/**
 * @module olcs.Camera
 */

import {unByKey as olObservableUnByKey} from 'ol/Observable.js';
import {toRadians, toDegrees} from './math.js';
import {getTransform} from 'ol/proj.js';
import olcsCore, {calcDistanceForResolution, calcResolutionForDistance} from './core.js';

class Camera {
  /**
   * This object takes care of additional 3d-specific properties of the view and
   * ensures proper synchronization with the underlying raw Cesium.Camera object.
   * @param {!Cesium.Scene} scene
   * @param {!ol.Map} map
   * @api
   */
  constructor(scene, map) {
    /**
     * @type {!Cesium.Scene}
     * @private
     */
    this.scene_ = scene;

    /**
     * @type {!Cesium.Camera}
     * @private
     */
    this.cam_ = scene.camera;

    /**
     * @type {!ol.Map}
     * @private
     */
    this.map_ = map;

    /**
     * @type {?ol.View}
     * @private
     */
    this.view_ = null;

    /**
     * @type {?ol.EventsKey}
     * @private
     */
    this.viewListenKey_ = null;

    /**
     * @type {!ol.TransformFunction}
     * @private
     */
    this.toLonLat_ = Camera.identityProjection;

    /**
     * @type {!ol.TransformFunction}
     * @private
     */
    this.fromLonLat_ = Camera.identityProjection;

    /**
     * 0 -- topdown, PI/2 -- the horizon
     * @type {number}
     * @private
     */
    this.tilt_ = 0;

    /**
     * @type {number}
     * @private
     */
    this.distance_ = 0;

    /**
     * @type {?Cesium.Matrix4}
     * @private
     */
    this.lastCameraViewMatrix_ = null;

    /**
     * This is used to discard change events on view caused by updateView method.
     * @type {boolean}
     * @private
     */
    this.viewUpdateInProgress_ = false;

    this.map_.on('change:view', (e) => {
      this.setView_(this.map_.getView());
    });
    this.setView_(this.map_.getView());
  }

  /**
   * @param {Array.<number>} input Input coordinate array.
   * @param {Array.<number>=} opt_output Output array of coordinate values.
   * @param {number=} opt_dimension Dimension.
   * @return {Array.<number>} Input coordinate array (same array as input).
   */
  static identityProjection(input, opt_output, opt_dimension) {
    const dim = opt_dimension || input.length;
    if (opt_output) {
      for (let i = 0; i < dim; ++i) {
        opt_output[i] = input[i];
      }
    }
    return input;
  }

  /**
   * @param {?ol.View} view New view to use.
   * @private
   */
  setView_(view) {
    if (this.view_) {
      olObservableUnByKey(this.viewListenKey_);
      this.viewListenKey_ = null;
    }

    this.view_ = view;
    if (view) {
      const toLonLat = getTransform(view.getProjection(), 'EPSG:4326');
      const fromLonLat = getTransform('EPSG:4326', view.getProjection());
      console.assert(toLonLat && fromLonLat);

      this.toLonLat_ = toLonLat;
      this.fromLonLat_ = fromLonLat;

      this.viewListenKey_ = view.on('propertychange', e => this.handleViewEvent_(e));

      this.readFromView();
    } else {
      this.toLonLat_ = Camera.identityProjection;
      this.fromLonLat_ = Camera.identityProjection;
    }
  }

  /**
   * @param {?} e
   * @private
   */
  handleViewEvent_(e) {
    if (!this.viewUpdateInProgress_) {
      this.readFromView();
    }
  }

  /**
   * @param {number} heading In radians.
   * @api
   */
  setHeading(heading) {
    if (!this.view_) {
      return;
    }

    this.view_.setRotation(heading);
  }

  /**
   * @return {number|undefined} Heading in radians.
   * @api
   */
  getHeading() {
    if (!this.view_) {
      return undefined;
    }
    const rotation = this.view_.getRotation();
    return rotation || 0;
  }

  /**
   * @param {number} tilt In radians.
   * @api
   */
  setTilt(tilt) {
    this.tilt_ = tilt;
    this.updateCamera_();
  }

  /**
   * @return {number} Tilt in radians.
   * @api
   */
  getTilt() {
    return this.tilt_;
  }

