(function (window) {
    'use strict';

    function define_CesiumControl() {
        var CesiumControl = {};
        CesiumControl.viewer = undefined;
        CesiumControl.startMousePosition = undefined;
        CesiumControl.mousePosition = undefined;
        CesiumControl.flags = {
            looking: false,
            moveForward: false,
            moveBackward: false,
            moveUp: false,
            moveDown: false,
            moveLeft: false,
            moveRight: false
        };
        CesiumControl.handler = undefined;

        CesiumControl.create = function (viewer) {
            this.viewer = viewer;
            this.handler = new Cesium.ScreenSpaceEventHandler(viewer.canvas);
        }
        CesiumControl.init = function () {
            let viewer = this.viewer,
                scene = viewer.scene,
                canvas = viewer.canvas,
                ellipsoid = viewer.ellipsoid;

            canvas.setAttribute('tabindex', '0'); // needed to put focus on the canvas
            canvas.onclick = function () {
                canvas.focus();
            };
            ellipsoid = scene.globe.ellipsoid;
            scene.screenSpaceCameraController.enableRotate = false;
            scene.screenSpaceCameraController.enableTranslate = false;
            scene.screenSpaceCameraController.enableZoom = false;
            scene.screenSpaceCameraController.enableTilt = false;
            scene.screenSpaceCameraController.enableLook = false;
            // disable the default event handlers
            let flags = this.flags,
            handler = this.handler,
            mousePosition = this.mousePosition,
            startMousePosition = this.startMousePosition;
            handler.setInputAction(function (movement) {
                flags.looking = true;
                mousePosition = startMousePosition = Cesium.Cartesian3.clone(movement.position);
            }, Cesium.ScreenSpaceEventType.LEFT_DOWN);
            handler.setInputAction(function (movement) {
                mousePosition = movement.endPosition;
            }, Cesium.ScreenSpaceEventType.MOUSE_MOVE);
            handler.setInputAction(function (position) {
                flags.looking = false;
            }, Cesium.ScreenSpaceEventType.LEFT_UP);
            document.addEventListener('keydown', this.down = function (e) {
                var flagName = CesiumControl.getFlagForKeyCode(e.keyCode);
                if (typeof flagName !== 'undefined') {
                    flags[flagName] = true;
                }
            }, false);

            document.addEventListener('keyup', this.up = function (e) {
                var flagName = CesiumControl.getFlagForKeyCode(e.keyCode);
                if (typeof flagName !== 'undefined') {
                    flags[flagName] = false;
                }
            }, false);

            viewer.clock.onTick.addEventListener(function (clock) {
                var camera = viewer.camera;

                if (flags.looking) {
                    var width = canvas.clientWidth;
                    var height = canvas.clientHeight;

                    // Coordinate (0.0, 0.0) will be where the mouse was clicked.
                    var x = (mousePosition.x - startMousePosition.x) / width;
                    var y = -(mousePosition.y - startMousePosition.y) / height;

                    var lookFactor = 0.05;
                    camera.lookRight(x * lookFactor);
                    camera.lookUp(y * lookFactor);
                }

                // Change movement speed based on the distance of the camera to the surface of the ellipsoid.
                var cameraHeight = ellipsoid.cartesianToCartographic(camera.position).height;
                var moveRate = cameraHeight / 100.0;

                if (flags.moveForward) {
                    camera.moveForward(moveRate);
                }
                if (flags.moveBackward) {
                    camera.moveBackward(moveRate);
                }
                if (flags.moveUp) {
                    camera.moveUp(moveRate);
                }
                if (flags.moveDown) {
                    camera.moveDown(moveRate);
                }
                if (flags.moveLeft) {
                    camera.moveLeft(moveRate);
                }
                if (flags.moveRight) {
                    camera.moveRight(moveRate);
                }
            });
        }

        CesiumControl.getFlagForKeyCode = function (keyCode) {
            switch (keyCode) {
                case 'W'.charCodeAt(0):
                    return 'moveForward';
                case 'S'.charCodeAt(0):
                    return 'moveBackward';
                case 'Q'.charCodeAt(0):
                    return 'moveUp';
                case 'E'.charCodeAt(0):
                    return 'moveDown';
                case 'D'.charCodeAt(0):
                    return 'moveRight';
                case 'A'.charCodeAt(0):
                    return 'moveLeft';
                default:
                    return undefined;
            }
        }


        CesiumControl.endControl = function () {
            this.handler  = this.handler  && this.handler .destroy();
            let viewer = this.viewer, scene = viewer.scene
            scene.screenSpaceCameraController.enableRotate = true;
            scene.screenSpaceCameraController.enableTranslate = true;
            scene.screenSpaceCameraController.enableZoom = true;
            scene.screenSpaceCameraController.enableTilt = true;
            scene.screenSpaceCameraController.enableLook = true;
            viewer.screenSpaceEventHandler.removeInputAction(Cesium.ScreenSpaceEventType.LEFT_DOWN)
            viewer.screenSpaceEventHandler.removeInputAction(Cesium.ScreenSpaceEventType.MOUSE_MOVE)
            viewer.screenSpaceEventHandler.removeInputAction(Cesium.ScreenSpaceEventType.LEFT_UP)
            document.removeEventListener('keydown', this.down, false)
            document.removeEventListener('keyup', this.up, false)
        }

        return CesiumControl;
    }
    if (typeof (CesiumControl) === 'undefined') {
        window.CesiumControl = define_CesiumControl();
    } else {
        console.log("CesiumControl already defined.");
    }

})(window);