/** @file IsingModel.hpp
 *
 *  @author Cory Alexander Balaton (coryab)
 *  @author Janita Ovidie Sandtrøen Willumsen (janitaws)
 *
 *  @version 0.1
 *
 *  @brief The definition of the Ising model.
 *
 *  @bug No known bugs
 * */
#ifndef __ISING_MODEL__
#define __ISING_MODEL__

#include "typedefs.hpp"

#include <armadillo>
#include <random>
#include <unordered_map>

// Faster modulo
#define INDEX(I, N) (I + N) % N

// Indeces for the neighbor matrix.
#define UP 0
#define LEFT 0
#define DOWN 1
#define RIGHT 1

/** @brief The Ising model in 2 dimensions.
 *
 *  @details Here we set \f$ J = 1 \f$, and the Boltzmann constant
 *  \f$ k_B = 1 \f$.
 * */
class IsingModel {
private:
    friend class IsingModelTest;
    /** @brief \f$ L \cross L \f$ matrix where element $ x \in {-1, 1}$.
     * */
    arma::Mat<int> lattice;

    arma::Mat<uint> neighbors;

    /** @brief A hash map containing all possible energy changes.
     * */
    std::unordered_map<int, double> energy_diff;

    /** @brief Temperature
     * */
    double T;

    uint L;

    /** @brief The current energy state. unit: \f$ J \f$.
     * */
    int E;

    /** @brief The current magnetic strength. unit: Unitless.
     * */
    int M;

    /** @brief Energy per spin. unit: \f$ J \f$.
     * */
    double eps;

    /** @brief Magnetization per spin. unit: Unitless.
     * */
    double m;

    /** @brief Initialize the lattice with a random distribution of 1s and
     *  -1s.
     * */
    void initialize_lattice();

    void initialize_neighbors();

    /** @brief Initialize the hashmap with the correct values.
     * */
    void initialize_energy_diff();

    /** @brief Initialize the model.
     * */
    void initialize_magnetization();

    void initialize_energy();

public:
    /** @brief Constructor for the Ising model.
     *
     *  @param L The size of the lattice.
     * */
    IsingModel(uint L, double T);

    /** @brief Constructor for the Ising model.
     *
     *  @param L The size of the lattice.
     * */
    IsingModel(uint L, double T, int val);

    void Metropolis(std::mt19937 engine);
};

#endif