//    Copyright 2021 Jij Inc.

//    Licensed under the Apache License, Version 2.0 (the "License");
//    you may not use this file except in compliance with the License.
//    You may obtain a copy of the License at

//        http://www.apache.org/licenses/LICENSE-2.0

//    Unless required by applicable law or agreed to in writing, software
//    distributed under the License is distributed on an "AS IS" BASIS,
//    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//    See the License for the specific language governing permissions and
//    limitations under the License.

#ifndef OPENJIJ_SYSTEM_TRANSVERSE_ISING_HPP__
#define OPENJIJ_SYSTEM_TRANSVERSE_ISING_HPP__

#include <cassert>
#include <system/system.hpp>
#include <graph/all.hpp>
#include <utility/eigen.hpp>
#include <vector>
#include <exception>

namespace openjij {
    namespace system {

        /**
         * @brief trotterized spin (std::vector<Spins>)
         * trotter_spins[i][j] -> jth spin in ith trotter slice.
         */
        using TrotterSpins = std::vector<graph::Spins>;

        /**
         * @brief TransverseIsing structure with discrete-time trotter spins
         *
         * @tparam GraphType
         */
        template<typename GraphType>
            struct TransverseIsing;

        /**
         * @brief naive Dense TransverseIsing structure with discrete-time trotter spins (with Eigen implementation)
         * The original Hamiltonian is like
         * \f[
         * H(s) = s\left(\sum_{i<j}J_{ij} \sigma_i^z \sigma_j^z + \sum_{i}h_{i} \sigma_i^z \right) + \Gamma (1-s)\sum_i \sigma_i^x,
         * \f]
         * where \f$ \Gamma \f$ shows the strength of transverse field (referred to as `gamma`) and \f$ s \f$ shows the annealing schedule (referred to as `s`).
         *
         * Quantum Monte Carlo simulation is performed under the finite (inverse) temperature (\f$ \beta \f$ or `beta`).
         *
         * @tparam FloatType
         */
        template<typename FloatType>
            struct TransverseIsing<graph::Dense<FloatType>> {
                using system_type = transverse_field_system;

                //matrix (row major)
                using MatrixXx = Eigen::Matrix<FloatType, Eigen::Dynamic, Eigen::Dynamic, Eigen::RowMajor>;
                //trotter matrix (col major)
                using TrotterMatrix = Eigen::Matrix<FloatType, Eigen::Dynamic, Eigen::Dynamic, Eigen::ColMajor>;

                /**
                 * @brief TransverseIsing Constructor
                 *
                 * @param init_trotter_spins
                 * @param init_interaction
                 */
                TransverseIsing(const TrotterSpins& init_trotter_spins, const graph::Dense<FloatType>& init_interaction, const FloatType gamma)
                : trotter_spins(utility::gen_matrix_from_trotter_spins<FloatType, Eigen::ColMajor>(init_trotter_spins)),
                interaction(init_interaction.get_interactions()),
                num_classical_spins(init_trotter_spins[0].size()), gamma(gamma){
                    if(!(init_trotter_spins.size() >= 2)){
                        throw std::invalid_argument("trotter slices must be equal or larger than 2.");
                    }

                    //initialize rand_pool
                    rand_pool = TrotterMatrix(num_classical_spins+1, trotter_spins.cols());

                    //reset dE
                    reset_dE();
                }

                /**
                 * @brief TransverseIsing Constuctor with initial classical spins
                 *
                 * @param classical_spins initial classical spins
                 * @param init_interaction
                 * @param num_trotter_slices
                 */
                TransverseIsing(const graph::Spins& init_classical_spins, const graph::Dense<FloatType>& init_interaction, const FloatType gamma, const size_t num_trotter_slices)
                :interaction(init_interaction.get_interactions()),
                 num_classical_spins(init_classical_spins.size()), gamma(gamma){
                    //initialize trotter_spins with classical_spins

                    if(!(num_trotter_slices >= 2)){
                        throw std::invalid_argument("trotter slices must be equal or larger than 2.");
                    }

                    TrotterSpins init_trotter_spins(num_trotter_slices);

                    for(auto& spins : init_trotter_spins){
                        spins = init_classical_spins;
                    }

                    //init trotter_spins
                    trotter_spins = utility::gen_matrix_from_trotter_spins<FloatType, Eigen::ColMajor>(init_trotter_spins);

                    //initialize rand_pool
                    rand_pool = TrotterMatrix(num_classical_spins+1, trotter_spins.cols());

                    //reset dE
                    reset_dE();
                }

                /**
                 * @brief reset spins with trotter spins
                 *
                 * @param init_trotter_spins
                 */
                void reset_spins(const TrotterSpins& init_trotter_spins){
                    this->trotter_spins = utility::gen_matrix_from_trotter_spins<FloatType, Eigen::ColMajor>(init_trotter_spins);

