CustomCollectionViewLayout copy.swift

//
//  CustomCollectionViewLayout.swift
//  YumaApp
//
//  Created by Yuma Usa on 2018-03-13.
//  Copyright © 2018 Yuma Usa. All rights reserved.
//

import UIKit

class CustomCollectionViewLayout: UICollectionViewLayout
{
	let CELL_HEIGHT: CGFloat = 30
	let CELL_WIDTH: CGFloat = 100
	
	var cellAttributesDictionary = Dictionary<IndexPath, UICollectionViewLayoutAttributes>()
	var contentSize = CGSize.zero
	var dataSourceDidUpdate = true

	
	override var collectionViewContentSize: CGSize
		{
		get
		{
			return contentSize
		}
	}
	
	
	override func prepare()
	{
		let STATUS_BAR_HEIGHT = UIApplication.shared.statusBarFrame.height
		let NAV_BAR_HEIGHT = UINavigationController().navigationBar.frame.size.height
		
		collectionView?.bounces = false
		
		if !dataSourceDidUpdate
		{
			let yOffSet = collectionView!.contentOffset.y
			
			for section in 0 ..< collectionView!.numberOfSections
			{
				if section == 0
				{
					for item in 0 ..< collectionView!.numberOfItems(inSection: section)
					{
						let cellIndexPath = IndexPath(item: item, section: section)
						if let attrs = cellAttributesDictionary[cellIndexPath]
						{
							var frame = attrs.frame
							frame.origin.y = yOffSet + STATUS_BAR_HEIGHT + NAV_BAR_HEIGHT
							attrs.frame = frame
						}
					}
				}
			}
			return
		}
		
		dataSourceDidUpdate = false
		
		for section in 0 ..< collectionView!.numberOfSections
		{
			for item in 0 ..< collectionView!.numberOfItems(inSection: section)
			{
				let cellIndexPath = IndexPath(item: item, section: section)
				let xPos = CGFloat(item) * CELL_WIDTH
				let yPos = CGFloat(section) * CELL_HEIGHT
				
				let cellAttributes = UICollectionViewLayoutAttributes(forCellWith: cellIndexPath)
				cellAttributes.frame = CGRect(x: xPos, y: yPos, width: CELL_WIDTH, height: CELL_HEIGHT)
				
				// Determine zIndex based on cell type.
				if section == 0 && item == 0
				{
					cellAttributes.zIndex = 4
				}
				else if section == 0
				{
					cellAttributes.zIndex = 3
				}
				else if item == 0
				{
					cellAttributes.zIndex = 2
				}
				else
				{
					cellAttributes.zIndex = 1
				}
				
				cellAttributesDictionary[cellIndexPath] = cellAttributes
				
			}
		}
		let contentWidth = CGFloat(collectionView!.numberOfItems(inSection: 0)) * CELL_WIDTH
		let contentHeight = CGFloat(collectionView!.numberOfSections) * CELL_HEIGHT
		contentSize = CGSize(width: contentWidth, height: contentHeight)
	}

	
	override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]?
	{
		var attributesInRect = [UICollectionViewLayoutAttributes]()
		
		for cellAttrs in cellAttributesDictionary.values
		{
			if rect.intersects(cellAttrs.frame)
			{
				attributesInRect.append(cellAttrs)
			}
		}
		
		return attributesInRect
	}
	
	
	override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes?
	{
		return cellAttributesDictionary[indexPath]
	}
	
	
	override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool
	{
		return true
	}

}