/*
 * Copyright © 2010-2022 Dynare Team
 *
 * This file is part of Dynare.
 *
 * Dynare is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Dynare 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Dynare.  If not, see <https://www.gnu.org/licenses/>.
 */

/*
 * This mex file computes particles at time t+1 given particles and innovations at time t,
 * using a second order approximation of the nonlinear state space model.
 */

#include <vector>
#include <algorithm>
#include <tuple>
#include <string>

#include <dynmex.h>
#include <dynblas.h>

#include <omp.h>

/*
  Uncomment the following line to use BLAS instead of loops when computing
  ghx·ŷ and ghu·ε.
  N.B.: Under MATLAB, this only works in single-threaded mode, otherwise one
  gets a crash (because of the incompatibility between Intel and GNU OpenMPs).
*/
//#define USE_BLAS_AT_FIRST_ORDER

std::tuple<std::vector<int>, std::vector<int>, std::vector<int>>
set_vector_of_indices(int n, int r)
{
  int m = n*(n+1)/2;
  std::vector<int> v1(m, 0), v2(m, 0), v3(m, 0);
  for (int i = 0, index = 0, jndex = 0; i < n; i++)
    {
      jndex += i;
      for (int j = i; j < n; j++, index++, jndex++)
        {
          v1[index] = i;
          v2[index] = j;
          v3[index] = jndex*r;
        }
    }
  return { v1, v2, v3 };
}

void
ss2Iteration_pruning(double *y2, double *y1, const double *yhat2, const double *yhat1, const double *epsilon,
                     const double *ghx, const double *ghu,
                     const double *constant, const double *ghxx, const double *ghuu, const double *ghxu, const double *ss,
                     blas_int m, blas_int n, blas_int q, blas_int s, int number_of_threads)
{
#ifdef USE_BLAS_AT_FIRST_ORDER
  const double one = 1.0;
  const blas_int ONE = 1;
#endif
  auto [ii1, ii2, ii3] = set_vector_of_indices(n, m); // vector indices for ghxx
  auto [jj1, jj2, jj3] = set_vector_of_indices(q, m); // vector indices for ghuu
#pragma omp parallel for num_threads(number_of_threads)
  for (int particle = 0; particle < s; particle++)
    {
      int particle_ = particle*m;
      int particle__ = particle*n;
      int particle___ = particle*q;
      std::copy_n(constant, m, &y2[particle_]);
      std::copy_n(ss, m, &y1[particle_]);
#ifdef USE_BLAS_AT_FIRST_ORDER
      dgemv("N", &m, &n, &one, ghx, &m, &yhat2[particle__], &ONE, &one, &y2[particle_], &ONE);
      dgemv("N", &m, &q, &one, ghu, &m, &epsilon[particle___], &ONE, &one, &y2[particle_], &ONE);
#endif
      for (int variable = 0; variable < m; variable++)
        {
          int variable_ = variable + particle_;
          // +ghx·ŷ₂+ghu·ε
#ifndef USE_BLAS_AT_FIRST_ORDER
          for (int column = 0, column_ = 0; column < n; column++, column_ += m)
            y2[variable_] += ghx[variable+column_]*yhat2[column+particle__];
          for (int column = 0, column_ = 0; column < q; column++, column_ += m)
            y2[variable_] += ghu[variable+column_]*epsilon[column+particle___];
#endif
          // +½ghxx·ŷ₁⊗ŷ₁
          for (int i = 0; i < n*(n+1)/2; i++)
            {
              int i1 = particle__+ii1[i];
              int i2 = particle__+ii2[i];
              if (i1 == i2)
                y2[variable_] += .5*ghxx[variable+ii3[i]]*yhat1[i1]*yhat1[i1];
              else
                y2[variable_] += ghxx[variable+ii3[i]]*yhat1[i1]*yhat1[i2];
            }
          // +½ghuu·ε⊗ε
          for (int j = 0; j < q*(q+1)/2; j++)
            {
              int j1 = particle___+jj1[j];
              int j2 = particle___+jj2[j];
              if (j1 == j2)
                y2[variable_] += .5*ghuu[variable+jj3[j]]*epsilon[j1]*epsilon[j1];
              else
                y2[variable_] += ghuu[variable+jj3[j]]*epsilon[j1]*epsilon[j2];
            }
          // +ghxu·ŷ₁⊗ε
          for (int v = particle__, i = 0; v < particle__+n; v++)
            for (int s = particle___; s < particle___+q; s++, i += m)
                y2[variable_] += ghxu[variable+i]*epsilon[s]*yhat1[v];
#ifndef USE_BLAS_AT_FIRST_ORDER
          for (int column = 0, column_ = 0; column < q; column++, column_ += m)
            {
              int i1 = variable+column_;
              int i2 = column+particle__;
              int i3 = column+particle___;
              y1[variable_] += ghx[i1]*yhat1[i2];
              y1[variable_] += ghu[i1]*epsilon[i3];
            }
          for (int column = q, column_ = q*m; column < n; column++, column_ += m)
            y1[variable_] += ghx[variable+column_]*yhat1[column+particle__];
#endif
        }
#ifdef USE_BLAS_AT_FIRST_ORDER
      dgemv("N", &m, &n, &one, &ghx[0], &m, &yhat1[particle__], &ONE, &one, &y1[particle_], &ONE);
      dgemv("N", &m, &q, &one, &ghu[0], &m, &epsilon[particle___], &ONE, &one, &y1[particle_], &ONE);
#endif
    }
}