                    //reset dE
                    reset_dE();
                }
                
                /**
                 * @brief reset spins with trotter spins
                 *
                 * @param classical_spins
                 */
                void reset_spins(const graph::Spins& classical_spins){
                    TrotterSpins init_trotter_spins(trotter_spins.cols()); //cols -> num_trotter_slices

                    for(auto& spins : init_trotter_spins){
                        spins = classical_spins;
                    }
                    //init trotter_spins
                    this->trotter_spins = utility::gen_matrix_from_trotter_spins<FloatType, Eigen::ColMajor>(init_trotter_spins);

                    //reset dE
                    reset_dE();
                }

                /**
                 * @brief reset dE
                 */
                inline void reset_dE(){
                    // reset dE and dEtrot

                    //initialize dE (spatial direction)
                    //we store only dE for spatial direction
                    const auto& spins = this->trotter_spins;
                    //std::size_t num_trotter_slices = this->trotter_spins.cols();

                    this->dE = -2 * spins.cwiseProduct(this->interaction * spins);

                    //for trotter direction
                    //this->dEtrot = TrotterMatrix::Zero(num_classical_spins+1, num_trotter_slices);
                    //for(std::size_t t=0; t<num_trotter_slices; t++){
                    //    this->dEtrot.col(t) = -2 * spins.col(t).cwiseProduct(
                    //            spins.col(mod_t((int64_t)t+1, num_trotter_slices)) +
                    //            spins.col(mod_t((int64_t)t-1, num_trotter_slices))
                    //            );
                    //}

                    //diffE = s * (beta/num_trotter_slices) * this->dE + (1/2.) * log(tanh(beta* gamma * (1.0-s) /num_trotter_slices)) * this->dEtrot
                }

                inline static std::size_t mod_t(std::int64_t a, std::size_t num_trotter_slices){
                    //a -> [-1:num_trotter_slices]
                    //return a%num_trotter_slices (a>0), num_trotter_slices-1 (a==-1)
                    return (a+num_trotter_slices)%num_trotter_slices;
                }

                /**
                 * @brief trotterlized spins
                 */
                TrotterMatrix trotter_spins;

                /**
                 * @brief interaction 
                 */
                const MatrixXx interaction;

                /**
                 * @brief number of real classical spins (dummy spin excluded)
                 */
                std::size_t num_classical_spins; //trotter_spins[0].size()-1

                /**
                 * @brief coefficient of transverse field term
                 */
                FloatType gamma;

                /**
                 * @brief rand_pool
                 */
                TrotterMatrix rand_pool;

                /**
                 * @brief trotterlized dE (spatial direction)
                 */
                TrotterMatrix dE;

            };

        /**
         * @brief naive Sparse TransverseIsing structure with discrete-time trotter spins (with Eigen implementation)
         * The original Hamiltonian is like
         * \f[
         * H(s) = s\left(\sum_{i<j}J_{ij} \sigma_i^z \sigma_j^z + \sum_{i}h_{i} \sigma_i^z \right) + \Gamma (1-s)\sum_i \sigma_i^x,
         * \f]
         * where \f$ \Gamma \f$ shows the strength of transverse field (referred to as `gamma`) and \f$ s \f$ shows the annealing schedule (referred to as `s`).
         *
         * Quantum Monte Carlo simulation is performed under the finite (inverse) temperature (\f$ \beta \f$ or `beta`).
         *
         * @tparam FloatType
         */
        template<typename FloatType>
            struct TransverseIsing<graph::Sparse<FloatType>> {
                using system_type = transverse_field_system;

                //matrix (row major)
                using SparseMatrixXx = Eigen::SparseMatrix<FloatType, Eigen::RowMajor>;
                //trotter matrix (col major)
                using TrotterMatrix = Eigen::Matrix<FloatType, Eigen::Dynamic, Eigen::Dynamic, Eigen::ColMajor>;

                /**
                 * @brief TransverseIsing Constructor
                 *
                 * @param init_trotter_spins
                 * @param init_interaction
                 */
                TransverseIsing(const TrotterSpins& init_trotter_spins, const graph::Sparse<FloatType>& init_interaction, FloatType gamma)
                :trotter_spins(utility::gen_matrix_from_trotter_spins<FloatType, Eigen::ColMajor>(init_trotter_spins)),
                interaction(utility::gen_matrix_from_graph<Eigen::RowMajor>(init_interaction)),
                num_classical_spins(init_trotter_spins[0].size()), gamma(gamma){
                    if(!(init_trotter_spins.size() >= 2)){
                        throw std::invalid_argument("trotter slices must be equal or larger than 2.");
                    }

                    //initialize rand_pool
                    rand_pool = TrotterMatrix(num_classical_spins+1, trotter_spins.cols());

                    //reset dE
                    reset_dE();
                }

                /**
                 * @brief TransverseIsing Constuctor with initial classical spins
                 *
                 * @param classical_spins initial classical spins
                 * @param init_interaction
                 * @param num_trotter_slices
                 */
                TransverseIsing(const graph::Spins& init_classical_spins, const graph::Sparse<FloatType>& init_interaction, const FloatType gamma, const size_t num_trotter_slices)
                :interaction(utility::gen_matrix_from_graph<Eigen::RowMajor>(init_interaction)),
                num_classical_spins(init_classical_spins.size()), gamma(gamma){
                    //initialize trotter_spins with classical_spins

