Add support for working with negative dates

See discussion https://groups.google.com/g/tiddlywiki/c/aHlyaHr93Io/m/vGcDa6lxAgAJ

boot/boot.js

@@ -305,7 +305,12 @@ $tw.utils.stringifyDate = function(value) {
 // Parse a date from a UTC YYYYMMDDHHMMSSmmm format string
 $tw.utils.parseDate = function(value) {
 	if(typeof value === "string") {
-		var year = parseInt(value.substr(0,4),10),
+		var negative = 1;
+		if(value.charAt(0) === "-") {
+			negative = -1;
+			value = value.substr(1);
+		}
+		var year = parseInt(value.substr(0,4),10) * negative,
 			d = new Date(Date.UTC(year,
 				parseInt(value.substr(4,2),10)-1,
 				parseInt(value.substr(6,2),10),

core/modules/utils/utils.js

@@ -302,7 +302,7 @@ exports.formatDateString = function(date,template) {
 				return $tw.utils.pad($tw.utils.getHours12(date));
 			}],
 			[/^wYYYY/, function() {
-				return $tw.utils.getYearForWeekNo(date);
+				return $tw.utils.pad($tw.utils.getYearForWeekNo(date),4);
 			}],
 			[/^hh12/, function() {
 				return $tw.utils.getHours12(date);
@@ -311,7 +311,14 @@ exports.formatDateString = function(date,template) {
 				return date.getDate() + $tw.utils.getDaySuffix(date);
 			}],
 			[/^YYYY/, function() {
-				return date.getFullYear();
+				return $tw.utils.pad(date.getFullYear(),4);
+			}],
+			[/^aYYYY/, function() {
+				return $tw.utils.pad(Math.abs(date.getFullYear()),4);
+			}],
+			[/^\{era:([^,\|}]*)\|([^}\|]*)\|([^}]*)\}/, function(match) {
+				var year = date.getFullYear();
+				return year === 0 ? match[2] : (year < 0 ? match[1] : match[3]);
 			}],
 			[/^0hh/, function() {
 				return $tw.utils.pad(date.getHours());
@@ -400,7 +407,7 @@ exports.formatDateString = function(date,template) {
 		$tw.utils.each(matches, function(m) {
 			var match = m[0].exec(t);
 			if(match) {
-				matchString = m[1].call();
+				matchString = m[1].call(null,match);
 				t = t.substr(match[0].length);
 				return false;
 			}

editions/test/tiddlers/tests/test-utils.js

@@ -25,6 +25,16 @@ describe("Utility tests", function() {
 		expect(psa(" [[Tidd\u00a0ler8]] two ")).toEqual(["Tidd\u00a0ler8","two"]);
 	});
 
+	it("should handle parsing a date", function() {
+		var pd = function(v) {
+			return $tw.utils.parseDate(v).toString();
+		};
+		expect(pd("20150428204930183")).toEqual("Tue Apr 28 2015 21:49:30 GMT+0100 (British Summer Time)");
+		expect(pd("-20150428204930183")).toEqual("Sun Apr 28 -2015 20:48:15 GMT-0001 (British Summer Time)");
+		expect(pd("00730428204930183")).toEqual("Fri Apr 28 0073 20:48:15 GMT-0001 (British Summer Time)");
+		expect(pd("-00730428204930183")).toEqual("Thu Apr 28 -0073 20:48:15 GMT-0001 (British Summer Time)");
+	});
+
 	it("should handle base64 encoding emojis", function() {
 		var booksEmoji = "📚";
 		expect(booksEmoji).toBe(booksEmoji);
@@ -62,6 +72,8 @@ describe("Utility tests", function() {
 		var fds = $tw.utils.formatDateString,
 			// nov is month: 10!
 			d = new Date(2014,10,9,17,41,28,542);
+		expect(fds(d,"{era:bce||ce}")).toBe("ce");
+		expect(fds(d,"YYYY")).toBe("2014");
 		expect(fds(d,"DDD DD MMM YYYY")).toBe("Sunday 9 November 2014");
 		expect(fds(d,"ddd hh mm ssss")).toBe("Sun 17 41 2828");
 		expect(fds(d,"MM0DD")).toBe("1109");
@@ -92,6 +104,19 @@ describe("Utility tests", function() {
 		d = new Date(2014,11,29,23,59,59);
 		expect(fds(d,"WW")).toBe("1");
 		expect(fds(d,"wYYYY")).toBe("2015");
+
+		// Negative years
+		d = new Date(-2014,10,9,17,41,28,542);
+		expect(fds(d,"YYYY")).toBe("-2014");
+		expect(fds(d,"aYYYY")).toBe("2014");
+		expect(fds(d,"{era:bce||ce}")).toBe("bce");
+
+		// Zero years
+		d = new Date(0,10,9,17,41,28,542);
+		d.setUTCFullYear(0); // See https://stackoverflow.com/a/5870822
+		expect(fds(d,"YYYY")).toBe("0000");
+		expect(fds(d,"aYYYY")).toBe("0000");
+		expect(fds(d,"{era:bce|z|ce}")).toBe("z");
 	});
 
