/* SPDX-License-Identifier: GPL-2.0-or-later */

/** \file
 * \ingroup bmesh
 *
 * Connect verts non-planer faces iteratively (splits faces).
 */

#include "BLI_alloca.h"
#include "BLI_linklist_stack.h"
#include "BLI_math.h"
#include "BLI_utildefines.h"

#include "bmesh.h"

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

#define EDGE_OUT (1 << 0)
#define FACE_OUT (1 << 1)

/**
 * Calculates how non-planar the face subset is.
 */
static float bm_face_subset_calc_planar(BMLoop *l_first, BMLoop *l_last, const float no[3])
{
  float axis_mat[3][3];
  float z_prev;
  float delta_z = 0.0f;

  /* Newell's Method */
  BMLoop *l_iter = l_first;
  BMLoop *l_term = l_last->next;

  axis_dominant_v3_to_m3(axis_mat, no);

  z_prev = dot_m3_v3_row_z(axis_mat, l_last->v->co);
  do {
    const float z_curr = dot_m3_v3_row_z(axis_mat, l_iter->v->co);
    delta_z += fabsf(z_curr - z_prev);
    z_prev = z_curr;
  } while ((l_iter = l_iter->next) != l_term);

  return delta_z;
}

static bool bm_face_split_find(BMesh *bm, BMFace *f, BMLoop *l_pair[2], float *r_angle_cos)
{
  BMLoop *l_iter, *l_first;
  BMLoop **l_arr = BLI_array_alloca(l_arr, f->len);
  const uint f_len = f->len;
  uint i_a, i_b;
  bool found = false;

  /* angle finding */
  float err_best = FLT_MAX;
  float angle_best_cos = -FLT_MAX;

  l_iter = l_first = BM_FACE_FIRST_LOOP(f);
  i_a = 0;
  do {
    l_arr[i_a++] = l_iter;
  } while ((l_iter = l_iter->next) != l_first);

  /* now for the big search, O(N^2), however faces normally aren't so large */
  for (i_a = 0; i_a < f_len; i_a++) {
    BMLoop *l_a = l_arr[i_a];
    for (i_b = i_a + 2; i_b < f_len; i_b++) {
      BMLoop *l_b = l_arr[i_b];
      /* check these are not touching
       * (we could be smarter here) */
      if (!BM_loop_is_adjacent(l_a, l_b)) {
        /* first calculate normals */
        float no_a[3], no_b[3];

        if (BM_face_calc_normal_subset(l_a, l_b, no_a) != 0.0f &&
            BM_face_calc_normal_subset(l_b, l_a, no_b) != 0.0f) {
          const float err_a = bm_face_subset_calc_planar(l_a, l_b, no_a);
          const float err_b = bm_face_subset_calc_planar(l_b, l_a, no_b);
          const float err_test = err_a + err_b;

          if (err_test < err_best) {
            /* check we're legal (we could batch this) */
            BMLoop *l_split[2] = {l_a, l_b};
            BM_face_splits_check_legal(bm, f, &l_split, 1);
            if (l_split[0]) {
              err_best = err_test;
              l_pair[0] = l_a;
              l_pair[1] = l_b;

              angle_best_cos = dot_v3v3(no_a, no_b);
              found = true;
            }
          }
        }
      }
    }
  }

  *r_angle_cos = angle_best_cos;

  return found;
}

static bool bm_face_split_by_angle(BMesh *bm,
                                   BMFace *f,
                                   BMFace *r_f_pair[2],
                                   const float angle_limit_cos)
{
  BMLoop *l_pair[2];
  float angle_cos;

  if (bm_face_split_find(bm, f, l_pair, &angle_cos) && (angle_cos < angle_limit_cos)) {
    BMFace *f_new;
    BMLoop *l_new;

    f_new = BM_face_split(bm, f, l_pair[0], l_pair[1], &l_new, NULL, false);
    if (f_new) {
      r_f_pair[0] = f;
      r_f_pair[1] = f_new;

      BMO_face_flag_enable(bm, f, FACE_OUT);
      BMO_face_flag_enable(bm, f_new, FACE_OUT);
      BMO_edge_flag_enable(bm, l_new->e, EDGE_OUT);
      return true;
    }
  }

  return false;
}

void bmo_connect_verts_nonplanar_exec(BMesh *bm, BMOperator *op)
{
  BMOIter siter;
  BMFace *f;
  bool changed = false;
  BLI_LINKSTACK_DECLARE(fstack, BMFace *);

  const float angle_limit_cos = cosf(BMO_slot_float_get(op->slots_in, "angle_limit"));

  BLI_LINKSTACK_INIT(fstack);

  BMO_ITER (f, &siter, op->slots_in, "faces", BM_FACE) {
    if (f->len > 3) {
      BLI_LINKSTACK_PUSH(fstack, f);
    }
  }

  while ((f = BLI_LINKSTACK_POP(fstack))) {
    BMFace *f_pair[2];
    if (bm_face_split_by_angle(bm, f, f_pair, angle_limit_cos)) {
      int j;
      for (j = 0; j < 2; j++) {
        BM_face_normal_update(f_pair[j]);
        if (f_pair[j]->len > 3) {
          BLI_LINKSTACK_PUSH(fstack, f_pair[j]);
        }
      }
      changed = true;
    }
  }

  BLI_LINKSTACK_FREE(fstack);

  if (changed) {
    BMO_slot_buffer_from_enabled_flag(bm, op, op->slots_out, "edges.out", BM_EDGE, EDGE_OUT);
    BMO_slot_buffer_from_enabled_flag(bm, op, op->slots_out, "faces.out", BM_FACE, FACE_OUT);
  }
}