vds_ios/VDS/Components/Buttons/ButtonGroup/ButtonGroupPositionLayout.swift

//
//  ButtonGroupPositionLayout.swift
//  VDS
//
//  Created by Matt Bruce on 11/18/22.
//

import Foundation
import UIKit


class ButtonCollectionViewRow {
    var attributes = [ButtonLayoutAttributes]()

    init() {}

    func add(attribute: ButtonLayoutAttributes) {
        attributes.append(attribute)
    }
    
    var hasButtons: Bool {
        attributes.contains(where: { $0.isButton })
    }

    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 rowY: CGFloat = 0 {
        didSet {
            for attribute in attributes {
                attribute.frame.origin.y = rowY
            }
        }
    }

    func layout(for position: ButtonPosition, with collectionViewWidth: CGFloat){
        var offset = 0.0
        
        attributes.last?.spacing = 0
        
        switch position {
        case .left:
            break
        case .center:
            offset = (collectionViewWidth - rowWidth) / 2
        case .right:
            offset = (collectionViewWidth - rowWidth)
        }
        
        for attribute in attributes {
            attribute.frame.origin.x = offset
            offset += attribute.frame.width + attribute.spacing
        }
    }
}

public enum ButtonPosition: String, CaseIterable {
    case left, center, right
}

protocol ButtongGroupPositionLayoutDelegate: AnyObject {
    func collectionView(_ collectionView: UICollectionView, sizeForItemAtIndexPath indexPath: IndexPath) -> CGSize
    func collectionView(_ collectionView: UICollectionView, buttonableAtIndexPath indexPath: IndexPath) -> any Buttonable
    func collectionView(_ collectionView: UICollectionView, insetsForItemsInSection section: Int) -> UIEdgeInsets
}

class ButtonLayoutAttributes: UICollectionViewLayoutAttributes{
    var spacing: CGFloat = 0
    var isButton: Bool = false
    convenience init(spacing: CGFloat,
                     forCellWith indexPath: IndexPath) {
        self.init(forCellWith: indexPath)
        self.spacing = spacing
    }
}

class ButtonGroupPositionLayout: UICollectionViewLayout {
    
    weak var delegate: ButtongGroupPositionLayoutDelegate?
    
    // Total height of the content. Will be used to configure the scrollview content
    var layoutHeight: CGFloat = 0.0
    var position: ButtonPosition = .left
    private var itemCache: [ButtonLayoutAttributes] = []
    
    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 ButtonGroup
        let section = 0
        
        // Get the necessary data (if implemented) from the delegates else provide default values
        let insets: UIEdgeInsets = delegate.collectionView(collectionView, insetsForItemsInSection: section)
        
        let rowSpacing: CGFloat = ButtonGroupConstants.rowSpacingButton
        
        // Variables to track individual item width and cumultative height of all items as they are being laid out.
        var itemSize: CGSize = .zero
        
        // add top
        layoutHeight += insets.top
        
        let totalItems = collectionView.numberOfItems(inSection: section)
        for item in 0..<totalItems {
            
            var itemSpacing = 0.0
            
            let indexPath = IndexPath(item: item, section: section)
            
            itemSize = delegate.collectionView(collectionView, sizeForItemAtIndexPath: indexPath)
            
            if (layoutWidthIterator + itemSize.width + insets.left + insets.right) > collectionView.frame.width {
                // 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
                layoutHeight += itemSize.height + rowSpacing
            }

            let itemButtonable = delegate.collectionView(collectionView, buttonableAtIndexPath: indexPath)
            
            let nextItem = item + 1
            if nextItem < totalItems {
                let neighbor = delegate.collectionView(collectionView, buttonableAtIndexPath: IndexPath(item: nextItem, section: section))
                itemSpacing = ButtonGroupConstants.getHorizontalSpacing(for: itemButtonable, neighboring: neighbor)
            }
            
            let frame = CGRect(x: layoutWidthIterator + insets.left, y: layoutHeight, width: itemSize.width, height: itemSize.height)
            //print(frame)
            let attributes = ButtonLayoutAttributes(spacing: itemSpacing, forCellWith: indexPath)
            attributes.frame = frame
            attributes.isButton = isButton(buttonable: itemButtonable)
            itemCache.append(attributes)
            
            layoutWidthIterator = layoutWidthIterator + frame.width + itemSpacing
        }

        //add bottom
        layoutHeight += itemSize.height + insets.bottom
        layoutWidthIterator = 0.0
        
        
        //Turn into rows and re-calculate
        var rows = [ButtonCollectionViewRow]()
        var currentRowY: CGFloat = -1
        
        for attribute in itemCache {
            if currentRowY != attribute.frame.midY {
                currentRowY = attribute.frame.midY
                rows.append(ButtonCollectionViewRow())
            }
            rows.last?.add(attribute: attribute)
        }
        
        //recalculate rows based off of positions
        rows.forEach { $0.layout(for: position, with: collectionView.frame.width) }
        let rowAttributes = rows.flatMap { $0.attributes }
        
        layoutHeight = insets.top
        for item in 0..<rows.count {
            let row = rows[item]
            var rowSpacing = 0.0
            
            if item > 0 && item < rows.count {
                rowSpacing = row.hasButtons ? ButtonGroupConstants.rowSpacingButton : ButtonGroupConstants.rowSpacingTextLink
            }
            
            if item > 0 {
                row.rowY = layoutHeight + rowSpacing
                layoutHeight += rowSpacing
            }
            
            layoutHeight += row.rowHeight
        }
        layoutHeight += insets.bottom
        
        
        itemCache = rowAttributes
        
    }
    
    func isButton(buttonable: Buttonable) -> Bool{
        if let _ = buttonable as? Button {
            return true
        } else {
            return false
        }
    }
        
    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
        }
        let insets = collectionView.contentInset
        return collectionView.bounds.width - (insets.left + insets.right)
    }
}