package com.tongran.agent.client.utils;

import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.List;

public class CpuUsageFromProcStat {

    private static final String PROC_STAT = "/proc/stat";
    private static long[] prevCpuTime = null;

    public static double getCpuUsage() throws Exception {
        List<String> lines = Files.readAllLines(Paths.get(PROC_STAT));
        for (String line : lines) {
            if (line.startsWith("cpu ")) {
                long[] current = parseCpuLine(line);
                if (prevCpuTime == null) {
                    prevCpuTime = current;
                    Thread.sleep(500); // 初始等待
                    return 0.0; // 第一次不返回数据
                }

                double usage = calculateCpuUsage(prevCpuTime, current);
                prevCpuTime = current; // 更新
                return usage;
            }
        }
        throw new RuntimeException("无法读取 /proc/stat 中的 cpu 数据");
    }

    private static long[] parseCpuLine(String line) {
        String[] parts = line.split("\\s+");
        // index: user, nice, system, idle, iowait, irq, softirq, steal
        long user = Long.parseLong(parts[1]);
        long nice = Long.parseLong(parts[2]);
        long system = Long.parseLong(parts[3]);
        long idle = Long.parseLong(parts[4]);
        long iowait = Long.parseLong(parts[5]);
        long irq = Long.parseLong(parts[6]);
        long softirq = Long.parseLong(parts[7]);

        long idleTotal = idle + iowait;
        long systemTotal = user + nice + system + irq + softirq;
        long total = idleTotal + systemTotal;

        return new long[]{idleTotal, total};
    }

    private static double calculateCpuUsage(long[] prev, long[] curr) {
        long idleDiff = curr[0] - prev[0];
        long totalDiff = curr[1] - prev[1];

        if (totalDiff <= 0) return 0.0;

        return 1.0 - ((double) idleDiff / totalDiff);
    }

    public static void main(String[] args) throws Exception {
        // 预热
        getCpuUsage();
        Thread.sleep(1000);

        // 正式采集
        for (int i = 0; i < 5; i++) {
            double usage = getCpuUsage();
            System.out.printf("CPU 使用率: %.2f%%\n", usage * 100);
            Thread.sleep(2000);
        }
    }
}