import UIKit

@objc(RnScratchCardViewManager)
class RnScratchCardViewManager: RCTViewManager {

  override func view() -> UIView? {
    return ScratchCardView()
  }
}

class ScratchCardView : UIView {

    private struct Segment {
        let start: CGPoint
        let end: CGPoint
    }

    private var startPoint: CGPoint!
    private var endPoint: CGPoint!
    private var context: CGContext!
    private var segments = [Segment]()
    private var swiped = false

    private var overlayImage: UIImage? = nil
    private var lineWidth: CGFloat = 0
    private var visibleRect: CGRect? = nil

    @objc var image: NSDictionary? = nil {
        didSet {
            guard let image = RCTConvert.uiImage(image) else { return }
            overlayImage = image
        }
    }

    @objc var brushWidth: NSNumber? = nil {
        didSet {
            lineWidth = RCTConvert.cgFloat(brushWidth)
        }
    }

    @objc var onScratch: RCTDirectEventBlock? = nil

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        startPoint = touches.first?.location(in: self)
        swiped = false
        notifyScratch(startPoint)
    }

    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        endPoint = touches.first?.location(in: self)

        guard let rect = visibleRect else { return }
        guard rect.contains(endPoint) else { return }

        swiped = true
        segments.append(Segment(start: startPoint, end: endPoint))

        startPoint = endPoint

        setNeedsDisplay()
        notifyScratch(endPoint)
    }

    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        if !swiped {
            segments.append(Segment(start: startPoint, end: startPoint))
            setNeedsDisplay()
        }
    }

    override func draw(_ rect: CGRect) {
        super.draw(rect)
        visibleRect = rect
        overlayImage?.draw(in: rect)

        context = UIGraphicsGetCurrentContext()

        for each in segments {
            drawLineFrom(fromPoint: each.start, toPoint: each.end)
        }
    }

    private func drawLineFrom(fromPoint: CGPoint, toPoint: CGPoint) {
        context.setLineWidth(lineWidth)
        context.move(to: fromPoint)
        context.setBlendMode(.clear)
        context.setLineCap(.round)
        context.addLine(to: toPoint)
        context.strokePath()
    }

    private func notifyScratch(_ point: CGPoint) {
        guard let onScratch = onScratch else { return }
        let dictionary: [NSString: NSNumber] = [
            "x": point.x as NSNumber,
            "y": point.y as NSNumber
        ]
        onScratch(dictionary)
    }
}