                    //assert(init_classical_spins.size() >= 2);
                    if(!(num_trotter_slices >= 2)){
                        throw std::invalid_argument("trotter slices must be equal or larger than 2.");
                    }

                    TrotterSpins init_trotter_spins(num_trotter_slices);

                    for(auto& spins : init_trotter_spins){
                        spins = init_classical_spins;
                    }

                    //init trotter_spins
                    trotter_spins = utility::gen_matrix_from_trotter_spins<FloatType, Eigen::ColMajor>(init_trotter_spins);

                    //initialize rand_pool
                    rand_pool = TrotterMatrix(num_classical_spins+1, trotter_spins.cols());

                    //reset dE
                    reset_dE();
                }

                /**
                 * @brief reset spins with trotter spins
                 *
                 * @param init_trotter_spins
                 */
                void reset_spins(const TrotterSpins& init_trotter_spins){
                    this->trotter_spins = utility::gen_matrix_from_trotter_spins<FloatType, Eigen::ColMajor>(init_trotter_spins);

                    //reset dE
                    reset_dE();
                }
                
                /**
                 * @brief reset spins with trotter spins
                 *
                 * @param classical_spins
                 */
                void reset_spins(const graph::Spins& classical_spins){
                    TrotterSpins init_trotter_spins(trotter_spins.cols()); //cols -> num_trotter_slices

                    for(auto& spins : init_trotter_spins){
                        spins = classical_spins;
                    }
                    //init trotter_spins
                    this->trotter_spins = utility::gen_matrix_from_trotter_spins<FloatType, Eigen::ColMajor>(init_trotter_spins);

                    //reset dE
                    reset_dE();
                }

                /**
                 * @brief reset dE
                 */
                inline void reset_dE(){
                    // reset dE and dEtrot

                    //initialize dE (spatial direction)
                    //we store only dE for spatial direction
                    const auto& spins = this->trotter_spins;
                    //std::size_t num_trotter_slices = this->trotter_spins.cols();

                    this->dE = -2 * spins.cwiseProduct(this->interaction * spins);

                    //for trotter direction
                    //this->dEtrot = TrotterMatrix::Zero(num_classical_spins+1, num_trotter_slices);
                    //for(std::size_t t=0; t<num_trotter_slices; t++){
                    //    this->dEtrot.col(t) = -2 * spins.col(t).cwiseProduct(
                    //            spins.col(mod_t((int64_t)t+1, num_trotter_slices)) +
                    //            spins.col(mod_t((int64_t)t-1, num_trotter_slices))
                    //            );
                    //}

                    //diffE = s * (beta/num_trotter_slices) * this->dE + (1/2.) * log(tanh(beta* gamma * (1.0-s) /num_trotter_slices)) * this->dEtrot
                }


                inline static std::size_t mod_t(const std::int64_t a, const std::size_t num_trotter_slices){
                    //a -> [-1:num_trotter_slices]
                    //return a%num_trotter_slices (a>0), num_trotter_slices-1 (a==-1)
                    return (a+num_trotter_slices)%num_trotter_slices;
                }

                /**
                 * @brief trotterlized spins
                 */
                TrotterMatrix trotter_spins;

                /**
                 * @brief interaction 
                 */
                const SparseMatrixXx interaction;

                /**
                 * @brief number of real classical spins (dummy spin excluded)
                 */
                std::size_t num_classical_spins; //trotter_spins[0].size()-1

                /**
                 * @brief coefficient of transverse field term
                 */
                FloatType gamma;

                /**
                 * @brief rand_pool
                 */
                TrotterMatrix rand_pool;

                /**
                 * @brief trotterlized dE (spatial direction)
                 */
                TrotterMatrix dE;

            };

        /**
         * @brief helper function for TransverseIsing constructor
         *
         * @tparam GraphType
         * @param init_trotter_spins
         * @param init_interaction
         * @param gamma
         *
         * @return generated object
         */
        template<typename GraphType>
            auto make_transverse_ising(const TrotterSpins& init_trotter_spins, const GraphType& init_interaction, const typename GraphType::value_type gamma){
                return TransverseIsing<GraphType>(init_trotter_spins, init_interaction, gamma);
            }

        /**
         * @brief helper function for TransverseIsing constructor
         *
         * @tparam GraphType
         * @param classical_spins
         * @param init_interaction
         * @param gamma
         * @param num_trotter_slices
         *
         * @return generated object
         */
        template<typename GraphType>
            auto make_transverse_ising(const graph::Spins& classical_spins, const GraphType& init_interaction, const typename GraphType::value_type gamma, const std::size_t num_trotter_slices){
                return TransverseIsing<GraphType>(classical_spins, init_interaction, gamma, num_trotter_slices);
            }
    } // namespace system
} // namespace openjij

#endif
