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

#pragma once
#include "Animation.hpp"
#include "easing.hpp"
#include "util/mathutils.hpp"

namespace Dawn {
  template<typename T>
  struct SimpleKeyframe {
    float_t time;
    T value;
  };

  template<typename T>
  struct SimpleAnimation : public Animation {
    protected:
      /**
       * Function for subclasses to be "notified" when the value has been 
       * modified.
       */
      virtual void onValueModified() {

      }

      /**
       * Sorts internal keyframes by their time to make them conform correctly.
       */
      void sortKeyframes() {
        std::sort(
          this->keyframes.begin(),
          this->keyframes.end(),
          [](struct SimpleKeyframe<T> &a, struct SimpleKeyframe<T>  &b) {
            return a.time < b.time;
          }
        );
      }

    public:
      std::function<float_t(const float_t)> easing = easeLinear;
      T *modifies;
      std::vector<struct SimpleKeyframe<T>> keyframes;

      /**
       * Constructs a new Simple Animation instance.
       * 
       * @param modifies Pointer to the value that will be modified.
       */
      SimpleAnimation(T *modifies) {
        assertNotNull(modifies, "Modifies cannot be null");
        this->modifies = modifies;
      }

      /**
       * Adds a keyframe that will be slerped to at a given time.
       * 
       * @param time Time the keyframe occurs.
       * @param value Value at this given time.
       */
      void addKeyframe(float_t time, T value) {
        assertTrue(time >= 0, "Time must be >= 0");
        
        struct SimpleKeyframe<T> keyframe;
        keyframe.time = time;
        keyframe.value = value;
        this->duration = mathMax<float_t>(this->duration, time);
        this->finished = false;
        this->keyframes.push_back(keyframe);

        if(time < this->duration) this->sortKeyframes();
      }

      /**
       * Quickly add a series of keyframes. For example, if you want to have a
       * keyframe series of;
       * [ 1, 3, 5, 7, 9 ]
       * 
       * And occur at times
       * [ 0, 2, 4, 6, 8 ]
       * 
       * You would pass frameTime as 2, and step as 2.
       * 
       * @param startTime When the first keyframe occurs.
       * @param frameTime At what rate do keyframes occur.
       * @param start Initial value (the value at startTime).
       * @param end The end value (for the last keyframe).
       * @param step How to step the value.
       */
      void addSequentialKeyframes(
        float_t startTime,
        float_t frameTime,
        T start,
        T end,
        T step
      ) {
        T v = start;
        float_t n = startTime;
        while(v != end) {
          this->addKeyframe(n, v);
          n += frameTime;
          v += step;
        }
      }

      /**
       * Shorthand addSequentialKeyframes, assumes a step of 1 and a startTime
       * of 0.
       * 
       * @param frameTime Time between frames.
       * @param start Initial value.
       * @param end End value.
       */
      void addSequentialKeyframes(float_t frameTime, T start, T end) {
        this->addSequentialKeyframes(0, frameTime, start, end, 1);
      }

      /**
       * Immediately sets the value, bypassing keyframes and ticks. Useful for
       * setting an initial value.
       * 
       * @param value Value to set.
       */
      void setValue(T value) {
        *modifies = value;
        this->onValueModified();
      }

      void tick(float_t delta) override {
        if(this->finished) return;

        float_t newTime = this->time + delta;

        struct SimpleKeyframe<T> *keyframeNext = nullptr;
        struct SimpleKeyframe<T> *keyframeCurrent = nullptr;
        
        // Find current and next keyframe(s)
        auto itKey = this->keyframes.begin();
        while(itKey != this->keyframes.end()) {
          if(itKey->time > newTime) {
            keyframeNext = &(*itKey);
            break;
          }
          keyframeCurrent = &(*itKey);
          ++itKey;
        }

        // Update values
        if(keyframeCurrent != nullptr && keyframeNext == nullptr) {
          // "End of animation"
          *this->modifies = keyframeCurrent->value;
          this->onValueModified();
        } else if(keyframeNext != nullptr) {
          T oldValue;
          float_t oldTime;

          if(keyframeCurrent == nullptr) {
            // "Start of animation"
            oldValue = keyframeCurrent->value;
            oldTime = keyframeCurrent->time;
          } else {
            // "Mid animation"
            oldTime = this->time;
            oldValue = *this->modifies;
          }

          // Slerp between keyframes
          float_t keyframeDelta = this->easing(
            (newTime - oldTime) / (keyframeNext->time - oldTime)
          );
          *this->modifies = oldValue + (
            (keyframeNext->value - oldValue) * keyframeDelta
          );
          this->onValueModified();
        }

        // First possible frame? I think this can be done cleaner
        if(this->time == 0 && keyframeCurrent->time == 0) {
          *this->modifies = keyframeCurrent->value;
          this->onValueModified();
        }

        // Update time.
        this->time = newTime;

        // Has the animation finished?
        if(newTime < this->duration) return;
        
        // Do we need to loop?
        if(this->loop) {
          this->time = 0;
          return;
        }

        // Animation end.
        this->finished = true;
        this->eventAnimationEnd.invoke();
      }
      
      void clear() override {
        Animation::clear();
        this->keyframes.clear();
      }
  };
}