#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>

#define ITERATIONS 100000

// Shared variables
pthread_mutex_t lock;
pthread_cond_t cond;
int signal_flag = 0; // 0 = LOW, 1 = HIGH
int counter = 0;

// set up an array of timespec structs to store timestamps
struct timespec timestamps[ITERATIONS]; 

void* high_thread(void* arg) {
    while (1) {

        if (counter >= ITERATIONS) {
            pthread_cond_signal(&cond);
            return NULL;
        }

        pthread_mutex_lock(&lock);

        // Wait for turn
        while (signal_flag != 1) {
            pthread_cond_wait(&cond, &lock);
        }
        #ifdef DEBUG
        printf("%d: HIGH\n", counter);
        #endif
        counter++;
        signal_flag = 0;

        if (clock_gettime(CLOCK_MONOTONIC, &timestamps[counter]) != 0) {
            perror("clock_gettime failed");
            exit(1);
        }

        // Signal the other thread
        pthread_mutex_unlock(&lock);
        pthread_cond_signal(&cond);
    }
    return NULL;
}

void* low_thread(void* arg) {
    while (1) {
        if (counter >= ITERATIONS) {
            pthread_cond_signal(&cond);
            return NULL;
        }

        pthread_mutex_lock(&lock);

        // Wait for turn
        while (signal_flag != 0) {
            pthread_cond_wait(&cond, &lock);
        }

        #ifdef DEBUG
        printf("%d: LOW\n", counter);
        #endif
        counter++;
        signal_flag = 1;

        if (clock_gettime(CLOCK_MONOTONIC, &timestamps[counter]) != 0) {
            perror("clock_gettime failed");
            exit(1);
        }

        // Signal the other thread
        pthread_mutex_unlock(&lock);
        pthread_cond_signal(&cond);
    }
    return NULL;
}

int main() {
    pthread_t high_tid, low_tid;

    // Initialize synchronization primitives
    pthread_mutex_init(&lock, NULL);
    pthread_cond_init(&cond, NULL);

    // Create threads
    pthread_create(&high_tid, NULL, high_thread, NULL);
    pthread_create(&low_tid, NULL, low_thread, NULL);


    printf("Start threads:\n");

    // Wait for threads to finish
    pthread_join(high_tid, NULL);
    pthread_join(low_tid, NULL);

    // Cleanup
    pthread_mutex_destroy(&lock);
    pthread_cond_destroy(&cond);


    for (int i = 1; i < ITERATIONS; i++) {
        printf("Period %zu: %ld.%09ld seconds\n", 
               i, 
               timestamps[i].tv_sec - timestamps[i-1].tv_sec,  
               timestamps[i].tv_nsec) - timestamps[i-1].tv_nsec;
    }

    return 0;
}