// Description: This program uses semaphores to create a square wave between two threads.
// The period of the square wave is timed and displayed after the threads have finished.

#include <stdio.h>
#include <pthread.h>
#include <semaphore.h>
#include <time.h>

#define DEBUG 0
#define NUM_PERIODS 100000

sem_t high_sem, low_sem;

struct timespec start_time, end_time;

// Array to store periods
int periods[NUM_PERIODS];

void* high() {
    for (int i = 0; i < NUM_PERIODS; i++) {
        sem_wait(&high_sem);

        if (i != 0) {
            // Calculate period
            clock_gettime(CLOCK_MONOTONIC, &end_time);
            periods[i] = (end_time.tv_sec - start_time.tv_sec) * 1e9 + (end_time.tv_nsec - start_time.tv_nsec);
        }
        clock_gettime(CLOCK_MONOTONIC, &start_time);

        #if DEBUG
        printf("%d: HIGH\n", i);
        #endif
        sem_post(&low_sem);

    }
    return NULL;
}

void* low() {
    for (int i = 0; i < NUM_PERIODS; i++) {
        sem_wait(&low_sem);
        #if DEBUG
        printf("%d: LOW\n", i);
        #endif
        sem_post(&high_sem);
    }
    return NULL;
}

int main() {
    pthread_t high_thread, low_thread;

    sem_init(&high_sem, 0, 1); // high_sem starts 
    sem_init(&low_sem, 0, 0);

    pthread_create(&high_thread, NULL, high, NULL);
    pthread_create(&low_thread, NULL, low, NULL);

    pthread_join(high_thread, NULL);
    pthread_join(low_thread, NULL);

    sem_destroy(&high_sem);
    sem_destroy(&low_sem);

    int min_period = periods[1];
    int max_period = periods[1];
    int sum_of_periods = 0;

    // Print periods for each iteration
    for (int i = 1; i < NUM_PERIODS; i++) {
        if (periods[i] < min_period) {
            min_period = periods[i];
        }
        if (periods[i] > max_period) {
            max_period = periods[i];
        }
        sum_of_periods += periods[i];
        //printf("Period %d: %lld nanoseconds\n", i, periods[i]);
        //printf("%lld\n", periods[i]);
    }
    printf("Minimum period: %d nanoseconds\n", min_period);
    printf("Maximum period: %d nanoseconds\n", max_period);
    printf("Average period: %f nanoseconds\n", (float)sum_of_periods / (NUM_PERIODS - 1));

    return 0;
}