package com.xiaopeng.itinerary.utils.map;

public class FastDistanceCalculator {
    private static final double R = 6371.0; // 地球半径（千米）
    private static final double DEG_TO_RAD = Math.PI / 180.0;
    
    /**
     * 快速近似算法 - 性能极高，误差<0.5%
     * 适合需要大量计算的场景（如KNN、聚类）
     * 米
     */
    public static double distanceFast(double lat1, double lon1, 
                                      double lat2, double lon2) {
        try {
            double x = (lon2 - lon1) * DEG_TO_RAD * Math.cos((lat1 + lat2) * 0.5 * DEG_TO_RAD);
            double y = (lat2 - lat1) * DEG_TO_RAD;
            return R * Math.sqrt(x * x + y * y)*1000;
        }catch (Exception e){
            e.printStackTrace();
        }
        return 0;

    }

    /**
     * 快速近似算法 - 误差<0.5%
     * 适合需要大量计算的场景（如KNN、聚类）
     * 千米
     */
    public static double distanceFastKm(double lat1, double lon1,
                                      double lat2, double lon2) {
        double x = (lon2 - lon1) * DEG_TO_RAD * Math.cos((lat1 + lat2) * 0.5 * DEG_TO_RAD);
        double y = (lat2 - lat1) * DEG_TO_RAD;
        return R * Math.sqrt(x * x + y * y);
    }

    /**
     * 平面近似 - 极高性能，适用于小范围（城市内）
     */
    public static double distanceFlatApprox(double lat1, double lon1,
                                           double lat2, double lon2) {
        // 每度纬度约111km，每度经度随纬度变化
        double kmPerDegreeLat = 111.0;
        double kmPerDegreeLon = 111.0 * Math.cos((lat1 + lat2) * 0.5 * DEG_TO_RAD);
        
        double dLat = lat2 - lat1;
        double dLon = lon2 - lon1;
        
        return Math.sqrt(Math.pow(dLat * kmPerDegreeLat, 2) + 
                        Math.pow(dLon * kmPerDegreeLon, 2));
    }
}