/**
 * @author 基础平台-龚瑞强
 * @description 针对不同分辨率来计算对应的瓦片错级
 */
export class TileResolution {
 constructor() {
 /**
 * key:瓦片尺寸 "256,512,1024"
 * val: 层级与分辨关系数组
 */
 this.levelResolutionToTileSizes = {};
 }

 // 赤道周长(单位:m)
 static get EQUATOR_PERIMTER() {
 return 6378137;
 }

 /**
 * 通过瓦片大小获取层级与分辨关系的数组
 * @param {*} tileSize 瓦片尺寸,三维用的瓦片尺寸为512的levelResolution数组
 * @returns 层级与分辨关系的数组
 */
 getLevelResolutionByTileSize(tileSize) {
 if (!this.levelResolutionToTileSizes[tileSize]) {
 const arr = [];
 for (let level = 0; level <= 24; level++) {
 const r = TileResolution.EQUATOR_PERIMTER; // 赤道半径
 const resolutionOnTheEquator = 360 / (tileSize * 2 ** level);
 arr.push({
 level,
 resolution: resolutionOnTheEquator
 });
 }
 this.levelResolutionToTileSizes[tileSize] = arr;
 }
 return this.levelResolutionToTileSizes[tileSize];
 }

 /**
 * 获取cesium层级与分辨率关系的数组
 * @returns 层级与分辨率关系的数组
 */
 getLevelResolutionCesium() {
 return this.getLevelResolutionByTileSize(512);
 }

 /**
 * 通过分辨率获取其在地图里面对应的层级
 * @param {number} resolution 当前层级分辨率
 * @param {Array<Record<string,number>>} levelResolutions 地图的层级与最大分辨率的对应关系
 * @returns 当前分辨对应地图里面的层级
 */
 getNearLevel(resolution, levelResolutions) {
 const levelResolutionsTemp = JSON.parse(JSON.stringify(levelResolutions));
 const nearlevel = levelResolutionsTemp.sort(function (a, b) {
 return Math.abs(a.resolution - resolution) - Math.abs(b.resolution - resolution);
 })[0].level;
 return nearlevel;
 }

 /**
 * 通过分辨率来计算偏移量
 * @param {number} resolution 当前层级分辨率
 * @param {Array<Record<string,number>>} levelResolutions 当前层级与分辨率关系数组
 * @param {number} levelValue 初始层级
 * @returns 偏移量
 */
 getZoomOffsetByResolution({ resolution, levelResolutions, levelValue }) {
 // 获取当前分辨率对应cesium里面的层级,计算偏移量
 const level = this.getNearLevel(resolution, levelResolutions);
 const zoomOffset = levelValue - level;

 return zoomOffset;
 }

 /**
 * 通过瓦片信息来计算偏移量
 * @param {number} tileInfo 瓦片信息
 * @param {boolean} isCesium 如果是三维图层,则不需要通过size去计算层级与瓦片的数组
 * @returns 偏移量
 */
 getZoomOffsetByTileInfo(tileInfo, isCesium = false, tileSize = 256) {
 let levelResolutions = [];
 const lodBegin = tileInfo.lods[0];
 if (!isCesium) {
 tileSize = tileSize || 256;
 if (tileInfo.size && tileInfo.size.length > 0) {
 tileSize = tileInfo.size[0];
 }
 levelResolutions = this.getLevelResolutionByTileSize(tileSize);
 } else {
 levelResolutions = this.getLevelResolutionCesium();
 }
 let zoomOffset = this.getZoomOffsetByResolution({
 resolution: lodBegin.resolution,
 levelResolutions: levelResolutions,
 levelValue: lodBegin.level
 });

 return zoomOffset;
 }
}
export default TileResolution;