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keyBoard/Class/Vender/UICollectionViewLeftAlignedLayout/UICollectionViewLeftAlignedLayout.m

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+// Copyright (c) 2014-2023 Giovanni Lodi
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy of
+// this software and associated documentation files (the "Software"), to deal in
+// the Software without restriction, including without limitation the rights to
+// use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+// the Software, and to permit persons to whom the Software is furnished to do so,
+// subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+// FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+// COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+// IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+// CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+#import "UICollectionViewLeftAlignedLayout.h"
+
+@interface UICollectionViewLayoutAttributes (LeftAligned)
+
+- (void)leftAlignFrameWithSectionInset:(UIEdgeInsets)sectionInset;
+
+@end
+
+@implementation UICollectionViewLayoutAttributes (LeftAligned)
+
+- (void)leftAlignFrameWithSectionInset:(UIEdgeInsets)sectionInset
+{
+    CGRect frame = self.frame;
+    frame.origin.x = sectionInset.left;
+    self.frame = frame;
+}
+
+@end
+
+#pragma mark -
+
+@implementation UICollectionViewLeftAlignedLayout
+
+#pragma mark - UICollectionViewLayout
+
+- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect {
+    NSArray *originalAttributes = [super layoutAttributesForElementsInRect:rect];
+    NSMutableArray *updatedAttributes = [NSMutableArray arrayWithArray:originalAttributes];
+    for (UICollectionViewLayoutAttributes *attributes in originalAttributes) {
+        if (!attributes.representedElementKind) {
+            NSUInteger index = [updatedAttributes indexOfObject:attributes];
+            updatedAttributes[index] = [self layoutAttributesForItemAtIndexPath:attributes.indexPath];
+        }
+    }
+
+    return updatedAttributes;
+}
+
+- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath {
+    UICollectionViewLayoutAttributes* currentItemAttributes = [[super layoutAttributesForItemAtIndexPath:indexPath] copy];
+    UIEdgeInsets sectionInset = [self evaluatedSectionInsetForItemAtIndex:indexPath.section];
+
+    BOOL isFirstItemInSection = indexPath.item == 0;
+    CGFloat layoutWidth = CGRectGetWidth(self.collectionView.frame) - sectionInset.left - sectionInset.right;
+
+    if (isFirstItemInSection) {
+        [currentItemAttributes leftAlignFrameWithSectionInset:sectionInset];
+        return currentItemAttributes;
+    }
+
+    NSIndexPath* previousIndexPath = [NSIndexPath indexPathForItem:indexPath.item-1 inSection:indexPath.section];
+    CGRect previousFrame = [self layoutAttributesForItemAtIndexPath:previousIndexPath].frame;
+    CGFloat previousFrameRightPoint = previousFrame.origin.x + previousFrame.size.width;
+    CGRect currentFrame = currentItemAttributes.frame;
+    CGRect strecthedCurrentFrame = CGRectMake(sectionInset.left,
+                                              currentFrame.origin.y,
+                                              layoutWidth,
+                                              currentFrame.size.height);
+    // if the current frame, once left aligned to the left and stretched to the full collection view
+    // width intersects the previous frame then they are on the same line
+    BOOL isFirstItemInRow = !CGRectIntersectsRect(previousFrame, strecthedCurrentFrame);
+
+    if (isFirstItemInRow) {
+        // make sure the first item on a line is left aligned
+        [currentItemAttributes leftAlignFrameWithSectionInset:sectionInset];
+        return currentItemAttributes;
+    }
+
+    CGRect frame = currentItemAttributes.frame;
+    frame.origin.x = previousFrameRightPoint + [self evaluatedMinimumInteritemSpacingForSectionAtIndex:indexPath.section];
+    currentItemAttributes.frame = frame;
+    return currentItemAttributes;
+}
+
+- (CGFloat)evaluatedMinimumInteritemSpacingForSectionAtIndex:(NSInteger)sectionIndex
+{
+    if ([self.collectionView.delegate respondsToSelector:@selector(collectionView:layout:minimumInteritemSpacingForSectionAtIndex:)]) {
+        id<UICollectionViewDelegateLeftAlignedLayout> delegate = (id<UICollectionViewDelegateLeftAlignedLayout>)self.collectionView.delegate;
+
+        return [delegate collectionView:self.collectionView layout:self minimumInteritemSpacingForSectionAtIndex:sectionIndex];
+    } else {
+        return self.minimumInteritemSpacing;
+    }
+}
+
+- (UIEdgeInsets)evaluatedSectionInsetForItemAtIndex:(NSInteger)index
+{
+    if ([self.collectionView.delegate respondsToSelector:@selector(collectionView:layout:insetForSectionAtIndex:)]) {
+        id<UICollectionViewDelegateLeftAlignedLayout> delegate = (id<UICollectionViewDelegateLeftAlignedLayout>)self.collectionView.delegate;
+
+        return [delegate collectionView:self.collectionView layout:self insetForSectionAtIndex:index];
+    } else {
+        return self.sectionInset;
+    }
+}
+
+@end