@interface HACollectionViewFlowLayout : UICollectionViewFlowLayout

@end

#import "HACollectionViewFlowLayout.h"

@interface HACollectionViewFlowLayout ()

/// 缩放系数
@property (nonatomic, assign) CGFloat scaleFactor;

/// 这个值越大，缩放比例越不明显，最小不能小于item的宽度
@property (nonatomic, assign) CGFloat activeDistance;

@end

@implementation HACollectionViewFlowLayout

/// 初始化
- (instancetype)init {
    self = [super init];
    if (self) {
        self.scaleFactor = 0.5;
        self.activeDistance = 130;
    }
    return self;
}

/// 要展示的cell的属性
- (NSArray<UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect {
    
    NSArray *array = [super layoutAttributesForElementsInRect: rect];
    
    CGRect frame = CGRectMake(self.collectionView.contentOffset.x, self.collectionView.contentOffset.y, self.collectionView.bounds.size.width, self.collectionView.bounds.size.height);
    
    for (UICollectionViewLayoutAttributes *attribute in array) {
        /// 确立cell相对于屏幕中央的距离
        CGFloat distance = CGRectGetMidX(frame) - attribute.center.x;
        /// 到中心位置的相对于x的比例,原则就是越近的越大，越远的越小。
        CGFloat normalDistance = fabs(distance / self.activeDistance);
        CGFloat scale = 1 - self.scaleFactor * normalDistance;
        CGFloat alpha = 1 - normalDistance;
        attribute.transform3D = CATransform3DMakeScale(scale, scale, 1);
        attribute.alpha = alpha;
        attribute.zIndex = alpha * 100;
    }
    return array;
}

/// 确定最终滚到的位置
- (CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset withScrollingVelocity:(CGPoint)velocity {
    CGRect targetRect = CGRectMake(proposedContentOffset.x, proposedContentOffset.y, self.collectionView.bounds.size.width, self.collectionView.bounds.size.height);
    NSArray *array = [super layoutAttributesForElementsInRect: targetRect];
    CGFloat horizontalCenterX = proposedContentOffset.x + self.collectionView.bounds.size.width / 2.;
    CGFloat offsetAdjustment = CGFLOAT_MAX;
    for (UICollectionViewLayoutAttributes *attribute in array) {
        CGFloat tempCenterX = attribute.center.x;
        if (fabs(horizontalCenterX - tempCenterX) < fabs(offsetAdjustment)) {
            offsetAdjustment = tempCenterX - horizontalCenterX;
        }
    }
    return CGPointMake(proposedContentOffset.x + offsetAdjustment, proposedContentOffset.y);
}

- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds {
    return YES;
}

@end

@interface HACycleHeadCollectionViewCell : UICollectionViewCell

@property (nonatomic, assign) NSInteger index;

/// 头像
@property (nonatomic, strong) UIImageView *imgHead;

@end

#import "HACycleHeadCollectionViewCell.h"

@implementation HACycleHeadCollectionViewCell

/// 初始化
- (instancetype)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];
    if (self) {
        
        self.contentView.backgroundColor = [UIColor clearColor];
        
        UIView *layerView = [[UIView alloc] initWithFrame: self.bounds];
        layerView.backgroundColor = HAHexColor(DDDDDD);
        layerView.layer.shadowColor = HAHexColor(DDDDDD).CGColor;
        layerView.layer.shadowOffset = CGSizeMake(0, 0);
        layerView.layer.shadowRadius = 2;
        layerView.layer.cornerRadius = frame.size.width * 0.5;
        layerView.layer.shadowOpacity = 0.7;
        [self.contentView addSubview: layerView];
        
        _imgHead = [[UIImageView alloc] initWithFrame: CGRectMake(0, 0, frame.size.width, frame.size.height)];
        _imgHead.layer.cornerRadius = frame.size.width * 0.5;
        _imgHead.layer.contentMode = UIViewContentModeScaleAspectFill;
        _imgHead.layer.borderWidth = 2;
        _imgHead.layer.borderColor = [UIColor whiteColor].CGColor;
        _imgHead.layer.masksToBounds = YES;
        [self.contentView addSubview: _imgHead];
        
    }
    return self;
}

@end

@interface HACycleHeadView : UIView

/// 自动滚动时间间隔，大于0开启自动轮播
@property (nonatomic, assign) CGFloat timerInterval;

@end

#import "HACycleHeadView.h"
#import "HACollectionViewFlowLayout.h"
#import "HACycleHeadCollectionViewCell.h"

static NSInteger sectionCount = 1000;

@interface HACycleHeadView () <UICollectionViewDelegate, UICollectionViewDataSource>

/// 存储图片
@property (nonatomic, strong) NSMutableArray<NSString *> *imageArr;

/// collectionView
@property (nonatomic, strong) UICollectionView *collectionView;

/// 计时器
@property (nonatomic, strong) NSTimer *timer;

@end

@implementation HACycleHeadView

/// 初始化
- (instancetype)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];
    if (self) {
        
        self.backgroundColor = [UIColor clearColor];
        
        _imageArr = [NSMutableArray arrayWithArray: @[
            @"cycle_head_1", @"cycle_head_2",
            @"cycle_head_3", @"cycle_head_4",
            @"cycle_head_5", @"cycle_head_6",
            @"cycle_head_7", @"cycle_head_8",
            @"cycle_head_9", @"cycle_head_10",
            @"cycle_head_11", @"cycle_head_12",
            @"cycle_head_13", @"cycle_head_14",
            @"cycle_head_15", @"cycle_head_16",
            @"cycle_head_17", @"cycle_head_18",
            @"cycle_head_19", @"cycle_head_20"
        ]];
        
