function pred = load_predicates(plant)
% LOAD_PREDICATES  Read predicates.json and resolve rhs_expr into numbers.
%
%  Each halfspace entry in the JSON stores rhs_expr as a string because
%  several of the bounds are defined relative to plant-derived constants
%  (T_c0, T_cold0, T_standby).  We evaluate those expressions here in a
%  controlled workspace that exposes exactly those names plus the
%  derived offsets from the JSON.
%
%  Returns a struct `pred` with one field per predicate, each a struct
%  holding an n_hs x 10 matrix A_poly and an n_hs x 1 vector b_poly such
%  that the predicate is { x : A_poly * x <= b_poly }.
%
%  Also returns:
%    pred.constants - a struct with T_c0, T_cold0, T_f0, T_standby, etc.
%
%  Usage:
%    plant = pke_params();
%    pred  = load_predicates(plant);
%    A = pred.t_avg_in_range.A_poly;     % 2 x 10
%    b = pred.t_avg_in_range.b_poly;     % 2 x 1
%    is_in = all(A * x <= b);            % predicate check on state x

    here = fileparts(mfilename('fullpath'));
    raw  = fileread(fullfile(here, 'predicates.json'));
    J    = jsondecode(raw);

    % --- Constants used in rhs_expr evaluations ---
    T_c0     = plant.T_c0;                                       %#ok<NASGU>
    T_f0     = plant.T_f0;                                       %#ok<NASGU>
    T_cold0  = plant.T_cold0;                                    %#ok<NASGU>
    T_standby_offset_C = J.derived.T_standby_offset_C;
    T_standby = T_c0 + T_standby_offset_C;                       %#ok<NASGU>

    pred.constants = struct( ...
        'T_c0', plant.T_c0, ...
        'T_f0', plant.T_f0, ...
        'T_cold0', plant.T_cold0, ...
        'T_standby', T_standby, ...
        'T_standby_offset_C', T_standby_offset_C, ...
        'T_standby_offset_F', J.derived.T_standby_offset_F, ...
        't_avg_in_range_halfwidth_C', J.derived.t_avg_in_range_halfwidth_C, ...
        'p_above_crit_threshold_n', J.derived.p_above_crit_threshold_n);

    % --- Loop over predicates, build A/b matrices ---
    names = fieldnames(J.predicates);
    for k = 1:numel(names)
        name = names{k};
        entry = J.predicates.(name);
        hs_list = entry.halfspaces;

        % jsondecode returns a struct array if entries are uniform, else cell.
        if iscell(hs_list)
            n_hs = numel(hs_list);
            get_hs = @(i) hs_list{i};
        else
            n_hs = numel(hs_list);
            get_hs = @(i) hs_list(i);
        end

        A_poly = zeros(n_hs, 10);
        b_poly = zeros(n_hs, 1);
        for i = 1:n_hs
            hs = get_hs(i);
            A_poly(i, hs.state_index) = hs.coeff;
            b_poly(i)                 = eval(hs.rhs_expr);   %#ok<EVLDF>
        end

        pred.(name).A_poly  = A_poly;
        pred.(name).b_poly  = b_poly;
        pred.(name).meaning = entry.meaning;
    end
end