/**
 * mds — A micro-display server
 * Copyright © 2014  Mattias Andrée (maandree@member.fsf.org)
 * 
 * This program 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 3 of the License, or
 * (at your option) any later version.
 * 
 * This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
 */
#include "registry.h"

#include "util.h"
#include "globals.h"
#include "slave.h"

#include "../mds-base.h"

#include <libmdsserver/util.h>
#include <libmdsserver/macros.h>
#include <libmdsserver/hash-help.h>
#include <libmdsserver/client-list.h>

#include <errno.h>
#include <inttypes.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>



/**
 * Handle the received message containing a ‘Client closed’-header
 * 
 * @return  Zero on success -1 on error or interruption,
 *          `errno` will be set accordingly
 */
static int handle_close_message(void)
{
  /* Servers do not close too often, there is no need to
     optimise this with another hash table. Doing so would
     also require some caution because the keys are 32-bit
     on 32-bit computers, and the client ID:s are 64-bit. */
  
  size_t i, j, ptr = 0, size = 1;
  size_t* keys = NULL;
  size_t* old_keys;
  
  
  /* Remove server for all protocols. */
  
  for (i = 0; i < received.header_count; i++)
    if (startswith(received.headers[i], "Client closed: "))
      {
	uint64_t client = parse_client_id(received.headers[i] + strlen("Client closed: "));
	hash_entry_t* entry;
	
	foreach_hash_table_entry (reg_table, j, entry)
	  {
	    /* Remove server from list of servers that support the protocol,
	       once, if it is in the list. */
	    client_list_t* list = (client_list_t*)(void*)(entry->value);
	    client_list_remove(list, client);
	    if (list->size)
	      continue;
	    
	    /* If no servers support the protocol, list the protocol for removal. */
	    fail_if ((keys == NULL) && xmalloc(keys, size, size_t));
	    fail_if (ptr == size ? growalloc(old_keys, keys, size, size_t) : 0);
	    keys[ptr++] = entry->key;
	  }
	
	
	/* Mark client as closed. */
	
	close_slaves(client);
      }
  
  
  /* Close slaves those clients have closed. */
  
  with_mutex (slave_mutex, pthread_cond_broadcast(&slave_cond););
  
  
  /* Remove protocol that no longer have any supporting servers. */
  
  for (i = 0; i < ptr; i++)
    {
      hash_entry_t* entry = hash_table_get_entry(&reg_table, keys[i]);
      client_list_t* list = (client_list_t*)(void*)(entry->value);
      char* command = (char*)(void*)(entry->key);
      
      hash_table_remove(&reg_table, entry->key);
      
      client_list_destroy(list);
      free(list);
      free(command);
    }
  
  free(keys);
  return 0;
 fail:
  xperror(*argv);
  free(keys);
  return -1;
}


/**
 * Add a protocol to the registry
 * 
 * @param   has_key      Whether the command is already in the registry
 * @param   command      The command
 * @param   command_key  The address of `command`
 * @param   client       The ID of the client that implements the server-side of the protocol
 * @return               Non-zero on error
 */
static int registry_action_add(int has_key, char* command, size_t command_key, uint64_t client)
{
  int saved_errno;
  
  if (has_key)
    {
      /* Add server to protocol if the protocol is already in the table. */
      size_t address = hash_table_get(&reg_table, command_key);
      client_list_t* list = (client_list_t*)(void*)address;
      fail_if (client_list_add(list, client) < 0);
    }
  else
    {
      /* If the protocol is not already in the table. */
      
      /* Allocate list of servers for the protocol. */
      client_list_t* list = malloc(sizeof(client_list_t));
      void* address = list;
      fail_if (list == NULL);
      /* Duplicate the protocol name so it can be accessed later. */
      if ((command = strdup(command)) == NULL)
	{
	  saved_errno = errno, free(list), errno = saved_errno;
	  fail_if (1);
	}
      /* Create list of servers, add server to list and add the protocol to the table. */
      command_key = (size_t)(void*)command;
      if (client_list_create(list, 1) ||
	  client_list_add(list, client) ||
	  (hash_table_put(&reg_table, command_key, (size_t)address) == 0))
	{
	  saved_errno = errno;
	  client_list_destroy(list);
	  free(list);
	  free(command);
	  errno = saved_errno;
	  fail_if (1);
	}
    }
  
  /* Notify slaves. */
  fail_if (advance_slaves(command));
  
  return 0;
 fail:
  xperror(*argv);
  return -1;
}


/**
 * Remove a protocol from the registry
 * 
 * @param   command_key  The address of a string that contains the command
 * @param   client       The ID of the client that implements the server-side of the protocol
 * @return               Non-zero on error
 */
static void registry_action_remove(size_t command_key, uint64_t client)
{
  hash_entry_t* entry = hash_table_get_entry(&reg_table, command_key);
  size_t address = entry->value;
  client_list_t* list = (client_list_t*)(void*)address;
  
