#include <aio.h>
#include <pthread.h>
#include <semaphore.h>
#include <limits.h>
#include <errno.h>
#include <unistd.h>
#include <stdlib.h>
#include "syscall.h"
#include "atomic.h"
#include "libc.h"
#include "pthread_impl.h"

/* The following is a threads-based implementation of AIO with minimal
 * dependence on implementation details. Most synchronization is
 * performed with pthread primitives, but atomics and futex operations
 * are used for notification in a couple places where the pthread
 * primitives would be inefficient or impractical.
 *
 * For each fd with outstanding aio operations, an aio_queue structure
 * is maintained. These are reference-counted and destroyed by the last
 * aio worker thread to exit. Accessing any member of the aio_queue
 * structure requires a lock on the aio_queue. Adding and removing aio
 * queues themselves requires a write lock on the global map object,
 * a 4-level table mapping file descriptor numbers to aio queues. A
 * read lock on the map is used to obtain locks on existing queues by
 * excluding destruction of the queue by a different thread while it is
 * being locked.
 *
 * Each aio queue has a list of active threads/operations. Presently there
 * is a one to one relationship between threads and operations. The only
 * members of the aio_thread structure which are accessed by other threads
 * are the linked list pointers, op (which is immutable), running (which
 * is updated atomically), and err (which is synchronized via running),
 * so no locking is necessary. Most of the other other members are used
 * for sharing data between the main flow of execution and cancellation
 * cleanup handler.
 *
 * Taking any aio locks requires having all signals blocked. This is
 * necessary because aio_cancel is needed by close, and close is required
 * to be async-signal safe. All aio worker threads run with all signals
 * blocked permanently.
 */

struct aio_args {
  struct aiocb* cb;
  int op;
  int err;
  sem_t sem;
};

struct aio_thread {
  pthread_t td;
  struct aiocb* cb;
  struct aio_thread *next, *prev;
  struct aio_queue* q;
  volatile int running;
  int err, op;
  ssize_t ret;
};

struct aio_queue {
  int fd, seekable, append, ref, init;
  pthread_mutex_t lock;
  pthread_cond_t cond;
  struct aio_thread* head;
};

static pthread_rwlock_t maplock = PTHREAD_RWLOCK_INITIALIZER;
static struct aio_queue***** map;
static volatile int aio_fd_cnt;
volatile int __aio_fut;

static struct aio_queue* __aio_get_queue(int fd, int need) {
  if (fd < 0)
    return 0;
  int a = fd >> 24;
  unsigned char b = fd >> 16, c = fd >> 8, d = fd;
  struct aio_queue* q = 0;
  pthread_rwlock_rdlock(&maplock);
  if ((!map || !map[a] || !map[a][b] || !map[a][b][c] ||
       !(q = map[a][b][c][d])) &&
      need) {
    pthread_rwlock_unlock(&maplock);
    pthread_rwlock_wrlock(&maplock);
    if (!map)
      map = calloc(sizeof *map, (-1U / 2 + 1) >> 24);
    if (!map)
      goto out;
    if (!map[a])
      map[a] = calloc(sizeof **map, 256);
    if (!map[a])
      goto out;
    if (!map[a][b])
      map[a][b] = calloc(sizeof ***map, 256);
    if (!map[a][b])
      goto out;
    if (!map[a][b][c])
      map[a][b][c] = calloc(sizeof ****map, 256);
    if (!map[a][b][c])
      goto out;
    if (!(q = map[a][b][c][d])) {
      map[a][b][c][d] = q = calloc(sizeof *****map, 1);
      if (q) {
        q->fd = fd;
        pthread_mutex_init(&q->lock, 0);
        pthread_cond_init(&q->cond, 0);
        a_inc(&aio_fd_cnt);
      }
    }
  }
  if (q)
    pthread_mutex_lock(&q->lock);
out:
  pthread_rwlock_unlock(&maplock);
  return q;
}

static void __aio_unref_queue(struct aio_queue* q) {
  if (q->ref > 1) {
    q->ref--;
    pthread_mutex_unlock(&q->lock);
    return;
  }

