function [pnames, enames, xnames, pid, eid, xid] = get_variables_and_parameters_in_equation(lhs, rhs, M_)
% [pnames, enames, xnames, pid, eid, xid] = get_variables_and_parameters_in_equation(lhs, rhs, M_)
% Returns the lists of parameters, endogenous variables and exogenous variables in an equation.
%
% INPUTS
% - lhs         [string]            Left hand side of an equation.
% - rhs         [string]            Right hand side of an equation.
% - M_          [struct]            Structure describing the current model.
%
% OUTPUTS
% - pnames      [cell]              Cell of row char arrays (p elements), names of the parameters.
% - enames      [cell]              Cell of row char arrays (n elements), names of the endogenous variables.
% - xnames      [cell]              Cell of row char arrays (m elements), names of the exogenous variables.
% - pid         [Integer]           p*1 vector of indices in M_.param_names for the listed parameters in params.
% - eid         [Integer]           n*1 vector of indices in M_.endo_names for the listed parameters in endogenous.
% - xid         [Integer]           m*1 vector of indices in M_.exo_names for the listed parameters in exogenous.

% Copyright © 2018-2023 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/>.

% Get the tokens in the rhs member of the equation.
rhs_ = get_variables_and_parameters_in_expression(rhs);

% Get the tokens in the lhs member of the equation.
lhs_ = get_variables_and_parameters_in_expression(lhs);

% Get list of parameters.
pnames = M_.param_names;
pnames = intersect([rhs_, lhs_], pnames);

if nargout>1
    % Get list of endogenous variables.
    enames = M_.endo_names;
    enames = intersect([rhs_, lhs_], enames);
    if nargout>2
        % Get list of exogenous variables
        xnames = M_.exo_names;
        xnames = intersect([rhs_,lhs_], xnames);
        if nargout>3
            % Returns vector of indices for parameters endogenous and exogenous variables if required.
            p = length(pnames);
            pid = zeros(p, 1);
            for i = 1:p
                pid(i) = find(strcmp(pnames{i}, M_.param_names));
            end
            p = length(enames);
            eid = zeros(p, 1);
            for i = 1:p
                eid(i) = find(strcmp(enames{i}, M_.endo_names));
            end
            p = length(xnames);
            xid = zeros(p, 1);
            for i = 1:p
                xid(i) = find(strcmp(xnames{i}, M_.exo_names));
            end
        end
    end
end