  /* Remove server from protocol. */
  client_list_remove(list, client);
  
  /* Remove protocol if no servers support it anymore. */
  if (list->size == 0)
    {
      client_list_destroy(list);
      free(list);
      hash_table_remove(&reg_table, command_key);
      reg_table_free_key(entry->key);
    }
}


/**
 * Modify the protocol registry or list missing protocols
 * 
 * @param   command      The command
 * @param   action       -1 to remove command, +1 to add commands, 0 to
 *                       wait until the message commnds are registered
 * @param   client       The ID of the client that implements the server-side of the protocol
 * @param   wait_set     Table to fill with missing protocols if `action == 0`
 * @return               Non-zero on error
 */
static int registry_action_act(char* command, int action, uint64_t client, hash_table_t* wait_set)
{
  size_t command_key = (size_t)(void*)command;
  int has_key = hash_table_contains_key(&reg_table, command_key);
  int saved_errno;
  
  if (action == 1)
    {
      /* Register server to protocol. */
      if (registry_action_add(has_key, command, command_key, client))
	return -1;
    }
  else if ((action == -1) && has_key)
    /* Unregister server from protocol. */
    registry_action_remove(command_key, client);
  else if ((action == 0) && !has_key)
    {
      /* Add protocl to wait set of not present in the protocol table. */
      fail_if ((command = strdup(command)) == NULL);
      command_key = (size_t)(void*)command;
      if (hash_table_put(wait_set, command_key, 1) == 0)
	if (errno)
	  {
	    saved_errno = errno, free(command), errno = saved_errno;
	    fail_if (1);
	  }
    }
  
  return 0;
 fail:
  xperror(*argv);
  hash_table_destroy(wait_set, (free_func*)reg_table_free_key, NULL);
  free(wait_set);
  return -1;
}


/**
 * Perform an action over the registry
 * 
 * @param   length           The length of the received message
 * @param   action           -1 to remove command, +1 to add commands, 0 to
 *                           wait until the message commnds are registered
 * @param   recv_client_id   The ID of the client
 * @param   recv_message_id  The ID of the received message
 * @return                   Zero on success -1 on error or interruption,
 *                           `errno` will be set accordingly
 */
static int registry_action(size_t length, int action, const char* recv_client_id, const char* recv_message_id)
{
  char* payload = received.payload;
  uint64_t client = action ? parse_client_id(recv_client_id) : 0;
  hash_table_t* wait_set = NULL;
  size_t begin;
  
  
  /* If ‘Action: wait’, create a set for the protocols that are not already available. */
  
  if (action == 0)
    {
      wait_set = malloc(sizeof(hash_table_t));
      if (wait_set == NULL)
	return -1;
      if (hash_table_create(wait_set))
	{
	  hash_table_destroy(wait_set, NULL, NULL);
	  free(wait_set);
	  return -1;
	}
      wait_set->key_comparator = (compare_func*)string_comparator;
      wait_set->hasher = (hash_func*)string_hash;
    }
  
  
  /* If the payload buffer is full, increase it so we can fit another character. */
  
  if (received.payload_size == length)
    {
      if (growalloc(old, received.payload, received.payload_size, char))
	{
	  if (wait_set != NULL)
	    hash_table_destroy(wait_set, NULL, NULL), free(wait_set);
	  return -1;
	}
      else
	payload = received.payload;
    }
  
  
  /* LF-terminate the payload, perhaps it did not have a terminal LF. */
  
  payload[length] = '\n';
  
  
  /* For all protocols in the payload, either add or remove
     them from or to the protocl table or the wait set. */
  
  for (begin = 0; begin < length;)
    {
      char* end = rawmemchr(payload + begin, '\n');
      size_t len = (size_t)(end - payload) - begin - 1;
      char* command = payload + begin;
      
      command[len] = '\0';
      begin += len + 1;
      
      if (len > 0)
	if (registry_action_act(command, action, client, wait_set))
	  return -1;
    }
  
  
  /* If ‘Action: wait’, start a new thread that waits for the protocols and the responds. */
  
  if (action == 0)
    return start_slave(wait_set, recv_client_id, recv_message_id);
  
  return 0;
}


/**
 * Send a list of all registered commands to a client
 * 
 * @param   recv_client_id   The ID of the client
 * @param   recv_message_id  The ID of the received message
 * @return                   Zero on success -1 on error or interruption,
 *                           `errno` will be set accordingly
 */
static int list_registry(const char* recv_client_id, const char* recv_message_id)
{
  size_t ptr = 0, i;
  hash_entry_t* entry;
  
