vds_ios/VDS/Components/Tilelet/TileletGroup/TileletGroupPositionLayout.swift

//
//  TileletGroupPositionLayout.swift
//  VDS
//
//  Created by Matt Bruce on 10/8/24.
//

import Foundation
import UIKit

class TileletCollectionViewRow {
    var attributes = [TileletLayoutAttributes]()
    
    init() {}

    func add(attribute: TileletLayoutAttributes) {
        attributes.append(attribute)
    }

    var rowWidth: CGFloat {
        return attributes.reduce(0, { result, attribute -> CGFloat in
            return result + attribute.frame.width + attribute.spacing
        })
    }
    
    var rowHeight: CGFloat {
        attributes.compactMap{$0.frame.height}.max() ?? 0
    }

    var maxHeightIndexPath: IndexPath {
        let maxHeight = rowHeight
        return attributes.first(where: {$0.frame.height == maxHeight})!.indexPath
    }
    
    var rowY: CGFloat = 0 {
        didSet {
            for attribute in attributes {
                attribute.frame.origin.y = rowY
            }
        }
    }

    func layout(with collectionViewWidth: CGFloat){
        var offset = 0.0
        let height = rowHeight

        attributes.last?.spacing = 0
        
        for attribute in attributes {
            attribute.frame.origin.x = offset
            if attribute.frame.height < height {
                //recalibrate the y to vertically center align rect
                attribute.frame.origin.y += (height - attribute.frame.size.height) / 2
            }
            offset += attribute.frame.width + attribute.spacing
        }
    }
}

protocol TileletGroupPositionLayoutDelegate: AnyObject {
    func collectionView(_ collectionView: UICollectionView, sizeForItemAtIndexPath indexPath: IndexPath) -> CGSize
    func collectionView(_ collectionView: UICollectionView, tileletAtIndexPath indexPath: IndexPath) -> Tilelet
}

class TileletLayoutAttributes: UICollectionViewLayoutAttributes{
    var spacing: CGFloat = 0
    
    var tilelet: Tilelet?

    convenience init(spacing: CGFloat,
                     tilelet: Tilelet,
                     forCellWith indexPath: IndexPath) {
        self.init(forCellWith: indexPath)
        self.spacing = spacing
        self.tilelet = tilelet
    }
}

class TileletGroupPositionLayout: UICollectionViewLayout {
    
    weak var delegate: TileletGroupPositionLayoutDelegate?
    var verticalSpacer: ((TileletCollectionViewRow, TileletCollectionViewRow?) -> CGFloat)?
    var axisSpacer: ((NSLayoutConstraint.Axis, Tilelet, Tilelet) -> CGFloat)?
    
    // Total height of the content. Will be used to configure the scrollview content
    var layoutHeight: CGFloat = 0.0
    var rowQuantity: Int = 0
    var tileletPercentage: CGFloat?
    
    private var itemCache: [TileletLayoutAttributes] = []

    override func prepare() {
        super.prepare()
                
        itemCache.removeAll()
        layoutHeight = 0.0
        
        guard let collectionView, let delegate else { return }
        
        // Variable to track the width of the layout at the current state when the item is being drawn
        var layoutWidthIterator: CGFloat = 0.0
        
        // Only 1 section in the TileletGroup
        let section = 0
                
        // Variables to track individual item width and cumultative height of all items as they are being laid out.
        var itemSize: CGSize = .zero
                
        // get number of tilelets
        let totalItems = collectionView.numberOfItems(inSection: section)
        
        //create rows
        var rows = [TileletCollectionViewRow]()
        rows.append(TileletCollectionViewRow())
        
        let collectionViewWidth = collectionView.horizontalPinnedWidth() ?? collectionView.frame.width
        
        for item in 0..<totalItems {
            
            // start out with no spacing after the item
            var itemSpacing = 0.0
            
            // create the indexPath
            let indexPath = IndexPath(item: item, section: section)
            
