#ifndef DRAWLIST_H
#define DRAWLIST_H

#include <vector>
#include <random>

#include <KLib/Assertions.h>

/**
 * add elements of a certain probability
 * and randomly draw from them
 */
template <typename T> class DrawList {

	/** one entry */
	struct Entry {

		/** the user element */
		T element;

		/** the cumulative probability up to this element */
		double cumProbability;

		/** ctor */
		Entry(T element, const double cumProbability) : element(element), cumProbability(cumProbability) {;}

		/** compare for searches */
		bool operator < (const double val) const {return cumProbability < val;}

	};

private:

	/** current cumulative probability */
	double cumProbability;

	/** all contained elements */
	std::vector<Entry> elements;

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

public:

	/** ctor */
	DrawList() : cumProbability(0) {
		;
	}

	/** reset */
	void reset() {
		cumProbability = 0;
		elements.clear();
	}

	/** add a new user-element and its probability */
	void add(T element, const double probability) {
		cumProbability += probability;
		elements.push_back(Entry(element, cumProbability));
	}

	/** get a random element based on its probability */
	T get() {

		// generate random number between [0:cumProbability]
		std::uniform_real_distribution<> dist(0, cumProbability);

		// get a random value
		const double rndVal = dist(gen);

		// binary search for the matching entry O(log(n))
		const auto tmp = std::lower_bound(elements.begin(), elements.end(), rndVal);

		// sanity check
		_assertFalse(tmp == elements.end(), "draw() did not find a valid element");

		// done
		return (*tmp).element;

	}

	/** get the current, cumulative probability */
	double getCumProbability() const {
		return cumProbability;
	}

};

#endif // DRAWLIST_H