Add "before" and "after" filter operators

Fixes #357 by adding new “before” and “after” filter operators.

core/modules/filters/after.js

@@ -0,0 +1,31 @@
+/*\
+title: $:/core/modules/filters/after.js
+type: application/javascript
+module-type: filteroperator
+
+Filter operator returning the tiddler from the current list that is after the tiddler named in the operand.
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+/*
+Export our filter function
+*/
+exports.after = function(source,operator,options) {
+	var results = [];
+	source(function(tiddler,title) {
+		results.push(title);
+	});
+	var index = results.indexOf(operator.operand);
+	if(index === -1 || index > (results.length - 2)) {
+		return [];
+	} else {
+		return [results[index + 1]];
+	}
+};
+
+})();

core/modules/filters/before.js

@@ -0,0 +1,31 @@
+/*\
+title: $:/core/modules/filters/before.js
+type: application/javascript
+module-type: filteroperator
+
+Filter operator returning the tiddler from the current list that is before the tiddler named in the operand.
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+/*
+Export our filter function
+*/
+exports.before = function(source,operator,options) {
+	var results = [];
+	source(function(tiddler,title) {
+		results.push(title);
+	});
+	var index = results.indexOf(operator.operand);
+	if(index <= 0) {
+		return [];
+	} else {
+		return [results[index - 1]];
+	}
+};
+
+})();

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

@@ -269,6 +269,15 @@ describe("Filter tests", function() {
 		expect(wiki.filterTiddlers("[modifier{!!modifier}] +[sort[title]]",fakeWidget).join(",")).toBe("$:/TiddlerTwo,a fourth tiddler,one,Tiddler Three");
 	});
 
+	it("should handle the before and after operators", function() {
+		expect(wiki.filterTiddlers("[list[TiddlerSeventh]after[TiddlerOne]]").join(",")).toBe("Tiddler Three");
+		expect(wiki.filterTiddlers("[list[TiddlerSeventh]after[a fourth tiddler]]").join(",")).toBe("MissingTiddler");
+		expect(wiki.filterTiddlers("[list[TiddlerSeventh]after[MissingTiddler]]").join(",")).toBe("");
+		expect(wiki.filterTiddlers("[list[TiddlerSeventh]before[TiddlerOne]]").join(",")).toBe("");
+		expect(wiki.filterTiddlers("[list[TiddlerSeventh]before[a fourth tiddler]]").join(",")).toBe("Tiddler Three");
+		expect(wiki.filterTiddlers("[list[TiddlerSeventh]before[MissingTiddler]]").join(",")).toBe("a fourth tiddler");
+	});
+
 });
 
 })();

editions/tw5.com/tiddlers/filters/FilterOperator after.tid

@@ -0,0 +1,20 @@
+created: 20140512103123179
+modified: 20140512103123179
+tags: filters
+title: FilterOperator: after
+type: text/vnd.tiddlywiki
+
+The ''after'' filter operator returns the tiddler from the current list that is after the tiddler named in the operand.
+
+The following examples assume a tiddler called `MyList` with a `list` field containing:
+
+```
+one two three four five
+```
+
+|!Filter String |!Description |
+|`[list[MyList]after[two]]` |Returns `three` |
+|`[list[MyList]after[five]]` |Returns an empty list |
+|`[list[MyList]after{!!title}]` |Returns `five` if the current tiddler is `four` |
+
+See also [[FilterOperator: before]], [[FilterOperator: previous]] and [[FilterOperator: next]].

editions/tw5.com/tiddlers/filters/FilterOperator before.tid

@@ -0,0 +1,20 @@
+created: 20140512103123179
+modified: 20140512103123179
+tags: filters
+title: FilterOperator: before
+type: text/vnd.tiddlywiki
+
+The ''before'' filter operator returns the tiddler from the current list that is before the tiddler named in the operand.
+
+The following examples assume a tiddler called `MyList` with a `list` field containing:
+
+```
+one two three four five
+```
+
+|!Filter String |!Description |
+|`[list[MyList]before[two]]` |Returns `one` |
+|`[list[MyList]before[one]]` |Returns an empty list |
+|`[list[MyList]before{!!title}]` |Returns `three` if the current tiddler is `four` |
+
+See also [[FilterOperator: after]], [[FilterOperator: previous]] and [[FilterOperator: next]].