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

#define DEBUG 1

#define ITERATIONS 100000

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


void* high_thread() {
    while (1) {

        pthread_mutex_lock(&lock);

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

        // Wait for turn
        while (state_flag != 1) {
            pthread_cond_wait(&cond, &lock);
        }

        // Critical section
        #if DEBUG
        printf("%d: HIGH\n", counter);
        #endif
        counter++;
        state_flag = 0; // Switch to LOW

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

void* low_thread() {
    while (1) {
        pthread_mutex_lock(&lock);

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

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

        // Critical section
        #if DEBUG
        printf("%d: LOW\n", counter);
        #endif
        counter++;
        state_flag = 1; // Switch to HIGH

        // 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);


    #if DEBUG
    printf("Start threads:\n");
    #endif

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

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

    return 0;
}