function config = normalize_config(config)
%NORMALIZE_CONFIG Normalize legacy GUI/runtime config to the current schema.

if nargin == 0 || isempty(config)
    config = create_empty_config();
    return;
end

defaults = create_empty_config();
config = merge_struct_defaults(config, defaults);

config.model.grid_model = first_nonempty_scalar(config.model.grid_model, 1);
config.model.flow_model = first_nonempty_scalar(config.model.flow_model, 1);
config.flow.gas_water.gas_model = 1;
config.flow.multi_component.gas_model = 1;

legacy_model_fields = {'modelflag'};
legacy_fracture_fields = {'input_style', 'fractureLines', 'fractureHeights', 'flowBarrierFlags'};

for i = 1:numel(legacy_model_fields)
    field_name = legacy_model_fields{i};
    if isfield(config.model, field_name)
        config.model = rmfield(config.model, field_name);
    end
end

for i = 1:numel(legacy_fracture_fields)
    field_name = legacy_fracture_fields{i};
    if isfield(config.fracture, field_name)
        config.fracture = rmfield(config.fracture, field_name);
    end
end
end

function s = merge_struct_defaults(s, defaults)
default_fields = fieldnames(defaults);
for i = 1:numel(default_fields)
    field_name = default_fields{i};
    if ~isfield(s, field_name) || isempty(s.(field_name))
        s.(field_name) = defaults.(field_name);
    elseif isstruct(defaults.(field_name)) && isstruct(s.(field_name))
        s.(field_name) = merge_struct_defaults(s.(field_name), defaults.(field_name));
    end
end
end

function value = first_nonempty_scalar(raw_value, fallback)
if isempty(raw_value)
    value = fallback;
elseif isscalar(raw_value)
    value = raw_value;
else
    value = raw_value(1);
end
end