// Copyright 2018 Google LLC. All Rights Reserved.
/*
  Copyright (C) 2005-2011 Steven L. Scott

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either
  version 2.1 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public
  License along with this library; if not, write to the Free Software
  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
*/

#ifndef BOOM_STATE_SPACE_MODEL_HPP_
#define BOOM_STATE_SPACE_MODEL_HPP_

#include "Models/DataTypes.hpp"
#include "Models/Policies/IID_DataPolicy.hpp"
#include "Models/Policies/PriorPolicy.hpp"
#include "Models/ZeroMeanGaussianModel.hpp"

#include "Models/StateSpace/StateSpaceModelBase.hpp"

namespace BOOM {

  namespace StateSpace {
    class MultiplexedDoubleData : public MultiplexedData {
     public:
      MultiplexedDoubleData();
      explicit MultiplexedDoubleData(double y);
      MultiplexedDoubleData *clone() const override;
      std::ostream &display(std::ostream &out) const override;
      void add_data(const Ptr<DoubleData> &data_point);

      double adjusted_observation() const;
      const DoubleData &double_data(int i) const;
      Ptr<DoubleData> double_data_ptr(int i);
      void set_value(double value, int i);

      // Returns true if data_ is empty, or if all elements of data_ are
      // missing.
      bool all_missing() const;

      int total_sample_size() const override { return data_.size(); }

     private:
      std::vector<Ptr<DoubleData>> data_;
    };
  }  // namespace StateSpace

  class StateSpaceModel
      : public ScalarStateSpaceModelBase,
        public IID_DataPolicy<StateSpace::MultiplexedDoubleData>,
        public PriorPolicy {
   public:
    StateSpaceModel();
    explicit StateSpaceModel(
        const Vector &y,
        const std::vector<bool> &y_is_observed = std::vector<bool>());
    StateSpaceModel(const StateSpaceModel &rhs);
    StateSpaceModel *clone() const override;

    int time_dimension() const override;
    double observation_variance(int t) const override;
    double adjusted_observation(int t) const override;
    bool is_missing_observation(int t) const override;
    ZeroMeanGaussianModel *observation_model() override;
    const ZeroMeanGaussianModel *observation_model() const override;
    void observe_data_given_state(int t) override;

    // Forecast the next nrow(newX) time steps given the current data,
    // using the Kalman filter.  The first column of the returned
    // Matrix is the mean of the forecast.  The second column is the
    // standard errors.
    Matrix forecast(int n);

    // Simulate the next n time periods, given current parameters and
    // state.
    Vector simulate_forecast(RNG &rng, int n, const Vector &final_state);

    // Return the vector of one-step-ahead predictions errors from a
    // holdout sample, following immediately after the training data.
    // 
    // Args:
    //   holdout_y: The vector of holdout data, assumed to follow immediately
    //     after the training data.
    //   final_state:  The state vector as of the end of the training data.
    //   standardize: Should the prediction errors be divided by the square root
    //     of the one step ahead forecast variance?
    //
    // Returns:
    //   The vector of one step ahead prediction errors for the holdout data.
    //   This is the same length as holdout_y.
    Vector one_step_holdout_prediction_errors(const Vector &holdout_y,
                                              const Vector &final_state,
                                              bool standardize = false) const;

    // Update the complete data sufficient statistics for the
    // observation model based on the posterior distribution of the
    // observation model error term at time t.
    //
    // Args:
    //   t: The time of the observation.
    //   observation_error_mean: Mean of the observation error given
    //     model parameters and all observed y's.
    //   observation_error_variance: Variance of the observation error given
    //     model parameters and all observed y's.
    void update_observation_model_complete_data_sufficient_statistics(
        int t, double observation_error_mean,
        double observation_error_variance) override;

    // Increment the portion of the log-likelihood gradient
    // pertaining to the parameters of the observation model.
    //
    // Args:
    //   gradient: The subset of the log likelihood gradient
    //     pertaining to the observation model.  The gradient will be
    //     incremented by the derivatives of log likelihood with
    //     respect to the observation model parameters.
    //   t:  The time index of the observation error.
    //   observation_error_mean: The posterior mean of the observation
    //     error at time t.
    //   observation_error_variance: The posterior variance of the
    //     observation error at time t.
    void update_observation_model_gradient(
        VectorView gradient, int t, double observation_error_mean,
        double observation_error_variance) override;

   private:
    Ptr<ZeroMeanGaussianModel> observation_model_;
    void setup();
  };
}  // namespace BOOM

#endif  // BOOM_STATE_SPACE_MODEL_HPP_
