#include <stdio.h>
#include <unistd.h>

typedef struct {
  long long idle;
  long long total;
} cpu_stats_t;

static int read_cpu_stats(cpu_stats_t *stats) {
  FILE *fp = fopen("/proc/stat", "r");
  if (!fp)
    return 1;

  long long user, nice, system, idle, iowait, irq, softirq;
  int ret = fscanf(fp, "cpu %lld %lld %lld %lld %lld %lld %lld", &user, &nice,
                   &system, &idle, &iowait, &irq, &softirq);
  fclose(fp);

  if (ret != 7)
    return 1;

  stats->idle = idle + iowait;
  stats->total = user + nice + system + idle + iowait + irq + softirq;
  return 0;
}

static double calculate_usage(cpu_stats_t *prev, cpu_stats_t *curr) {
  long long diff_total = curr->total - prev->total;
  long long diff_idle = curr->idle - prev->idle;

  if (diff_total == 0)
    return 0.0;
  return 100.0 * (diff_total - diff_idle) / diff_total;
}

int main() {
  cpu_stats_t prev, curr;

  if (read_cpu_stats(&prev) < 0) {
    fprintf(stderr, "Error reading CPU stats\n");
    return 1;
  }

  sleep(1);

  if (read_cpu_stats(&curr) < 0) {
    fprintf(stderr, "Error reading CPU stats\n");
    return 1;
  }

  printf("CPU: %.0f%%\n", calculate_usage(&prev, &curr));
  return 0;
}