#ifndef GRIDWALKRANDOMHEADINGUPDATEADV_H
#define GRIDWALKRANDOMHEADINGUPDATEADV_H


#include "../../geo/Heading.h"
#include "../Grid.h"

#include "../../math/DrawList.h"
#include <KLib/math/distribution/Normal.h>
#include <KLib/math/distribution/Exponential.h>

#include "../../nav/dijkstra/Dijkstra.h"

#include "GridWalkState.h"
#include "GridWalkHelper.h"

/**
 * for every walked edge: slightly update (scatter) the current heading
 * pick the edge (neighbor) best matching the current heading
 * if this neighbor's heading highly differs from the requested heading: start over
 *
 * PROs
 *  - simple
 *  - fixes the issues of GridWalkRandomHeadingUpdate by incorporating floor information
 *  - adds additional randomness which should be more stable
 *
 */
template <typename T> class GridWalkRandomHeadingUpdateAdv {

	friend class GridWalkHelper;

private:

	/** per-edge: change heading with this sigma */
	static constexpr float HEADING_CHANGE_SIGMA = Angle::degToRad(5);

	/** fast random-number-generator */
	std::minstd_rand gen;

	/** 0-mean normal distribution */
	std::normal_distribution<float> headingChangeDist = std::normal_distribution<float>(0.0, HEADING_CHANGE_SIGMA);

public:

	/** ctor */
	GridWalkRandomHeadingUpdateAdv() {
		;
	}

	GridWalkState<T> getDestination(Grid<T>& grid, const GridWalkState<T> start, const float distance_m) {

		return GridWalkHelper::retryOrInvert(*this, 2, grid, start, distance_m);

	}

private:

	// https://de.wikipedia.org/wiki/Logistische_Verteilung
	/** alpha = move the center, beta = slope */
	const float logisticDist(const float x, const float alpha, const float beta) {
		return 1 / (1 + std::exp( -((x-alpha)/beta) ) );
	}


	// NOTE: allocate >>ONCE<<! otherwise random numbers will NOT work!
	DrawList<T*> drawer;

	GridWalkState<T> walk(Grid<T>& grid, const GridWalkState<T> cur, float distRest_m) {

		drawer.reset();
		GridWalkState<T> next;

		// get a new random heading
		next.heading = cur.heading + headingChangeDist(gen);

		// weight all neighbors based on this heading
		for (T& neighbor : grid.neighbors(*cur.node)) {

			// get the heading between the current node and its neighbor
			const Heading potentialHeading = GridWalkHelper::getHeading(*cur.node, neighbor);

			// calculate the difference from the requested heading
			const float diffRad = potentialHeading.getDiffHalfRAD(cur.heading);

			// weight this change
			const float prob1 = K::NormalDistribution::getProbability(0, Angle::degToRad(40), diffRad);

			// add the node's importance factor into the calculation
			const float prob2 = logisticDist(neighbor.imp, 1.0, 0.05);
			//const float prob2 = std::pow(neighbor.imp, 10);

			// final importance
			const float prob = prob1 * prob2;

			// add for drawing
			drawer.add(&neighbor, prob);

		}

		// all neighbors are unlikely? -> start over
		if (drawer.getCumProbability() < 0.01) {return GridWalkState<T>();}

		// pick the neighbor best matching this new heading
		next.node = drawer.get();

//		// if the best matching neighbor is far of this requested heading
//		// (e.g. no good neighbor due to walls) cancel the walk. to force a retry
//		const float diff = GridWalkHelper::getHeading(*cur.node, *next.node).getDiffHalfRAD(next.heading);
//		if (diff > Angle::degToRad(45)) {
//			return GridWalkState<T>();
//		}

		// get the distance up to this neighbor
		distRest_m -= next.node->getDistanceInMeter(*cur.node);

		// done?
		if (distRest_m <= 0) {return next;}

		// another round..
		return walk(grid, next, distRest_m);

	}

};

#endif // GRIDWALKRANDOMHEADINGUPDATEADV_H