/*
 * Copyright (c) 2010, Swedish Institute of Computer Science.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the Institute nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * This file is part of the Contiki operating system.
 *
 */

/**
 * \file
 *         An implementation of RPL's objective function 0, RFC6552
 *
 * \author Joakim Eriksson <joakime@sics.se>, Nicolas Tsiftes <nvt@sics.se>
 */

/**
 * \addtogroup uip6
 * @{
 */

#include "net/rpl/rpl.h"
#include "net/rpl/rpl-private.h"
#include "net/nbr-table.h"
#include "net/link-stats.h"

#define DEBUG DEBUG_NONE
#include "net/ip/uip-debug.h"

/* Constants from RFC6552. We use the default values. */
#define RANK_STRETCH       0 /* Must be in the range [0;5] */
#define RANK_FACTOR        1 /* Must be in the range [1;4] */

#define MIN_STEP_OF_RANK   1
#define MAX_STEP_OF_RANK   9

/* OF0 computes rank increase as follows:
 * rank_increase = (RANK_FACTOR * STEP_OF_RANK + RANK_STRETCH) * min_hop_rank_increase
 * STEP_OF_RANK is an implementation-specific scalar value in the range [1;9].
 * RFC6552 provides a default value of 3 but recommends to use a dynamic link metric
 * such as ETX.
 * */

#define RPL_OF0_FIXED_SR      0
#define RPL_OF0_ETX_BASED_SR  1
/* Select RPL_OF0_FIXED_SR or RPL_OF0_ETX_BASED_SR */
#ifdef RPL_OF0_CONF_SR
#define RPL_OF0_SR            RPL_OF0_CONF_SR
#else /* RPL_OF0_CONF_SR */
#define RPL_OF0_SR            RPL_OF0_ETX_BASED_SR
#endif /* RPL_OF0_CONF_SR */

#if RPL_OF0_FIXED_SR
#define STEP_OF_RANK(p)       (3)
#endif /* RPL_OF0_FIXED_SR */

#if RPL_OF0_ETX_BASED_SR
/* Numbers suggested by P. Thubert for in the 6TiSCH WG. Anything that maps ETX to
 * a step between 1 and 9 works. */
#define STEP_OF_RANK(p)       (((3 * parent_link_metric(p)) / LINK_STATS_ETX_DIVISOR) - 2)
#endif /* RPL_OF0_ETX_BASED_SR */

/*---------------------------------------------------------------------------*/
static void
reset(rpl_dag_t *dag)
{
  PRINTF("RPL: Reset OF0\n");
}
/*---------------------------------------------------------------------------*/
static uint16_t
parent_link_metric(rpl_parent_t *p)
{
  /* OF0 operates without metric container; the only metric we have is ETX */
  const struct link_stats *stats = rpl_get_parent_link_stats(p);
  return stats != NULL ? stats->etx : 0xffff;
}
/*---------------------------------------------------------------------------*/
static uint16_t
parent_rank_increase(rpl_parent_t *p)
{
  uint16_t min_hoprankinc;
  if(p == NULL || p->dag == NULL || p->dag->instance == NULL) {
    return INFINITE_RANK;
  }
  min_hoprankinc = p->dag->instance->min_hoprankinc;
  return (RANK_FACTOR * STEP_OF_RANK(p) + RANK_STRETCH) * min_hoprankinc;
}
/*---------------------------------------------------------------------------*/
static uint16_t
parent_path_cost(rpl_parent_t *p)
{
  if(p == NULL) {
    return 0xffff;
  }
  /* path cost upper bound: 0xffff */
  return MIN((uint32_t)p->rank + parent_link_metric(p), 0xffff);
}
/*---------------------------------------------------------------------------*/
static rpl_rank_t
rank_via_parent(rpl_parent_t *p)
{
  if(p == NULL) {
    return INFINITE_RANK;
  } else {
    return MIN((uint32_t)p->rank + parent_rank_increase(p), INFINITE_RANK);
  }
}
/*---------------------------------------------------------------------------*/
static int
parent_is_acceptable(rpl_parent_t *p)
{
  return STEP_OF_RANK(p) >= MIN_STEP_OF_RANK
      && STEP_OF_RANK(p) <= MAX_STEP_OF_RANK;
}
/*---------------------------------------------------------------------------*/
static rpl_parent_t *
best_parent(rpl_parent_t *p1, rpl_parent_t *p2)
{
  rpl_dag_t *dag;
  uint16_t p1_cost;
  uint16_t p2_cost;
  int p1_is_acceptable;
  int p2_is_acceptable;

  if(p1 == NULL || p2 == NULL) {
    /* Return non-null parent if any */
    return p1 == NULL ? p2 : p1;
  }

  p1_is_acceptable = parent_is_acceptable(p1);
  p2_is_acceptable = parent_is_acceptable(p2);
  /* Is only one parent is acceptable, select it. If both are acceptable, or
   * both non-acceptable, proceed to traditional parent comparison. This is a
   * slight departure from the standard but allows to keep connectivity even
   * all neighbors appear to have a bad link. */
  if(p1_is_acceptable != p2_is_acceptable) {
    return p1_is_acceptable ? p1 : p2;
  }

  dag = p1->dag; /* Both parents are in the same DAG. */
  p1_cost = parent_path_cost(p1);
  p2_cost = parent_path_cost(p2);

  /* Paths costs coarse-grained (multiple of min_hoprankinc), we operate without hysteresis */
  if(p1_cost != p2_cost) {
    /* Pick parent with lowest path cost */
    return p1_cost < p2_cost ? p1 : p2;
  } else {
    /* We have a tie! */
    /* Stik to current preferred parent if possible */
    if(p1 == dag->preferred_parent || p2 == dag->preferred_parent) {
      return dag->preferred_parent;
    }
    /* None of the nodes is the current preferred parent,
     * choose parent with best link metric */
    return parent_link_metric(p1) < parent_link_metric(p2) ? p1 : p2;
  }
}
/*---------------------------------------------------------------------------*/
static rpl_dag_t *
best_dag(rpl_dag_t *d1, rpl_dag_t *d2)
{
  if(d1->grounded != d2->grounded) {
    return d1->grounded ? d1 : d2;
  }

  if(d1->preference != d2->preference) {
    return d1->preference > d2->preference ? d1 : d2;
  }

  return d1->rank < d2->rank ? d1 : d2;
}
/*---------------------------------------------------------------------------*/
static void
update_metric_container(rpl_instance_t *instance)
{
  instance->mc.type = RPL_DAG_MC_NONE;
}
/*---------------------------------------------------------------------------*/
rpl_of_t rpl_of0 = {
  reset,
#if RPL_WITH_DAO_ACK
  NULL,
#endif
  parent_link_metric,
  parent_path_cost,
  rank_via_parent,
  best_parent,
  best_dag,
  update_metric_container,
  RPL_OCP_OF0
};

/** @}*/