%
% -----------------
% Copyright © 2019 ACK Cyfronet AGH, Poland. 
%
% This work was partially funded by EPOS Project funded in frame of PL-POIR4.2
% --------------
%
function [varargout] = extractColumns(catalog, varargin)
% EXTRACTCOLUMNS Extracts specified columns from a catalog structure
%
%   [col1, col2, ...] = EXTRACTCOLUMNS(catalog, 'colName1', 'colName2', ...)
%   extracts the columns with the specified names from the catalog
%   structure. The catalog is expected to be an array of structures where
%   each structure has fields 'field' and 'val'. The function returns the
%   values of the requested columns.
%
%   For more details on the catalog format, see:
%   https://docs.cyfronet.pl/display/ISDOC/Catalog+-+description
%
%   Example:
%       catalog(1).field = 'ID'; catalog(1).val = [1, 2, 3];
%       catalog(2).field = 'Time'; catalog(2).val = [100, 200, 300];
%       [id, time] = extractColumns(catalog, 'ID', 'Time');
%       % Result: id = [1, 2, 3], time = [100, 200, 300]
%
%   See also: FINDCATALOGCOLUMN.

    for i = 1:length(varargin)
        colName = varargin{i};
        varargout{i} = findColumn(catalog, colName);
    end
end

function column = findColumn(catalog, colName)
% FINDCOLUMN Helper function to find the values of a column in a catalog
%
%   column = FINDCOLUMN(catalog, colName) searches the catalog structure
%   for the specified column name and returns its values. If the column
%   does not exist, an error is thrown.
%
%   Refer to the catalog documentation for further information:
%   https://docs.cyfronet.pl/display/ISDOC/Catalog+-+description

    for c = 1:length(catalog)
        if strcmp(catalog(c).field, colName)
            column = catalog(c).val;
            break;
        end
    end
    if exist('column') ~= 1
        error('no column named %s', colName);
    end
end