function ax = plotRgaData(tbl, tStart, tEnd)
%PLOTRGADATA Plot RGA partial pressures vs time (companion to plotCryoData).
%
%   ax = plotRgaData(tbl, tStart, tEnd)
%   Plots every channel column of an rgaImportData table against its shared
%   datetime axis. tStart/tEnd (datetime) optionally subset the range, just
%   like plotCryoData. Returns a struct with the axes handle.
%
%   By default the y-axis is linear (RGA scans contain small near-noise
%   negatives that a log axis cannot show). To switch to the classic
%   semilog view afterwards:
%       set(ax.partial, 'YScale', 'log');
%   (values <= 0 are simply not drawn on a log axis).
%
%   EXAMPLE
%     tbl = rgaImportData('rga1_Jul_01_2026_08-23-06_AM.txt');
%     ax  = plotRgaData(tbl);
%     ax  = plotRgaData(tbl, t1, t2);       % zoom to a window
%
%   See also RGAIMPORTDATA, PLOTCRYODATA

    %--- Extract datetime column ---
    dt = tbl.datetime;

    %--- If start/stop provided, subset the table ---
    if nargin >= 3 && ~isempty(tStart) && ~isempty(tEnd)
        mask = dt >= tStart & dt <= tEnd;
        tbl  = tbl(mask, :);
        dt   = dt(mask);
    end

    %--- Channel columns = everything except datetime & time_s ---
    chVars = setdiff(tbl.Properties.VariableNames, {'datetime','time_s'}, 'stable');

    units = 'a.u.';
    if isfield(tbl.Properties.UserData, 'units')
        units = tbl.Properties.UserData.units;
    end

    %--- Plot ---
    figure;
    tl = tiledlayout(1, 1);
    tl.TileSpacing = 'compact';
    tl.Padding     = 'compact';

    ax.partial = nexttile;
    hold on;
    for k = 1:numel(chVars)
        plot(dt, tbl.(chVars{k}), '-', 'LineWidth', 1, ...
            'DisplayName', prettyName(chVars{k}));
    end
    grid on;
    ylabel(sprintf('Partial pressure [%s]', units));
    xlabel('Date & Time');
    title('RGA partial pressures');
    legend('Location', 'best', 'Interpreter', 'none');

    % Match plotCryoData's datetime tick style
    ax.partial.XAxis.TickLabelFormat = 'dd-MMM HH:mm';
end

% -------------------------------------------------------------------------
function s = prettyName(v)
% "Water_m18" -> "Water (m18)"
    s = regexprep(v, '_m(\d+)$', ' (m$1)');
    s = strrep(s, '_', ' ');
end