import Foundation
import AsyncDisplayKit
import Display

private enum CornerType {
    case topLeft
    case topRight
    case bottomLeft
    case bottomRight
}

private func drawFullCorner(context: CGContext, color: UIColor, at point: CGPoint, type: CornerType, radius: CGFloat) {
    context.setFillColor(color.cgColor)
    switch type {
        case .topLeft:
            context.clear(CGRect(origin: point, size: CGSize(width: radius, height: radius)))
            context.fillEllipse(in: CGRect(origin: point, size: CGSize(width: radius * 2.0, height: radius * 2.0)))
        case .topRight:
            context.clear(CGRect(origin: CGPoint(x: point.x - radius, y: point.y), size: CGSize(width: radius, height: radius)))
            context.fillEllipse(in: CGRect(origin: CGPoint(x: point.x - radius * 2.0, y: point.y), size: CGSize(width: radius * 2.0, height: radius * 2.0)))
        case .bottomLeft:
            context.clear(CGRect(origin: CGPoint(x: point.x, y: point.y - radius), size: CGSize(width: radius, height: radius)))
            context.fillEllipse(in: CGRect(origin: CGPoint(x: point.x, y: point.y - radius * 2.0), size: CGSize(width: radius * 2.0, height: radius * 2.0)))
        case .bottomRight:
            context.clear(CGRect(origin: CGPoint(x: point.x - radius, y: point.y - radius), size: CGSize(width: radius, height: radius)))
            context.fillEllipse(in: CGRect(origin: CGPoint(x: point.x - radius * 2.0, y: point.y - radius * 2.0), size: CGSize(width: radius * 2.0, height: radius * 2.0)))
    }
}

private func drawConnectingCorner(context: CGContext, color: UIColor, at point: CGPoint, type: CornerType, radius: CGFloat) {
    context.setFillColor(color.cgColor)
    switch type {
        case .topLeft:
            context.fill(CGRect(origin: CGPoint(x: point.x - radius, y: point.y - radius), size: CGSize(width: radius, height: radius)))
            context.setFillColor(UIColor.clear.cgColor)
            context.fillEllipse(in: CGRect(origin: CGPoint(x: point.x - radius * 2.0, y: point.y - radius * 2.0), size: CGSize(width: radius * 2.0, height: radius * 2.0)))
        case .topRight:
            context.fill(CGRect(origin: CGPoint(x: point.x, y: point.y), size: CGSize(width: radius, height: radius)))
            context.setFillColor(UIColor.clear.cgColor)
            context.fillEllipse(in: CGRect(origin: CGPoint(x: point.x, y: point.y), size: CGSize(width: radius * 2.0, height: radius * 2.0)))
        case .bottomLeft:
            context.fill(CGRect(origin: CGPoint(x: point.x - radius, y: point.y - radius), size: CGSize(width: radius, height: radius)))
            context.setFillColor(UIColor.clear.cgColor)
            context.fillEllipse(in: CGRect(origin: CGPoint(x: point.x - radius * 2.0, y: point.y - radius * 2.0), size: CGSize(width: radius * 2.0, height: radius * 2.0)))
        case .bottomRight:
            context.fill(CGRect(origin: CGPoint(x: point.x, y: point.y - radius), size: CGSize(width: radius, height: radius)))
            context.setFillColor(UIColor.clear.cgColor)
            context.fillEllipse(in: CGRect(origin: CGPoint(x: point.x, y: point.y - radius * 2.0), size: CGSize(width: radius * 2.0, height: radius * 2.0)))
    }
}

private func generateRectsImage(color: UIColor, rects: [CGRect]) -> (CGPoint, UIImage?) {
    if rects.isEmpty {
        return (CGPoint(), nil)
    }
    
    let inset: CGFloat = 2.0
    
    var topLeft = rects[0].origin
    var bottomRight = CGPoint(x: rects[0].maxX, y: rects[0].maxY)
    for i in 1 ..< rects.count {
        topLeft.x = min(topLeft.x, rects[i].origin.x)
        topLeft.y = min(topLeft.x, rects[i].origin.y)
        bottomRight.x = max(bottomRight.x, rects[i].maxX)
        bottomRight.y = max(bottomRight.x, rects[i].maxY)
    }
    
    topLeft.x -= inset
    topLeft.y -= inset
    bottomRight.x += inset * 2.0
    bottomRight.y += inset * 2.0
    
