Revert "Removed datenum Conversion for isodatetime"

This reverts commit eac0130.

Author: Lawrence

+types/+util/checkDtype.m

@@ -111,19 +111,35 @@
             end
         end
     elseif strcmp(type, 'isodatetime')
-        assert(ischar(val)...
-            || iscellstr(val)...
-            || isdatetime(val) ...
-            || (iscell(val) && all(cellfun('isclass', val, 'datetime'))),...
-            errid, errmsg);
+        addpath(fullfile(fileparts(which('NwbFile')), 'external_packages', 'datenum8601'));
+        assert(ischar(val) || iscellstr(val) || isdatetime(val) ||...
+            (iscell(val) && all(cellfun('isclass', val, 'datetime'))), errid, errmsg);
         if ischar(val) || iscellstr(val)
             if ischar(val)
                 val = {val};
             end
 
             datevals = cell(size(val));
+            % one of:
+            % +-hh:mm
+            % +-hhmm
+            % +-hh
+            % Z
+            tzre_pattern = '(?:[+-]\d{2}(?::?\d{2})?|Z)$';
             for i = 1:length(val)
-                datevals{i} = datetime8601(val{i});
+                dnum = datenum8601(val{i});
+                
+                tzre_match = regexp(val{i}, tzre_pattern, 'once');
+                if isempty(tzre_match)
+                    tz = 'local';
+                else
+                    tz = val{i}(tzre_match:end);
+                    if strcmp(tz, 'Z')
+                        tz = 'UTC';
+                    end
+                end
+                datevals{i} = ...
+                    datetime(dnum(1), 'TimeZone', tz, 'ConvertFrom', 'datenum');
             end
             val = datevals;
         end
@@ -132,7 +148,7 @@
             val = {val};
         end
 
-        for i = 1:length(val)
+        for i=1:length(val)
             if isempty(val{i}.TimeZone)
                 val{i}.TimeZone = 'local';
             end
@@ -171,74 +187,4 @@
         val = truval;
     end
 end
-end
-
-function date_time = datetime8601(datestr)
-addpath(fullfile(fileparts(which('NwbFile')), 'external_packages', 'datenum8601'));
-[~, ~, format] = datenum8601(datestr);
-format = format{1};
-has_delimiters = format(1) == '*';
-if has_delimiters
-    format = format(2:end);
-end
-
-assert(strncmp(format, 'ymd', 3),...
-    'MatNWB:Types:Util:CheckDType:DateTime:Unsupported8601',...
-    'non-ymd formats not supported.');
-separator = format(4);
-if separator ~= ' '
-    % non-space digits will error when specifying import format
-    separator = ['''' separator ''''];
-end
-
-has_fractional_sec = isstrprop(format(8:end), 'digit');
-if has_fractional_sec
-   seconds_precision = str2double(format(8:end));
-   if seconds_precision > 9
-       warning('MatNWB:Types:Util:CheckDType:DateTime:LossySeconds',...
-           ['Potential loss of time data detected.  MATLAB fractional seconds '...
-           'precision is limited to 1 ns.  Extra precision will be truncated.']);
-   end
-end
-day_segments = {'yyyy', 'MM', 'dd'};
-time_segments = {'HH', 'mm', 'ss'};
-
-if has_delimiters
-    day_delimiter = '-';
-    time_delimiter = ':';
-else
-    day_delimiter = '';
-    time_delimiter = '';
-end
-
-day_format = strjoin(day_segments, day_delimiter);
-time_format = strjoin(time_segments, time_delimiter);
-format = [day_format separator time_format];
-if has_fractional_sec
-    format = sprintf('%s.%s', format, repmat('S', 1, seconds_precision));
-end
-
-[datestr, timezone] = derive_timezone(datestr);
-date_time = datetime(datestr,...
-    'InputFormat', format,...
-    'TimeZone', timezone);
-end
-
-function [datestr, timezone] = derive_timezone(datestr)
-% one of:
-% +-hh:mm
-% +-hhmm
-% +-hh
-% Z
-tzre_pattern = '(?:[+-]\d{2}(?::?\d{2})?|Z)$';
-tzre_match = regexp(datestr, tzre_pattern, 'once');
-if isempty(tzre_match)
-    timezone = 'local';
-else
-    timezone = datestr(tzre_match:end);
-    if strcmp(timezone, 'Z')
-        timezone = 'UTC';
-    end
-    datestr = datestr(1:(tzre_match - 1));
-end
 end