/*
 * async_nif: An async thread-pool layer for Erlang's NIF API
 *
 * Copyright (c) 2012 Basho Technologies, Inc. All Rights Reserved.
 * Author: Gregory Burd <greg@basho.com> <greg@burd.me>
 *
 * This file is provided to you under the Apache License,
 * Version 2.0 (the "License"); you may not use this file
 * except in compliance with the License.  You may obtain
 * a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

#ifndef __ASYNC_NIF_H__
#define __ASYNC_NIF_H__

#if defined(__cplusplus)
extern "C" {
#endif

#ifdef ASYNC_NIF_STATS
#include "stats.h" // TODO: measure, measure... measure again
#endif

#define ASYNC_NIF_MAX_WORKERS 128
#define ASYNC_NIF_WORKER_QUEUE_SIZE 500

#define FIFO_QUEUE_TYPE(name)             \
  struct fifo_q__ ## name *
#define DECL_FIFO_QUEUE(name, type)       \
  struct fifo_q__ ## name {               \
    unsigned int h, t, s;                 \
    type *items[];                        \
  };                                      \
  static struct fifo_q__ ## name *fifo_q_ ## name ## _new(unsigned int n) { \
    int sz = sizeof(struct fifo_q__ ## name) + ((n+1) * sizeof(type *));\
    struct fifo_q__ ## name *q = enif_alloc(sz);                        \
    if (!q)                                                             \
        return 0;                                                       \
    memset(q, 0, sz);                                                   \
    q->s = n + 1;                                                       \
    return q;                                                           \
  }                                                                     \
  static type *fifo_q_ ## name ## _put(struct fifo_q__ ## name *q, type *n) { \
    q->items[q->h] = n;                                                 \
    q->h = (q->h + 1) % q->s;                                           \
    return n;                                                           \
  }                                                                     \
  static type *fifo_q_ ## name ## _get(struct fifo_q__ ## name *q) {    \
    type *n = q->items[q->t];                                           \
    q->items[q->t] = 0;                                                 \
    q->t = (q->t + 1) % q->s;                                           \
    return n;                                                           \
  }                                                                     \
  static void fifo_q_ ## name ## _free(struct fifo_q__ ## name *q) {    \
    memset(q, 0, sizeof(*q));                                            \
    enif_free(q);                                                       \
  }                                                                     \
  static unsigned int fifo_q_ ## name ## _size(struct fifo_q__ ## name *q) { \
    return (q->h - q->t + q->s) % q->s;                                 \
  }                                                                     \
  static unsigned int fifo_q_ ## name ## _capacity(struct fifo_q__ ## name *q) { \
    return q->s - 1;                                                    \
  }                                                                     \
  static int fifo_q_ ## name ## _empty(struct fifo_q__ ## name *q) {    \
    return (q->t == q->h);                                              \
  }

#define fifo_q_new(name, size) fifo_q_ ## name ## _new(size)
#define fifo_q_free(name, queue) fifo_q_ ## name ## _free(queue)
#define fifo_q_get(name, queue) fifo_q_ ## name ## _get(queue)
#define fifo_q_put(name, queue, item) fifo_q_ ## name ## _put(queue, item)
#define fifo_q_size(name, queue) fifo_q_ ## name ## _size(queue)
#define fifo_q_capacity(name, queue) fifo_q_ ## name ## _capacity(queue)
#define fifo_q_empty(name, queue) fifo_q_ ## name ## _empty(queue)
#define fifo_q_foreach(name, queue, item, task) do {                    \
    while((item = fifo_q_ ## name ## _get(queue)) != NULL) {            \
      do task while(0);                                                 \
    }                                                                   \
  } while(0);

struct async_nif_req_entry {
  ERL_NIF_TERM ref;
  ErlNifEnv *env;
  ErlNifPid pid;
  void *args;
  void (*fn_work)(ErlNifEnv*, ERL_NIF_TERM, ErlNifPid*, unsigned int, void *);
  void (*fn_post)(void *);
};

DECL_FIFO_QUEUE(reqs, struct async_nif_req_entry);

struct async_nif_work_queue {
  ErlNifMutex *reqs_mutex;
  ErlNifCond *reqs_cnd;
  FIFO_QUEUE_TYPE(reqs) reqs;
};

struct async_nif_worker_entry {
  ErlNifTid tid;
  unsigned int worker_id;
  struct async_nif_state *async_nif;
  struct async_nif_work_queue *q;
};

struct async_nif_state {
  unsigned int shutdown;
  unsigned int num_workers;
  struct async_nif_worker_entry worker_entries[ASYNC_NIF_MAX_WORKERS];
  unsigned int num_queues;
  unsigned int next_q;
  struct async_nif_work_queue queues[ASYNC_NIF_MAX_WORKERS]; // TODO: this should be alloc'ed
};

