/*
 * Copyright © 2010-2025 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 <algorithm>
#include <string>
#include <tuple>
#include <vector>

#include <dynblas.h>
#include <dynmex.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::ranges::copy_n(constant, m, &y2[particle_]);
      std::ranges::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::ranges::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 (nrhs == 9 && nlhs != 1)
    mexErrMsgTxt(
        "One output argument is required if there is no pruning (9 input arguments passed)");

  if (nrhs == 11 && nlhs != 2)
    mexErrMsgTxt(
        "Two output arguments are required if there is pruning (11 input arguments passed).");

  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 = mxGetDoubles(prhs[0]);
  const double* epsilon = mxGetDoubles(prhs[1]);
  const double* ghx = mxGetDoubles(prhs[2]);
  const double* ghu = mxGetDoubles(prhs[3]);
  const double* constant = mxGetDoubles(prhs[4]);
  const double* ghxx = mxGetDoubles(prhs[5]);
  const double* ghuu = mxGetDoubles(prhs[6]);
  const double* ghxu = mxGetDoubles(prhs[7]);
  const double *yhat_ = nullptr, *ss = nullptr;
  if (nrhs > 9)
    {
      yhat_ = mxGetDoubles(prhs[8]);
      ss = mxGetDoubles(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 = mxGetDoubles(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 = mxGetDoubles(plhs[0]);
      double* y_ = mxGetDoubles(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);
    }
}
