// Copyright 2020-2024 CesiumGS, Inc. and Contributors

#pragma once

#include "CesiumGeospatial/Ellipsoid.h"
#include "CesiumGeospatial/LocalHorizontalCoordinateSystem.h"
#include "HAL/Platform.h"
#include "Math/Matrix.h"
#include <glm/fwd.hpp>
#include <glm/vec3.hpp>

/**
 * @brief A lightweight structure to encapsulate coordinate transforms.
 *
 * It encapsulates the conversions between...
 * - Earth-Centered, Earth-Fixed (ECEF) coordinates
 * - Georeferenced coordinates (Latitude/Longitude/Height)
 * - Unreal coordinates (relative to the unreal world origin)
 *
 */
class CESIUMRUNTIME_API GeoTransforms {

public:
  /**
   * @brief Creates a new instance.
   */
  GeoTransforms();

  /**
   * @brief Creates a new instance.
   *
   * The center position is the position of the origin of the
   * local coordinate system that is established by this instance.
   *
   * @param ellipsoid The ellipsoid to use for the georeferenced coordinates
   * @param center The center position.
   * @param scale The scale factor of the globe in the Unreal world.
   */
  GeoTransforms(
      const CesiumGeospatial::Ellipsoid& ellipsoid,
      const glm::dvec3& center,
      double scale);

  /**
   * @brief Set the center position of this instance
   *
   * The center position is the position of the origin of the
   * local coordinate system that is established by this instance.
   *
   * @param center The center position.
   */
  void setCenter(const glm::dvec3& center) noexcept;

  /**
   * @brief Set the ellipsoid of this instance
   *
   * @param ellipsoid The ellipsoid
   */
  void setEllipsoid(const CesiumGeospatial::Ellipsoid& ellipsoid) noexcept;

  /**
   * Transforms the given longitude in degrees (x), latitude in
   * degrees (y), and height in meters (z) into Earth-Centered, Earth-Fixed
   * (ECEF) coordinates.
   */
  glm::dvec3 TransformLongitudeLatitudeHeightToEcef(
      const glm::dvec3& LongitudeLatitudeHeight) const noexcept;

  /**
   * Transforms the given Earth-Centered, Earth-Fixed (ECEF) coordinates into
   * longitude in degrees (x), latitude in degrees (y), and height in
   * meters (z).
   */
  glm::dvec3
  TransformEcefToLongitudeLatitudeHeight(const glm::dvec3& Ecef) const noexcept;

  /**
   * Transforms the given longitude in degrees (x), latitude in
   * degrees (y), and height in meters (z) into Unreal world coordinates
   * (relative to the floating origin).
   */
  glm::dvec3 TransformLongitudeLatitudeHeightToUnreal(
      const glm::dvec3& origin,
      const glm::dvec3& LongitudeLatitudeHeight) const noexcept;

  /**
   * Transforms Unreal world coordinates (relative to the floating origin) into
   * longitude in degrees (x), latitude in degrees (y), and height in
   * meters (z).
   */
  glm::dvec3 TransformUnrealToLongitudeLatitudeHeight(
      const glm::dvec3& origin,
      const glm::dvec3& Ue) const noexcept;

  /**
   * Transforms the given point from Earth-Centered, Earth-Fixed (ECEF) into
   * Unreal world coordinates (relative to the floating origin).
   */
  glm::dvec3 TransformEcefToUnreal(
      const glm::dvec3& origin,
      const glm::dvec3& Ecef) const noexcept;

  /**
   * Transforms the given point from Unreal world coordinates (relative to the
   * floating origin) to Earth-Centered, Earth-Fixed (ECEF).
   */
  glm::dvec3 TransformUnrealToEcef(
      const glm::dvec3& origin,
      const glm::dvec3& Ue) const noexcept;

  /**
   * Transforms a rotator from Unreal world to East-South-Up at the given
   * Unreal relative world location (relative to the floating origin).
   */
  glm::dquat TransformRotatorUnrealToEastSouthUp(
      const glm::dvec3& origin,
      const glm::dquat& UeRotator,
      const glm::dvec3& UeLocation) const noexcept;

  /**
   * Transforms a rotator from East-South-Up to Unreal world at the given
   * Unreal world location (relative to the floating origin).
   */
  glm::dquat TransformRotatorEastSouthUpToUnreal(
      const glm::dvec3& origin,
      const glm::dquat& EnuRotator,
      const glm::dvec3& UeLocation) const noexcept;

