package org.example;import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.Date;
import java.util.List;public class LttbUtils {/*** LTTB算法，用于优化抽样，入参为两个double值，第一个是时间戳，第二个是要抽样的变量值* @param data* @param threshold* @return*/public static List<double[]> lttb(List<double[]> data, int threshold) {// Step 1: Sort the data by x-axis (ascending order)data.sort(Comparator.comparingDouble(a -> a[0]));// Step 2: Divide the data into bucketsint bucketSize = (int) Math.ceil(data.size() / (double) threshold);List<List<double[]>> buckets = new ArrayList<>(bucketSize);for (int i = 0; i < data.size(); i += bucketSize) {buckets.add(data.subList(i, Math.min(i + bucketSize, data.size())));}// Step 3: Compute the largest triangle in each bucketList<double[]> result = new ArrayList<>(threshold);for (List<double[]> bucket : buckets) {if (bucket.size() < 3) {result.addAll(bucket);continue;}double areaMax = 0;int indexMax = 0;//增加极值//在找到每个 bucket 中最大三角形面积时，不仅记录最大面积和对应索引，还需要记录包含该最大面积的三角形的三个点。//将这些记录下来的三角形点加入结果集中，而不仅仅只是最大面积对应的点。
//            double[] p0Max = null;
//            double[] p1Max = null;
//            double[] p2Max = null;//for (int i = 1; i < bucket.size() - 1; i++) {double[] p0 = bucket.get(0);double[] p1 = bucket.get(i);double[] p2 = bucket.get(i + 1);double area = Math.abs((p1[0] - p0[0]) * (p2[1] - p0[1]) - (p2[0] - p0[0]) * (p1[1] - p0[1])) / 2.0;if (area > areaMax) {areaMax = area;indexMax = i;//增加极值
//                    p0Max = p0;
//                    p1Max = p1;
//                    p2Max = p2;//}}// 增加极值
//            if (p0Max != null)
//                result.add(p0Max);
//            if (p1Max != null)
//                result.add(p1Max);
//            if (p2Max != null)
//                result.add(p2Max);//result.add(bucket.get(indexMax));}//        // Step 4: Interpolate the data points
//        LinearInterpolator interpolator = new LinearInterpolator();
//        PolynomialSplineFunction function = interpolator.interpolate(result.stream().mapToDouble(p -> p[0]).toArray(),
//                result.stream().mapToDouble(p -> p[1]).toArray());
//
//        // Step 5: Sample the interpolated function to get the final output
//        List<double[]> output = new ArrayList<>(threshold);
//        double step = (result.get(result.size() - 1)[0] - result.get(0)[0]) / (double) (threshold - 1);
//        for (int i = 0; i < threshold; i++) {
//            double x = result.get(0)[0] + i * step;
//            output.add(new double[]{x, function.value(x)});
//        }
//        return output;return result;}public static String formatTimestampToTime(double timestamp) {SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy/M/d H:mm:ss");Date date = new Date((long) timestamp);return dateFormat.format(date);}public static double parseTimeToTimestamp(String timeString) {SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy/M/d H:mm:ss");try {Date date = dateFormat.parse(timeString);return date.getTime(); // Convert milliseconds to seconds} catch (ParseException e) {e.printStackTrace();return 0; // Return 0 if parsing fails}}
}