            // get the rect size of the tilelet
            itemSize = delegate.collectionView(collectionView, sizeForItemAtIndexPath: indexPath)
            
            // ensure the width is not greater than the collectionViewWidth
            itemSize.width = min(itemSize.width, collectionViewWidth)
            
            // determine if the current tilelet will fit in the row
            let rowItemCount = rows.last?.attributes.count ?? 0
            
            if (layoutWidthIterator + itemSize.width) > collectionViewWidth && rowQuantity == 0
                || (rowQuantity > 0 && rowItemCount == rowQuantity) {
               
                // If the current row width (after this item being laid out) is exceeding
                // the width of the collection view content, put it in the next line
                layoutWidthIterator = 0.0
                        
                // set the spacing of the last item of the current row to 0
                rows.last?.attributes.last?.spacing = 0
                
                // add a new row
                rows.append(TileletCollectionViewRow())
            }

            // get the tilelet
            let itemTilelet = delegate.collectionView(collectionView, tileletAtIndexPath: indexPath)
            
            // see if there is another item in the array
            let nextItem = item + 1
            
            // if so, get the tilelet
            // and get the spacing based of the
            // current tilelet and the next tilelet
            if nextItem < totalItems {
                
                //get the next tilelet
                let neighbor = delegate.collectionView(collectionView, tileletAtIndexPath: IndexPath(item: nextItem, section: section))
                
                // get the spacing to go between the current and next tilelet
                itemSpacing = getAxisSpacing(for: .horizontal, with: itemTilelet, neighboring: neighbor)
            }
            
            // create the custom layout attribute
            let attributes = TileletLayoutAttributes(spacing: itemSpacing, tilelet: itemTilelet, forCellWith: indexPath)
            attributes.frame = CGRect(x: 0, y: 0, width: min(itemSize.width, collectionViewWidth), height: itemSize.height)
            
            // add it to the array
            rows.last?.add(attribute: attributes)
            
            // update the current width
            // add the current frame width + the found spacing
            layoutWidthIterator = layoutWidthIterator + attributes.frame.width + itemSpacing
        }

        layoutWidthIterator = 0.0
                
        // calculate the
        layoutHeight = 0.0
        
        // loop through the rows and set
        // the row y position for each element
        // also add to the layoutHeight
        for item in 0..<rows.count {
            let row = rows[item]
            var rowSpacing = 0.0
                        
            if item > 0 {
                let prevRow = rows[item - 1]
                rowSpacing = getVerticalSpacing(for: prevRow, neighboringRow: row)
                row.rowY = layoutHeight + rowSpacing
                layoutHeight += rowSpacing
            }
            
            layoutHeight += row.rowHeight
        }
        
        // recalculate rows x based off of positions
        rows.forEach {
            $0.layout(with: collectionViewWidth)
        }
        
        let rowAttributes = rows.flatMap { $0.attributes }
        itemCache = rowAttributes
        
    }
        
    override func layoutAttributesForElements(in rect: CGRect)-> [UICollectionViewLayoutAttributes]? {
        var visibleLayoutAttributes: [UICollectionViewLayoutAttributes] = []
        
        for attributes in itemCache {
            if attributes.frame.intersects(rect) {
                visibleLayoutAttributes.append(attributes)
            }
        }
        
        return visibleLayoutAttributes
    }
    
    override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        return itemCache[indexPath.row]
    }
    
    override var collectionViewContentSize: CGSize {
        return CGSize(width: contentWidth, height: layoutHeight)
    }
    
    private var contentWidth: CGFloat {
        guard let collectionView = collectionView else {
            return 0
        }
        return collectionView.bounds.width
    }
    
    private func getAxisSpacing(for axis: NSLayoutConstraint.Axis, with primary: Tilelet, neighboring: Tilelet) -> CGFloat {
        20
    }
    
    private func getVerticalSpacing(for row: TileletCollectionViewRow, neighboringRow: TileletCollectionViewRow?) -> CGFloat {
        20
    }
}