//
//  CenterAlineCollectionViewLayout.swift
//  savePassword
//
//  Created by FFIB on 16/3/21.
//  Copyright © 2016年 FFIB. All rights reserved.
//

import UIKit

protocol WaterFlowCollectionViewLayoutDelegate: UICollectionViewDelegateFlowLayout {
    func collectionLayoutHasPrepared(_ collectionView: UICollectionView )
    func collectionViewLayout(collectionView: UICollectionView, sizeOfHeaderViewAtIndex indexpath: IndexPath) -> CGSize
}

class WaterFlowCollectionViewLayout: UICollectionViewFlowLayout {
    var paddingX: CGFloat = 6
    var paddingY: CGFloat = 6

    var layoutCacheLeft = [UICollectionViewLayoutAttributes]()
    var layoutCacheRight = [UICollectionViewLayoutAttributes]()
    var layoutCache = [UICollectionViewLayoutAttributes]()

    var headerHeight: CGFloat = 0

    override func prepare() {
        layoutCacheLeft.removeAll()
        layoutCacheRight.removeAll()
        guard let collectionView = collectionView else {
            return
        }
        headerHeight =  (collectionView.delegate as? UICollectionViewDelegateFlowLayout)?.collectionView!(self.collectionView!, layout: self, referenceSizeForHeaderInSection: 0).height ?? 0

        let lastRowHeight: CGFloat = headerHeight + 6
        for section in 0..<collectionView.numberOfSections {
            autoreleasepool(invoking: { () in
                let itemsCount = collectionView.numberOfItems(inSection: section)
                for row in 0..<itemsCount {
                    autoreleasepool(invoking: { ()  in
                        let indexPath = IndexPath(item: row, section: section)
                        var itemSize = CGSize(width: 10, height: 10)

                        if let layoutDelegate = collectionView.delegate as? UICollectionViewDelegateFlowLayout, let size = layoutDelegate.collectionView?(collectionView, layout: self, sizeForItemAt: indexPath) {
                            itemSize = size
                        }
                        let attributes = UICollectionViewLayoutAttributes(forCellWith: indexPath)
                        if layoutCacheLeft.count == 0 {
                            attributes.frame = CGRect(x: 0, y: lastRowHeight, width: itemSize.width, height: itemSize.height)
                            layoutCacheLeft.append(attributes)
                        } else if layoutCacheRight.count == 0 {
                            attributes.frame = CGRect(x: layoutCacheLeft.last!.frame.maxX + paddingX, y: lastRowHeight, width: itemSize.width, height: itemSize.height)
                            layoutCacheRight.append(attributes)
                        } else {
                            if Int((layoutCacheRight.last?.frame.maxY)!) >= Int((layoutCacheLeft.last?.frame.maxY)!) {
                                attributes.frame = CGRect(x: 0, y: layoutCacheLeft.last!.frame.maxY + paddingY, width: itemSize.width, height: itemSize.height)
                                layoutCacheLeft.append(attributes)

                            } else {
                                attributes.frame = CGRect(x: layoutCacheLeft.last!.frame.maxX + paddingX, y: layoutCacheRight.last!.frame.maxY + paddingY, width: itemSize.width, height: itemSize.height)
                                layoutCacheRight.append(attributes)

                            }
                        }

                    })
                }
            })

        }
                (collectionView.delegate as? WaterFlowCollectionViewLayoutDelegate)?.collectionLayoutHasPrepared(self.collectionView!)
    }

      override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        var result = [UICollectionViewLayoutAttributes]()
        let layoutCache = layoutCacheLeft + layoutCacheRight
        result = layoutCache.filter({ (attr) -> Bool in
            return attr.frame.intersects(rect)
        })
        if headerHeight != 0 {
            let size = CGSize(width: kScreenWidth, height: headerHeight)

            let headerAttributes = UICollectionViewLayoutAttributes(forSupplementaryViewOfKind: UICollectionElementKindSectionHeader, with: IndexPath(item: 0, section: 0))
            headerAttributes.frame = CGRect(x: 0, y: 0, width: (size.width), height: (size.height))
            headerAttributes.frame.intersects(rect)
            result.append(headerAttributes)

        }

        return result
    }

    override func layoutAttributesForSupplementaryView(ofKind elementKind: String, at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        return nil
    }

    override var collectionViewContentSize: CGSize {
        guard let collectionView = collectionView, let lastLeft = layoutCacheLeft.last else {
            return CGSize.zero
        }
        var height: CGFloat = 0
        if let lastRight = layoutCacheRight.last {
            height = max(lastLeft.frame.maxY, lastRight.frame.maxY)
        } else {
            height = lastLeft.frame.maxY
        }
        return CGSize(width: collectionView.frame.size.width, height: height)
    }
    func collectionViewVisiableMinSize() -> CGSize {
        guard let collectionView = collectionView, let lastLeft = layoutCacheLeft.last else {
            return CGSize.zero
        }
        var height: CGFloat = 0
        if let lastRight = layoutCacheRight.last {
            height = min(lastLeft.frame.maxY, lastRight.frame.maxY)
        } else {
            height = lastLeft.frame.maxY
        }
        return CGSize(width: collectionView.frame.size.width, height: height)
    }

}