import hilog from '@ohos.hilog';
import file from '@ohos.file.fs'

export class CpuUsageMonitor {
  private static readonly TAG: string = 'CpuUsageMonitor';

  // 读取/proc/stat文件的第一行，获取CPU的总时间信息
  private static getCpuUsage(): number[] {
    let cpuTimes: number[] = [];
    try {
      let result = file.openSync('/proc/stat', file.OpenMode.READ_ONLY);
      let buffer = new ArrayBuffer(1024);
      let len = file.readSync(result.fd, buffer, { offset: 0 });
      let content = String.fromCharCode.apply(null, new Uint8Array(buffer, 0, len));
      file.closeSync(result.fd);

      let lines = content.split('\n');
      if (lines.length > 0 && lines[0].startsWith('cpu ')) {
        let parts = lines[0].split(/\s+/);
        for (let i = 1; i <= 7; i++) {
          cpuTimes.push(parseInt(parts[i]));
        }
      }
    } catch (err) {
      hilog.error(0x0000, this.TAG, `Failed to read /proc/stat: ${err.message}`);
    }
    return cpuTimes;
  }

  // 计算CPU使用率
  private static calculateCpuUsage(prevCpuTimes: number[], currCpuTimes: number[]): number {
    let prevIdle = prevCpuTimes[3] + prevCpuTimes[4]; // idle + iowait
    let currIdle = currCpuTimes[3] + currCpuTimes[4]; // idle + iowait

    let prevTotal = prevCpuTimes.reduce((a, b) => a + b, 0);
    let currTotal = currCpuTimes.reduce((a, b) => a + b, 0);

    let totalDiff = currTotal - prevTotal;
    let idleDiff = currIdle - prevIdle;

    if (totalDiff === 0) {
      return 0;
    }

    return 100 * (totalDiff - idleDiff) / totalDiff;
  }

  public static printCpuUsage(): void {
    setInterval(() => {
      let prevCpuTimes = this.getCpuUsage();
      setTimeout(() => {
        let currCpuTimes = this.getCpuUsage();
        let cpuUsage = this.calculateCpuUsage(prevCpuTimes, currCpuTimes);
        hilog.info(0x0000, this.TAG, `Current CPU Usage: ${cpuUsage.toFixed(2)}%`);
      }, 1000); // 等待1秒
    }, 5000)
  }
}