 	it("should parse text references", function() {

editions/tw5.com/tiddlers/concepts/Date Fields.tid

@@ -1,28 +0,0 @@
-created: 20150117190213631
-modified: 20150124214537000
-tags: Concepts
-title: Date Fields
-type: text/vnd.tiddlywiki
-
-Certain [[fields|TiddlerFields]] of a tiddler are used to store dates and times.
-
-The two standard date fields are <<.field created>> and <<.field modified>>.
-
-Values of date fields are 17-character strings:
-
-* 4 digits for the year
-* 2 digits for the month
-* 2 digits for the day
-* 2 digits for the hour
-* 2 digits for the minute
-* 2 digits for the second
-* 3 digits for the millisecond
-
-To avoid problems arising from differences of time zone, TiddlyWiki always uses [[UTC|https://en.wikipedia.org/wiki/Coordinated_Universal_Time]].
-
-As an example, the <<.field created>> field of this tiddler has the value <<.value """<$view field="created"/>""">>.
-
-Dates can be [[converted to other formats|DateFormat]] for display:
-
-<$macrocall $name="wikitext-example-without-html"
-src="""<$view field="created" format="date" template="DDD DDth MMM YYYY"/>""">

editions/tw5.com/tiddlers/features/DateFormat.tid

@@ -1,48 +0,0 @@
-created: 20140418142957325
-modified: 20180730201626985
-tags: Features
-title: DateFormat
-type: text/vnd.tiddlywiki
-
-When used to display date values (with the `format` attribute set to ''date''), the ViewWidget accepts a `template` attribute that allows the format of the date values to be specified. The format string is processed with the following substitutions:
-
-|!Token |!Substituted Value |
-|`DDD` |Day of week in full (eg, "Monday") |
-|`ddd` |Short day of week (eg, "Mon") |
-|`DD` |Day of month |
-|`0DD` |Adds a leading zero |
-|`DDth` |Adds a suffix |
-|`WW` |ISO-8601 week number of year |
-|`0WW` |Adds a leading zero |
-|`MMM` |Month in full (eg, "July") |
-|`mmm` |Short month (eg, "Jul") |
-|`MM` |Month number |
-|`0MM` |Adds leading zero |
-|`YYYY` |Full year |
-|`YY` |Two digit year |
-|`wYYYY` |Full year with respect to week number |
-|`wYY` |Two digit year with respect to week number |
-|`hh` |Hours |
-|`0hh` |Adds a leading zero |
-|`hh12` |Hours in 12 hour clock |
-|`0hh12` |Hours in 12 hour clock with leading zero |
-|`mm` |Minutes |
-|`0mm` |Minutes with leading zero |
-|`ss` |Seconds |
-|`0ss` |Seconds with leading zero |
-|`XXX` |Milliseconds |
-|`0XXX` |Milliseconds with leading zero |
-|`am` or `pm` |Lower case AM/PM indicator |
-|`AM` or `PM` |Upper case AM/PM indicator |
-|`TZD` |Timezone offset |
-|`\x` |Used to escape a character that would otherwise have special meaning |
-|`[UTC]`|Time-shift the represented date to UTC. Must be at very start of format string|
-
-Note that other text is passed through unchanged, allowing commas, colons or other separators to be used.
-
-! Examples
-
-|!Template |!Output |
-|`DDth MMM YYYY` |16th February 2011 |
-|`DDth MMM \M\M\M YYYY` |16th February MMM 2011 |
-|`DDth mmm YYYY 0hh:0mm:0ss` |16th Feb 2011 11:38:42 |