  
  /* Allocate the send buffer for the first time, it cannot be doubled if it is zero. */
  
  if (send_buffer_size == 0)
    {
      if (xmalloc(send_buffer, 256, char))
	return -1;
      send_buffer_size = 256;
    }
  
  
  /* Add all protocols to the send buffer. */
  
  foreach_hash_table_entry (reg_table, i, entry)
    {
      size_t key = entry->key;
      char* command = (char*)(void*)key;
      size_t len = strlen(command);
      
      /* Make sure the send buffer can fit all protocols. */
      while (ptr + len + 1 >= send_buffer_size)
	if (growalloc(old, send_buffer, send_buffer_size, char))
	  return -1;
      
      memcpy(send_buffer + ptr, command, len * sizeof(char));
      ptr += len;
      send_buffer[ptr++] = '\n';
    }
  
  
  /* Make sure the message headers can fit the send buffer. */
  
  i = strlen(recv_message_id) + strlen(recv_client_id) + 10 + 19;
  i += strlen("To: %s\nIn response to: %s\nMessage ID: %" PRIu32 "\nLength: %" PRIu64 "\n\n");
  
  while (ptr + i >= send_buffer_size)
    if (growalloc(old, send_buffer, send_buffer_size, char))
      return -1;
  
  
  /* Construct message headers. */
  sprintf(send_buffer + ptr, "To: %s\nIn response to: %s\nMessage ID: %" PRIu32 "\nLength: %" PRIu64 "\n\n",
	  recv_client_id, recv_message_id, message_id, ptr);
  
  /* Increase message ID. */
  with_mutex (slave_mutex, message_id = message_id == UINT32_MAX ? 0 : (message_id + 1););
  
  /* Send message. */
  if (full_send(send_buffer + ptr, strlen(send_buffer + ptr)))
    return 1;
  return full_send(send_buffer, ptr);
}


/**
 * Handle the received message containing ‘Command: register’-header–value
 * 
 * @return  Zero on success -1 on error or interruption,
 *          `errno` will be set accordingly
 */
static int handle_register_message(void)
{
  /* Fetch message headers. */
  
  const char* recv_client_id = NULL;
  const char* recv_message_id = NULL;
  const char* recv_length = NULL;
  const char* recv_action = NULL;
  size_t i, length = 0;
  
#define __get_header(storage, header)			\
  (startswith(received.headers[i], header))		\
    storage = received.headers[i] + strlen(header)
  
  for (i = 0; i < received.header_count; i++)
    {
      if      __get_header(recv_client_id,  "Client ID: ");
      else if __get_header(recv_message_id, "Message ID: ");
      else if __get_header(recv_length,     "Length: ");
      else if __get_header(recv_action,     "Action: ");
      else
	continue;
      
      /* Stop if we got all headers we recognised, except ‘Time to live’. */
      if (recv_client_id && recv_message_id && recv_length && recv_action)
	break;
    }
  
#undef __get_header
  
  
  /* Validate headers. */
  
  if ((recv_client_id == NULL) || (strequals(recv_client_id, "0:0")))
    {
      eprint("received message from anonymous sender, ignoring.");
      return 0;
    }
  else if (strchr(recv_client_id, ':') == NULL)
    {
      eprint("received message from sender without a colon it its ID, ignoring, invalid ID.");
      return 0;
    }
  else if ((recv_length == NULL) && ((recv_action == NULL) || !strequals(recv_action, "list")))
    {
      eprint("received empty message without `Action: list`, ignoring, has no effect.");
      return 0;
    }
  else if (recv_message_id == NULL)
    {
      eprint("received message with ID, ignoring, master server is misbehaving.");
      return 0;
    }
  
  
  /* Get message length, and make sure the action is defined. */
  
  if (recv_length != NULL)
    length = atoz(recv_length);
  if (recv_action != NULL)
    recv_action = "add";
  
  
  /* Perform action. */
  
#define __registry_action(action)  registry_action(length, action, recv_client_id, recv_message_id)
  
  if      (strequals(recv_action, "add"))     return __registry_action(1);
  else if (strequals(recv_action, "remove"))  return __registry_action(-1);
  else if (strequals(recv_action, "wait"))    return __registry_action(0);
  else if (strequals(recv_action, "list"))    return list_registry(recv_client_id, recv_message_id);
  else
    {
      eprint("received invalid action, ignoring.");
      return 0;
    }
  
#undef __registry_action
}


/**
 * Handle the received message
 * 
 * @return  Zero on success -1 on error or interruption,
 *          `errno` will be set accordingly
 */
int handle_message(void)
{
  size_t i;
  for (i = 0; i < received.header_count; i++)
    if (strequals(received.headers[i], "Command: register"))
      return handle_register_message();
  return handle_close_message();
}