/*
     This file is part of GNUnet.
     (C) 2010 Christian Grothoff (and other contributing authors)

     GNUnet is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published
     by the Free Software Foundation; either version 2, or (at your
     option) any later version.

     GNUnet is distributed in the hope that it will be useful, but
     WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     General Public License for more details.

     You should have received a copy of the GNU General Public License
     along with GNUnet; see the file COPYING.  If not, write to the
     Free Software Foundation, Inc., 59 Temple Place - Suite 330,
     Boston, MA 02111-1307, USA.
*/

/**
 * @file util/server_nc.c
 * @brief convenience functions for transmission of
 *        a notification stream 
 * @author Christian Grothoff
 */

#include "platform.h"
#include "gnunet_common.h"
#include "gnunet_connection_lib.h"
#include "gnunet_scheduler_lib.h"
#include "gnunet_server_lib.h"
#include "gnunet_time_lib.h"


#define DEBUG_SERVER_NC GNUNET_NO

/**
 * Entry in list of messages pending to be transmitted.
 */
struct PendingMessageList
{

  /**
   * This is a linked list.
   */ 
  struct PendingMessageList *next;

  /**
   * Message to transmit (allocated at the end of this
   * struct, do not free)
   */
  const struct GNUNET_MessageHeader *msg;

  /**
   * Can this message be dropped?
   */ 
  int can_drop;

};


/**
 * Lists of clients we manage for notifications.
 */
struct ClientList
{

  /**
   * This is a linked list.
   */ 
  struct ClientList *next;

  /**
   * Overall context this client belongs to. 
   */
  struct GNUNET_SERVER_NotificationContext *nc;

  /**
   * Handle to the client.
   */
  struct GNUNET_SERVER_Client *client;

  /**
   * Handle for pending transmission request to the client (or NULL).
   */
  struct GNUNET_CONNECTION_TransmitHandle *th;

  /**
   * Head of linked list of requests queued for transmission.
   */ 
  struct PendingMessageList *pending_head;

  /**
   * Tail of linked list of requests queued for transmission.
   */ 
  struct PendingMessageList *pending_tail;

  /**
   * Number of messages currently in the list.
   */
  unsigned int num_pending;

};


/**
 * The notification context is the key datastructure for a conveniance
 * API used for transmission of notifications to the client until the
 * client disconnects (or the notification context is destroyed, in
 * which case we disconnect these clients).  Essentially, all
 * (notification) messages are queued up until the client is able to
 * read them.
 */
struct GNUNET_SERVER_NotificationContext
{

  /**
   * Server we do notifications for.
   */
  struct GNUNET_SERVER_Handle *server;

  /**
   * List of clients receiving notifications.
   */
  struct ClientList *clients;

  /**
   * Maximum number of optional messages to queue per client.
   */
  unsigned int queue_length;

};


/**
 * Client has disconnected, clean up.
 *
 * @param cls our 'struct GNUNET_SERVER_NotificationContext *'
 * @param client handle of client that disconnected
 */
static void
handle_client_disconnect (void *cls,
			  struct GNUNET_SERVER_Client *client)
{
  struct GNUNET_SERVER_NotificationContext *nc = cls;
  struct ClientList *pos;
  struct ClientList *prev;
  struct PendingMessageList *pml;

  if (client == NULL)
    {
      nc->server = NULL;
      return;
    }
  prev = NULL;
  pos = nc->clients;
  while (NULL != pos)
    {
      if (pos->client == client)
	break;
      prev = pos;
      pos = pos->next;
    }
  if (pos == NULL)
    return;
#if DEBUG_SERVER_NC
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
	      "Client disconnected, cleaning up %u messages in NC queue\n",
	      pos->num_pending);
#endif
  if (prev == NULL)
    nc->clients = pos->next;
  else
    prev->next = pos->next;
  while (NULL != (pml = pos->pending_head))
    {
      pos->pending_head = pml->next;
      GNUNET_free (pml);
    }
  GNUNET_SERVER_client_drop (client);
  if (pos->th != NULL)
    {
      GNUNET_CONNECTION_notify_transmit_ready_cancel (pos->th);
      pos->th = NULL;
    }
  GNUNET_free (pos);
}