void
ss2Iteration(double *y, const double *yhat, const double *epsilon,
             const double *ghx, const double *ghu,
             const double *constant, const double *ghxx, const double *ghuu, const double *ghxu,
             blas_int m, blas_int n, blas_int q, blas_int s, int number_of_threads)
{
#ifdef USE_BLAS_AT_FIRST_ORDER
  const double one = 1.0;
  const blas_int ONE = 1;
#endif
  auto [ii1, ii2, ii3] = set_vector_of_indices(n, m); // vector indices for ghxx
  auto [jj1, jj2, jj3] = set_vector_of_indices(q, m); // vector indices for ghuu
#pragma omp parallel for num_threads(number_of_threads)
  for (int particle = 0; particle < s; particle++)
    {
      int particle_ = particle*m;
      int particle__ = particle*n;
      int particle___ = particle*q;
      std::copy_n(constant, m, &y[particle_]);
#ifdef USE_BLAS_AT_FIRST_ORDER
      dgemv("N", &m, &n, &one, ghx, &m, &yhat[particle__], &ONE, &one, &y[particle_], &ONE);
      dgemv("N", &m, &q, &one, ghu, &m, &epsilon[particle___], &ONE, &one, &y[particle_], &ONE);
#endif
      for (int variable = 0; variable < m; variable++)
        {
          int variable_ = variable + particle_;
          // +ghx·ŷ+ghu·ε
#ifndef USE_BLAS_AT_FIRST_ORDER
          for (int column = 0, column_ = 0; column < n; column++, column_ += m)
            y[variable_] += ghx[variable+column_]*yhat[column+particle__];
          for (int column = 0, column_ = 0; column < q; column++, column_ += m)
            y[variable_] += ghu[variable+column_]*epsilon[column+particle___];
#endif
          // +½ghxx·ŷ⊗ŷ
          for (int i = 0; i < n*(n+1)/2; i++)
            {
              int i1 = particle__+ii1[i];
              int i2 = particle__+ii2[i];
              if (i1 == i2)
                y[variable_] += .5*ghxx[variable+ii3[i]]*yhat[i1]*yhat[i1];
              else
                y[variable_] += ghxx[variable+ii3[i]]*yhat[i1]*yhat[i2];
            }
          // +½ghuu·ε⊗ε
          for (int j = 0; j < q*(q+1)/2; j++)
            {
              int j1 = particle___+jj1[j];
              int j2 = particle___+jj2[j];
              if (j1 == j2)
                y[variable_] += .5*ghuu[variable+jj3[j]]*epsilon[j1]*epsilon[j1];
              else
                y[variable_] += ghuu[variable+jj3[j]]*epsilon[j1]*epsilon[j2];
            }
          // +ghxu·ŷ⊗ε
          for (int v = particle__, i = 0; v < particle__+n; v++)
            for (int s = particle___; s < particle___+q; s++, i += m)
              y[variable_] += ghxu[variable+i]*epsilon[s]*yhat[v];
        }
    }
}

void
mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
{
  /*
    prhs[0] yhat          [double]  n×s array, time t particles.
    prhs[1] epsilon       [double]  q×s array, time t innovations.
    prhs[2] ghx           [double]  m×n array, first order reduced form.
    prhs[3] ghu           [double]  m×q array, first order reduced form.
    prhs[4] constant      [double]  m×1 array, deterministic steady state + second order correction for the union of the states and observed variables.
    prhs[5] ghxx          [double]  m×n² array, second order reduced form.
    prhs[6] ghuu          [double]  m×q² array, second order reduced form.
    prhs[7] ghxu          [double]  m×nq array, second order reduced form.
    prhs[8] yhat_         [double]  [OPTIONAL] n×s array, time t particles (pruning additional latent variables).
    prhs[9] ss            [double]  [OPTIONAL] m×1 array, steady state for the union of the states and the observed variables (needed for the pruning mode).

    prhs[8 or 10]         [double]  num of threads

    plhs[0] y             [double]  m×s array, time t+1 particles.
    plhs[1] y_            [double]  m×s array, time t+1 particles for the pruning latent variables.
  */

