/* SPDX-FileCopyrightText: 2023 Blender Authors
 *
 * SPDX-License-Identifier: GPL-2.0-or-later */

/** \file
 * \ingroup bmesh
 *
 * Create a convex hull using bullet physics library.
 */

#ifdef WITH_BULLET

#  include "MEM_guardedalloc.h"

#  include "BLI_listbase.h"
#  include "BLI_math_geom.h"
#  include "BLI_vector.hh"

#  include "RBI_hull_api.h"

/* XXX: using 128 for totelem and `pchunk` of `mempool`, no idea what good
 * values would be though */

#  include "bmesh.hh"

#  include "intern/bmesh_operators_private.hh" /* own include */

using blender::Vector;

/* Internal operator flags */
enum {
  HULL_FLAG_INPUT = (1 << 0),

  HULL_FLAG_INTERIOR_ELE = (1 << 1),
  HULL_FLAG_OUTPUT_GEOM = (1 << 2),

  HULL_FLAG_DEL = (1 << 3),
  HULL_FLAG_HOLE = (1 << 4),
};

/* Store hull triangles separate from BMesh faces until the end; this
 * way we don't have to worry about cleaning up extraneous edges or
 * incorrectly deleting existing geometry. */
struct HullTriangle {
  BMVert *v[3];
  float no[3];
  int skip;
};

/*************************** Hull Triangles ***************************/

static void hull_add_triangle(
    BMesh *bm, BLI_mempool *hull_triangles, BMVert *v1, BMVert *v2, BMVert *v3)
{
  HullTriangle *t;
  int i;

  t = static_cast<HullTriangle *>(BLI_mempool_calloc(hull_triangles));
  t->v[0] = v1;
  t->v[1] = v2;
  t->v[2] = v3;

  /* Mark triangles vertices as not interior */
  for (i = 0; i < 3; i++) {
    BMO_vert_flag_disable(bm, t->v[i], HULL_FLAG_INTERIOR_ELE);
  }

  normal_tri_v3(t->no, v1->co, v2->co, v3->co);
}

static BMFace *hull_find_example_face(BMesh *bm, BMEdge *e)
{
  BMIter iter;
  BMFace *f;

  BM_ITER_ELEM (f, &iter, e, BM_FACES_OF_EDGE) {
    if (BMO_face_flag_test(bm, f, HULL_FLAG_INPUT) ||
        BMO_face_flag_test(bm, f, HULL_FLAG_OUTPUT_GEOM) == false)
    {
      return f;
    }
  }

  return nullptr;
}

static void hull_output_triangles(BMesh *bm, BLI_mempool *hull_triangles)
{
  BLI_mempool_iter iter;
  BLI_mempool_iternew(hull_triangles, &iter);
  HullTriangle *t;

  while ((t = static_cast<HullTriangle *>(BLI_mempool_iterstep(&iter)))) {
    int i;

    if (!t->skip) {
      BMEdge *edges[3] = {
          BM_edge_create(bm, t->v[0], t->v[1], nullptr, BM_CREATE_NO_DOUBLE),
          BM_edge_create(bm, t->v[1], t->v[2], nullptr, BM_CREATE_NO_DOUBLE),
          BM_edge_create(bm, t->v[2], t->v[0], nullptr, BM_CREATE_NO_DOUBLE),
      };
      BMFace *f, *example = nullptr;

      f = BM_face_exists(t->v, 3);
      if (f != nullptr) {
        /* If the operator is run with "use_existing_faces"
         * disabled, but an output face in the hull is the
         * same as a face in the existing mesh, it should not
         * be marked as unused or interior. */
        BMO_face_flag_enable(bm, f, HULL_FLAG_OUTPUT_GEOM);
        BMO_face_flag_disable(bm, f, HULL_FLAG_HOLE);
        BMO_face_flag_disable(bm, f, HULL_FLAG_INTERIOR_ELE);
      }
      else {
        /* Look for an adjacent face that existed before the hull */
        for (i = 0; i < 3; i++) {
          if (!example) {
            example = hull_find_example_face(bm, edges[i]);
          }
        }