/**
 * Create a new notification context.
 *
 * @param server server for which this function creates the context
 * @param queue_length maximum number of messages to keep in
 *        the notification queue; optional messages are dropped
 *        it the queue gets longer than this number of messages
 * @return handle to the notification context
 */
struct GNUNET_SERVER_NotificationContext *
GNUNET_SERVER_notification_context_create (struct GNUNET_SERVER_Handle *server,
					   unsigned int queue_length)
{
  struct GNUNET_SERVER_NotificationContext *ret;

  ret = GNUNET_malloc (sizeof (struct GNUNET_SERVER_NotificationContext));
  ret->server = server;
  ret->queue_length = queue_length;
  GNUNET_SERVER_disconnect_notify (server,
				   &handle_client_disconnect,
				   ret);
  return ret;
}


/**
 * Destroy the context, force disconnect for all clients.
 *
 * @param nc context to destroy.
 */
void
GNUNET_SERVER_notification_context_destroy (struct GNUNET_SERVER_NotificationContext *nc)
{
  struct ClientList *pos;
  struct PendingMessageList *pml;

  while (NULL != (pos = nc->clients))
    {
      nc->clients = pos->next;
      GNUNET_SERVER_client_drop (pos->client); 
      GNUNET_SERVER_receive_done (pos->client, GNUNET_NO);
      while (NULL != (pml = pos->pending_head))
	{
	  pos->pending_head = pml->next;
	  GNUNET_free (pml);
	}
      GNUNET_free (pos);
    }
  if (nc->server != NULL)
    GNUNET_SERVER_disconnect_notify_cancel (nc->server,
					    &handle_client_disconnect,
					    nc);
  GNUNET_free (nc);
}


/**
 * Add a client to the notification context.
 *
 * @param nc context to modify
 * @param client client to add
 */
void
GNUNET_SERVER_notification_context_add (struct GNUNET_SERVER_NotificationContext *nc,
					struct GNUNET_SERVER_Client *client)
{
  struct ClientList *cl;

  cl = GNUNET_malloc (sizeof (struct ClientList));
  cl->next = nc->clients;
  cl->nc = nc;
  cl->client = client;
  GNUNET_SERVER_client_keep (client);
  nc->clients = cl;
}


/**
 * Function called to notify a client about the socket begin ready to
 * queue more data.  "buf" will be NULL and "size" zero if the socket
 * was closed for writing in the meantime.
 *
 * @param cls the 'struct ClientList *'
 * @param size number of bytes available in buf
 * @param buf where the callee should write the message
 * @return number of bytes written to buf
 */
static size_t
transmit_message (void *cls,
		  size_t size,
		  void *buf)
{
  struct ClientList *cl = cls;
  char *cbuf = buf;
  struct PendingMessageList *pml;
  uint16_t msize;
  size_t ret;

  cl->th = NULL;
  if (buf == NULL)
    {
      /* 'cl' should be freed via disconnect notification shortly */
#if DEBUG_SERVER_NC
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
		  "Failed to transmit message from NC queue to client\n");
#endif
      return 0;
    }
  ret = 0;
  while (cl->pending_head != NULL)
    {
      pml = cl->pending_head;
      msize = ntohs (pml->msg->size);
      if (size < msize)
	break;
      cl->pending_head = pml->next;
      if (pml->next == NULL)
	cl->pending_tail = NULL;
#if DEBUG_SERVER_NC
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
		  "Copying message of type %u and size %u from pending queue to transmission buffer\n",
		  ntohs (pml->msg->type),
		  msize);
#endif
      memcpy (&cbuf[ret], pml->msg, msize);
      ret += msize;
      size -= msize;
      GNUNET_free (pml);
      cl->num_pending--;
    }
  if (cl->pending_head != NULL)    
    {
#if DEBUG_SERVER_NC
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
		  "Have %u messages left in NC queue, will try transmission again\n",
		  cl->num_pending);
#endif
      cl->th = GNUNET_SERVER_notify_transmit_ready (cl->client,
						    ntohs (cl->pending_head->msg->size),
						    GNUNET_TIME_UNIT_FOREVER_REL,
						    &transmit_message,
						    cl);
    }
  else
    GNUNET_assert (cl->num_pending == 0);
  return ret;
}


