#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <time.h>
#include <signal.h>


#define STAT_FILE "/proc/stat"
#define OUT_FILE "/tmp/cputild"

volatile int running = 1;

void signal_handler_sigint(const int _signal) {
    assert(_signal == SIGINT && "ERROR: Signal except SIGINT received by the SIGINT handler");

    printf("hello there\n");
    running = 0;
}

int main(void) {
    int ret = 0;

    // register the SIGINT handler
    signal(SIGINT, signal_handler_sigint);

    FILE *out_file = fopen(OUT_FILE, "w");
    FILE *stat_file = fopen(STAT_FILE, "r");

    uint64_t total_jiffies_active = 0;
    uint64_t total_jiffies_idle = 0;

    size_t line_len = 1024;
    char *line_buffer = (char*)malloc(line_len);

    while (running) {
        struct timespec now;
        struct timespec request;
        struct timespec remain;

        request.tv_sec = 1;
        request.tv_nsec = 0;
        nanosleep(&request, &remain);
        clock_gettime(CLOCK_REALTIME, &now);

        fflush(stat_file);
        fseek(stat_file, 0, SEEK_SET);
        const ssize_t read = getline(&line_buffer, &line_len, stat_file);
        if (read == -1) {
            printf("Failed to read the stat file!\n");
            ret = 1;
            goto exit_label;
        }

        uint64_t user, user_nice, system, idle, iowait, irq, softirq, steal, guest, guest_nice;
        const int n_read = sscanf(line_buffer, "cpu %lu %lu %lu %lu %lu %lu %lu %lu %lu %lu", &user, &user_nice, &system, &idle, &iowait, &irq, &softirq, &steal, &guest, &guest_nice); // NOLINT(*-err34-c)
        if (n_read != 10) {
            printf("Failed to read the stat file: Invalid format?\n");
            ret = 1;
            goto exit_label;
        }

        const uint64_t current_total_jiffies_active = user + user_nice + system + irq + softirq + guest + guest_nice;
        const uint64_t current_total_jiffies_idle = iowait + idle;

        const uint64_t delta_jiffies_active = current_total_jiffies_active - total_jiffies_active;
        const uint64_t delta_jiffies_idle = current_total_jiffies_idle - total_jiffies_idle;

        const double utilization = (double)(delta_jiffies_active) / (double)(delta_jiffies_idle + delta_jiffies_active);

        total_jiffies_active = current_total_jiffies_active;
        total_jiffies_idle = current_total_jiffies_idle;

        out_file = freopen(OUT_FILE, "w", out_file);
        fseek(out_file, 0, SEEK_SET);
        fprintf(out_file, "%.02f", utilization * 100);
        fflush(out_file);
    }

exit_label:
    free(line_buffer);

    printf("Terminating...\n");
    return ret;
}