  /**
   * @param {number} distance In meters.
   * @api
   */
  setDistance(distance) {
    this.distance_ = distance;
    this.updateCamera_();
    this.updateView();
  }

  /**
   * @return {number} Distance in meters.
   * @api
   */
  getDistance() {
    return this.distance_;
  }

  /**
   * Shortcut for ol.View.setCenter().
   * @param {!ol.Coordinate} center Same projection as the ol.View.
   * @api
   */
  setCenter(center) {
    if (!this.view_) {
      return;
    }
    this.view_.setCenter(center);
  }

  /**
   * Shortcut for ol.View.getCenter().
   * @return {ol.Coordinate|undefined} Same projection as the ol.View.
   * @api
   */
  getCenter() {
    if (!this.view_) {
      return undefined;
    }
    return this.view_.getCenter();
  }

  /**
   * Sets the position of the camera.
   * @param {!ol.Coordinate} position Same projection as the ol.View.
   * @api
   */
  setPosition(position) {
    if (!this.toLonLat_) {
      return;
    }
    const ll = this.toLonLat_(position);
    console.assert(ll);

    const carto = new Cesium.Cartographic(
        toRadians(ll[0]),
        toRadians(ll[1]),
        this.getAltitude());

    this.cam_.setView({
      destination: Cesium.Ellipsoid.WGS84.cartographicToCartesian(carto)
    });
    this.updateView();
  }

  /**
   * Calculates position under the camera.
   * @return {!ol.Coordinate|undefined} Same projection as the ol.View.
   * @api
   */
  getPosition() {
    if (!this.fromLonLat_) {
      return undefined;
    }
    const carto = Cesium.Ellipsoid.WGS84.cartesianToCartographic(this.cam_.position);

    const pos = this.fromLonLat_([
      toDegrees(carto.longitude),
      toDegrees(carto.latitude)
    ]);
    console.assert(pos);
    return pos;
  }

  /**
   * @param {number} altitude In meters.
   * @api
   */
  setAltitude(altitude) {
    const carto = Cesium.Ellipsoid.WGS84.cartesianToCartographic(
        this.cam_.position);
    carto.height = altitude;
    this.cam_.position = Cesium.Ellipsoid.WGS84.cartographicToCartesian(carto);

    this.updateView();
  }

  /**
   * @return {number} Altitude in meters.
   * @api
   */
  getAltitude() {
    const carto = Cesium.Ellipsoid.WGS84.cartesianToCartographic(
        this.cam_.position);

    return carto.height;
  }

  /**
   * Updates the state of the underlying Cesium.Camera
   * according to the current values of the properties.
   * @private
   */
  updateCamera_() {
    if (!this.view_ || !this.toLonLat_) {
      return;
    }
    const center = this.view_.getCenter();
    if (!center) {
      return;
    }
    const ll = this.toLonLat_(center);
    console.assert(ll);

    const carto = new Cesium.Cartographic(toRadians(ll[0]),
        toRadians(ll[1]));
    if (this.scene_.globe) {
      const height = this.scene_.globe.getHeight(carto);
      carto.height = height || 0;
    }

    const destination = Cesium.Ellipsoid.WGS84.cartographicToCartesian(carto);

    /** @type {Cesium.optionsOrientation} */
    const orientation = {
      pitch: this.tilt_ - Cesium.Math.PI_OVER_TWO,
      heading: -this.view_.getRotation(),
      roll: undefined
    };
    this.cam_.setView({
      destination,
      orientation
    });

    this.cam_.moveBackward(this.distance_);

    this.checkCameraChange(true);
  }

  /**
   * Calculates the values of the properties from the current ol.View state.
   * @api
   */
  readFromView() {
    if (!this.view_ || !this.toLonLat_) {
      return;
    }
    const center = this.view_.getCenter();
    if (center === undefined || center === null) {
      return;
    }
    const ll = this.toLonLat_(center);
    console.assert(ll);

    const resolution = this.view_.getResolution();
    this.distance_ = this.calcDistanceForResolution(
        resolution || 0, toRadians(ll[1]));

    this.updateCamera_();
  }

  /**
   * Calculates the values of the properties from the current Cesium.Camera state.
   * Modifies the center, resolution and rotation properties of the view.
   * @api
   */
  updateView() {
    if (!this.view_ || !this.fromLonLat_) {
      return;
    }
    this.viewUpdateInProgress_ = true;

