package com.davidmedenjak.overlappinginvertview

import android.content.Context
import android.graphics.*
import android.util.AttributeSet
import android.view.View
import android.widget.FrameLayout


class InvertViewLayout(context: Context, attrs: AttributeSet? = null) : FrameLayout(context, attrs) {
    lateinit var backgroundView: View
    lateinit var overlay: View
    lateinit var bitmap: Bitmap

    val inversePaint: Paint = Paint()
    val rectPaint: Paint = Paint().apply {
        isAntiAlias = true
        color = Color.RED
    }

    init {
        // https://stackoverflow.com/q/5941926/1837367
        val mx = floatArrayOf(-1.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, -1.0f, 0.0f, 1.0f, 0.0f, 0.0f, 0.0f, -1.0f, 1.0f, 0.0f, 1.0f, 1.0f, 1.0f, 1.0f, 0.0f)
        val cm = ColorMatrix(mx)

        inversePaint.colorFilter = ColorMatrixColorFilter(cm)

    }

    override fun onLayout(changed: Boolean, left: Int, top: Int, right: Int, bottom: Int) {
        super.onLayout(changed, left, top, right, bottom)
        backgroundView = getChildAt(0)
        overlay = getChildAt(1)

        bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888)
    }

    override fun drawChild(canvas: Canvas, child: View, drawingTime: Long): Boolean {
        if (child !== overlay) {
            return super.drawChild(canvas, child, drawingTime)
        }

        val overlayCanvas = Canvas(bitmap)
        val result = super.drawChild(overlayCanvas, child, drawingTime)

        canvas.save()
        canvas.clipRect(backgroundView.left, backgroundView.top, backgroundView.right, backgroundView.bottom)
        canvas.drawBitmap(bitmap, 0F, 0F, inversePaint)
        canvas.restore()

        canvas.save()
        canvas.clipOutRect(backgroundView.left, backgroundView.top, backgroundView.right, backgroundView.bottom)
        canvas.drawBitmap(bitmap, 0F, 0F, null)
        canvas.restore()
        return result
    }

}