function dtstr = cnv2icudf(formatstr,escaping)

%   CNV2ICUDF maps date format tokens to ICU date format tokens

%   ICUFORMAT = CNV2ICUDF(MLFORMAT) transforms a date/time format that uses

%   DATESTR's format tokens into one that uses the ICU format tokens. MLFORMAT

%   is a char vector containing a user specified format as described below.

%   ICUFORMAT is a char vector containing the transformed format. Characters in

%   MLFORMAT not listed in Note 1 are "escaped" with single quotes in ICUFORMAT.

%

%   ICUFORMAT = CNV2ICUDF(MLFORMAT,FALSE) does not escape invalid characters.

%   This is useful only for use by FORMATDATE.

%

%   The format specifier allows free-style date/time format using the following

%   tokens:

%      dddd => day is formatted as full name of weekday

%      ddd  => day is formatted as abbreviated name of weekday

%      dd   => day is formatted as two digit day of month

%      d    => day is formatted as first letter of name of weekday

%      mmmm => month is formatted as full of name of month

%      mmm  => month is formatted as three letter abbreviation of name of month

%      mm   => month is formatted as two digit month of year

%      m    => month is formatted as one or two digit month of year

%      yyyy => year is formatted as four digit year

%      yy   => year is formatted as two digit year

%      QQ   => quarter is formatted as 'Q' and one digit quarter of year

%      HH   => hour is formatted as two digit hour of the day

%      MM   => minute is formatted as two digit minute of the hour

%      SS   => second is formatted as two digit second of the minute

%      FFF  => millisecond is formatted as three digit ms of the second

%      PM or PM  => day period is formatted as 'AM' or 'PM'

%   MLFORMAT may contain separators and other delimiters. At most one of

%   the year tokens, is allowed; similarly for the month tokens or the day

%   name tokens (although both day number and day name are allowed). The

%   quarter token is only allowed with one of the year tokens.

%

%

%------------------------------------------------------------------------------

% Copyright 2002-2019 The MathWorks, Inc.

dtstr = formatstr; 

if nargin == 1 

    escaping = true; 

end 

% Replace AM/PM with 'a' to avoid confusion with months and minutes.

showAmPm = [strfind(lower(dtstr), 'am'), strfind(lower(dtstr), 'pm')]; 

wrtAmPm = numel(showAmPm); 

if wrtAmPm > 0 

    if wrtAmPm > 1

        error(message('MATLAB:formatdate:ampmFormat', formatstr));

    end

    dtstr(showAmPm) = [];  % delete the 'a' or the 'p'

    dtstr(showAmPm) = 'a'; % overwrite the 'm'

end 

% Day, millisecond, hour, quarter, second, and year are case insensitive, standardize them.

dtstr = strrep(dtstr, 'd', 'D'); % some of which ultimately become 'd', some 'e' 

dtstr = strrep(dtstr, 'f', 'F'); % which ultimately becomes 'S' 

dtstr = strrep(dtstr, 'h', 'H'); % which MAY ultimately become 'h', if AM/PM is present 

dtstr = strrep(dtstr, 'q', 'Q'); 

dtstr = strrep(dtstr, 'S', 's'); 

dtstr = strrep(dtstr, 'Y', 'y'); 

% Swap 'm' and 'M' to output 'M' for month and 'm' for minute.

minuteLocs = strfind(dtstr,'M'); 

dtstr = strrep(dtstr,'m','M'); 

dtstr(minuteLocs) = 'm'; 

% Escape unused characters.

if escaping 

    dtstr = regexprep(dtstr,'((?=[A-Za-z])([^amsyDFHMQ]))*','''$1'''); 

end 

showYr   = strfind(dtstr,'y'); wrtYr   = numel(showYr); 

showMo   = strfind(dtstr,'M'); wrtMo   = numel(showMo); 

showDay  = strfind(dtstr,'D'); wrtDay  = numel(showDay); 

showHr   = strfind(dtstr,'H'); wrtHr   = numel(showHr); 

showMin  = strfind(dtstr,'m'); wrtMin  = numel(showMin); 

showSec  = strfind(dtstr,'s'); wrtSec  = numel(showSec); 

showMsec = strfind(dtstr,'F'); wrtMsec = numel(showMsec); 

showQrt  = strfind(dtstr,'Q'); wrtQrt  = numel(showQrt); 

