// Written by Dor Verbin, October 2021
// This is based on: http://thenewcode.com/364/Interactive-Before-and-After-Video-Comparison-in-HTML5-Canvas
// With additional modifications based on: https://jsfiddle.net/7sk5k4gp/13/

function playVids(videoId) {
    var videoMerge = document.getElementById(videoId + "Merge");
    var vid = document.getElementById(videoId);

    var position = 0.5;
    var vidWidth = vid.videoWidth/2;
    var vidHeight = vid.videoHeight;

    var mergeContext = videoMerge.getContext("2d");

    
    if (vid.readyState > 3) {
        vid.play();

        function trackLocation(e) {
            // Normalize to [0, 1]
            bcr = videoMerge.getBoundingClientRect();
            position = ((e.pageX - bcr.x) / bcr.width);
        }
        function trackLocationTouch(e) {
            // Normalize to [0, 1]
            bcr = videoMerge.getBoundingClientRect();
            position = ((e.touches[0].pageX - bcr.x) / bcr.width);
        }

        videoMerge.addEventListener("mousemove",  trackLocation, false); 
        videoMerge.addEventListener("touchstart", trackLocationTouch, false);
        videoMerge.addEventListener("touchmove",  trackLocationTouch, false);


        function drawLoop() {
            mergeContext.drawImage(vid, 0, 0, vidWidth, vidHeight, 0, 0, vidWidth, vidHeight);
            var colStart = (vidWidth * position).clamp(0.0, vidWidth);
            var colWidth = (vidWidth - (vidWidth * position)).clamp(0.0, vidWidth);
            mergeContext.drawImage(vid, colStart+vidWidth, 0, colWidth, vidHeight, colStart, 0, colWidth, vidHeight);
            requestAnimationFrame(drawLoop);

            
            var arrowLength = 0.09 * vidHeight;
            var arrowheadWidth = 0.025 * vidHeight;
            var arrowheadLength = 0.04 * vidHeight;
            var arrowPosY = vidHeight / 2;
            var arrowWidth = 0.007 * vidHeight;
            var currX = vidWidth * position;

            // Draw circle
            mergeContext.arc(currX, arrowPosY, arrowLength*0.7, 0, Math.PI * 2, false);
            mergeContext.fillStyle = "#FFD79340";
            mergeContext.fill()
            //mergeContext.strokeStyle = "#444444";
            //mergeContext.stroke()
            
            // Draw border
            mergeContext.beginPath();
            mergeContext.moveTo(vidWidth*position, 0);
            mergeContext.lineTo(vidWidth*position, vidHeight);
            mergeContext.closePath()
            mergeContext.strokeStyle = "#444444";
            mergeContext.lineWidth = 5;            
            mergeContext.stroke();

            // Draw arrow
            mergeContext.beginPath();
            mergeContext.moveTo(currX, arrowPosY - arrowWidth/2);
            
            // Move right until meeting arrow head
            mergeContext.lineTo(currX + arrowLength/2 - arrowheadLength/2, arrowPosY - arrowWidth/2);
            
            // Draw right arrow head
            mergeContext.lineTo(currX + arrowLength/2 - arrowheadLength/2, arrowPosY - arrowheadWidth/2);
            mergeContext.lineTo(currX + arrowLength/2, arrowPosY);
            mergeContext.lineTo(currX + arrowLength/2 - arrowheadLength/2, arrowPosY + arrowheadWidth/2);
            mergeContext.lineTo(currX + arrowLength/2 - arrowheadLength/2, arrowPosY + arrowWidth/2);

            // Go back to the left until meeting left arrow head
            mergeContext.lineTo(currX - arrowLength/2 + arrowheadLength/2, arrowPosY + arrowWidth/2);
            
            // Draw left arrow head
            mergeContext.lineTo(currX - arrowLength/2 + arrowheadLength/2, arrowPosY + arrowheadWidth/2);
            mergeContext.lineTo(currX - arrowLength/2, arrowPosY);
            mergeContext.lineTo(currX - arrowLength/2 + arrowheadLength/2, arrowPosY  - arrowheadWidth/2);
            mergeContext.lineTo(currX - arrowLength/2 + arrowheadLength/2, arrowPosY);
            
            mergeContext.lineTo(currX - arrowLength/2 + arrowheadLength/2, arrowPosY - arrowWidth/2);
            mergeContext.lineTo(currX, arrowPosY - arrowWidth/2);

            mergeContext.closePath();

            mergeContext.fillStyle = "#444444";
            mergeContext.fill();

            
            
        }
        requestAnimationFrame(drawLoop);
    } 
}

Number.prototype.clamp = function(min, max) {
  return Math.min(Math.max(this, min), max);
};
    
    
function resizeAndPlay(element)
{
  var cv = document.getElementById(element.id + "Merge");
  cv.width = element.videoWidth/2;
  cv.height = element.videoHeight;
  element.play();
  element.style.height = "0px";  // Hide video without stopping it
    
  playVids(element.id);
}
