function [endogenousvariables, info] = sim1_purely_forward(endogenousvariables, exogenousvariables, steadystate, M, options)
% Performs deterministic simulation of a purely forward model

% Copyright © 2012-2022 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.
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% You should have received a copy of the GNU General Public License
% along with Dynare.  If not, see <https://www.gnu.org/licenses/>.

ny0 = nnz(M.lead_lag_incidence(1,:));    % Number of variables at current period

if ny0 ~= M.endo_nbr
    error('All endogenous variables must appear at the current period!')
end

if ismember(options.solve_algo, [12,14])
    [funcs, feedback_vars_idxs] = setup_time_recursive_block_simul(M);
else
    iyf = find(M.lead_lag_incidence(2,:)>0); % Indices of variables at next period
    dynamicmodel = str2func(sprintf('%s.%s', M.fname, 'dynamic'));
    dynamicmodel_s = str2func('dynamic_forward_model_for_simulation');
end

function [r, J] = block_wrapper(z, feedback_vars_idx, func, y_dynamic, x, sparse_rowval, sparse_colval, sparse_colptr, T)
    % NB: do as few computations as possible inside this function, since it is
    % called a very large number of times
    y_dynamic(feedback_vars_idx) = z;
    [~, ~, r, J] = feval(func, y_dynamic, x, M.params, steadystate, ...
                         sparse_rowval, sparse_colval, sparse_colptr, T);
end

info.status = true;

for it = options.periods:-1:1
    yf = endogenousvariables(:,it+1); % Values at next period, also used as guess value for current period
    if ismember(options.solve_algo, [12,14])
        x = exogenousvariables(it,:);
        T = NaN(M.block_structure.dyn_tmp_nbr);
        y_dynamic = [NaN(M.endo_nbr, 1); yf; yf];
        for blk = 1:length(M.block_structure.block)
            sparse_rowval = M.block_structure.block(blk).g1_sparse_rowval;
            sparse_colval = M.block_structure.block(blk).g1_sparse_colval;
            sparse_colptr = M.block_structure.block(blk).g1_sparse_colptr;
            if M.block_structure.block(blk).Simulation_Type ~= 2 % Not an evaluate backward block
                [z, check, ~, ~, errorcode] = dynare_solve(@block_wrapper, y_dynamic(feedback_vars_idxs{blk}), ...
                                                           options.simul.maxit, options.dynatol.f, ...
                                                           options.dynatol.x, options, ...
                                                           feedback_vars_idxs{blk}, funcs{blk}, y_dynamic, x, sparse_rowval, sparse_colval, sparse_colptr, T);
                if check
                    info.status = false;
                    if options.debug
                        dprintf('sim1_purely_forward: Nonlinear solver routine failed with errorcode=%i in block %i and period %i.', errorcode, blk, it)
                    end
                end
                y_dynamic(feedback_vars_idxs{blk}) = z;
            end
            %% Compute endogenous if the block is of type evaluate or if there are recursive variables in a solve block.
            %% Also update the temporary terms vector.
            [y_dynamic, T] = feval(funcs{blk}, y_dynamic, x, M.params, ...
                                   steadystate, sparse_rowval, sparse_colval, ...
                                   sparse_colptr, T);
        end
        endogenousvariables(:,it) = y_dynamic(M.endo_nbr+(1:M.endo_nbr));
    else
        [tmp, check, ~, ~, errorcode] = dynare_solve(dynamicmodel_s, yf, ...
                                                     options.simul.maxit, options.dynatol.f, options.dynatol.x, ...
                                                     options, ...
                                                     dynamicmodel, yf(iyf), exogenousvariables, M.params, steadystate, it);
        if check
            info.status = false;
            dprintf('sim1_purely_forward: Nonlinear solver routine failed with errorcode=%i in period %i.', errorcode, it)
            break
        end
        endogenousvariables(:,it) = tmp(1:M.endo_nbr);
    end
end

end
