero,
       scale: 3,
       monthHeaderHeight: monthHeaderHeight)
   }

Tests/VisibleItemsProviderTests.swift

@@ -1535,6 +1535,7 @@ final class VisibleItemsProviderTests: XCTestCase {
         visibleDateRange: dateRange,
         monthsLayout: .vertical(options: VerticalMonthsLayoutOptions()))),
     size: size,
+    layoutMargins: .zero,
     scale: 2,
     monthHeaderHeight: 50)
 
@@ -1546,6 +1547,7 @@ final class VisibleItemsProviderTests: XCTestCase {
         visibleDateRange: dateRange,
         monthsLayout: .vertical(options: VerticalMonthsLayoutOptions(pinDaysOfWeekToTop: true)))),
     size: size,
+    layoutMargins: .zero,
     scale: 2,
     monthHeaderHeight: 50)
 
@@ -1558,6 +1560,7 @@ final class VisibleItemsProviderTests: XCTestCase {
         monthsLayout: .vertical(
           options: VerticalMonthsLayoutOptions(alwaysShowCompleteBoundaryMonths: false)))),
     size: size,
+    layoutMargins: .zero,
     scale: 2,
     monthHeaderHeight: 50)
 
@@ -1569,6 +1572,7 @@ final class VisibleItemsProviderTests: XCTestCase {
         visibleDateRange: dateRange,
         monthsLayout: .horizontal(monthWidth: 300))),
     size: size,
+    layoutMargins: .zero,
     scale: 2,
     monthHeaderHeight: 50)