        /* Create new hull face */
        f = BM_face_create_verts(bm, t->v, 3, example, BM_CREATE_NO_DOUBLE, true);
        BM_face_copy_shared(bm, f, nullptr, nullptr);
      }
      /* Mark face for 'geom.out' slot and select */
      BMO_face_flag_enable(bm, f, HULL_FLAG_OUTPUT_GEOM);
      BM_face_select_set(bm, f, true);

      /* Mark edges for 'geom.out' slot */
      for (i = 0; i < 3; i++) {
        BMO_edge_flag_enable(bm, edges[i], HULL_FLAG_OUTPUT_GEOM);
      }
    }
    else {
      /* Mark input edges for 'geom.out' slot */
      for (i = 0; i < 3; i++) {
        const int next = (i == 2 ? 0 : i + 1);
        BMEdge *e = BM_edge_exists(t->v[i], t->v[next]);
        if (e && BMO_edge_flag_test(bm, e, HULL_FLAG_INPUT) &&
            !BMO_edge_flag_test(bm, e, HULL_FLAG_HOLE))
        {
          BMO_edge_flag_enable(bm, e, HULL_FLAG_OUTPUT_GEOM);
        }
      }
    }

    /* Mark verts for 'geom.out' slot */
    for (i = 0; i < 3; i++) {
      BMO_vert_flag_enable(bm, t->v[i], HULL_FLAG_OUTPUT_GEOM);
    }
  }
}

/***************************** Final Edges ****************************/

struct HullFinalEdges {
  GHash *edges;
  BLI_mempool *base_pool, *link_pool;
};

static LinkData *final_edges_find_link(ListBase *adj, BMVert *v)
{
  LISTBASE_FOREACH (LinkData *, link, adj) {
    if (link->data == v) {
      return link;
    }
  }

  return nullptr;
}

static int hull_final_edges_lookup(HullFinalEdges *final_edges, BMVert *v1, BMVert *v2)
{
  ListBase *adj;

  /* Use lower vertex pointer for hash key */
  if (v1 > v2) {
    std::swap(v1, v2);
  }

  adj = static_cast<ListBase *>(BLI_ghash_lookup(final_edges->edges, v1));
  if (!adj) {
    return false;
  }

  return !!final_edges_find_link(adj, v2);
}

/* Used for checking whether a pre-existing edge lies on the hull */
static HullFinalEdges *hull_final_edges(BLI_mempool *hull_triangles)
{
  HullFinalEdges *final_edges;

  final_edges = MEM_callocN<HullFinalEdges>("HullFinalEdges");
  final_edges->edges = BLI_ghash_ptr_new("final edges ghash");
  final_edges->base_pool = BLI_mempool_create(sizeof(ListBase), 0, 128, BLI_MEMPOOL_NOP);
  final_edges->link_pool = BLI_mempool_create(sizeof(LinkData), 0, 128, BLI_MEMPOOL_NOP);

  BLI_mempool_iter iter;
  BLI_mempool_iternew(hull_triangles, &iter);
  HullTriangle *t;

  while ((t = static_cast<HullTriangle *>(BLI_mempool_iterstep(&iter)))) {
    LinkData *link;
    int i;

    for (i = 0; i < 3; i++) {
      BMVert *v1 = t->v[i];
      BMVert *v2 = t->v[(i + 1) % 3];
      ListBase *adj;

      /* Use lower vertex pointer for hash key */
      if (v1 > v2) {
        std::swap(v1, v2);
      }

      adj = static_cast<ListBase *>(BLI_ghash_lookup(final_edges->edges, v1));
      if (!adj) {
        adj = static_cast<ListBase *>(BLI_mempool_calloc(final_edges->base_pool));
        BLI_ghash_insert(final_edges->edges, v1, adj);
      }

      if (!final_edges_find_link(adj, v2)) {
        link = static_cast<LinkData *>(BLI_mempool_calloc(final_edges->link_pool));
        link->data = v2;
        BLI_addtail(adj, link);
      }
    }
  }

  return final_edges;
}

static void hull_final_edges_free(HullFinalEdges *final_edges)
{
  BLI_ghash_free(final_edges->edges, nullptr, nullptr);
  BLI_mempool_destroy(final_edges->base_pool);
  BLI_mempool_destroy(final_edges->link_pool);
  MEM_freeN(final_edges);
}

