(function() {

    var Engine = Matter.Engine,
        World = Matter.World,
        Bodies = Matter.Bodies,
        Body = Matter.Body,
        Composite = Matter.Composite,
        Composites = Matter.Composites,
        Common = Matter.Common,
        Constraint = Matter.Constraint,
        Events = Matter.Events,
        Bounds = Matter.Bounds,
        Vector = Matter.Vector,
        Vertices = Matter.Vertices,
        MouseConstraint = Matter.MouseConstraint,
        Mouse = Matter.Mouse,
        Query = Matter.Query,
        Svg = Matter.Svg;

    Example.views = function(demo) {
        var engine = demo.engine,
            world = engine.world,
            sceneEvents = demo.sceneEvents,
            mouseConstraint = demo.mouseConstraint;

        var stack = Composites.stack(20, 20, 15, 4, 0, 0, function(x, y, column, row) {
            switch (Math.round(Common.random(0, 1))) {

            case 0:
                if (Common.random() < 0.8) {
                    return Bodies.rectangle(x, y, Common.random(20, 50), Common.random(20, 50));
                } else {
                    return Bodies.rectangle(x, y, Common.random(80, 120), Common.random(20, 30));
                }
                break;
            case 1:
                var sides = Math.round(Common.random(1, 8));
                sides = (sides === 3) ? 4 : sides;
                return Bodies.polygon(x, y, sides, Common.random(20, 50));
            }
        });
        
        World.add(world, stack);

        // get the centre of the viewport
        var viewportCentre = {
            x: engine.render.options.width * 0.5,
            y: engine.render.options.height * 0.5
        };

        // make the world bounds a little bigger than the render bounds
        world.bounds.min.x = -300;
        world.bounds.min.y = -300;
        world.bounds.max.x = 1100;
        world.bounds.max.y = 900;

        // keep track of current bounds scale (view zoom)
        var boundsScaleTarget = 1,
            boundsScale = {
                x: 1,
                y: 1
            };

        // use the engine tick event to control our view
        sceneEvents.push(
            Events.on(engine, 'beforeTick', function() {
                var world = engine.world,
                    mouse = mouseConstraint.mouse,
                    render = engine.render,
                    translate;

                // mouse wheel controls zoom
                var scaleFactor = mouse.wheelDelta * -0.1;
                if (scaleFactor !== 0) {
                    if ((scaleFactor < 0 && boundsScale.x >= 0.6) || (scaleFactor > 0 && boundsScale.x <= 1.4)) {
                        boundsScaleTarget += scaleFactor;
                    }
                }

                // if scale has changed
                if (Math.abs(boundsScale.x - boundsScaleTarget) > 0.01) {
                    // smoothly tween scale factor
                    scaleFactor = (boundsScaleTarget - boundsScale.x) * 0.2;
                    boundsScale.x += scaleFactor;
                    boundsScale.y += scaleFactor;

                    // scale the render bounds
                    render.bounds.max.x = render.bounds.min.x + render.options.width * boundsScale.x;
                    render.bounds.max.y = render.bounds.min.y + render.options.height * boundsScale.y;

                    // translate so zoom is from centre of view
                    translate = {
                        x: render.options.width * scaleFactor * -0.5,
                        y: render.options.height * scaleFactor * -0.5
                    };

                    Bounds.translate(render.bounds, translate);

                    // update mouse
                    Mouse.setScale(mouse, boundsScale);
                    Mouse.setOffset(mouse, render.bounds.min);
                }

                // get vector from mouse relative to centre of viewport
                var deltaCentre = Vector.sub(mouse.absolute, viewportCentre),
                    centreDist = Vector.magnitude(deltaCentre);

                // translate the view if mouse has moved over 50px from the centre of viewport
                if (centreDist > 50) {
                    // create a vector to translate the view, allowing the user to control view speed
                    var direction = Vector.normalise(deltaCentre),
                        speed = Math.min(10, Math.pow(centreDist - 50, 2) * 0.0002);

                    translate = Vector.mult(direction, speed);

                    // prevent the view moving outside the world bounds
                    if (render.bounds.min.x + translate.x < world.bounds.min.x)
                        translate.x = world.bounds.min.x - render.bounds.min.x;

                    if (render.bounds.max.x + translate.x > world.bounds.max.x)
                        translate.x = world.bounds.max.x - render.bounds.max.x;

                    if (render.bounds.min.y + translate.y < world.bounds.min.y)
                        translate.y = world.bounds.min.y - render.bounds.min.y;

                    if (render.bounds.max.y + translate.y > world.bounds.max.y)
                        translate.y = world.bounds.max.y - render.bounds.max.y;

                    // move the view
                    Bounds.translate(render.bounds, translate);

                    // we must update the mouse too
                    Mouse.setOffset(mouse, render.bounds.min);
                }
            })
        );

        // must enable renderOptions.hasBounds for views to work
        var renderOptions = engine.render.options;
        renderOptions.hasBounds = true;
    };

})();