  /**
   * Computes the rotation matrix from the local East-South-Up to Unreal at the
   * specified Unreal world location (relative to the floating
   * origin). The returned transformation works in Unreal's left-handed
   * coordinate system.
   */
  glm::dmat4 ComputeEastSouthUpToUnreal(
      const glm::dvec3& origin,
      const glm::dvec3& Ue) const noexcept;

  /**
   * Computes the rotation matrix from the local East-North-Up to
   * Earth-Centered, Earth-Fixed (ECEF) at the specified ECEF location.
   */
  glm::dmat3 ComputeEastNorthUpToEcef(const glm::dvec3& Ecef) const noexcept;

  /*
   * GEOREFERENCE TRANSFORMS
   */

  /**
   * @brief Gets the transformation from the _absolute_ "Unreal World" reference
   * frame to the "Ellipsoid-centered" reference frame (i.e. ECEF).
   *
   * Gets a matrix that transforms coordinates from the absolute "Unreal World"
   * reference frame (with respect to the absolute world origin, not the
   * floating origin) to the "Ellipsoid-centered" reference frame (which is
   * usually Earth-centered, Earth-fixed). See {@link reference-frames.md}.
   */
  const glm::dmat4&
  GetAbsoluteUnrealWorldToEllipsoidCenteredTransform() const noexcept {
    return this->_coordinateSystem.getLocalToEcefTransformation();
  }

  /**
   * @brief Gets the transformation from the "Ellipsoid-centered" reference
   * frame (i.e. ECEF) to the absolute "Unreal World" reference frame.
   *
   * Gets a matrix that transforms coordinates from the "Ellipsoid-centered"
   * reference frame (which is usually Earth-centered, Earth-fixed) to the
   * absolute "Unreal world" reference frame (with respect to the absolute world
   * origin, not the floating origin). See {@link reference-frames.md}.
   */
  const glm::dmat4&
  GetEllipsoidCenteredToAbsoluteUnrealWorldTransform() const noexcept {
    return this->_coordinateSystem.getEcefToLocalTransformation();
  }

  /**
   * @brief Computes the normal of the plane tangent to the surface of the
   * ellipsoid that is used by this instance, at the provided position.
   *
   * @param position The cartesian position for which to to determine the
   * surface normal.
   * @return The normal.
   */
  glm::dvec3 ComputeGeodeticSurfaceNormal(const glm::dvec3& position) const {
    return _ellipsoid.geodeticSurfaceNormal(position);
  }

  /**
   * Computes the rotation in ellipsoid surface normal between an old position
   * and a new position. This rotation is expressed in terms of Unreal world
   * coordinates, and can be used to maintain an object's orientation relative
   * to the local horizontal as it moves over the globe.
   *
   * @param oldPosition The old ECEF position that the object moved from.
   * @param newPosition The new ECEF position that the object moved to.
   * @return The rotation from the ellipsoid surface normal at the old position
   * to the ellipsoid surface normal at the new position.
   */
  glm::dquat ComputeSurfaceNormalRotation(
      const glm::dvec3& oldPosition,
      const glm::dvec3& newPosition) const;

  /**
   * Computes the rotation in ellipsoid surface normal between an old position
   * and a new position. This rotation is expressed in terms of Unreal world
   * coordinates, and can be used to maintain an object's orientation relative
   * to the local horizontal as it moves over the globe.
   *
   * @param oldPosition The old ECEF position that the object moved from.
   * @param newPosition The new ECEF position that the object moved to.
   * @return The rotation from the ellipsoid surface normal at the old position
   * to the ellipsoid surface normal at the new position.
   */
  glm::dquat ComputeSurfaceNormalRotationUnreal(
      const glm::dvec3& oldPosition,
      const glm::dvec3& newPosition) const;

  const FMatrix& GetEllipsoidCenteredToAbsoluteUnrealWorldMatrix() const {
    return this->_ecefToUnreal;
  }
  const FMatrix& GetAbsoluteUnrealWorldToEllipsoidCenteredMatrix() const {
    return this->_unrealToEcef;
  }

private:
  /**
   * Update the derived state (i.e. the local horizontal coordinate system) when
   * either the center or the ellipsoid has changed.
   */
  void updateTransforms() noexcept;

  CesiumGeospatial::LocalHorizontalCoordinateSystem _coordinateSystem;

  // Modifiable state
  CesiumGeospatial::Ellipsoid _ellipsoid;
  glm::dvec3 _center;
  double _scale;
  FMatrix _ecefToUnreal;
  FMatrix _unrealToEcef;
};