    return (topLeft, generateImage(CGSize(width: bottomRight.x - topLeft.x, height: bottomRight.y - topLeft.y), rotatedContext: { size, context in
        context.clear(CGRect(origin: CGPoint(), size: size))
        context.setFillColor(color.cgColor)
        
        context.setBlendMode(.copy)
        
        let radius: CGFloat = 4.0
        
        for i in 0 ..< rects.count {
            let rect = rects[i].insetBy(dx: -inset, dy: -inset)
            context.fill(rect.offsetBy(dx: -topLeft.x, dy: -topLeft.y))
        }
        
        for i in 0 ..< rects.count {
            let rect = rects[i].insetBy(dx: -inset, dy: -inset).offsetBy(dx: -topLeft.x, dy: -topLeft.y)
            
            var previous: CGRect?
            if i != 0 {
                previous = rects[i - 1].insetBy(dx: -inset, dy: -inset).offsetBy(dx: -topLeft.x, dy: -topLeft.y)
            }
            
            var next: CGRect?
            if i != rects.count - 1 {
                next = rects[i + 1].insetBy(dx: -inset, dy: -inset).offsetBy(dx: -topLeft.x, dy: -topLeft.y)
            }
            
            if let previous = previous {
                if previous.contains(rect.topLeft) {
                    if abs(rect.topLeft.x - previous.minX) >= radius {
                        drawConnectingCorner(context: context, color: color, at: CGPoint(x: rect.topLeft.x, y: previous.maxY), type: .topLeft, radius: radius)
                    }
                } else {
                    drawFullCorner(context: context, color: color, at: rect.topLeft, type: .topLeft, radius: radius)
                }
                if previous.contains(rect.topRight.offsetBy(dx: -1.0, dy: 0.0)) {
                    if abs(rect.topRight.x - previous.maxX) >= radius {
                        drawConnectingCorner(context: context, color: color, at: CGPoint(x: rect.topRight.x, y: previous.maxY), type: .topRight, radius: radius)
                    }
                } else {
                    drawFullCorner(context: context, color: color, at: rect.topRight, type: .topRight, radius: radius)
                }
            } else {
                drawFullCorner(context: context, color: color, at: rect.topLeft, type: .topLeft, radius: radius)
                drawFullCorner(context: context, color: color, at: rect.topRight, type: .topRight, radius: radius)
            }
            
            if let next = next {
                if next.contains(rect.bottomLeft) {
                    if abs(rect.bottomRight.x - next.maxX) >= radius {
                        drawConnectingCorner(context: context, color: color, at: CGPoint(x: rect.bottomLeft.x, y: next.minY), type: .bottomLeft, radius: radius)
                    }
                } else {
                    drawFullCorner(context: context, color: color, at: rect.bottomLeft, type: .bottomLeft, radius: radius)
                }
                if next.contains(rect.bottomRight.offsetBy(dx: -1.0, dy: 0.0)) {
                    if abs(rect.bottomRight.x - next.maxX) >= radius {
                        drawConnectingCorner(context: context, color: color, at: CGPoint(x: rect.bottomRight.x, y: next.minY), type: .bottomRight, radius: radius)
                    }
                } else {
                    drawFullCorner(context: context, color: color, at: rect.bottomRight, type: .bottomRight, radius: radius)
                }
            } else {
                drawFullCorner(context: context, color: color, at: rect.bottomLeft, type: .bottomLeft, radius: radius)
                drawFullCorner(context: context, color: color, at: rect.bottomRight, type: .bottomRight, radius: radius)
            }
        }
    }))
    
}

final class LinkHighlightingNode: ASDisplayNode {
    private var rects: [CGRect] = []
    private let imageNode: ASImageNode
    
    var color: UIColor {
        didSet {
            if !self.rects.isEmpty {
                self.updateImage()
            }
        }
    }
    
    init(color: UIColor) {
        self.imageNode = ASImageNode()
        self.imageNode.isLayerBacked = true
        self.imageNode.displaysAsynchronously = false
        self.imageNode.displayWithoutProcessing = true
        
        self.color = color
        
        super.init()
        
        self.addSubnode(self.imageNode)
    }
    
    func updateRects(_ rects: [CGRect]) {
        if self.rects != rects {
            self.rects = rects
            
            self.updateImage()
        }
    }
    
    private func updateImage() {
        if rects.isEmpty {
            self.imageNode.image = nil
        }
        let (offset, image) = generateRectsImage(color: self.color, rects: self.rects)
        
        if let image = image {
            self.imageNode.image = image
            self.imageNode.frame = CGRect(origin: offset, size: image.size)
        }
    }
}