var createBaseScene = function(engineProxy, headless) {
    // Scene
    var scene = new BABYLON.Scene(engineProxy)
    scene.clearColor = BABYLON.Color3.Purple();
    // Camera
    var camera = new BABYLON.ArcRotateCamera("Camera", 3 * Math.PI / 2, Math.PI / 2, 50, BABYLON.Vector3.Zero(), scene);
    // Box
    var box1 = BABYLON.MeshBuilder.CreateBox("Box", {size:4}, scene);
    box1.position = new BABYLON.Vector3(-2, 4, 0);
    var box2 = BABYLON.MeshBuilder.CreateBox("Box", {size:4}, scene);
    box2.position = new BABYLON.Vector3(-2, 4, 0);
    // Ground
    var ground = BABYLON.MeshBuilder.CreateBox("Ground", {width: 100, height: 1, depth: 100}, scene);
    ground.position.y = -5.0;

    if(!headless) {
        camera.attachControl(canvas, true);

        // Light
        var light = new BABYLON.DirectionalLight("dir02", new BABYLON.Vector3(0.2, -1, 0), scene);
        light.position = new BABYLON.Vector3(0, 80, 0);
        // // Shadows
        var shadowGenerator = new BABYLON.ShadowGenerator(2048, light);
        shadowGenerator.addShadowCaster(box1);
        shadowGenerator.addShadowCaster(box2);
        // Materials
        var materialWood = new BABYLON.StandardMaterial("wood", scene);
        materialWood.diffuseTexture = new BABYLON.Texture("textures/crate.png", scene);
        materialWood.emissiveColor = new BABYLON.Color3(0.5, 0.5, 0.5);
        box1.material = materialWood;
        box2.material = materialWood;
        var groundMat = new BABYLON.StandardMaterial("groundMat", scene);
        groundMat.diffuseColor = new BABYLON.Color3(0.5, 0.5, 0.5);
        groundMat.emissiveColor = new BABYLON.Color3(0.2, 0.2, 0.2);
        groundMat.backFaceCulling = false;
        ground.material = groundMat;
        ground.receiveShadows = true;
    }

    // Physics
    const physics = new BABYLON.AmmoJSPlugin(false)
    physics.setTimeStep(1/10)
    physics.setFixedTimeStep(1/10)

    scene.enablePhysics(null, physics);
    box1.physicsImpostor = new BABYLON.PhysicsImpostor(box1, BABYLON.PhysicsImpostor.BoxImpostor, { mass: 10, friction: 10, restitution: 0.3 }, scene);
    box2.physicsImpostor = new BABYLON.PhysicsImpostor(box2, BABYLON.PhysicsImpostor.BoxImpostor, { mass: 10, friction: 10, restitution: 0.3 }, scene);
    ground.physicsImpostor = new BABYLON.PhysicsImpostor(ground, BABYLON.PhysicsImpostor.BoxImpostor, { mass: 0, friction: 10, restitution: 0.7 }, scene);
    box1.physicsImpostor.friction = 10;
    box2.physicsImpostor.friction = 10;
    ground.physicsImpostor.friction = 10;

    return [scene, box1, box2, ground, camera]
}

var createScene = function () {
    var engine1 = engine

    var engine2 = new BABYLON.NullEngine({
        renderWidth: 512,
        renderHeight: 256,
        textureSize: 512,
        deterministicLockstep: false,
        lockstepMaxSteps: 4,
    })

    var [scene1, box1, box1a, ground1, camera1] = createBaseScene(engine1, false)
    var [scene2, box2, box2a, ground2, camera2] = createBaseScene(engine2, true)

    var lastMousePosition = null
    var grabbed = false
    var grabbedBox = null

    box1.position.z = 15
    box1a.position.z = 15
    box2.position.z = 0
    box2a.position.z = 0

    var box2Proxy = BABYLON.MeshBuilder.CreateBox("Box", {size:4}, scene1);
    var box2aProxy = BABYLON.MeshBuilder.CreateBox("Box", {size:4}, scene1);

    scene1.registerAfterRender(function() {
        scene2.render()

        const result = scene1.pick(
            scene1.pointerX,
            scene1.pointerY,
            (mesh) => mesh === ground1)

        if(result && result.pickedPoint) {
            lastMousePosition = result.pickedPoint
        }

        if(lastMousePosition && grabbed && grabbedBox) {
            const targetPosition = new BABYLON.Vector3(
                lastMousePosition.x,
                lastMousePosition.y + 5,
                lastMousePosition.z
            )

            // Position
            grabbedBox.physicsImpostor.applyForce((
                targetPosition
                    .subtract(grabbedBox.position))
                    .scale(16 * 5 * grabbedBox.physicsImpostor.mass),
                grabbedBox.getAbsolutePosition());

            // Rotation
            const targetRotation = BABYLON.Quaternion.RotationAxis(BABYLON.Vector3.Up(), 0).multiply(BABYLON.Quaternion.Identity())
            grabbedBox.rotationQuaternion = BABYLON.Quaternion.Slerp(grabbedBox.rotationQuaternion, targetRotation, 0.09)

            // Dampening
            const linearVelocity = grabbedBox.physicsImpostor.getLinearVelocity()
            const angularVelocity = grabbedBox.physicsImpostor.getAngularVelocity()

            if(linearVelocity != null)
                grabbedBox.physicsImpostor.setLinearVelocity(linearVelocity.scale(0.05))
            if(angularVelocity != null)
                grabbedBox.physicsImpostor.setAngularVelocity(angularVelocity.scale(0.05))
        }
    })

    scene2.registerAfterRender(function() {
        box2Proxy.position = box2.position
        box2Proxy.rotation = box2.rotation

        box2aProxy.position = box2a.position
        box2aProxy.rotation = box2a.rotation
    })

    function onGrab() {
        const result = scene1.pick(
            scene1.pointerX,
            scene1.pointerY,
            (mesh) => mesh === box1 || mesh === box2Proxy)

        if(result.pickedMesh === box2Proxy)
            result.pickedMesh = box2

        if(result && result.pickedMesh && !grabbed) {
            grabbed = true
            grabbedBox = result.pickedMesh
            camera1.detachControl(canvas)
        }
    }

    function onRelease() {
        camera1.attachControl(canvas, true);
        grabbed = false
    }

    canvas.addEventListener('pointerdown', (ev) => onGrab())
    canvas.addEventListener('pointerup', (ev) => onRelease())

    function pulse() {
        box1.physicsImpostor.applyForce(BABYLON.Vector3.Up().scale(5000), box1.getAbsolutePosition());
        box2.physicsImpostor.applyForce(BABYLON.Vector3.Up().scale(5000), box2.getAbsolutePosition());
    }

    var button = BABYLON.GUI.Button.CreateSimpleButton("Button", "Apply Impulse");
    button.width = 0.2;
    button.height = "40px";
    button.color = "white";
    button.background = "black";
    button.top = "-10px";
    button.horizontalAlignment = BABYLON.GUI.Control.HORIZONTAL_ALIGNMENT_CENTER;
    button.verticalAlignment = BABYLON.GUI.Control.VERTICAL_ALIGNMENT_BOTTOM;
    button.onPointerClickObservable.add(pulse);

    var ui = BABYLON.GUI.AdvancedDynamicTexture.CreateFullscreenUI("UI", true, scene1);
    ui.addControl(button);

    return scene1
}