// Copyright (c) 2022 Dominic Masters
// 
// This software is released under the MIT License.
// https://opensource.org/licenses/MIT

#pragma once
#include "dawnlibs.hpp"
#include "assert/assert.hpp"
#include "util/flag.hpp"
#include "state/StateEvent.hpp"

namespace Dawn {
  class SceneItem;

  class Transform {
    private:
      // Local (real) values
      glm::vec3 localPosition;
      glm::vec3 localScale;
      glm::quat localRotation;

      // Cached (non-real) values
      glm::mat4 transformLocal;
      glm::mat4 transformWorld;

      // glm::vec3 position;
      // glm::vec3 scale;
      // glm::quat rotation;

      // Heirarchy
      Transform *parent = nullptr;
      std::vector<Transform *> children;

      // Hidden methods
      void updateLocalValuesFromLocalTransform();
      void updateLocalTransformFromLocalValues();
      void updateWorldTransformFromLocalTransform();
      void updateLocalTransformFromWorldTransform();
      void updateChildrenTransforms();

    public:
      // I have no idea if I'm keeping this
      // Event<> eventTransformUpdated;
      StateEvent<> eventTransformUpdated;
      SceneItem *item;

      /**
       * Constructs a new transform instance. Currently I have bound transforms
       * to their parent SceneItem, but in future I may allow them to become
       * disconnected from each other, for example I really could use a special
       * transform designed purely for UI elements, since they don't act like
       * normal scene items, but for now Transforms and SceneItems are 1:1
       * 
       * @param item Item that this transform belongs to.
       */
      Transform(SceneItem *item);

      /**
       * Orients this transform to look at a given point in world space.
       * 
       * @param position Position of the origin of this transform.
       * @param look Position in world space this transform looks at.
       */
      void lookAt(glm::vec3 position, glm::vec3 look);
      void lookAt(glm::vec3 position, glm::vec3 look, glm::vec3 up);

      /**
       * Shorthand combined for lookAt and perspectivePixelPerfectDistance
       * to allow you to create pixel perfect lookAt camera view matricies.
       * 
       * @param position Position of the camera. Z is for an offset.
       * @param look Position in world space this transform looks at.
       * @param viewportHeight Height of the viewport.
       * @param fov Field of view (in radians).
       * @return The Z distance that was calculated.
       */
      float_t lookAtPixelPerfect(
        glm::vec3 position, glm::vec3 look, float_t viewportHeight, float_t fov
      );

      /**
       * Returns the local position (position relative to "my parent").
       * @return The 3D local position in parent-relative space.
       */
      glm::vec3 getLocalPosition();

      /**
       * Update / Set the local position of this transform relative to my parent
       * @param position Position to set for the local transform.
       */
      void setLocalPosition(glm::vec3 position);

      /**
       * Retusn the scale of this item, relative to my parent.
       * @return 3D Scale vector of this item in parent-relative space.
       */
      glm::vec3 getLocalScale();

      /**
       * Set the local scale of this item.
       * @param scale Scale of this item, relative to its parent.
       */
      void setLocalScale(glm::vec3 scale);

      /**
       * Returns the local rotation for this transform.
       * @return The local rotation (parent-relative).
       */
      glm::quat getLocalRotation();
      
      /**
       * Set the local (parent-relative) rotation for this transform.
       * @param rotation Rotation in parent relative space.
       */
      void setLocalRotation(glm::quat rotation);

      /**
       * Returns the transform matrix for this transform, in parent-relative 
       * space.
       * @return The transform origin in parent-relative space.
       */
      glm::mat4 getLocalTransform();

      /**
       * Sets the local transform matrix for this transform.
       * @param transform Local (parent-relative) transform to set.
       */
      void setLocalTransform(glm::mat4 transform);

      /**
       * Returns the position of the origin of this transform in world-space.
       * 
       * @return Transform origin in world-space.
       */
      glm::vec3 getWorldPosition();

      /**
       * Returns the transformation matrix for this transform, in world-space.
       * @return The transform origin in world-space.
       */
      glm::mat4 getWorldTransform();

      /**
       * Updates the transform's world-space.
       * @param transform Sets the transform position in world-space.
       */
      void setWorldTransform(glm::mat4 transform);
    
      /**
       * Updates the transform that this transform is a child of. Will also
       * handle disconnecting any existing parent.
       * 
       * @param p Parent that this transform is now a child of.
       */
      void setParent(Transform *p);

      /**
       * Returns the parent transform of this transform, or nullptr if there is
       * no parent for this transform.
       * @return Pointer to the parent transform, or nullptr.
       */
      Transform * getParent();

      /**
       * Returns true if this transform is a child of the given transform, this
       * climbs up the heirarchy until it finds a match.
       * 
       * @param p Transform to check if this transform is a child of.
       * @return True if this transform is a child of the given transform.
       */
      bool_t isChildOf(Transform *p);

      /**
       * Dispose and clenaup this transform, also removes self from parent.
       */
      ~Transform();

      friend SceneItem;
  };
}