#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <unistd.h>     // for usleep
#include <time.h>       // for time (srand)

#define NUM_THREADS 4
#define NUM_TRANSACTIONS_PER_THREAD 5

int balance = 1000;                 // shared account balance
pthread_mutex_t balance_lock;       // mutex to protect balance

typedef struct {
    int thread_id;
} ThreadArgs;

void *transaction_worker(void *arg) {
    ThreadArgs *targs = (ThreadArgs *)arg;
    int id = targs->thread_id;

    for (int i = 0; i < NUM_TRANSACTIONS_PER_THREAD; i++) {
        int amount = (rand() % 400) + 100;  // 100–499
        int action = rand() % 2;            // 0 = withdraw, 1 = deposit

        // Lock before accessing/modifying shared balance
        pthread_mutex_lock(&balance_lock);

        if (action == 0) {  // withdraw
            if (balance >= amount) {
                balance -= amount;
                printf("[Thread %d] Withdraw %d | New balance = %d\n",
                       id, amount, balance);
            } else {
                printf("[Thread %d] Withdraw %d FAILED (Insufficient funds) | Balance = %d\n",
                       id, amount, balance);
            }
        } else {            // deposit
            balance += amount;
            printf("[Thread %d] Deposit  %d | New balance = %d\n",
                   id, amount, balance);
        }

        // Unlock after updating balance
        pthread_mutex_unlock(&balance_lock);

        // Sleep a bit to better interleave threads
        usleep(100000);   // 0.1s
    }

    return NULL;
}

int main() {
    pthread_t threads[NUM_THREADS];
    ThreadArgs args[NUM_THREADS];

    // Initialize random seed
    srand((unsigned int)time(NULL));

    // Initialize mutex
    if (pthread_mutex_init(&balance_lock, NULL) != 0) {
        perror("Mutex init failed");
        return 1;
    }

    printf("Initial balance = %d\n\n", balance);

    // Create threads
    for (int i = 0; i < NUM_THREADS; i++) {
        args[i].thread_id = i;
        if (pthread_create(&threads[i], NULL, transaction_worker, &args[i]) != 0) {
            perror("pthread_create failed");
            return 1;
        }
    }

    // Wait for all threads to finish
    for (int i = 0; i < NUM_THREADS; i++) {
        pthread_join(threads[i], NULL);
    }

    printf("\nFinal balance = %d\n", balance);

    // Destroy mutex
    pthread_mutex_destroy(&balance_lock);

    return 0;
}