keyboard/keyBoard/Class/Pay/V/KBSvipFlowLayout.m

//
//  KBSvipFlowLayout.m
//  keyBoard
//
//  SVIP 页面自定义布局，支持多个 Section 背景装饰视图
//

#import "KBSvipFlowLayout.h"
#import "KBSvipBenefitBgView.h"

static NSString * const kKBSvipOuterBgKind = @"KBSvipOuterBgDecoration";    // 外层大背景（18圆角，包裹全部）
static NSString * const kKBSvipBenefitBgKind = @"KBSvipBenefitBgDecoration"; // 内层权益背景（15圆角）

#pragma mark - 外层大背景视图（18圆角，包裹订阅选项+权益列表）

@interface KBSvipOuterBgView : UICollectionReusableView
@end

@implementation KBSvipOuterBgView

- (instancetype)initWithFrame:(CGRect)frame {
    if (self = [super initWithFrame:frame]) {
        self.backgroundColor = [UIColor whiteColor];
        self.layer.cornerRadius = 18;
        self.layer.masksToBounds = YES;
    }
    return self;
}

@end

#pragma mark - KBSvipFlowLayout

@interface KBSvipFlowLayout ()
@property (nonatomic, strong) NSMutableArray<UICollectionViewLayoutAttributes *> *decorationAttributes;
@end

@implementation KBSvipFlowLayout

- (instancetype)init {
    if (self = [super init]) {
        _decorationSection = 1; // Section 1 是权益列表
        [self registerClass:[KBSvipOuterBgView class] forDecorationViewOfKind:kKBSvipOuterBgKind];
        [self registerClass:[KBSvipBenefitBgView class] forDecorationViewOfKind:kKBSvipBenefitBgKind];
    }
    return self;
}

- (void)prepareLayout {
    [super prepareLayout];
    
    self.decorationAttributes = [NSMutableArray array];
    
    NSInteger numberOfSections = [self.collectionView numberOfSections];
    if (numberOfSections < 2) { return; }
    
    NSInteger itemCount0 = [self.collectionView numberOfItemsInSection:0];
    NSInteger itemCount1 = [self.collectionView numberOfItemsInSection:1];
    if (itemCount0 == 0 || itemCount1 == 0) { return; }
    
    // 获取 Section 0 第一个 item
    UICollectionViewLayoutAttributes *firstItemAttr = [self layoutAttributesForItemAtIndexPath:[NSIndexPath indexPathForItem:0 inSection:0]];
    // 获取 Section 1 Header
    UICollectionViewLayoutAttributes *benefitHeaderAttr = [self layoutAttributesForSupplementaryViewOfKind:UICollectionElementKindSectionHeader atIndexPath:[NSIndexPath indexPathForItem:0 inSection:1]];
    // 获取 Section 1 最后一个 item
    UICollectionViewLayoutAttributes *lastBenefitAttr = [self layoutAttributesForItemAtIndexPath:[NSIndexPath indexPathForItem:itemCount1 - 1 inSection:1]];
    
    if (!firstItemAttr || !benefitHeaderAttr || !lastBenefitAttr) { return; }
    
    UIEdgeInsets sectionInset0 = [self insetForSection:0];
    UIEdgeInsets sectionInset1 = [self insetForSection:1];
    
    // 固定的外层背景边距（不跟随 Section inset）
    CGFloat outerPadding = 16;
    
    // 1. 外层大背景（18圆角）：固定距离屏幕左右 16
    {
        CGFloat minY = CGRectGetMinY(firstItemAttr.frame) - sectionInset0.top;
        CGFloat maxY = CGRectGetMaxY(lastBenefitAttr.frame) + 16;
        CGFloat x = outerPadding;
        CGFloat width = self.collectionView.bounds.size.width - outerPadding * 2;
        
        CGRect frame = CGRectMake(x, minY, width, maxY - minY);
        
        UICollectionViewLayoutAttributes *attr = [UICollectionViewLayoutAttributes layoutAttributesForDecorationViewOfKind:kKBSvipOuterBgKind withIndexPath:[NSIndexPath indexPathForItem:0 inSection:0]];
        attr.frame = frame;
        attr.zIndex = -2; // 最底层
        [self.decorationAttributes addObject:attr];
    }
    
    // 2. 内层权益背景（15圆角）：从 Section 1 Header 到 Section 1 底部，左右距离外层 8px
    {
        CGFloat innerPadding = 8; // 距离外层背景的边距
        CGFloat minY = CGRectGetMinY(benefitHeaderAttr.frame);
        CGFloat maxY = CGRectGetMaxY(lastBenefitAttr.frame) + 16;
        CGFloat x = outerPadding + innerPadding;
        CGFloat width = self.collectionView.bounds.size.width - (outerPadding + innerPadding) * 2;
        
        CGRect frame = CGRectMake(x, minY, width, maxY - minY);
        
        UICollectionViewLayoutAttributes *attr = [UICollectionViewLayoutAttributes layoutAttributesForDecorationViewOfKind:kKBSvipBenefitBgKind withIndexPath:[NSIndexPath indexPathForItem:0 inSection:1]];
        attr.frame = frame;
        attr.zIndex = -1; // 在外层背景之上
        [self.decorationAttributes addObject:attr];
    }
}

- (UIEdgeInsets)insetForSection:(NSInteger)section {
    UIEdgeInsets sectionInset = self.sectionInset;
    if ([self.collectionView.delegate respondsToSelector:@selector(collectionView:layout:insetForSectionAtIndex:)]) {
        sectionInset = [(id<UICollectionViewDelegateFlowLayout>)self.collectionView.delegate collectionView:self.collectionView layout:self insetForSectionAtIndex:section];
    }
    return sectionInset;
}

- (NSArray<__kindof UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect {
    NSMutableArray *attrs = [[super layoutAttributesForElementsInRect:rect] mutableCopy];
    
    for (UICollectionViewLayoutAttributes *decorationAttr in self.decorationAttributes) {
        if (CGRectIntersectsRect(rect, decorationAttr.frame)) {
            [attrs addObject:decorationAttr];
        }
    }
    
    return attrs;
}

- (UICollectionViewLayoutAttributes *)layoutAttributesForDecorationViewOfKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath {
    for (UICollectionViewLayoutAttributes *attr in self.decorationAttributes) {
        if ([attr.representedElementKind isEqualToString:elementKind] && attr.indexPath.section == indexPath.section) {
            return attr;
        }
    }
    return [super layoutAttributesForDecorationViewOfKind:elementKind atIndexPath:indexPath];
}

@end