function [S, meta] = tdcs_scenario_data(scenario)
%TDCS_SCENARIO_DATA Build one merge/window scenario from the curated tDCS data.
%   [S, META] = TDCS_SCENARIO_DATA(SCENARIO) loads the curated 12-animal
%   table via TDCS_LOAD_DATA, applies the requested group-merge map from
%   TDCS_CONFIG, restricts to day <= maxDay per the scenario's window
%   suffix, adds mean-centered day covariates DAY_C / DAY_C2, and recodes
%   GROUP as a categorical with CFG.REF ('Electrode-Box-B2') as the FIRST
%   (reference) category via REORDERCATS. S is also written to
%   analysis/matlab/derived/<SCENARIO>.csv via WRITETABLE (the derived/
%   folder is created if it does not already exist).
%
%   SCENARIO must be one of:
%     unmerged_full, unmerged_d0_10, mergeA2_full, mergeA2_d0_10,
%     mergeB2_full, mergeB2_d0_10
%
%   The scenario name is split into:
%     - a merge key: 'unmerged' | 'mergeA2' | 'mergeB2', selecting which
%       containers.Map from TDCS_CONFIG (if any) to apply to relabel
%       GROUP. 'unmerged' applies no relabeling (identity) -- it is not
%       backed by a config map at all, since only the two "unknown"
%       conditions (Electrode-Box-A, Right-Electrode) are ever merge
%       targets, and the unmerged scenario reports them unmerged/as-is.
%     - a day window: '_full' -> maxDay = 26, '_d0_10' -> maxDay = 10.
%
%   META is a struct with fields:
%     .mergeKey    'unmerged' | 'mergeA2' | 'mergeB2'
%     .maxDay      26 or 10
%     .isUnmerged  true only when mergeKey == 'unmerged'

[mergeKey, maxDay] = localParseScenario(scenario);

cfg = tdcs_config();
T = tdcs_load_data();

switch mergeKey
    case 'unmerged'
        % Identity: no relabeling. An empty map means isKey(...) is
        % always false below, so every group passes through unchanged.
        mergeMap = containers.Map('KeyType', 'char', 'ValueType', 'char');
    case 'mergeA2'
        mergeMap = cfg.mergeA2;
    case 'mergeB2'
        mergeMap = cfg.mergeB2;
    otherwise
        error('tdcs_scenario_data:badScenario', ...
            'Unrecognized scenario "%s".', scenario);
end

% Relabel GROUP per the merge map. Groups that are not a key in the map
% (e.g. Naive, Electrode-Box-A2, Electrode-Box-B2 under mergeA2/mergeB2,
% or every group under the empty 'unmerged' map) are left unchanged --
% only the two "unknown" conditions are ever merge-map keys.
groupCell = cellstr(T.group);
for i = 1:numel(groupCell)
    if isKey(mergeMap, groupCell{i})
        groupCell{i} = mergeMap(groupCell{i});
    end
end

% Day window (applied after relabeling, before centering, per the plan).
dayMask = T.day <= maxDay;
S = T(dayMask, :);
groupCell = groupCell(dayMask);

% Recode GROUP as categorical with cfg.ref first (the GLME reference
% level). Only categories actually present after merge+window survive.
S.group = categorical(groupCell);
allCats = categories(S.group);
otherCats = allCats(~strcmp(allCats, cfg.ref));
S.group = reordercats(S.group, [{cfg.ref}; otherCats]);

% Mean-centered day covariates, computed on the post-window data.
S.day_c = S.day - mean(S.day);
S.day_c2 = S.day_c .^ 2;

% Persist the derived scenario table.
thisDir = fileparts(mfilename('fullpath'));
derivedDir = fullfile(thisDir, 'derived');
if ~exist(derivedDir, 'dir')
    mkdir(derivedDir);
end
outFile = fullfile(derivedDir, [char(scenario) '.csv']);
writetable(S, outFile);

meta = struct();
meta.mergeKey = mergeKey;
meta.maxDay = maxDay;
meta.isUnmerged = strcmp(mergeKey, 'unmerged');

end

function [mergeKey, maxDay] = localParseScenario(scenario)
%LOCALPARSESCENARIO Split "<mergeKey>_full" / "<mergeKey>_d0_10" apart.
scenario = char(scenario);
if endsWith(scenario, '_full')
    maxDay = 26;
    mergeKey = scenario(1:end - numel('_full'));
elseif endsWith(scenario, '_d0_10')
    maxDay = 10;
    mergeKey = scenario(1:end - numel('_d0_10'));
else
    error('tdcs_scenario_data:badScenario', ...
        'Scenario "%s" does not end in "_full" or "_d0_10".', scenario);
end

if ~ismember(mergeKey, {'unmerged', 'mergeA2', 'mergeB2'})
    error('tdcs_scenario_data:badScenario', ...
        'Scenario "%s" has unrecognized merge key "%s".', scenario, mergeKey);
end

end