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

struct account {
    pthread_mutex_t mutex;  // protects balance
    int balance;
};

struct thread_info {
    struct account *from;
    struct account *to;
    int n;
    int amount;
};

static void *
transfer_thread(void *_arg)
{
    struct thread_info *info = _arg;
    for (int i = 0; i < info->n; i++) {
        pthread_mutex_t *l1 = &info->from->mutex;
        pthread_mutex_t *l2 = &info->to->mutex;        
        if (l1 < l2) {
            pthread_mutex_lock(l1);
            pthread_mutex_lock(l2);
        } else {
            pthread_mutex_lock(l2);
            pthread_mutex_lock(l1);
        }
            
        if (info->from->balance >= info->amount) {
            info->from->balance -= info->amount;
            info->to->balance += info->amount;
        }

        if (l1 < l2) {
            pthread_mutex_unlock(l2);
            pthread_mutex_unlock(l1);
        } else {
            pthread_mutex_unlock(l1);
            pthread_mutex_unlock(l2);
        }
    }
    free(info);
    return 0;
}

static pthread_t
start_transfer_thread(struct account *from, 
                      struct account *to,
                      int n, int amount)
{
    struct thread_info * info = malloc(sizeof(*info));
    info->from = from;
    info->to = to;
    info->n = n;
    info->amount = amount;
    pthread_t t;
    pthread_create(&t, NULL, transfer_thread, info);
    return t;
}

int
main()
{
    struct account alice = {
        .balance = 1000000,
        .mutex = PTHREAD_MUTEX_INITIALIZER
    };
    struct account bob = {
        .balance = 1000000,
        .mutex = PTHREAD_MUTEX_INITIALIZER
    };

    printf("total balance before %d\n", alice.balance + bob.balance);
    pthread_t s = start_transfer_thread(&bob, &alice, 10000, 10);
    pthread_t t = start_transfer_thread(&alice, &bob, 10000, 10);
    pthread_join(t, (void **) NULL);
    pthread_join(s, (void **) NULL);
    printf("alice.balance %d bob.balance %d\n", alice.balance, bob.balance);
    printf("total balance after %d\n", alice.balance + bob.balance);
    return 0;
}