#define ASYNC_NIF_DECL(decl, frame, pre_block, work_block, post_block)  \
  struct decl ## _args frame;                                           \
  static void fn_work_ ## decl (ErlNifEnv *env, ERL_NIF_TERM ref, ErlNifPid *pid, unsigned int worker_id, struct decl ## _args *args) work_block \
  static void fn_post_ ## decl (struct decl ## _args *args) {           \
    do post_block while(0);						\
  }                                                                     \
  static ERL_NIF_TERM decl(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv_in[]) { \
    struct decl ## _args on_stack_args;                                 \
    struct decl ## _args *args = &on_stack_args;                        \
    struct decl ## _args *copy_of_args;                                 \
    struct async_nif_req_entry *req;                                    \
    const char *affinity = NULL;                                        \
    ErlNifEnv *new_env = NULL;                                          \
    /* argv[0] is a ref used for selective recv */                      \
    const ERL_NIF_TERM *argv = argv_in + 1;                             \
    argc -= 1;                                                          \
    struct async_nif_state *async_nif = (struct async_nif_state*)enif_priv_data(env); \
    if (async_nif->shutdown)						\
      return enif_make_tuple2(env, enif_make_atom(env, "error"),        \
                              enif_make_atom(env, "shutdown"));         \
    if (!(new_env = enif_alloc_env())) {                                \
      return enif_make_tuple2(env, enif_make_atom(env, "error"),        \
                              enif_make_atom(env, "enomem"));           \
    }                                                                   \
    do pre_block while(0);                                              \
    req = (struct async_nif_req_entry*)enif_alloc(sizeof(struct async_nif_req_entry)); \
    if (!req) {                                                         \
      fn_post_ ## decl (args);                                          \
      enif_free_env(new_env);                                           \
      return enif_make_tuple2(env, enif_make_atom(env, "error"),        \
                              enif_make_atom(env, "enomem"));           \
    }                                                                   \
    copy_of_args = (struct decl ## _args *)enif_alloc(sizeof(struct decl ## _args)); \
    if (!copy_of_args) {                                                \
      fn_post_ ## decl (args);                                          \
      enif_free_env(new_env);                                           \
      return enif_make_tuple2(env, enif_make_atom(env, "error"),        \
                              enif_make_atom(env, "enomem"));           \
    }                                                                   \
    memcpy(copy_of_args, args, sizeof(struct decl ## _args));           \
    req->env = new_env;                                                 \
    req->ref = enif_make_copy(new_env, argv_in[0]);                     \
    enif_self(env, &req->pid);                                          \
    req->args = (void*)copy_of_args;                                    \
    req->fn_work = (void (*)(ErlNifEnv *, ERL_NIF_TERM, ErlNifPid*, unsigned int, void *))fn_work_ ## decl ; \
    req->fn_post = (void (*)(void *))fn_post_ ## decl;                 \
    unsigned int h = 0;                                                \
    if (affinity)                                                      \
        h = async_nif_str_hash_func(affinity) % async_nif->num_queues; \
    return async_nif_enqueue_req(async_nif, req, h);                   \
  }

#define ASYNC_NIF_INIT(name)                                            \
        static ErlNifMutex *name##_async_nif_coord = NULL;

#define ASYNC_NIF_LOAD(name, priv) do {                                 \
        if (!name##_async_nif_coord)                                    \
            name##_async_nif_coord = enif_mutex_create(NULL);           \
        enif_mutex_lock(name##_async_nif_coord);                        \
        priv = async_nif_load();                                        \
        enif_mutex_unlock(name##_async_nif_coord);                      \
    } while(0);
#define ASYNC_NIF_UNLOAD(name, env) do {                                \
        if (!name##_async_nif_coord)                                    \
            name##_async_nif_coord = enif_mutex_create(NULL);           \
        enif_mutex_lock(name##_async_nif_coord);                        \
        async_nif_unload(env);                                          \
        enif_mutex_unlock(name##_async_nif_coord);                      \
        enif_mutex_destroy(name##_async_nif_coord);                     \
        name##_async_nif_coord = NULL;                                  \
    } while(0);
#define ASYNC_NIF_UPGRADE(name, env) do {                               \
        if (!name##_async_nif_coord)                                    \
            name##_async_nif_coord = enif_mutex_create(NULL);           \
        enif_mutex_lock(name##_async_nif_coord);                        \
        async_nif_upgrade(env);                                         \
        enif_mutex_unlock(name##_async_nif_coord);                      \
    } while(0);