        HACollectionViewFlowLayout *layout = [[HACollectionViewFlowLayout alloc] init];
        layout.scrollDirection = UICollectionViewScrollDirectionHorizontal;
        layout.minimumLineSpacing = -60;
        layout.minimumInteritemSpacing = 0.0;
        layout.itemSize = CGSizeMake(110, 110);
        layout.sectionInset = UIEdgeInsetsMake(0, -30, 0, -30);
        
        _collectionView = [[UICollectionView alloc] initWithFrame: CGRectMake((frame.size.width - 270) * 0.5, (frame.size.height - 110) * 0.5, 270, 110) collectionViewLayout: layout];
        _collectionView.delegate = self;
        _collectionView.dataSource = self;
        _collectionView.showsHorizontalScrollIndicator = NO;
        _collectionView.backgroundColor = [UIColor clearColor];
        [_collectionView registerClass: [HACycleHeadCollectionViewCell class] forCellWithReuseIdentifier: @"HACycleHeadCollectionViewCell"];
        [self addSubview: _collectionView];
        
        if (@available(iOS 11.0, *)) {
            _collectionView.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;
        }
    }
    return self;
}

- (void)layoutSubviews {
    [super layoutSubviews];
    if (!CGRectEqualToRect(_collectionView.frame, CGRectZero)) {
        [_collectionView scrollToItemAtIndexPath: [NSIndexPath indexPathForRow: 0 inSection: sectionCount / 2] atScrollPosition: UICollectionViewScrollPositionCenteredHorizontally animated: NO];
    }
}

/// 组个数
- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {
    return sectionCount;
}

/// cell个数
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
    return _imageArr.count;
}

/// cell样式
- (__kindof UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    HACycleHeadCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier: @"HACycleHeadCollectionViewCell" forIndexPath: indexPath];
    cell.index = indexPath.row;
    NSString *imageUrl = _imageArr[indexPath.row];
    if ([imageUrl hasPrefix: @"http"]) {
        [cell.imgHead ol_setHeadImageWithURL: imageUrl];
    } else {
        cell.imgHead.image = [UIImage imageNamed: imageUrl];
    }
    return cell;
}

/// 点击cell
- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath {
    NSIndexPath *index = [self indexPathForMiddleVisibleCell];
    if (index.row == indexPath.row) {
        return;
    }
    [self removeTimer];
    _collectionView.userInteractionEnabled = NO;
    [_collectionView scrollToItemAtIndexPath: indexPath atScrollPosition: UICollectionViewScrollPositionCenteredHorizontally animated: YES];
}

/// 滚动动画结束
- (void)scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView {
    _collectionView.userInteractionEnabled = YES;
    [self addTimer];
}

/// scrollView开始拖拽
- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {
    [self removeTimer];
}

/// scrollView结束拖拽
- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset {
    _collectionView.userInteractionEnabled = YES;
    [self addTimer];
}

/// scrollView结束拖拽
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {
    _collectionView.userInteractionEnabled = YES;
    [self addTimer];
}

/// 中间的indexPath
- (NSIndexPath *)indexPathForMiddleVisibleCell {
    return [_collectionView indexPathForItemAtPoint: CGPointMake(_collectionView.contentOffset.x + _collectionView.frame.size.width / 2, 0)];
}

/// 计时器回调
- (void)timeHandle {
    
    _collectionView.userInteractionEnabled = NO;
    
    NSInteger itemsCount = _imageArr.count;
    __block NSIndexPath *index = [self indexPathForMiddleVisibleCell];
    
    [UIView animateWithDuration: 0.001 animations:^{
        if (index.row == itemsCount - 1) {
            index = [NSIndexPath indexPathForRow: index.row inSection: sectionCount / 2 - 1];
        } else {
            index = [NSIndexPath indexPathForRow: index.row inSection: sectionCount / 2];
        }
        [self.collectionView scrollToItemAtIndexPath: index atScrollPosition: UICollectionViewScrollPositionCenteredHorizontally animated: NO];
    } completion:^(BOOL finished) {
        if (index.row == itemsCount - 1) {
            index = [NSIndexPath indexPathForRow: 0 inSection: sectionCount / 2];
        } else {
            index = [NSIndexPath indexPathForRow: index.row + 1 inSection: sectionCount / 2];
        }
        [self.collectionView scrollToItemAtIndexPath: index atScrollPosition: UICollectionViewScrollPositionCenteredHorizontally animated: YES];
    }];
}

/// 设置自动滚动时间间隔
- (void)setTimerInterval:(CGFloat)timerInterval {
    _timerInterval = timerInterval;
    [self addTimer];
}

/// 添加计时器
- (void)addTimer {
    if (_timerInterval > 0 && !_timer) {
        _timer = [NSTimer scheduledTimerWithTimeInterval: _timerInterval target: self selector: @selector(timeHandle) userInfo: nil repeats: YES];
    }
}

/// 移除计时器
- (void)removeTimer {
    if (_timer) {
        [_timer invalidate];
        _timer = nil;
    }
}

/// 移除
- (void)removeFromSuperview {
    [super removeFromSuperview];
    [self removeTimer];
}

@end