/**************************** Final Output ****************************/

static void hull_remove_overlapping(BMesh *bm,
                                    BLI_mempool *hull_triangles,
                                    HullFinalEdges *final_edges)
{
  BLI_mempool_iter iter;
  BLI_mempool_iternew(hull_triangles, &iter);
  HullTriangle *t;

  while ((t = static_cast<HullTriangle *>(BLI_mempool_iterstep(&iter)))) {
    BMIter bm_iter1, bm_iter2;
    BMFace *f;
    bool f_on_hull;

    BM_ITER_ELEM (f, &bm_iter1, t->v[0], BM_FACES_OF_VERT) {
      BMEdge *e;

      /* Check that all the face's edges are on the hull,
       * otherwise can't reuse it */
      f_on_hull = true;
      BM_ITER_ELEM (e, &bm_iter2, f, BM_EDGES_OF_FACE) {
        if (!hull_final_edges_lookup(final_edges, e->v1, e->v2)) {
          f_on_hull = false;
          break;
        }
      }

      /* NOTE: can't change ghash while iterating, so mark
       * with 'skip' flag rather than deleting triangles */
      if (BM_vert_in_face(t->v[1], f) && BM_vert_in_face(t->v[2], f) && f_on_hull) {
        t->skip = true;
        BMO_face_flag_disable(bm, f, HULL_FLAG_INTERIOR_ELE);
        BMO_face_flag_enable(bm, f, HULL_FLAG_HOLE);
      }
    }
  }
}

static void hull_mark_interior_elements(BMesh *bm, BMOperator *op, HullFinalEdges *final_edges)
{
  BMEdge *e;
  BMFace *f;
  BMOIter oiter;

  /* Check for interior edges too */
  BMO_ITER (e, &oiter, op->slots_in, "input", BM_EDGE) {
    if (!hull_final_edges_lookup(final_edges, e->v1, e->v2)) {
      BMO_edge_flag_enable(bm, e, HULL_FLAG_INTERIOR_ELE);
    }
  }

  /* Mark all input faces as interior, some may be unmarked in
   * hull_remove_overlapping() */
  BMO_ITER (f, &oiter, op->slots_in, "input", BM_FACE) {
    BMO_face_flag_enable(bm, f, HULL_FLAG_INTERIOR_ELE);
  }
}

static void hull_tag_unused(BMesh *bm, BMOperator *op)
{
  BMIter iter;
  BMOIter oiter;
  BMVert *v;
  BMEdge *e;
  BMFace *f;

  /* Mark vertices, edges, and faces that are already marked
   * interior (i.e. were already part of the input, but not part of
   * the hull), but that aren't also used by elements outside the
   * input set */
  BMO_ITER (v, &oiter, op->slots_in, "input", BM_VERT) {
    if (BMO_vert_flag_test(bm, v, HULL_FLAG_INTERIOR_ELE)) {
      bool del = true;

      BM_ITER_ELEM (e, &iter, v, BM_EDGES_OF_VERT) {
        if (!BMO_edge_flag_test(bm, e, HULL_FLAG_INPUT)) {
          del = false;
          break;
        }
      }

      BM_ITER_ELEM (f, &iter, v, BM_FACES_OF_VERT) {
        if (!BMO_face_flag_test(bm, f, HULL_FLAG_INPUT)) {
          del = false;
          break;
        }
      }

      if (del) {
        BMO_vert_flag_enable(bm, v, HULL_FLAG_DEL);
      }
    }
  }

  BMO_ITER (e, &oiter, op->slots_in, "input", BM_EDGE) {
    if (BMO_edge_flag_test(bm, e, HULL_FLAG_INTERIOR_ELE)) {
      bool del = true;

      BM_ITER_ELEM (f, &iter, e, BM_FACES_OF_EDGE) {
        if (!BMO_face_flag_test(bm, f, HULL_FLAG_INPUT)) {
          del = false;
          break;
        }
      }

      if (del) {
        BMO_edge_flag_enable(bm, e, HULL_FLAG_DEL);
      }
    }
  }

  BMO_ITER (f, &oiter, op->slots_in, "input", BM_FACE) {
    if (BMO_face_flag_test(bm, f, HULL_FLAG_INTERIOR_ELE)) {
      BMO_face_flag_enable(bm, f, HULL_FLAG_DEL);
    }
  }
}

static void hull_tag_holes(BMesh *bm, BMOperator *op)
{
  BMIter iter;
  BMOIter oiter;
  BMFace *f;
  BMEdge *e;