/**
 * Send a message to a particular client.
 *
 * @param nc context to modify
 * @param client client to transmit to
 * @param msg message to send
 * @param can_drop can this message be dropped due to queue length limitations
 */
static void
do_unicast (struct GNUNET_SERVER_NotificationContext *nc,
	    struct ClientList *client,
	    const struct GNUNET_MessageHeader *msg,
	    int can_drop)
{
  struct PendingMessageList *pml;
  uint16_t size;

  if ( (client->num_pending > nc->queue_length) &&
       (GNUNET_YES == can_drop) )
    {
      GNUNET_log (GNUNET_ERROR_TYPE_INFO,
		  "Dropping message of type %u and size %u due to full queue (%u entries)\n",
		  ntohs (msg->type),
		  ntohs (msg->size),
		  (unsigned int) nc->queue_length);
      return; /* drop! */
    }
  if (client->num_pending > nc->queue_length)
    {
      /* FIXME: consider checking for other messages in the
	 queue that are 'droppable' */
    }
  client->num_pending++;
  size = ntohs (msg->size);
  pml = GNUNET_malloc (sizeof (struct PendingMessageList) + size);
  pml->msg = (const struct GNUNET_MessageHeader*) &pml[1];
  pml->can_drop = can_drop; 
#if DEBUG_SERVER_NC
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
	      "Adding message of type %u and size %u to pending queue (which has %u entries)\n",
	      ntohs (msg->type),
	      ntohs (msg->size),
	      (unsigned int) nc->queue_length);
#endif
  memcpy (&pml[1], msg, size);
  /* append */
  if (client->pending_tail != NULL)
    client->pending_tail->next = pml;
  else
    client->pending_head = pml;
  client->pending_tail = pml;
  if (client->th == NULL)
    client->th = GNUNET_SERVER_notify_transmit_ready (client->client,
						      ntohs (client->pending_head->msg->size),
						      GNUNET_TIME_UNIT_FOREVER_REL,
						      &transmit_message,
						      client);
} 


/**
 * Send a message to a particular client; must have
 * already been added to the notification context.
 *
 * @param nc context to modify
 * @param client client to transmit to
 * @param msg message to send
 * @param can_drop can this message be dropped due to queue length limitations
 */
void
GNUNET_SERVER_notification_context_unicast (struct GNUNET_SERVER_NotificationContext *nc,
					    struct GNUNET_SERVER_Client *client,
					    const struct GNUNET_MessageHeader *msg,
					    int can_drop)
{
  struct ClientList *pos;
  
  pos = nc->clients;
  while (NULL != pos)
    {
      if (pos->client == client)
	break;
      pos = pos->next;
    }
  GNUNET_assert (pos != NULL);
  do_unicast (nc, pos, msg, can_drop); 
}


/**
 * Send a message to all clients of this context.
 *
 * @param nc context to modify
 * @param msg message to send
 * @param can_drop can this message be dropped due to queue length limitations
 */
void
GNUNET_SERVER_notification_context_broadcast (struct GNUNET_SERVER_NotificationContext *nc,
					      const struct GNUNET_MessageHeader *msg,
					      int can_drop)
{
  struct ClientList *pos;
  
  pos = nc->clients;
  while (NULL != pos)
    {
      do_unicast (nc, pos, msg, can_drop);
      pos = pos->next;
    }
}


/* end of server_nc.c */