  // Check the number of input and output.
  if (nrhs != 9 && nrhs != 11)
    mexErrMsgTxt("Nine or eleven input arguments are required.");

  if (nlhs > 2)
    mexErrMsgTxt("Too many output arguments.");

  auto check_input_real_dense_array = [=](int i)
  {
    if (!mxIsDouble(prhs[i]) || mxIsComplex(prhs[i]) || mxIsSparse(prhs[i]))
      mexErrMsgTxt(("Input argument " + std::to_string(i+1) + " should be a real dense array").c_str());
  };

  for (int i = 0; i < 8; i++)
    check_input_real_dense_array(i);

  // Get dimensions.
  size_t n = mxGetM(prhs[0]); // Number of states.
  size_t s = mxGetN(prhs[0]); // Number of particles.
  size_t q = mxGetM(prhs[1]); // Number of innovations.
  size_t m = mxGetM(prhs[2]); // Number of elements in the union of states and observed variables.
  // Check the dimensions.
  if (s != mxGetN(prhs[1]) // Number of columns for epsilon
      || n != mxGetN(prhs[2]) // Number of columns for ghx
      || m != mxGetM(prhs[3]) // Number of rows for ghu
      || q != mxGetN(prhs[3]) // Number of columns for ghu
      || m != mxGetM(prhs[4]) // Number of rows for 2nd order constant correction + deterministic steady state
      || m != mxGetM(prhs[5]) // Number of rows for ghxx
      || n*n != mxGetN(prhs[5]) // Number of columns for ghxx
      || m != mxGetM(prhs[6]) // Number of rows for ghuu
      || q*q != mxGetN(prhs[6]) // Number of columns for ghuu
      || m != mxGetM(prhs[7]) // Number of rows for ghxu
      || n*q != mxGetN(prhs[7])) // Number of rows for ghxu
    mexErrMsgTxt("Input dimension mismatch!.");
  if (nrhs > 9)
    {
      for (int i = 8; i < 10; i++)
        check_input_real_dense_array(i);

      if (n != mxGetM(prhs[8]) // Number of rows for yhat_
          || s != mxGetN(prhs[8]) // Number of columns for yhat_
          || m != mxGetM(prhs[9])) // Number of rows for ss
        mexErrMsgTxt("Input dimension mismatch!.");
    }

  // Get Input arrays.
  const double *yhat = mxGetPr(prhs[0]);
  const double *epsilon = mxGetPr(prhs[1]);
  const double *ghx = mxGetPr(prhs[2]);
  const double *ghu = mxGetPr(prhs[3]);
  const double *constant = mxGetPr(prhs[4]);
  const double *ghxx = mxGetPr(prhs[5]);
  const double *ghuu = mxGetPr(prhs[6]);
  const double *ghxu = mxGetPr(prhs[7]);
  const double *yhat_ = nullptr, *ss = nullptr;
  if (nrhs > 9)
    {
      yhat_ = mxGetPr(prhs[8]);
      ss = mxGetPr(prhs[9]);
    }

  const mxArray *numthreads_mx = prhs[nrhs == 9 ? 8 : 10];
  if (!(mxIsScalar(numthreads_mx) && mxIsNumeric(numthreads_mx)))
    mexErrMsgTxt("Last argument should be a numeric scalar");
  int numthreads = static_cast<int>(mxGetScalar(numthreads_mx));
  if (numthreads <= 0)
    mexErrMsgTxt("Last argument should be a positive integer");

#if defined(USE_BLAS_AT_FIRST_ORDER) && defined(MATLAB_MEX_FILE)
  if (numthreads != 1)
    mexErrMsgTxt("Parallelization is not possible when compiled with USE_BLAS_AT_FIRST_ORDER.");
#endif
  if (nrhs == 9)
    {
      plhs[0] = mxCreateDoubleMatrix(m, s, mxREAL);
      double *y = mxGetPr(plhs[0]);
      ss2Iteration(y, yhat, epsilon, ghx, ghu, constant, ghxx, ghuu, ghxu, static_cast<int>(m), static_cast<int>(n), static_cast<int>(q), static_cast<int>(s), numthreads);
    }
  else
    {
      plhs[0] = mxCreateDoubleMatrix(m, s, mxREAL);
      plhs[1] = mxCreateDoubleMatrix(m, s, mxREAL);
      double *y = mxGetPr(plhs[0]);
      double *y_ = mxGetPr(plhs[1]);
      ss2Iteration_pruning(y, y_, yhat, yhat_, epsilon, ghx, ghu, constant, ghxx, ghuu, ghxu, ss, static_cast<int>(m), static_cast<int>(n), static_cast<int>(q), static_cast<int>(s), numthreads);
    }
}