/*************************************************************************
 * Copyright (C) 2012-2014 Tavian Barnes <tavianator@tavianator.com>     *
 *                                                                       *
 * This file is part of The Dimension Library.                           *
 *                                                                       *
 * The Dimension Library is free software; you can redistribute it and/  *
 * or modify it under the terms of the GNU Lesser General Public License *
 * as published by the Free Software Foundation; either version 3 of the *
 * License, or (at your option) any later version.                       *
 *                                                                       *
 * The Dimension Library 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  *
 * Lesser General Public License for more details.                       *
 *                                                                       *
 * You should have received a copy of the GNU Lesser General Public      *
 * License along with this program.  If not, see                         *
 * <http://www.gnu.org/licenses/>.                                       *
 *************************************************************************/

/**
 * @file
 * BVH implementation.  These are the hottest code paths in libdimension.
 */

#include "dimension-internal.h"

/** Implementation for DMNSN_BVH_NONE: just stick all objects in one node. */
static dmnsn_bvh_node *
dmnsn_new_stupid_bvh(const dmnsn_array *objects)
{
  dmnsn_bvh_node *root = dmnsn_new_bvh_node(dmnsn_array_size(objects));

  DMNSN_ARRAY_FOREACH (dmnsn_object **, object, objects) {
    dmnsn_bvh_node *leaf = dmnsn_new_bvh_leaf_node(*object);
    dmnsn_bvh_node_add(root, leaf);
  }

  return root;
}

/* Implementation of opaque dmnsn_bvh type. */
struct dmnsn_bvh {
  dmnsn_array *unbounded;           /**< The unbounded objects. */
  dmnsn_array *bounded;             /**< The BVH of the bounded objects. */
  pthread_key_t intersection_cache; /**< The thread-local intersection cache. */
};

/** A flat BVH node for storing in an array for fast pre-order traversal. */
typedef struct dmnsn_flat_bvh_node {
  dmnsn_bounding_box bounding_box; /* The bounding box of this node. */
  dmnsn_object *object;            /* The referenced object, for leaf nodes. */
  ptrdiff_t skip;                  /* Displacement to the next sibling. */
} dmnsn_flat_bvh_node;

/** Add an object or its children, if any, to an array. */
static void
dmnsn_split_add_object(dmnsn_array *objects, const dmnsn_object *object)
{
  if (object->split_children) {
    DMNSN_ARRAY_FOREACH (const dmnsn_object **, child, object->children) {
      dmnsn_split_add_object(objects, *child);
    }
  } else {
    dmnsn_array_push(objects, &object);
  }
}

/** Split unions to create the input for the BVH. */
static dmnsn_array *
dmnsn_split_objects(const dmnsn_array *objects)
{
  dmnsn_array *split = dmnsn_new_array(sizeof(dmnsn_object *));
  DMNSN_ARRAY_FOREACH (const dmnsn_object **, object, objects) {
    dmnsn_split_add_object(split, *object);
  }
  return split;
}

/** Split unbounded objects into a new array. */
static dmnsn_array *
dmnsn_split_unbounded(dmnsn_array *objects)
{
  dmnsn_array *unbounded = dmnsn_new_array(sizeof(dmnsn_object *));

  dmnsn_object **array = dmnsn_array_first(objects);
  size_t i, skip;
  for (i = 0, skip = 0; i < dmnsn_array_size(objects); ++i) {
    if (dmnsn_bounding_box_is_infinite(array[i]->bounding_box)) {
      dmnsn_array_push(unbounded, &array[i]);
      ++skip;
    } else {
      array[i - skip] = array[i];
    }
  }
  dmnsn_array_resize(objects, i - skip);

  return unbounded;
}

/** Recursively flatten a BVH into an array of flat nodes. */
static void
dmnsn_flatten_bvh_recursive(dmnsn_bvh_node *node, dmnsn_array *flat)
{
  size_t currenti = dmnsn_array_size(flat);
  dmnsn_array_resize(flat, currenti + 1);
  dmnsn_flat_bvh_node *flatnode = dmnsn_array_at(flat, currenti);

  flatnode->bounding_box = node->bounding_box;
  flatnode->object       = node->object;

  for (size_t i = 0; i < node->nchildren && node->children[i]; ++i) {
    dmnsn_flatten_bvh_recursive(node->children[i], flat);
  }

  /* Array could have been realloc()'d somewhere else above */
  flatnode = dmnsn_array_at(flat, currenti);
  flatnode->skip = dmnsn_array_size(flat) - currenti;
}