    // target & distance
    const ellipsoid = Cesium.Ellipsoid.WGS84;
    const scene = this.scene_;
    const target = olcsCore.pickCenterPoint(scene);

    let bestTarget = target;
    if (!bestTarget) {
      //TODO: how to handle this properly ?
      const globe = scene.globe;
      const carto = this.cam_.positionCartographic.clone();
      const height = globe.getHeight(carto);
      carto.height = height || 0;
      bestTarget = Cesium.Ellipsoid.WGS84.cartographicToCartesian(carto);
    }
    this.distance_ = Cesium.Cartesian3.distance(bestTarget, this.cam_.position);
    const bestTargetCartographic = ellipsoid.cartesianToCartographic(bestTarget);
    this.view_.setCenter(this.fromLonLat_([
      toDegrees(bestTargetCartographic.longitude),
      toDegrees(bestTargetCartographic.latitude)]));

    // resolution
    this.view_.setResolution(
        this.calcResolutionForDistance(this.distance_,
            bestTargetCartographic ? bestTargetCartographic.latitude : 0));


    /*
     * Since we are positioning the target, the values of heading and tilt
     * need to be calculated _at the target_.
     */
    if (target) {
      const pos = this.cam_.position;

      // normal to the ellipsoid at the target
      const targetNormal = new Cesium.Cartesian3();
      ellipsoid.geocentricSurfaceNormal(target, targetNormal);

      // vector from the target to the camera
      const targetToCamera = new Cesium.Cartesian3();
      Cesium.Cartesian3.subtract(pos, target, targetToCamera);
      Cesium.Cartesian3.normalize(targetToCamera, targetToCamera);


      // HEADING
      const up = this.cam_.up;
      const right = this.cam_.right;
      const normal = new Cesium.Cartesian3(-target.y, target.x, 0); // what is it?
      const heading = Cesium.Cartesian3.angleBetween(right, normal);
      const cross = Cesium.Cartesian3.cross(target, up, new Cesium.Cartesian3());
      const orientation = cross.z;

      this.view_.setRotation((orientation < 0 ? heading : -heading));

      // TILT
      const tiltAngle = Math.acos(
          Cesium.Cartesian3.dot(targetNormal, targetToCamera));
      this.tilt_ = isNaN(tiltAngle) ? 0 : tiltAngle;
    } else {
      // fallback when there is no target
      this.view_.setRotation(this.cam_.heading);
      this.tilt_ = -this.cam_.pitch + Math.PI / 2;
    }

    this.viewUpdateInProgress_ = false;
  }

  /**
   * Check if the underlying camera state has changed and ensure synchronization.
   * @param {boolean=} opt_dontSync Do not synchronize the view.
   */
  checkCameraChange(opt_dontSync) {
    const old = this.lastCameraViewMatrix_;
    const current = this.cam_.viewMatrix;

    if (!old || !Cesium.Matrix4.equalsEpsilon(old, current, 1e-5)) {
      this.lastCameraViewMatrix_ = current.clone();
      if (opt_dontSync !== true) {
        this.updateView();
      }
    }
  }

  /**
   * calculate the distance between camera and centerpoint based on the resolution and latitude value
   * @param {number} resolution Number of map units per pixel.
   * @param {number} latitude Latitude in radians.
   * @return {number} The calculated distance.
   * @api
   */
  calcDistanceForResolution(resolution, latitude) {
    return calcDistanceForResolution(resolution, latitude, this.scene_, this.view_.getProjection());
  }

  /**
   * calculate the resolution based on a distance(camera to position) and latitude value
   * @param {number} distance
   * @param {number} latitude
   * @return {number} The calculated resolution.
   * @api
   */
  calcResolutionForDistance(distance, latitude) {
    return calcResolutionForDistance(distance, latitude, this.scene_, this.view_.getProjection());
  }
}


export default Camera;