  /* This is potentially the last reference, but a new reference
   * may arrive since we cannot free the queue object without first
   * taking the maplock, which requires releasing the queue lock. */
  pthread_mutex_unlock(&q->lock);
  pthread_rwlock_wrlock(&maplock);
  pthread_mutex_lock(&q->lock);
  if (q->ref == 1) {
    int fd = q->fd;
    int a = fd >> 24;
    unsigned char b = fd >> 16, c = fd >> 8, d = fd;
    map[a][b][c][d] = 0;
    a_dec(&aio_fd_cnt);
    pthread_rwlock_unlock(&maplock);
    pthread_mutex_unlock(&q->lock);
    free(q);
  } else {
    q->ref--;
    pthread_rwlock_unlock(&maplock);
    pthread_mutex_unlock(&q->lock);
  }
}

static void cleanup(void* ctx) {
  struct aio_thread* at = ctx;
  struct aio_queue* q = at->q;
  struct aiocb* cb = at->cb;
  struct sigevent sev = cb->aio_sigevent;

  /* There are four potential types of waiters we could need to wake:
   *   1. Callers of aio_cancel/close.
   *   2. Callers of aio_suspend with a single aiocb.
   *   3. Callers of aio_suspend with a list.
   *   4. AIO worker threads waiting for sequenced operations.
   * Types 1-3 are notified via atomics/futexes, mainly for AS-safety
   * considerations. Type 4 is notified later via a cond var. */

  cb->__ret = at->ret;
  if (a_swap(&at->running, 0) < 0)
    __wake(&at->running, -1, 1);
  if (a_swap(&cb->__err, at->err) != EINPROGRESS)
    __wake(&cb->__err, -1, 1);
  if (a_swap(&__aio_fut, 0))
    __wake(&__aio_fut, -1, 1);

  pthread_mutex_lock(&q->lock);

  if (at->next)
    at->next->prev = at->prev;
  if (at->prev)
    at->prev->next = at->next;
  else
    q->head = at->next;

  /* Signal aio worker threads waiting for sequenced operations. */
  pthread_cond_broadcast(&q->cond);

  __aio_unref_queue(q);

  if (sev.sigev_notify == SIGEV_SIGNAL) {
    siginfo_t si = {.si_signo = sev.sigev_signo,
                    .si_value = sev.sigev_value,
                    .si_code = SI_ASYNCIO,
                    .si_pid = getpid(),
                    .si_uid = getuid()};
    __syscall(SYS_rt_sigqueueinfo, si.si_pid, si.si_signo, &si);
  }
  if (sev.sigev_notify == SIGEV_THREAD) {
    a_store(&__pthread_self()->cancel, 0);
    sev.sigev_notify_function(sev.sigev_value);
  }
}

static void* io_thread_func(void* ctx) {
  struct aio_thread at, *p;

  struct aio_args* args = ctx;
  struct aiocb* cb = args->cb;
  int fd = cb->aio_fildes;
  int op = args->op;
  void* buf = (void*)cb->aio_buf;
  size_t len = cb->aio_nbytes;
  off_t off = cb->aio_offset;

  struct aio_queue* q = __aio_get_queue(fd, 1);
  ssize_t ret;

  args->err = q ? 0 : EAGAIN;
  sem_post(&args->sem);
  if (!q)
    return 0;

  at.op = op;
  at.running = 1;
  at.ret = -1;
  at.err = ECANCELED;
  at.q = q;
  at.td = __pthread_self();
  at.cb = cb;
  at.prev = 0;
  if ((at.next = q->head))
    at.next->prev = &at;
  q->head = &at;
  q->ref++;

  if (!q->init) {
    int seekable = lseek(fd, 0, SEEK_CUR) >= 0;
    q->seekable = seekable;
    q->append = !seekable || (fcntl(fd, F_GETFL) & O_APPEND);
    q->init = 1;
  }

  pthread_cleanup_push(cleanup, &at);