/** Flatten a BVH into an array of flat nodes. */
static dmnsn_array *
dmnsn_flatten_bvh(dmnsn_bvh_node *root)
{
  dmnsn_array *flat = dmnsn_new_array(sizeof(dmnsn_flat_bvh_node));
  if (root) {
    dmnsn_flatten_bvh_recursive(root, flat);
  }
  return flat;
}

dmnsn_bvh *dmnsn_new_bvh(const dmnsn_array *objects, dmnsn_bvh_kind kind)
{
  dmnsn_bvh *bvh = DMNSN_MALLOC(dmnsn_bvh);

  dmnsn_array *bounded = dmnsn_split_objects(objects);
  bvh->unbounded = dmnsn_split_unbounded(bounded);

  dmnsn_bvh_node *root = NULL;
  if (dmnsn_array_size(bounded) > 0) {
    switch (kind) {
    case DMNSN_BVH_NONE:
      root = dmnsn_new_stupid_bvh(bounded);
      break;
    case DMNSN_BVH_PRTREE:
      root = dmnsn_new_prtree(bounded);
      break;
    default:
      dmnsn_unreachable("Invalid BVH kind.");
    }
  }
  bvh->bounded = dmnsn_flatten_bvh(root);

  dmnsn_delete_bvh_node(root);
  dmnsn_delete_array(bounded);

  dmnsn_key_create(&bvh->intersection_cache, dmnsn_free);

  return bvh;
}

void
dmnsn_delete_bvh(dmnsn_bvh *bvh)
{
  if (bvh) {
    dmnsn_free(pthread_getspecific(bvh->intersection_cache));
    dmnsn_key_delete(bvh->intersection_cache);
    dmnsn_delete_array(bvh->bounded);
    dmnsn_delete_array(bvh->unbounded);
    dmnsn_free(bvh);
  }
}

/** A line with pre-calculated reciprocals to avoid divisions. */
typedef struct dmnsn_optimized_line {
  dmnsn_vector x0;    /**< The origin of the line. */
  dmnsn_vector n_inv; /**< The inverse of each component of the line's slope .*/
} dmnsn_optimized_line;

/** Precompute inverses for faster ray-box intersection tests. */
static inline dmnsn_optimized_line
dmnsn_optimize_line(dmnsn_line line)
{
  dmnsn_optimized_line optline = {
    .x0    = line.x0,
    .n_inv = dmnsn_new_vector(1.0/line.n.x, 1.0/line.n.y, 1.0/line.n.z)
  };
  return optline;
}

/** Ray-AABB intersection test, by the slab method.  Highly optimized. */
static inline bool
dmnsn_ray_box_intersection(dmnsn_optimized_line optline,
                           dmnsn_bounding_box box, double t)
{
  /*
   * This is actually correct, even though it appears not to handle edge cases
   * (line.n.{x,y,z} == 0).  It works because the infinities that result from
   * dividing by zero will still behave correctly in the comparisons.  Lines
   * which are parallel to an axis and outside the box will have tmin == inf
   * or tmax == -inf, while lines inside the box will have tmin and tmax
   * unchanged.
   */

  double tx1 = (box.min.x - optline.x0.x)*optline.n_inv.x;
  double tx2 = (box.max.x - optline.x0.x)*optline.n_inv.x;

  double tmin = dmnsn_min(tx1, tx2);
  double tmax = dmnsn_max(tx1, tx2);

  double ty1 = (box.min.y - optline.x0.y)*optline.n_inv.y;
  double ty2 = (box.max.y - optline.x0.y)*optline.n_inv.y;

  tmin = dmnsn_max(tmin, dmnsn_min(ty1, ty2));
  tmax = dmnsn_min(tmax, dmnsn_max(ty1, ty2));

  double tz1 = (box.min.z - optline.x0.z)*optline.n_inv.z;
  double tz2 = (box.max.z - optline.x0.z)*optline.n_inv.z;

  tmin = dmnsn_max(tmin, dmnsn_min(tz1, tz2));
  tmax = dmnsn_min(tmax, dmnsn_max(tz1, tz2));

  return tmax >= dmnsn_max(0.0, tmin) && tmin < t;
}

/** The number of intersections to cache. */
#define DMNSN_INTERSECTION_CACHE_SIZE 32

/** An array of cached intersections. */
typedef struct dmnsn_intersection_cache {
  size_t i;
  dmnsn_object *objects[DMNSN_INTERSECTION_CACHE_SIZE];
} dmnsn_intersection_cache;

static dmnsn_intersection_cache *
dmnsn_get_intersection_cache(const dmnsn_bvh *bvh)
{
  dmnsn_intersection_cache *cache
    = pthread_getspecific(bvh->intersection_cache);

  if (!cache) {
    cache = DMNSN_MALLOC(dmnsn_intersection_cache);
    cache->i = 0;
    for (size_t i = 0; i < DMNSN_INTERSECTION_CACHE_SIZE; ++i) {
      cache->objects[i] = NULL;
    }
    dmnsn_setspecific(bvh->intersection_cache, cache);
  }

  return cache;
}

/** Test for a closer object intersection than we've found so far. */
static inline bool
dmnsn_closer_intersection(dmnsn_object *object, dmnsn_line ray,
                          dmnsn_intersection *intersection, double *t)
{
  dmnsn_intersection local_intersection;
  if (dmnsn_object_intersection(object, ray, &local_intersection)) {
    if (local_intersection.t < *t) {
      *intersection = local_intersection;
      *t = local_intersection.t;
      return true;
    }
  }
  return false;
}