% Format date

if wrtYr > 0 

    if (wrtYr ~= 4 && wrtYr ~= 2) || showYr(end) - showYr(1) >= wrtYr 

        error(message('MATLAB:formatdate:yearFormat', formatstr));

    end 

end 

if wrtQrt > 0 

    if wrtQrt ~= 2 || showQrt(2) - showQrt(1) > 1

        error(message('MATLAB:formatdate:quarterFormat', formatstr));

    end

    if any([wrtMo, wrtDay, wrtAmPm, wrtHr, wrtMin, wrtSec, wrtMsec] > 0)

        error(message('MATLAB:formatdate:quarterFormatMismatch',formatstr));

    end

    dtstr = strrep(dtstr, 'QQ', 'QQQ'); % output exactly 'QQQ' for quarter

end 

if wrtMo > 0 

    if wrtMo > 4 || showMo(end) - showMo(1) >= wrtMo 

        error(message('MATLAB:formatdate:monthFormat', formatstr));

    end 

end 

if wrtDay > 0 

    % 'D' is special in that it ultimately maps to _two_ tokens, one of which is

    % a literal char. Ultimately the day name token will be 'e', but that can be

    % confused with 'e' intended as a literal. d/D have been standardized to

    % 'D', so recognize day name vs. day number fields and temporarily

    % distinguish between them using case. d/D are non-literal chars, so we're

    % not stepping on anything.

    dtstr = strrep(dtstr, 'DDDDDD', 'DDDDdd'); % split into day name/number pieces 

    dtstr = strrep(dtstr, 'DDDDD',  'DDDdd'); % split into day name/number pieces 

    % The above two strreps match _all_ 'DDDDDD' or 'DDDDD' ovelapping substrings,

    % so seven or more contiguous D's become something illegal caught below. One to

    % four contiguous D's are left alone, to be handled next.

    % Leave 'DDDD' as is

    % Leave 'DDD' as is

    dtstr = regexprep(dtstr,'(?<!D)(DD)(?!D)','dd'); % 'DD'->'dd', leaving DDDD and DDD alone 

    dtstr = regexprep(dtstr,'(?<!D)(D)(?!D)','DDDDD'); % 'D'->'DDDDD', leaving DDDD and DDD alone 

    showNday = strfind(dtstr,'d'); wrtNday = numel(showNday); 

    if wrtNday > 0 

        if wrtNday ~= 2 || showNday(2) - showNday(1) ~= 1 

            error(message('MATLAB:formatdate:dayFormat', formatstr));

        end 

    end 

    if escaping 

        % Find D's to validate the format, and only then replace 'D' with 'e'.

        showWday = strfind(dtstr,'D'); wrtWday = numel(showWday); 

        dtstr = strrep(dtstr,'D','e'); % now replace 'D' with 'e' 

    else 

        % Preserve existing behavior: formatDate (and therefore datestr) is the

        % one caller who doesn't want escaped literals, and it expects E's. If we're

        % not escaping, replace 'D' with 'E' before looking for E's, which means that

        % E's don't work correctly when intended as literals. Also formatdate expects

        % only one E where there was a single D.

        dtstr = strrep(dtstr,'DDDDD','D'); % exactly 'DDDDD' -> exactly 'D' 

        dtstr = strrep(dtstr,'D','E'); % all D's -> 'E' 

        showWday = strfind(dtstr,'E'); wrtWday = numel(showWday); 

    end 

    if wrtWday > 0 

        if wrtWday > 5 || showWday(end) - showWday(1) >= wrtWday

            error(message('MATLAB:formatdate:dayFormat', formatstr));

        end

    end 

end 

% Format time

if wrtHr > 0 

    if wrtHr == 2 && showHr(2) - showHr(1) == 1 

        if wrtAmPm 

            dtstr = strrep(dtstr,'H','h'); % output 12-hour field if am/pm present

        end 

    else

        error(message('MATLAB:formatdate:hourFormat', formatstr));

    end 

end 

if wrtMin > 0 

    if wrtMin ~= 2 || showMin(2) - showMin(1) ~= 1 

        error(message('MATLAB:formatdate:minuteFormat', formatstr));

    end 

end 

if wrtSec > 0 

    if wrtSec ~= 2 || showSec(2) - showSec(1) ~= 1 

        error(message('MATLAB:formatdate:secondFormat', formatstr));

    end 

end 

if wrtMsec > 0 

    if wrtMsec ~= 3 || showMsec(3) - showMsec(1) ~= 2

        error(message('MATLAB:formatdate:millisecondFormat', formatstr));

    end

    dtstr = strrep(dtstr, 'F', 'S'); % output 'S' for milliseconds.

end