class Canvas: UIView {
    
    var lines = [Line]()
    
    var strokeColor = UIColor.red
    
    var strokeWidth: Float = 1
    
    override func draw(_ rect: CGRect) {
        super.draw(rect)
        
        guard let context = UIGraphicsGetCurrentContext() else { return }
        
        lines.forEach { (line) in
            
            context.setStrokeColor(line.color.cgColor)
            context.setLineWidth(CGFloat(line.strokeWidth))
            context.setLineCap(.round)
            
            for (endPoint, startPoint) in line.points.enumerated() {
                if endPoint == 0 {
                    context.move(to: startPoint)
                } else {
                    context.addLine(to: startPoint)
                }
            }
            context.strokePath()
        }
    }
    
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {

        lines.append(Line.init(color: strokeColor,
                               strokeWidth: strokeWidth,
                               points: []))
    }
    
    // track the finger as we move across screen
    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        
        guard
            let point = touches.first?.location(in: self),
            var lastLine = lines.popLast()
        else { return }

        lastLine.points.append(point)

        lines.append(lastLine)
        
        setNeedsDisplay()
    }
    
    func undo() {
        
        _ = lines.popLast()
        
        setNeedsDisplay()
    }
    
    func clear() {
        
        lines.removeAll()
        
        setNeedsDisplay()
    }
    
    func setStrokeColor(color: UIColor) {
        
        strokeColor = color
    }
    
    func setStrokeWidth(width: Float) {
        
        strokeWidth = width
    }
}

class FaceDetection {
    
    weak var delegate: FaceDetectionDelegate?
    
    func faceDetection(detect image: UIImage?) {
        
        let detectRequest = VNDetectFaceRectanglesRequest(completionHandler: self.handleFaces)
        
        guard let image = image?.cgImage else { return }
        
        let detectRequestHandler = VNImageRequestHandler(cgImage: image,
                                                         options: [ : ])
        
        do {
            
            try detectRequestHandler.perform([detectRequest])
            
        } catch {
            
            PiggyJonAlert.showCustomIcon(icon: UIImage.asset(.exclamation_mark),
                                         message: "人臉偵測錯誤 (つд⊂)")
        }
    }
    
    func handleFaces(request: VNRequest, error: Error?) {
        
        guard
            let faceDetectResults = request.results as? [VNFaceObservation]
        else {
            fatalError("Unexpected result type from VNDetectFaceRetanglesRequest.")
        }
        
        if faceDetectResults.count == 0 {
            
            PiggyJonAlert.showCustomIcon(icon: UIImage.asset(.exclamation_mark),
                                         message: "這張照片偵測不到人臉 இдஇ")
            return
        }
        
        delegate?.faceDetecter(self, didGet: faceDetectResults)
    }
}