/**
 * Copyright (c) 2026 Dominic Masters
 *
 * This software is released under the MIT License.
 * https://opensource.org/licenses/MIT
 */

#include "sphere.h"
#include "assert/assert.h"

mesh_t SPHERE_MESH_SIMPLE;
meshvertex_t SPHERE_MESH_SIMPLE_VERTICES[SPHERE_VERTEX_COUNT];

errorret_t sphereInit() {
  vec3 center = { 0.0f, 0.0f, 0.0f };
  sphereBuffer(
    SPHERE_MESH_SIMPLE_VERTICES,
    center,
    0.5f,
    SPHERE_STACKS,
    SPHERE_SECTORS
    #if MESH_ENABLE_COLOR
      , COLOR_WHITE_4B
    #endif
  );
  errorChain(meshInit(
    &SPHERE_MESH_SIMPLE,
    SPHERE_PRIMITIVE_TYPE,
    SPHERE_VERTEX_COUNT,
    SPHERE_MESH_SIMPLE_VERTICES
  ));
  errorOk();
}

void sphereBuffer(
  meshvertex_t *vertices,
  const vec3 center,
  const float_t radius,
  const int32_t stacks,
  const int32_t sectors
  #if MESH_ENABLE_COLOR
    , const color_t color
  #endif
) {
  assertNotNull(vertices, "Vertices cannot be NULL");
  assertNotNull(center, "Center vector cannot be NULL");

  const float_t stackStep   = (float_t)GLM_PI / (float_t)stacks;
  const float_t sectorStep  = 2.0f * (float_t)GLM_PI / (float_t)sectors;
  int32_t vi = 0;

  for(int32_t i = 0; i < stacks; i++) {
    /* Latitude angles: top of band -> bottom of band */
    const float_t phi1 = (float_t)GLM_PI_2 - (float_t)i       * stackStep;
    const float_t phi2 = (float_t)GLM_PI_2 - (float_t)(i + 1) * stackStep;

    const float_t y1  = radius * sinf(phi1);
    const float_t y2  = radius * sinf(phi2);
    const float_t xz1 = radius * cosf(phi1);
    const float_t xz2 = radius * cosf(phi2);

    const float_t v1 = 1.0f - (float_t)i       / (float_t)stacks;
    const float_t v2 = 1.0f - (float_t)(i + 1) / (float_t)stacks;

    for(int32_t j = 0; j < sectors; j++) {
      const float_t theta1 = (float_t)j       * sectorStep;
      const float_t theta2 = (float_t)(j + 1) * sectorStep;

      const float_t x11 = xz1 * cosf(theta1);
      const float_t z11 = xz1 * sinf(theta1);
      const float_t x12 = xz1 * cosf(theta2);
      const float_t z12 = xz1 * sinf(theta2);

      const float_t x21 = xz2 * cosf(theta1);
      const float_t z21 = xz2 * sinf(theta1);
      const float_t x22 = xz2 * cosf(theta2);
      const float_t z22 = xz2 * sinf(theta2);

      const float_t u1 = (float_t)j       / (float_t)sectors;
      const float_t u2 = (float_t)(j + 1) / (float_t)sectors;

      /* Triangle 1: top-left, bottom-left, top-right */
      #if MESH_ENABLE_COLOR
        vertices[vi].color = color;
      #endif
      vertices[vi].pos[0] = center[0] + x11;
      vertices[vi].pos[1] = center[1] + y1;
      vertices[vi].pos[2] = center[2] + z11;
      vertices[vi].uv[0]  = u1;
      vertices[vi].uv[1]  = v1;
      vi++;

      #if MESH_ENABLE_COLOR
        vertices[vi].color = color;
      #endif
      vertices[vi].pos[0] = center[0] + x21;
      vertices[vi].pos[1] = center[1] + y2;
      vertices[vi].pos[2] = center[2] + z21;
      vertices[vi].uv[0]  = u1;
      vertices[vi].uv[1]  = v2;
      vi++;

      #if MESH_ENABLE_COLOR
        vertices[vi].color = color;
      #endif
      vertices[vi].pos[0] = center[0] + x12;
      vertices[vi].pos[1] = center[1] + y1;
      vertices[vi].pos[2] = center[2] + z12;
      vertices[vi].uv[0]  = u2;
      vertices[vi].uv[1]  = v1;
      vi++;

      /* Triangle 2: top-right, bottom-left, bottom-right */
      #if MESH_ENABLE_COLOR
        vertices[vi].color = color;
      #endif
      vertices[vi].pos[0] = center[0] + x12;
      vertices[vi].pos[1] = center[1] + y1;
      vertices[vi].pos[2] = center[2] + z12;
      vertices[vi].uv[0]  = u2;
      vertices[vi].uv[1]  = v1;
      vi++;

      #if MESH_ENABLE_COLOR
        vertices[vi].color = color;
      #endif
      vertices[vi].pos[0] = center[0] + x21;
      vertices[vi].pos[1] = center[1] + y2;
      vertices[vi].pos[2] = center[2] + z21;
      vertices[vi].uv[0]  = u1;
      vertices[vi].uv[1]  = v2;
      vi++;

      #if MESH_ENABLE_COLOR
        vertices[vi].color = color;
      #endif
      vertices[vi].pos[0] = center[0] + x22;
      vertices[vi].pos[1] = center[1] + y2;
      vertices[vi].pos[2] = center[2] + z22;
      vertices[vi].uv[0]  = u2;
      vertices[vi].uv[1]  = v2;
      vi++;
    }
  }
}