/* Copyright (c) 2009 Ryan Dahl (ry@tinyclouds.org)
 *
 * All rights reserved.
 * 
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 * 
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. 
 */
#include "coupling.h"

#include <sys/types.h> 
#include <sys/uio.h>
#include <sys/select.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <assert.h>

#include <pthread.h>

#ifdef PIPE_BUF
# define BUFSIZE  PIPE_BUF
#else
# define BUFSIZE  4096
#endif

#define MAX(a,b) ((a) > (b) ? (a) : (b))

// ring buffer
typedef struct {
  int head;
  int tail;
  int size;
  char buf[BUFSIZE]; 
} ring_buffer; 

static inline void
ring_buffer_inspect (ring_buffer *ring)
{
  printf("size %5d  head %5d  tail %5d\n", ring->size, ring->head, ring->tail);
}

static inline void
ring_buffer_init (ring_buffer *ring)
{
  ring->head = 0;
  ring->tail = 0;
  ring->size = 0;
}

static inline int
ring_buffer_filled_p (ring_buffer *ring)
{
  assert(BUFSIZE - (long)ring->size >= 0);
  return (BUFSIZE == ring->size);
}

static inline int
ring_buffer_empty_p (ring_buffer *ring)
{
  return 0 == ring->size;
}

static ssize_t
ring_buffer_pull (ring_buffer *ring, int fd)
{
  // DO NOT CALL WHEN FILLED
  assert(!ring_buffer_filled_p(ring));

  struct iovec iov[2];
  int iovcnt = 1;

  // Very tough logic. Can you follow? Barely can I.
  iov[0].iov_base = ring->buf + ring->tail;
  if (ring->tail < ring->head) {
    iov[0].iov_len = ring->head - ring->tail;
  } else {
    iov[0].iov_len = BUFSIZE - ring->tail;
    if (ring->head != 0) {
      iovcnt = 2; 
      iov[1].iov_base = ring->buf;
      iov[1].iov_len = ring->head;
    }
  }

  int r = readv(fd, iov, iovcnt);

  if (r > 0) {
    ring->size += r;
    ring->tail = (ring->tail + r) % BUFSIZE;
  }
  assert(ring->size <= BUFSIZE);

  return r;
}

static ssize_t
ring_buffer_push (ring_buffer *ring, int fd)
{
  // DO NOT CALL WHEN EMPTY
  assert(!ring_buffer_empty_p(ring));

  struct iovec iov[2];
  int iovcnt = 1;

  iov[0].iov_base = ring->buf + ring->head;
  if (ring->head < ring->tail) {
    iov[0].iov_len = ring->tail - ring->head;
  } else {
    iov[0].iov_len = BUFSIZE - ring->head;
    if (ring->tail != 0) {
      iovcnt = 2; 
      iov[1].iov_base = ring->buf;
      iov[1].iov_len = ring->tail;
    }
  }

  int r = writev(fd, iov, iovcnt);

  if (r > 0) {
    ring->size -= r;
    ring->head = (ring->head + r) % BUFSIZE;
  }
  assert(0 <= (long)ring->size);

  return r;
}


static void
pump (int pullfd, int pushfd)
{
  int r;
  ring_buffer ring;
  fd_set readfds, writefds, exceptfds;

  ring_buffer_init(&ring);

  int maxfd;

  while (pushfd >= 0 && (pullfd >= 0 || !ring_buffer_empty_p(&ring))) {
    FD_ZERO(&exceptfds);
    FD_ZERO(&readfds);
    FD_ZERO(&writefds);
    
    maxfd = pushfd;
    FD_SET(pushfd, &exceptfds);

    if (pullfd >= 0) {
      FD_SET(pullfd, &exceptfds);
      maxfd = MAX(pushfd, pullfd);
      if (!ring_buffer_filled_p(&ring)) FD_SET(pullfd, &readfds);
    }

    if (!ring_buffer_empty_p(&ring)) {
      FD_SET(pushfd, &writefds);
    }

    r = select(maxfd+1, &readfds, &writefds, &exceptfds, NULL);

    if (r < 0 || FD_ISSET(pushfd, &exceptfds)) {
      pushfd = pullfd = -1;
      return;
    }

    if (pullfd >= 0 && FD_ISSET(pullfd, &exceptfds)) {
      pullfd = -1;
    }

    if (pullfd >= 0 && FD_ISSET(pullfd, &readfds)) {
      r = ring_buffer_pull(&ring, pullfd);
      if (r == 0) {
        /* eof */
        pullfd = -1;

      } else if (r < 0) {
        if (errno != EINTR && errno != EAGAIN) goto error;
      }
    }

    if (FD_ISSET(pushfd, &writefds)) {
      r = ring_buffer_push(&ring, pushfd);
      if (r < 0) {
        switch (errno) {
          case EINTR:
          case EAGAIN:
            continue;

          case EPIPE:
            /* TODO catch SIGPIPE? */
            pushfd = pullfd = -1;
            return;

          default:
            goto error;
        }
      }
    }
  }

  return;

error:
  perror("(coupling) pump");
}

static inline int
set_nonblock (int fd)
{
  int flags = fcntl(fd, F_GETFL, 0);
  if (flags == -1) return -1;

  int r = fcntl(fd, F_SETFL, flags | O_NONBLOCK);
  if (r == -1) return -1;

  return 0;
}

struct coupling {
  int is_pull;
  int pullfd;
  int pushfd;
  int exposedfd;
  pthread_t tid;
};

static void *
pump_thread (void *data)
{
  struct coupling *c = (struct coupling*)data;

  pump(c->pullfd, c->pushfd);

  return NULL;
}

static struct coupling*
create_coupling (int fd, int is_pull)
{
  int pipefd[2];

  struct coupling *c = malloc(sizeof(struct coupling));
  if (!c) return NULL;
  
  int r = pipe(pipefd);
  if (r < 0) return NULL;

  r = set_nonblock(pipefd[0]);
  if (r < 0) return NULL;
  assert(pipefd[0] >= 0);

  r = set_nonblock(pipefd[1]);
  if (r < 0) return NULL;
  assert(pipefd[1] >= 0);

  if (is_pull) {
    c->is_pull = 1;
    c->pullfd = fd;
    c->pushfd = pipefd[1];
    c->exposedfd = pipefd[0];
  } else {
    c->is_pull = 0;
    c->pushfd = fd;
    c->pullfd = pipefd[0];
    c->exposedfd = pipefd[1];
  }

  r = pthread_create(&c->tid, NULL, pump_thread, c);
  if (r < 0) return NULL;

  return c;
}

struct coupling*
coupling_new_pull (int fd)
{
  return create_coupling(fd, 1);
}

struct coupling*
coupling_new_push (int fd)
{
  return create_coupling(fd, 0);
}

int 
coupling_nonblocking_fd (struct coupling *c)
{
  return c->exposedfd;
}

void 
coupling_join (struct coupling *c)
{
  int r = pthread_join(c->tid, NULL);
  assert(r == 0);
}

void
coupling_destroy (struct coupling *c)
{
  close(c->is_pull ? c->pushfd : c->pullfd);
  free(c);
}