DMNSN_HOT bool
dmnsn_bvh_intersection(const dmnsn_bvh *bvh, dmnsn_line ray,
                       dmnsn_intersection *intersection, bool reset)
{
  double t = INFINITY;

  /* Search the unbounded objects */
  DMNSN_ARRAY_FOREACH (dmnsn_object **, object, bvh->unbounded) {
    dmnsn_closer_intersection(*object, ray, intersection, &t);
  }

  /* Precalculate 1.0/ray.n.{x,y,z} to save time in intersection tests */
  dmnsn_optimized_line optline = dmnsn_optimize_line(ray);

  /* Search the intersection cache */
  dmnsn_intersection_cache *cache = dmnsn_get_intersection_cache(bvh);
  if (dmnsn_unlikely(reset)) {
    cache->i = 0;
  }
  dmnsn_object *cached = NULL, *found = NULL;
  if (dmnsn_likely(cache->i < DMNSN_INTERSECTION_CACHE_SIZE)) {
    cached = cache->objects[cache->i];
  }
  if (cached && dmnsn_ray_box_intersection(optline, cached->bounding_box, t)) {
    if (dmnsn_closer_intersection(cached, ray, intersection, &t)) {
      found = cached;
    }
  }

  /* Search the bounded objects */
  dmnsn_flat_bvh_node *node = dmnsn_array_first(bvh->bounded);
  dmnsn_flat_bvh_node *last = dmnsn_array_last(bvh->bounded);
  while (node <= last) {
    if (dmnsn_ray_box_intersection(optline, node->bounding_box, t)) {
      if (node->object && node->object != cached) {
        if (dmnsn_closer_intersection(node->object, ray, intersection, &t)) {
          found = node->object;
        }
      }
      ++node;
    } else {
      node += node->skip;
    }
  }

  /* Update the cache */
  if (dmnsn_likely(cache->i < DMNSN_INTERSECTION_CACHE_SIZE)) {
    cache->objects[cache->i] = found;
    ++cache->i;
  }

  return !isinf(t);
}

DMNSN_HOT bool
dmnsn_bvh_inside(const dmnsn_bvh *bvh, dmnsn_vector point)
{
  /* Search the unbounded objects */
  DMNSN_ARRAY_FOREACH (dmnsn_object **, object, bvh->unbounded) {
    if (dmnsn_object_inside(*object, point))
      return true;
  }

  /* Search the bounded objects */
  dmnsn_flat_bvh_node *node = dmnsn_array_first(bvh->bounded);
  dmnsn_flat_bvh_node *last = dmnsn_array_last(bvh->bounded);
  while (node <= last) {
    if (dmnsn_bounding_box_contains(node->bounding_box, point)) {
      if (node->object && dmnsn_object_inside(node->object, point)) {
        return true;
      }
      ++node;
    } else {
      node += node->skip;
    }
  }

  return false;
}

dmnsn_bounding_box
dmnsn_bvh_bounding_box(const dmnsn_bvh *bvh)
{
  if (dmnsn_array_size(bvh->unbounded) > 0) {
    return dmnsn_infinite_bounding_box();
  } else if (dmnsn_array_size(bvh->bounded) > 0) {
    dmnsn_flat_bvh_node *root = dmnsn_array_first(bvh->bounded);
    return root->bounding_box;
  } else {
    return dmnsn_zero_bounding_box();
  }
}

dmnsn_bvh_node *
dmnsn_new_bvh_node(size_t max_children)
{
  dmnsn_bvh_node *node = dmnsn_malloc(sizeof(dmnsn_bvh_node)
                                      + max_children*sizeof(dmnsn_bvh_node *));
  node->bounding_box = dmnsn_zero_bounding_box();
  node->object = NULL;
  node->nchildren = 0;
  node->max_children = max_children;
  return node;
}

dmnsn_bvh_node *
dmnsn_new_bvh_leaf_node(dmnsn_object *object)
{
  dmnsn_bvh_node *node = DMNSN_MALLOC(dmnsn_bvh_node);
  node->bounding_box = object->bounding_box;
  node->object = object;
  node->nchildren = 0;
  node->max_children = 0;
  return node;
}

void
dmnsn_delete_bvh_node(dmnsn_bvh_node *node)
{
  if (node) {
    for (size_t i = 0; i < node->nchildren; ++i) {
      dmnsn_delete_bvh_node(node->children[i]);
    }
    dmnsn_free(node);
  }
}

void
dmnsn_bvh_node_add(dmnsn_bvh_node *parent, dmnsn_bvh_node *child)
{
  dmnsn_assert(parent->nchildren < parent->max_children,
               "Too many BVH children inserted.");

  parent->bounding_box.min = dmnsn_vector_min(parent->bounding_box.min,
                                              child->bounding_box.min);
  parent->bounding_box.max = dmnsn_vector_max(parent->bounding_box.max,
                                              child->bounding_box.max);
  parent->children[parent->nchildren++] = child;
}