function [] = sac2ascii(sac, asciiFilePath)
%sac2ascii Saves given sac data in ascii file in slist format

    % check required fields
    checkValue(sac.knetwk, 'knetwk');
    checkValue(sac.kstnm, 'kstnm');
    checkValue(sac.kcmpnm, 'kcmpnm');
    checkValue(sac.delta, 'delta');
    checkValue(sac.nzyear, 'nzyear');
    checkValue(sac.nzjday, 'nzjday');
    checkValue(sac.nzhour, 'nzhour');
    checkValue(sac.nzmin, 'nzmin');
    checkValue(sac.sec, 'sec');
    
    networkCode = sac.knetwk;
    stationCode = sac.kstnm;
    locationCode = sac.khole;
    if isUndefined(locationCode); locationCode = ''; end
    channelCode = sac.kcmpnm;
    frequency = int32(1 / sac.delta);
    unit = extractUnit(sac);
    startTime = extractStartTime(sac);
    samples = length(sac.trace);
    
    fileID = fopen(asciiFilePath, 'w');
    fprintf(fileID, 'TIMESERIES %s_%s_%s_%s, %d samples, %d sps, %s, SLIST, FLOAT, %s\n',...
          networkCode, stationCode, locationCode, channelCode, samples, frequency, startTime, unit);
    fprintf(fileID, '%f\n', sac.trace);
    fclose(fileID);

end

function [unit] = extractUnit(sac)
    switch sac.idep
        case 6
            unit = 'NM';
        case 7
            unit = 'NM/S';
        case 8
            unit = 'NM/S^2';
        otherwise
            unit = 'COUNTS';
    end
end

function [startTime] = extractStartTime(sac)
    % converting day of the year to day of the month
    yearString = ['01-01-', num2str(sac.nzyear)];
    date = datenum(yearString, 'dd-mm-yyyy') + sac.nzjday - 1;
    dateString = datestr(date, 'yyyy-mm-dd');
    
    startTime = sprintf('%sT%02d:%02d:%09.6f', dateString, sac.nzhour, sac.nzmin, sac.sec);
end

function [] = checkValue(value, fieldName)
    if isUndefined(value)
        error('sac does not contain required field - [%s]', fieldName);
    end
end

function [undefined] = isUndefined(value)
    if isa(value, 'char')
        undefined = strcmp(value, '-12345');
    elseif isa(value, 'logical')
        undefined = value == false;
    else
        undefined = abs(-12345 - value) < 1e-10;
    end
end