Add getNextDST() and getLastDST() functions

moment-timezone.js

@@ -161,6 +161,10 @@
 			}
 		},
 
+		getNextTransition : getNextTransition,
+
+		getPreviousTransition : getPreviousTransition,
+
 		parse : function (timestamp) {
 			var target  = +timestamp,
 				offsets = this.offsets,
@@ -362,6 +366,34 @@
 		return cachedGuess;
 	}
 
+	function getNextTransition (dateObject) {
+		var currentTimezone = guess(),
+			time = dateObject ? dateObject.valueOf() : Date.now(),
+			untils = getZone(currentTimezone).untils;
+
+		for(var i = 0; i < untils.length; i++) {
+			if (untils[i] > time) {
+				return new moment(untils[i]);
+			}
+		}
+	}
+
+	function getPreviousTransition (dateObject) {
+		var currentTimezone = guess(),
+			time = dateObject ? dateObject.valueOf() : Date.now(),
+			untils = getZone(currentTimezone).untils,
+			nextDSTIndex;
+
+		for(var i = 0; i < untils.length; i++) {
+			if (untils[i] > time) {
+				nextDSTIndex = i;
+				break;
+			}
+		}
+
+		return new moment(untils[nextDSTIndex - 1]);
+	}
+
 	/************************************
 		Global Methods
 	************************************/
@@ -510,6 +542,8 @@
 	tz.needsOffset  = needsOffset;
 	tz.moveInvalidForward   = true;
 	tz.moveAmbiguousForward = false;
+	tz.getNextTransition   = getNextTransition;
+	tz.getPreviousTransition   = getPreviousTransition;
 
 	/************************************
 		Interface with Moment.js

tests/moment-timezone/get-nearest-transition.js

@@ -0,0 +1,69 @@
+"use strict";
+
+var tz = require("../../").tz;
+var moment = require('../../index');
+
+var guess = tz.prototype.guess;
+var now = Date.prototype.now;
+
+exports.getNextTransition = {
+  setUp : function (done) {
+    tz.prototype.guess = 'America/New_York';
+    Date.now = function() { return 1361481581996 };
+    done();
+  },
+
+  tearDown : function (done) {
+    tz.prototype.guess = guess;
+    Date.now = now;
+    done();
+  },
+
+  "returns moment object with the date of next transition date relative to the moment or date object given as argument" : function (test) {
+    var resultWithDate = tz.getNextTransition(new Date(1461481581996));
+    test.equal(resultWithDate.valueOf(), 1478412000000);
+
+    var resultWithMoment = tz.getNextTransition(moment(1461481581996));
+    test.equal(resultWithMoment.valueOf(), 1478412000000);
+
+    test.done();
+  },
+
+  "when no argument is given, returns moment object with the date of next transition date relative to current time" : function (test) {
+    var result = tz.getNextTransition();
+    test.equal(result.valueOf(), 1362898800000);
+
+    test.done();
+  }
+};
+
+exports.getPreviousTransition = {
+  setUp : function (done) {
+    tz.prototype.guess = 'America/New_York';
+    Date.now = function() { return 1361481581996 };
+    done();
+  },
+
+  tearDown : function (done) {
+    tz.prototype.guess = guess;
+    Date.now = now;
+    done();
+  },
+
+  "returns moment object with the date of previous transition date relative to the moment or date object given as argument" : function (test) {
+    var resultWithDate = tz.getPreviousTransition(new Date(1461481581996));
+    test.equal(resultWithDate.valueOf(), 1457852400000);
+
+    var resultWithMoment = tz.getPreviousTransition(moment(1461481581996));
+    test.equal(resultWithMoment.valueOf(), 1457852400000);
+
+    test.done();
+  },
+
+  "when no argument is given, returns moment object with the date of previous transition date relative to current time" : function (test) {
+    var result = tz.getPreviousTransition();
+    test.equal(result.valueOf(), 1352008800000);
+
+    test.done();
+  }
+};

tests/moment-timezone/zone.js

@@ -1,6 +1,9 @@
 "use strict";
 
 var tz = require("../../").tz;
+var guess = tz.prototype.guess;
+var now = Date.prototype.now;
+var moment = require('../../index');
 
 // gE = 1000; 1E = 100; 2k = 140
 var PACKED = "SomeZone|TIM TAM IAM|60.u 50 60|012101|gE 1E 2k 1E 2k";
@@ -11,12 +14,16 @@ exports.zone = {
 	setUp : function (done) {
 		moveAmbiguousForward = tz.moveAmbiguousForward;
 		moveInvalidForward = tz.moveInvalidForward;
+    tz.prototype.guess = 'America/New_York';
+    Date.now = function() { return 82400000 };
 		done();
 	},
 
 	tearDown : function (done) {
 		tz.moveAmbiguousForward = moveAmbiguousForward;
 		tz.moveInvalidForward = moveInvalidForward;
+    tz.prototype.guess = guess;
+    Date.now = now;
 		done();
 	},
 
@@ -144,5 +151,35 @@ exports.zone = {
 		}
 
 		test.done();
-	}
+	},
+
+  getNextTransition : function (test) {
+    var zone = new tz.Zone(PACKED);
+
+    var resultWithDate = zone.getNextTransition(new Date(65000000));
+    test.equal(resultWithDate.valueOf(), 66000000);
+
+    var resultWithMoment = zone.getNextTransition(moment(65000000));
+    test.equal(resultWithMoment.valueOf(), 66000000);
+
+    var result = zone.getNextTransition();
+    test.equal(result.valueOf(), 88800000);
+
+    test.done();
+  },
+
+  getPreviousTransition : function (test) {
+    var zone = new tz.Zone(PACKED);
+
+    var resultWithDate = zone.getPreviousTransition(new Date(65000000));
+    test.equal(resultWithDate.valueOf(), 60000000);
+
+    var resultWithMoment = zone.getPreviousTransition(moment(65000000));
+    test.equal(resultWithMoment.valueOf(), 60000000);
+
+    var result = zone.getPreviousTransition();
+    test.equal(result.valueOf(), 80400000);
+
+    test.done();
+  }
 };