Swiftgram/submodules/TelegramUI/Components/Stories/StoryContainerScreen/Sources/MediaNavigationStripComponent.swift

import Foundation
import UIKit
import Display
import ComponentFlow

final class MediaNavigationStripComponent: Component {
    let index: Int
    let count: Int
    
    init(index: Int, count: Int) {
        self.index = index
        self.count = count
    }

    static func ==(lhs: MediaNavigationStripComponent, rhs: MediaNavigationStripComponent) -> Bool {
        if lhs.index != rhs.index {
            return false
        }
        if lhs.count != rhs.count {
            return false
        }
        return true
    }
    
    private final class ItemLayer: SimpleLayer {
        override init() {
            super.init()
            
            self.cornerRadius = 1.5
        }
        
        required init?(coder: NSCoder) {
            fatalError("init(coder:) has not been implemented")
        }
        
        override init(layer: Any) {
            super.init(layer: layer)
        }
    }

    final class View: UIView {
        private var visibleItems: [Int: ItemLayer] = [:]
        
        override init(frame: CGRect) {
            super.init(frame: frame)
            
            self.clipsToBounds = true
            self.layer.cornerRadius = 1.0
        }
        
        required init?(coder: NSCoder) {
            fatalError("init(coder:) has not been implemented")
        }
        
        func update(component: MediaNavigationStripComponent, availableSize: CGSize, state: EmptyComponentState, environment: Environment<Empty>, transition: Transition) -> CGSize {
            let spacing: CGFloat = 3.0
            let itemHeight: CGFloat = 2.0
            let minItemWidth: CGFloat = 3.0
            
            var validIndices: [Int] = []
            if component.count != 0 {
                var idealItemWidth: CGFloat = (availableSize.width - CGFloat(component.count - 1) * spacing) / CGFloat(component.count)
                idealItemWidth = round(idealItemWidth)
                
                let itemWidth: CGFloat
                if idealItemWidth < minItemWidth {
                    itemWidth = minItemWidth
                } else {
                    itemWidth = idealItemWidth
                }
                
                let globalWidth: CGFloat = CGFloat(component.count) * itemWidth + CGFloat(component.count - 1) * spacing
                let globalFocusedFrame = CGRect(origin: CGPoint(x: CGFloat(component.index) * (itemWidth + spacing), y: 0.0), size: CGSize(width: itemWidth, height: itemHeight))
                var globalOffset: CGFloat = floor(globalFocusedFrame.midX - availableSize.width * 0.5)
                if globalOffset > globalWidth - availableSize.width {
                    globalOffset = globalWidth - availableSize.width
                }
                if globalOffset < 0.0 {
                    globalOffset = 0.0
                }
                
                //itemWidth * itemCount + (itemCount - 1) * spacing = width
                //itemWidth * itemCount + itemCount * spacing - spacing = width
                //itemCount * (itemWidth + spacing) = width + spacing
                //itemCount = (width + spacing) / (itemWidth + spacing)
                let potentiallyVisibleCount = Int(ceil((availableSize.width + spacing) / (itemWidth + spacing)))
                for i in (component.index - potentiallyVisibleCount) ... (component.index + potentiallyVisibleCount) {
                    if i < 0 {
                        continue
                    }
                    if i >= component.count {
                        continue
                    }
                    let itemFrame = CGRect(origin: CGPoint(x: -globalOffset + CGFloat(i) * (itemWidth + spacing), y: 0.0), size: CGSize(width: itemWidth, height: itemHeight))
                    if itemFrame.maxY < 0.0 || itemFrame.minY >= availableSize.width {
                        continue
                    }
                    
                    validIndices.append(i)
                    
                    let itemLayer: ItemLayer
                    if let current = self.visibleItems[i] {
                        itemLayer = current
                    } else {
                        itemLayer = ItemLayer()
                        self.layer.addSublayer(itemLayer)
                        self.visibleItems[i] = itemLayer
                        itemLayer.cornerRadius = itemHeight * 0.5
                    }
                    
                    transition.setFrame(layer: itemLayer, frame: itemFrame)
                    
                    itemLayer.backgroundColor = UIColor(white: 1.0, alpha: i == component.index ? 1.0 : 0.5).cgColor
                }
            }
            
            var removedIndices: [Int] = []
            for (index, itemLayer) in self.visibleItems {
                if !validIndices.contains(index) {
                    removedIndices.append(index)
                    itemLayer.removeFromSuperlayer()
                }
            }
            for index in removedIndices {
                self.visibleItems.removeValue(forKey: index)
            }
            
            return availableSize
        }
    }

    func makeView() -> View {
        return View(frame: CGRect())
    }
    
    func update(view: View, availableSize: CGSize, state: EmptyComponentState, environment: Environment<Empty>, transition: Transition) -> CGSize {
        return view.update(component: self, availableSize: availableSize, state: state, environment: environment, transition: transition)
    }
}