#define ASYNC_NIF_RETURN_BADARG() return enif_make_badarg(env);
#define ASYNC_NIF_WORK_ENV new_env

#define ASYNC_NIF_REPLY(msg) enif_send(NULL, pid, env, enif_make_tuple2(env, ref, msg))

/**
 * TODO:
 */
static inline unsigned int async_nif_str_hash_func(const char *s)
{
  unsigned int h = (unsigned int)*s;
  if (h) for (++s ; *s; ++s) h = (h << 5) - h + (unsigned int)*s;
  return h;
}

/**
 * TODO:
 */
static ERL_NIF_TERM
async_nif_enqueue_req(struct async_nif_state* async_nif, struct async_nif_req_entry *req, unsigned int hint)
{
  /* If we're shutting down return an error term and ignore the request. */
  if (async_nif->shutdown) {
    ERL_NIF_TERM reply = enif_make_tuple2(req->env, enif_make_atom(req->env, "error"),
			    enif_make_atom(req->env, "shutdown"));
    enif_free(req->args);
    enif_free_env(req->env);
    enif_free(req);
    return reply;
  }

  unsigned int qid = hint ? hint : async_nif->next_q; // Keep a local to avoid the race.
  struct async_nif_work_queue *q = &async_nif->queues[qid];
  while (fifo_q_size(reqs, q->reqs) == fifo_q_capacity(reqs, q->reqs)) {
      qid = (qid + 1) % async_nif->num_queues;
      q = &async_nif->queues[qid];
  }
  /* TODO:
  if (q->avg_latency > 5) {
      async_nif->next_q = (qid + 1) % async_nif->num_queues;
  }
  */

  /* Otherwise, add the request to the work queue. */
  enif_mutex_lock(q->reqs_mutex);
  fifo_q_put(reqs, q->reqs, req);

  /* Build the term before releasing the lock so as not to race on the use of
     the req pointer (which will soon become invalid). */
  ERL_NIF_TERM reply = enif_make_tuple2(req->env, enif_make_atom(req->env, "ok"),
                          enif_make_atom(req->env, "enqueued"));
  enif_mutex_unlock(q->reqs_mutex);
  enif_cond_signal(q->reqs_cnd);
  return reply;
}

static void *
async_nif_worker_fn(void *arg)
{
  struct async_nif_worker_entry *we = (struct async_nif_worker_entry *)arg;
  unsigned int worker_id = we->worker_id;
  struct async_nif_state *async_nif = we->async_nif;
  struct async_nif_work_queue *q = we->q;

  for(;;) {
    struct async_nif_req_entry *req = NULL;

    /* Examine the request queue, are there things to be done? */
    enif_mutex_lock(q->reqs_mutex);
    check_again_for_work:
    if (async_nif->shutdown) {
        enif_mutex_unlock(q->reqs_mutex);
        break;
    }
    if (fifo_q_empty(reqs, q->reqs)) {
      /* Queue is empty, wait for work */
      enif_cond_wait(q->reqs_cnd, q->reqs_mutex);
      goto check_again_for_work;
    } else {
      /* At this point the next req is ours to process and we hold the
         reqs_mutex lock. */

      do {
        /* Take the request off the queue. */
        req = fifo_q_get(reqs, q->reqs);
        enif_mutex_unlock(q->reqs_mutex);

        /* Wake up another thread working on this queue. */
        enif_cond_signal(q->reqs_cnd);

        /* Finally, do the work. */
        req->fn_work(req->env, req->ref, &req->pid, worker_id, req->args);
        req->fn_post(req->args);
        enif_free(req->args);
        enif_free_env(req->env);
        enif_free(req);

	/* Continue working if more requests are in the queue, otherwise wait
           for new work to arrive. */
        if (fifo_q_empty(reqs, q->reqs))
            req = NULL;
        else
            enif_mutex_lock(q->reqs_mutex);

      } while(req);
    }
  }
  enif_thread_exit(0);
  return 0;
}

static void
async_nif_unload(ErlNifEnv *env)
{
  unsigned int i;
  struct async_nif_state *async_nif = (struct async_nif_state*)enif_priv_data(env);