  /* Unmark any hole faces if they are isolated or part of a
   * border */
  BMO_ITER (f, &oiter, op->slots_in, "input", BM_FACE) {
    if (BMO_face_flag_test(bm, f, HULL_FLAG_HOLE)) {
      BM_ITER_ELEM (e, &iter, f, BM_EDGES_OF_FACE) {
        if (BM_edge_is_boundary(e)) {
          BMO_face_flag_disable(bm, f, HULL_FLAG_HOLE);
          break;
        }
      }
    }
  }

  /* Mark edges too if all adjacent faces are holes and the edge is
   * not already isolated */
  BMO_ITER (e, &oiter, op->slots_in, "input", BM_EDGE) {
    bool hole = true;
    bool any_faces = false;

    BM_ITER_ELEM (f, &iter, e, BM_FACES_OF_EDGE) {
      any_faces = true;
      if (!BMO_face_flag_test(bm, f, HULL_FLAG_HOLE)) {
        hole = false;
        break;
      }
    }

    if (hole && any_faces) {
      BMO_edge_flag_enable(bm, e, HULL_FLAG_HOLE);
    }
  }
}

static int hull_input_vert_count(BMOperator *op)
{
  BMOIter oiter;
  BMVert *v;
  int count = 0;

  BMO_ITER (v, &oiter, op->slots_in, "input", BM_VERT) {
    count++;
  }

  return count;
}

static BMVert **hull_input_verts_copy(BMOperator *op, const int num_input_verts)
{
  BMOIter oiter;
  BMVert *v;
  BMVert **input_verts = static_cast<BMVert **>(
      MEM_callocN(sizeof(*input_verts) * num_input_verts, AT));
  int i = 0;

  BMO_ITER (v, &oiter, op->slots_in, "input", BM_VERT) {
    input_verts[i++] = v;
  }

  return input_verts;
}

static float (*hull_verts_for_bullet(BMVert **input_verts, const int num_input_verts))[3]
{
  float(*coords)[3] = static_cast<float(*)[3]>(
      MEM_callocN(sizeof(*coords) * num_input_verts, __func__));
  int i;

  for (i = 0; i < num_input_verts; i++) {
    copy_v3_v3(coords[i], input_verts[i]->co);
  }

  return coords;
}

static BMVert **hull_verts_from_bullet(plConvexHull hull,
                                       BMVert **input_verts,
                                       const int num_input_verts)
{
  const int num_verts = plConvexHullNumVertices(hull);
  BMVert **hull_verts = MEM_malloc_arrayN<BMVert *>(num_verts, AT);
  int i;

  for (i = 0; i < num_verts; i++) {
    float co[3];
    int original_index;
    plConvexHullGetVertex(hull, i, co, &original_index);

    if (original_index >= 0 && original_index < num_input_verts) {
      hull_verts[i] = input_verts[original_index];
    }
    else {
      BLI_assert_msg(0, "Unexpected new vertex in hull output");
    }
  }

  return hull_verts;
}

static void hull_from_bullet(BMesh *bm, BMOperator *op, BLI_mempool *hull_triangles)
{
  BMVert **input_verts;
  float(*coords)[3];
  BMVert **hull_verts;

  plConvexHull hull;
  int i, count = 0;

  const int num_input_verts = hull_input_vert_count(op);

  input_verts = hull_input_verts_copy(op, num_input_verts);
  coords = hull_verts_for_bullet(input_verts, num_input_verts);

  hull = plConvexHullCompute(coords, num_input_verts);
  hull_verts = hull_verts_from_bullet(hull, input_verts, num_input_verts);

  count = plConvexHullNumFaces(hull);
  Vector<int> fvi;
  for (i = 0; i < count; i++) {
    const int len = plConvexHullGetFaceSize(hull, i);

    if (len > 2) {
      BMVert *fv[3];
      int j;

      /* Get face vertex indices */
      fvi.reinitialize(len);
      plConvexHullGetFaceVertices(hull, i, fvi.data());

