#include <celeritas.h>

vec3 vec3_create(f32 x, f32 y, f32 z) { return (vec3){ x, y, z }; }
vec3 vec3_add(vec3 u, vec3 v) { return (vec3){ .x = u.x + v.x, .y = u.y + v.y, .z = u.z + v.z }; }
vec3 vec3_sub(vec3 a, vec3 b) { return (vec3){ a.x - b.x, a.y - b.y, a.z - b.z }; }
vec3 vec3_mult(vec3 a, f32 s) { return (vec3){ a.x * s, a.y * s, a.z * s }; }
vec3 vec3_div(vec3 a, f32 s) { return (vec3){ a.x / s, a.y / s, a.z / s }; }

f32 vec3_len_squared(vec3 a) { return (a.x * a.x) + (a.y * a.y) + (a.z * a.z); }
f32 vec3_len(vec3 a) { return sqrtf(vec3_len_squared(a)); }
vec3 vec3_negate(vec3 a) { return (vec3){ -a.x, -a.y, -a.z }; }

vec3 vec3_normalise(vec3 a) {
  f32 length = vec3_len(a);
  return vec3_div(a, length);
}

f32 vec3_dot(vec3 a, vec3 b) { return a.x * b.x + a.y * b.y + a.z * b.z; }

vec3 vec3_cross(vec3 a, vec3 b) {
  return (vec3){ .x = a.y * b.z - a.z * b.y, .y = a.z * b.x - a.x * b.z, .z = a.x * b.y - a.y * b.x };
}

vec4 vec4_create(f32 x, f32 y, f32 z, f32 w) { return (vec4){ x, y, z, w }; }

f32 quat_dot(quat a, quat b) { return a.x * b.x + a.y * b.y + a.z * b.z + a.w * b.w; }

quat quat_normalise(quat a) {
  f32 length = sqrtf(quat_dot(a, a));  // same as len squared

  return (quat){ a.x / length, a.y / length, a.z / length, a.w / length };
}

quat quat_from_axis_angle(vec3 axis, f32 angle, bool normalize) {
  const f32 half_angle = 0.5f * angle;
  f32 s = sinf(half_angle);
  f32 c = cosf(half_angle);

  quat q = (quat){ s * axis.x, s * axis.y, s * axis.z, c };
  if (normalize) {
    return quat_normalise(q);
  }
  return q;
}

mat4 mat4_ident() { return (mat4){ .data = { 1.0, 0., 0., 0., 0., 1., 0., 0., 0., 0., 1., 0., 0., 0., 0., 1.0 } }; }

mat4 mat4_translation(vec3 position) {
  mat4 out_matrix = mat4_ident();
  out_matrix.data[12] = position.x;
  out_matrix.data[13] = position.y;
  out_matrix.data[14] = position.z;
  return out_matrix;
}

mat4 mat4_scale(vec3 scale) {
  mat4 out_matrix = mat4_ident();
  out_matrix.data[0] = scale.x;
  out_matrix.data[5] = scale.y;
  out_matrix.data[10] = scale.z;
  return out_matrix;
}

// TODO: double check this
mat4 mat4_rotation(quat rotation) {
  mat4 out_matrix = mat4_ident();
  quat n = quat_normalise(rotation);

  out_matrix.data[0] = 1.0f - 2.0f * n.y * n.y - 2.0f * n.z * n.z;
  out_matrix.data[1] = 2.0f * n.x * n.y - 2.0f * n.z * n.w;
  out_matrix.data[2] = 2.0f * n.x * n.z + 2.0f * n.y * n.w;

  out_matrix.data[4] = 2.0f * n.x * n.y + 2.0f * n.z * n.w;
  out_matrix.data[5] = 1.0f - 2.0f * n.x * n.x - 2.0f * n.z * n.z;
  out_matrix.data[6] = 2.0f * n.y * n.z - 2.0f * n.x * n.w;

  out_matrix.data[8] = 2.0f * n.x * n.z - 2.0f * n.y * n.w;
  out_matrix.data[9] = 2.0f * n.y * n.z + 2.0f * n.x * n.w;
  out_matrix.data[10] = 1.0f - 2.0f * n.x * n.x - 2.0f * n.y * n.y;

  return out_matrix;
}

// mat4 mat4_mult(mat4 lhs, mat4 rhs) {
//   mat4 out_matrix = mat4_ident();

//   const f32* m1_ptr = lhs.data;
//   const f32* m2_ptr = rhs.data;
//   f32* dst_ptr = out_matrix.data;

//   for (i32 i = 0; i < 4; ++i) {
//     for (i32 j = 0; j < 4; ++j) {
//       *dst_ptr = m1_ptr[0] * m2_ptr[0 + j] + m1_ptr[1] * m2_ptr[4 + j] + m1_ptr[2] * m2_ptr[8 + j] +
//                  m1_ptr[3] * m2_ptr[12 + j];
//       dst_ptr++;
//     }
//     m1_ptr += 4;
//   }

//   return out_matrix;
// }
mat4 mat4_mult(mat4 lhs, mat4 rhs) {
  mat4 out_matrix = mat4_ident();

  for (i32 row = 0; row < 4; row++) {
    for (i32 col = 0; col < 4; col++) {
      f32 sum = 0;
      for (i32 i = 0; i < 4; i++) {
        // column-major: first matrix columns × second matrix rows
        sum += lhs.data[row + i * 4] * rhs.data[i + col * 4];
      }
      out_matrix.data[row + col * 4] = sum;
    }
  }

  return out_matrix;
}

mat4 mat4_perspective(f32 fov_radians, f32 aspect_ratio, f32 near_z, f32 far_z) {
  f32 half_tan_fov = tanf(fov_radians * 0.5f);
  mat4 out_matrix = { .data = { 0 } };
  out_matrix.data[0] = 1.0f / (aspect_ratio * half_tan_fov);
  out_matrix.data[5] = 1.0f / half_tan_fov;
  out_matrix.data[10] = -((far_z + near_z) / (far_z - near_z));
  out_matrix.data[11] = -1.0f;
  out_matrix.data[14] = -((2.0f * far_z * near_z) / (far_z - near_z));
  return out_matrix;
}

mat4 mat4_look_at(vec3 position, vec3 target, vec3 up) {
  mat4 out_matrix;
  vec3 z_axis;
  z_axis.x = target.x - position.x;
  z_axis.y = target.y - position.y;
  z_axis.z = target.z - position.z;

  z_axis = vec3_normalise(z_axis);
  vec3 x_axis = vec3_normalise(vec3_cross(z_axis, up));
  vec3 y_axis = vec3_cross(x_axis, z_axis);

  out_matrix.data[0] = x_axis.x;
  out_matrix.data[1] = y_axis.x;
  out_matrix.data[2] = -z_axis.x;
  out_matrix.data[3] = 0;
  out_matrix.data[4] = x_axis.y;
  out_matrix.data[5] = y_axis.y;
  out_matrix.data[6] = -z_axis.y;
  out_matrix.data[7] = 0;
  out_matrix.data[8] = x_axis.z;
  out_matrix.data[9] = y_axis.z;
  out_matrix.data[10] = -z_axis.z;
  out_matrix.data[11] = 0;
  out_matrix.data[12] = -vec3_dot(x_axis, position);
  out_matrix.data[13] = -vec3_dot(y_axis, position);
  out_matrix.data[14] = vec3_dot(z_axis, position);
  out_matrix.data[15] = 1.0f;

  return out_matrix;
}