  /* Wait for sequenced operations. */
  if (op != LIO_READ && (op != LIO_WRITE || q->append)) {
    for (;;) {
      for (p = at.next; p && p->op != LIO_WRITE; p = p->next)
        ;
      if (!p)
        break;
      pthread_cond_wait(&q->cond, &q->lock);
    }
  }

  pthread_mutex_unlock(&q->lock);

  switch (op) {
    case LIO_WRITE:
      ret = q->append ? write(fd, buf, len) : pwrite(fd, buf, len, off);
      break;
    case LIO_READ:
      ret = !q->seekable ? read(fd, buf, len) : pread(fd, buf, len, off);
      break;
    case O_SYNC:
      ret = fsync(fd);
      break;
    case O_DSYNC:
      ret = fdatasync(fd);
      break;
  }
  at.ret = ret;
  at.err = ret < 0 ? errno : 0;

  pthread_cleanup_pop(1);

  return 0;
}

static int submit(struct aiocb* cb, int op) {
  int ret = 0;
  pthread_attr_t a;
  sigset_t allmask, origmask;
  pthread_t td;
  struct aio_args args = {.cb = cb, .op = op};
  sem_init(&args.sem, 0, 0);

  if (cb->aio_sigevent.sigev_notify == SIGEV_THREAD) {
    if (cb->aio_sigevent.sigev_notify_attributes)
      a = *cb->aio_sigevent.sigev_notify_attributes;
    else
      pthread_attr_init(&a);
  } else {
    pthread_attr_init(&a);
    pthread_attr_setstacksize(&a, PTHREAD_STACK_MIN);
    pthread_attr_setguardsize(&a, 0);
  }
  pthread_attr_setdetachstate(&a, PTHREAD_CREATE_DETACHED);
  sigfillset(&allmask);
  pthread_sigmask(SIG_BLOCK, &allmask, &origmask);
  cb->__err = EINPROGRESS;
  if (pthread_create(&td, &a, io_thread_func, &args)) {
    errno = EAGAIN;
    ret = -1;
  }
  pthread_sigmask(SIG_SETMASK, &origmask, 0);

  if (!ret) {
    while (sem_wait(&args.sem))
      ;
    if (args.err) {
      errno = args.err;
      ret = -1;
    }
  }

  return ret;
}

int aio_read(struct aiocb* cb) {
  return submit(cb, LIO_READ);
}

int aio_write(struct aiocb* cb) {
  return submit(cb, LIO_WRITE);
}

int aio_fsync(int op, struct aiocb* cb) {
  if (op != O_SYNC && op != O_DSYNC) {
    errno = EINVAL;
    return -1;
  }
  return submit(cb, op);
}

ssize_t aio_return(struct aiocb* cb) {
  return cb->__ret;
}

int aio_error(const struct aiocb* cb) {
  a_barrier();
  return cb->__err & 0x7fffffff;
}

int aio_cancel(int fd, struct aiocb* cb) {
  sigset_t allmask, origmask;
  int ret = AIO_ALLDONE;
  struct aio_thread* p;
  struct aio_queue* q;

  /* Unspecified behavior case. Report an error. */
  if (cb && fd != cb->aio_fildes) {
    errno = EINVAL;
    return -1;
  }

  sigfillset(&allmask);
  pthread_sigmask(SIG_BLOCK, &allmask, &origmask);

  if (!(q = __aio_get_queue(fd, 0))) {
    if (fcntl(fd, F_GETFD) < 0)
      ret = -1;
    goto done;
  }

  for (p = q->head; p; p = p->next) {
    if (cb && cb != p->cb)
      continue;
    /* Transition target from running to running-with-waiters */
    if (a_cas(&p->running, 1, -1)) {
      pthread_cancel(p->td);
      __wait(&p->running, 0, -1, 1);
      if (p->err == ECANCELED)
        ret = AIO_CANCELED;
    }
  }

  pthread_mutex_unlock(&q->lock);
done:
  pthread_sigmask(SIG_SETMASK, &origmask, 0);
  return ret;
}

int __aio_close(int fd) {
  a_barrier();
  if (aio_fd_cnt)
    aio_cancel(fd, 0);
  return fd;
}