var Example = Example || {};

Example.catapult = function() {
    var Engine = Matter.Engine,
        Render = Matter.Render,
        Runner = Matter.Runner,
        Composites = Matter.Composites,
        Constraint = Matter.Constraint,
        MouseConstraint = Matter.MouseConstraint,
        Mouse = Matter.Mouse,
        World = Matter.World,
        Bodies = Matter.Bodies,
        Body = Matter.Body,
        Vector = Matter.Vector;

    // create engine
    var engine = Engine.create(),
        world = engine.world;

    // create renderer
    var render = Render.create({
        element: document.body,
        engine: engine,
        options: {
            width: 800,
            height: 600,
            showAngleIndicator: true,
            showCollisions: true,
            showVelocity: true
        }
    });

    Render.run(render);

    // create runner
    var runner = Runner.create();
    Runner.run(runner, engine);

    // add bodies
    var group = Body.nextGroup(true);

    var stack = Composites.stack(250, 255, 1, 6, 0, 0, function(x, y) {
        return Bodies.rectangle(x, y, 30, 30);
    });

    var catapult = Bodies.rectangle(400, 520, 320, 20, { collisionFilter: { group: group } });

    World.add(world, [
        stack,
        catapult,
        Bodies.rectangle(400, 600, 800, 50.5, { isStatic: true }),
        Bodies.rectangle(250, 555, 20, 50, { isStatic: true }),
        Bodies.rectangle(400, 535, 20, 80, { isStatic: true, collisionFilter: { group: group } }),
        Bodies.circle(560, 100, 50, { density: 0.005 }),
        Constraint.create({ 
            bodyA: catapult, 
            pointB: Vector.clone(catapult.position),
            stiffness: 1,
            length: 0
        })
    ]);

    // add mouse control
    var mouse = Mouse.create(render.canvas),
        mouseConstraint = MouseConstraint.create(engine, {
            mouse: mouse,
            constraint: {
                stiffness: 0.2,
                render: {
                    visible: false
                }
            }
        });

    World.add(world, mouseConstraint);

    // keep the mouse in sync with rendering
    render.mouse = mouse;

    // fit the render viewport to the scene
    Render.lookAt(render, {
        min: { x: 0, y: 0 },
        max: { x: 800, y: 600 }
    });

    // context for MatterTools.Demo
    return {
        engine: engine,
        runner: runner,
        render: render,
        canvas: render.canvas,
        stop: function() {
            Matter.Render.stop(render);
            Matter.Runner.stop(runner);
        }
    };
};

if (typeof module !== 'undefined' && module.exports) {
    module.exports = Example[Object.keys(Example)[0]];
}