      /* NOTE: here we throw away any NGons from Bullet and turn
       * them into triangle fans. Would be nice to use these
       * directly, but will have to wait until HullTriangle goes
       * away (TODO) */
      fv[0] = hull_verts[fvi[0]];
      for (j = 2; j < len; j++) {
        fv[1] = hull_verts[fvi[j - 1]];
        fv[2] = hull_verts[fvi[j]];

        hull_add_triangle(bm, hull_triangles, fv[0], fv[1], fv[2]);
      }
    }
  }

  plConvexHullDelete(hull);

  MEM_freeN(hull_verts);
  MEM_freeN(coords);
  MEM_freeN(input_verts);
}

/* Check that there are at least three vertices in the input */
static bool hull_num_input_verts_is_ok(BMOperator *op)
{
  BMOIter oiter;
  BMVert *v;
  int partial_num_verts = 0;

  BMO_ITER (v, &oiter, op->slots_in, "input", BM_VERT) {
    partial_num_verts++;
    if (partial_num_verts >= 3) {
      break;
    }
  }

  return (partial_num_verts >= 3);
}

void bmo_convex_hull_exec(BMesh *bm, BMOperator *op)
{
  HullFinalEdges *final_edges;
  BLI_mempool *hull_triangles;
  BMElemF *ele;
  BMOIter oiter;

  /* Verify that at least three verts in the input */
  if (!hull_num_input_verts_is_ok(op)) {
    BMO_error_raise(bm, op, BMO_ERROR_CANCEL, "Requires at least three vertices");
    return;
  }

  /* Tag input elements */
  BMO_ITER (ele, &oiter, op->slots_in, "input", BM_ALL) {

    /* Mark all vertices as interior to begin with */
    if (ele->head.htype == BM_VERT) {
      BMO_vert_flag_enable(bm, (BMVert *)ele, HULL_FLAG_INPUT | HULL_FLAG_INTERIOR_ELE);
    }
    else if (ele->head.htype == BM_EDGE) {
      BMO_edge_flag_enable(bm, (BMEdge *)ele, HULL_FLAG_INPUT);
    }
    else {
      BMO_face_flag_enable(bm, (BMFace *)ele, HULL_FLAG_INPUT);
    }
  }

  hull_triangles = BLI_mempool_create(sizeof(HullTriangle), 0, 128, BLI_MEMPOOL_ALLOW_ITER);

  hull_from_bullet(bm, op, hull_triangles);

  final_edges = hull_final_edges(hull_triangles);

  hull_mark_interior_elements(bm, op, final_edges);

  /* Remove hull triangles covered by an existing face */
  if (BMO_slot_bool_get(op->slots_in, "use_existing_faces")) {
    hull_remove_overlapping(bm, hull_triangles, final_edges);

    hull_tag_holes(bm, op);
  }

  /* Done with edges */
  hull_final_edges_free(final_edges);

  /* Convert hull triangles to BMesh faces */
  hull_output_triangles(bm, hull_triangles);
  BLI_mempool_destroy(hull_triangles);

  hull_tag_unused(bm, op);

  /* Output slot of input elements that ended up inside the hull
   * rather than part of it */
  BMO_slot_buffer_from_enabled_flag(
      bm, op, op->slots_out, "geom_interior.out", BM_ALL_NOLOOP, HULL_FLAG_INTERIOR_ELE);

  /* Output slot of input elements that ended up inside the hull and
   * are unused by other geometry. */
  BMO_slot_buffer_from_enabled_flag(
      bm, op, op->slots_out, "geom_unused.out", BM_ALL_NOLOOP, HULL_FLAG_DEL);

  /* Output slot of faces and edges that were in the input and on
   * the hull (useful for cases like bridging where you want to
   * delete some input geometry) */
  BMO_slot_buffer_from_enabled_flag(
      bm, op, op->slots_out, "geom_holes.out", BM_ALL_NOLOOP, HULL_FLAG_HOLE);

  /* Output slot of all hull vertices, faces, and edges */
  BMO_slot_buffer_from_enabled_flag(
      bm, op, op->slots_out, "geom.out", BM_ALL_NOLOOP, HULL_FLAG_OUTPUT_GEOM);
}

#endif /* WITH_BULLET */