  /* Signal the worker threads, stop what you're doing and exit. */
  async_nif->shutdown = 1;

  /* Wake up any waiting worker threads. */
  for (i = 0; i < async_nif->num_queues; i++) {
      struct async_nif_work_queue *q = &async_nif->queues[i];
      enif_cond_broadcast(q->reqs_cnd);
  }

  /* Join for the now exiting worker threads. */
  for (i = 0; i < async_nif->num_workers; ++i) {
    void *exit_value = 0; /* Ignore this. */
    enif_thread_join(async_nif->worker_entries[i].tid, &exit_value);
  }

  /* Cleanup requests, mutexes and conditions in each work queue. */
  for (i = 0; i < async_nif->num_queues; i++) {
      struct async_nif_work_queue *q = &async_nif->queues[i];
      enif_mutex_destroy(q->reqs_mutex);
      enif_cond_destroy(q->reqs_cnd);

      /* Worker threads are stopped, now toss anything left in the queue. */
      struct async_nif_req_entry *req = NULL;
      fifo_q_foreach(reqs, q->reqs, req, {
          enif_send(NULL, &req->pid, req->env,
                    enif_make_tuple2(req->env, enif_make_atom(req->env, "error"),
                                     enif_make_atom(req->env, "shutdown")));
          req->fn_post(req->args);
          enif_free(req->args);
          enif_free_env(req->env);
          enif_free(req);
          });
      fifo_q_free(reqs, q->reqs);
  }
  memset(async_nif, 0, sizeof(struct async_nif_state));
  enif_free(async_nif);
}

static void *
async_nif_load(void)
{
  static int has_init = 0;
  unsigned int i, j;
  ErlNifSysInfo info;
  struct async_nif_state *async_nif;

  /* Don't init more than once. */
  if (has_init) return 0;
  else has_init = 1;

  /* Find out how many schedulers there are. */
  enif_system_info(&info, sizeof(ErlNifSysInfo));

  /* Init our portion of priv_data's module-specific state. */
  async_nif = enif_alloc(sizeof(struct async_nif_state));
  if (!async_nif)
      return NULL;
  memset(async_nif, 0, sizeof(struct async_nif_state));

  async_nif->num_queues = info.scheduler_threads;
  async_nif->next_q = 0;
  async_nif->shutdown = 0;

  for (i = 0; i < async_nif->num_queues; i++) {
      struct async_nif_work_queue *q = &async_nif->queues[i];
      q->reqs = fifo_q_new(reqs, ASYNC_NIF_WORKER_QUEUE_SIZE);
      q->reqs_mutex = enif_mutex_create(NULL);
      q->reqs_cnd = enif_cond_create(NULL);
  }

  /* Setup the thread pool management. */
  memset(async_nif->worker_entries, 0, sizeof(struct async_nif_worker_entry) * ASYNC_NIF_MAX_WORKERS);

  /* Start the worker threads. */
  unsigned int num_workers = async_nif->num_queues;

  for (i = 0; i < num_workers; i++) {
    struct async_nif_worker_entry *we = &async_nif->worker_entries[i];
    we->async_nif = async_nif;
    we->worker_id = i;
    we->q = &async_nif->queues[i % async_nif->num_queues];
    if (enif_thread_create(NULL, &async_nif->worker_entries[i].tid,
                            &async_nif_worker_fn, (void*)we, NULL) != 0) {
      async_nif->shutdown = 1;

      for (j = 0; j < async_nif->num_queues; j++) {
          struct async_nif_work_queue *q = &async_nif->queues[j];
          enif_cond_broadcast(q->reqs_cnd);
          enif_mutex_destroy(q->reqs_mutex);
          enif_cond_destroy(q->reqs_cnd);
      }

      while(i-- > 0) {
        void *exit_value = 0; /* Ignore this. */
        enif_thread_join(async_nif->worker_entries[i].tid, &exit_value);
      }

      memset(async_nif->worker_entries, 0, sizeof(struct async_nif_worker_entry) * ASYNC_NIF_MAX_WORKERS);
      return NULL;
    }
  }
  async_nif->num_workers = i;
  return async_nif;
}

static void
async_nif_upgrade(ErlNifEnv *env)
{
    // TODO:
}


#if defined(__cplusplus)
}
#endif

#endif // __ASYNC_NIF_H__