/* Based on --> http://phrogz.net/tmp/canvas_zoom_to_cursor.html */

let gkhead;
let ball;
const loadCanvas = ( canvas ) => {		
    
    var ctx = canvas.getContext('2d');
    trackTransforms(ctx);
    function redraw(){
        // Clear the entire canvas
        var p1 = ctx.transformedPoint(0,0);
        var p2 = ctx.transformedPoint(canvas.width,canvas.height);
        ctx.clearRect(p1.x,p1.y,p2.x-p1.x,p2.y-p1.y);

        // Alternatively:
        // ctx.save();
        // ctx.setTransform(1,0,0,1,0,0);
        // ctx.clearRect(0,0,canvas.width,canvas.height);
        // ctx.restore();

        ctx.drawImage(gkhead,200,50);

        ctx.beginPath();
        ctx.lineWidth = 6;
        ctx.moveTo(399,250);
        ctx.lineTo(474,256);
        ctx.stroke();

        ctx.save();
        ctx.translate(4,2);
        ctx.beginPath();
        ctx.lineWidth = 1;
        ctx.moveTo(436,253);
        ctx.lineTo(437.5,233);
        ctx.stroke();

        ctx.save();
        ctx.translate(438.5,223);
        ctx.strokeStyle = '#06c';
        ctx.beginPath();
        ctx.lineWidth = 0.05;
        for (var i=0;i<60;++i){
            ctx.rotate(6*i*Math.PI/180);
            ctx.moveTo(9,0);
            ctx.lineTo(10,0);
            ctx.rotate(-6*i*Math.PI/180);
        }
        ctx.stroke();
        ctx.restore();

        ctx.beginPath();
        ctx.lineWidth = 0.2;
        ctx.arc(438.5,223,10,0,Math.PI*2);
        ctx.stroke();
        ctx.restore();
        
        ctx.drawImage(ball,379,233,40,40);
        ctx.drawImage(ball,454,239,40,40);
        ctx.drawImage(ball,310,295,20,20);
        ctx.drawImage(ball,314.5,296.5,5,5);
        ctx.drawImage(ball,319,297.2,5,5);
    }
    redraw();
    
    var lastX=canvas.width/2, lastY=canvas.height/2;
    var dragStart,dragged;
    canvas.addEventListener('mousedown',function(evt){
        (document.body.style as any).mozUserSelect = document.body.style.webkitUserSelect = document.body.style.userSelect = 'none';
        lastX = evt.offsetX || (evt.pageX - canvas.offsetLeft);
        lastY = evt.offsetY || (evt.pageY - canvas.offsetTop);
        dragStart = ctx.transformedPoint(lastX,lastY);
        dragged = false;
    },false);
    canvas.addEventListener('mousemove',function(evt){
        lastX = evt.offsetX || (evt.pageX - canvas.offsetLeft);
        lastY = evt.offsetY || (evt.pageY - canvas.offsetTop);
        dragged = true;
        if (dragStart){
            var pt = ctx.transformedPoint(lastX,lastY);
            ctx.translate(pt.x-dragStart.x,pt.y-dragStart.y);
            redraw();
        }
    },false);
    canvas.addEventListener('mouseup',function(evt){
        dragStart = null;
        if (!dragged) zoom(evt.shiftKey ? -1 : 1 );
    },false);

    var scaleFactor = 1.1;
    var zoom = function(clicks){
        var pt = ctx.transformedPoint(lastX,lastY);
        ctx.translate(pt.x,pt.y);
        var factor = Math.pow(scaleFactor,clicks);
        ctx.scale(factor,factor);
        ctx.translate(-pt.x,-pt.y);
        redraw();
    }

    var handleScroll = function(evt){
        var delta = evt.wheelDelta ? evt.wheelDelta/40 : evt.detail ? -evt.detail : 0;
        if (delta) zoom(delta);
        return evt.preventDefault() && false;
    };
    canvas.addEventListener('DOMMouseScroll',handleScroll,false);
    canvas.addEventListener('mousewheel',handleScroll,false);
};

gkhead.src = 'http://phrogz.net/tmp/gkhead.jpg';
ball.src   = 'http://phrogz.net/tmp/alphaball.png';

// Adds ctx.getTransform() - returns an SVGMatrix
// Adds ctx.transformedPoint(x,y) - returns an SVGPoint
const trackTransforms = (ctx) => {
    
    let svg = document.createElementNS("http://www.w3.org/2000/svg",'svg');
    let xform = svg.createSVGMatrix();
    
    ctx.getTransform = () => { return xform; };
    
    let savedTransforms = [];
    let save = ctx.save;

    ctx.save = () => {
        savedTransforms.push(xform.translate(0,0));
        return save.call(ctx);
    };

    let restore = ctx.restore;
    ctx.restore = () => {
        xform = savedTransforms.pop();
        return restore.call(ctx);
    };

    let scale = ctx.scale;
    ctx.scale = (sx,sy) => {
        xform = xform.scaleNonUniform(sx,sy);
        return scale.call(ctx,sx,sy);
    };

    let rotate = ctx.rotate;
    ctx.rotate = (radians) => {
        xform = xform.rotate(radians*180/Math.PI);
        return rotate.call(ctx,radians);
    };

    let translate = ctx.translate;
    ctx.translate = (dx,dy) => {
        xform = xform.translate(dx,dy);
        return translate.call(ctx,dx,dy);
    };

    let transform = ctx.transform;
    ctx.transform = (a,b,c,d,e,f) => {
        let m2 = svg.createSVGMatrix();
        m2.a=a; m2.b=b; m2.c=c; m2.d=d; m2.e=e; m2.f=f;
        xform = xform.multiply(m2);
        return transform.call(ctx,a,b,c,d,e,f);
    };

    let setTransform = ctx.setTransform;
    ctx.setTransform = (a,b,c,d,e,f) => {
        xform.a = a;
        xform.b = b;
        xform.c = c;
        xform.d = d;
        xform.e = e;
        xform.f = f;
        return setTransform.call(ctx,a,b,c,d,e,f);
    };

    let pt  = svg.createSVGPoint();
    ctx.transformedPoint = (x,y) => {
        pt.x=x; pt.y=y;
        return pt.matrixTransform(xform.inverse());
    }

}