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

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

static NSString * const kKBSvipDecorationViewKind = @"KBSvipBenefitBgDecoration";

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

@implementation KBSvipFlowLayout

- (instancetype)init {
    if (self = [super init]) {
        _decorationSection = 1; // 默认 Section 1 需要背景
        [self registerClass:[KBSvipBenefitBgView class] forDecorationViewOfKind:kKBSvipDecorationViewKind];
    }
    return self;
}

- (void)prepareLayout {
    [super prepareLayout];
    
    self.decorationAttributes = [NSMutableArray array];
    
    NSInteger numberOfSections = [self.collectionView numberOfSections];
    if (self.decorationSection >= numberOfSections) { return; }
    
    NSInteger numberOfItems = [self.collectionView numberOfItemsInSection:self.decorationSection];
    if (numberOfItems == 0) { return; }
    
    // 获取 Section Header 的布局属性
    UICollectionViewLayoutAttributes *headerAttr = [self layoutAttributesForSupplementaryViewOfKind:UICollectionElementKindSectionHeader atIndexPath:[NSIndexPath indexPathForItem:0 inSection:self.decorationSection]];
    
    // 获取第一个和最后一个 item 的布局属性
    UICollectionViewLayoutAttributes *firstItemAttr = [self layoutAttributesForItemAtIndexPath:[NSIndexPath indexPathForItem:0 inSection:self.decorationSection]];
    UICollectionViewLayoutAttributes *lastItemAttr = [self layoutAttributesForItemAtIndexPath:[NSIndexPath indexPathForItem:numberOfItems - 1 inSection:self.decorationSection]];
    
    if (!firstItemAttr || !lastItemAttr) { return; }
    
    // 计算背景区域
    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:self.decorationSection];
    }
    
    CGFloat minY = CGRectGetMinY(headerAttr.frame);
    CGFloat maxY = CGRectGetMaxY(lastItemAttr.frame) + 16; // 底部留 16 间距
    CGFloat x = sectionInset.left;
    CGFloat width = self.collectionView.bounds.size.width - sectionInset.left - sectionInset.right;
    
    CGRect decorationFrame = CGRectMake(x, minY, width, maxY - minY);
    
    UICollectionViewLayoutAttributes *decorationAttr = [UICollectionViewLayoutAttributes layoutAttributesForDecorationViewOfKind:kKBSvipDecorationViewKind withIndexPath:[NSIndexPath indexPathForItem:0 inSection:self.decorationSection]];
    decorationAttr.frame = decorationFrame;
    decorationAttr.zIndex = -1; // 放在最底层
    
    [self.decorationAttributes addObject:decorationAttr];
}

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

@end