Allow tooltipFormat to be a function. Provide a default tooltipFormat

docs/axes/cartesian/time.md

@@ -33,7 +33,7 @@ The following options are provided by the time scale. They are all located in th
 | `min` | [Time](#date-formats) | | If defined, this will override the data minimum
 | `parser` | `String` or `Function` | | Custom parser for dates. [more...](#parser)
 | `round` | `String` | `false` | If defined, dates will be rounded to the start of this unit. See [Time Units](#time-units) below for the allowed units.
-| `tooltipFormat` | `String` | | The moment js format string to use for the tooltip.
+| `tooltipFormat` | `String` or `Function` | | The Moment.js format string to use for the tooltip. [more...](#tooltip-format)
 | `unit` | `String` | `false` | If defined, will force the unit to be a certain type. See [Time Units](#time-units) section below for details.
 | `stepSize` | `Number` | `1` | The number of units between grid lines.
 | `minUnit` | `String` | `'millisecond'` | The minimum display format to be used for a time unit.
@@ -107,6 +107,11 @@ var chart = new Chart(ctx, {
 ```
 
 ### Parser
-If this property is defined as a string, it is interpreted as a custom format to be used by moment to parse the date. 
+If this property is defined as a string, it is interpreted as a custom format to be used by Moment.js to parse the date. 
 
-If this is a function, it must return a moment.js object given the appropriate data value.
+If this is a function, it must return a Moment.js object given the appropriate data value.
+
+### Tooltip Format
+If this property is defined as a string, it is interpreted as a custom format to be used by Moment.js to format the date. 
+
+If this is a function, it must return a custom format to be used by Moment.js to format the date given a Moment.js object, the index of the dataset, and index within the dataset.

src/scales/scale.time.js

@@ -213,6 +213,11 @@ function parse(input, scale) {
 /**
  * Returns the number of unit to skip to be able to display up to `capacity` number of ticks
  * in `unit` for the given `min` / `max` range and respecting the interval steps constraints.
+ * @param min {number} minimum tick millis
+ * @param max {number} maximum tick millis
+ * @param unit {string} the time unit the ticks are being displayed as
+ * @param capacity {number} the number of labels we have room to display
+ * @return {string} the number of ticks to skip before displaying the next one
  */
 function determineStepSize(min, max, unit, capacity) {
 	var range = max - min;
@@ -329,6 +334,19 @@ function ticksFromTimestamps(values, majorUnit) {
 	return ticks;
 }
 
+/**
+ * Show the most specific time format by default
+ */
+function defaultTooltipFormat(momentDate) {
+	if (momentDate.millisecond() !== 0) {
+		return 'MMM D, YYYY h:mm:ss.SSS a';
+	}
+	if (momentDate.second() !== 0 || momentDate.minute() !== 0 || momentDate.hour() !== 0) {
+		return 'MMM D, YYYY h:mm:ss a';
+	}
+	return 'MMM D, YYYY';
+}
+
 module.exports = function(Chart) {
 
 	var defaultConfig = {
@@ -342,6 +360,7 @@ module.exports = function(Chart) {
 			displayFormat: false, // DEPRECATED
 			isoWeekday: false, // override week start day - see http://momentjs.com/docs/#/get-set/iso-weekday/
 			minUnit: 'millisecond',
+			tooltipFormat: defaultTooltipFormat,
 
 			// defaults to unit's corresponding unitFormat below or override using pattern string from http://momentjs.com/docs/#/displaying/format/
 			displayFormats: {
@@ -549,17 +568,20 @@ module.exports = function(Chart) {
 			var me = this;
 			var data = me.chart.data;
 			var timeOpts = me.options.time;
+			var tooltipFormat = timeOpts.tooltipFormat;
 			var label = data.labels && index < data.labels.length ? data.labels[index] : '';
 			var value = data.datasets[datasetIndex].data[index];
+			var momentDate;
 
-			if (helpers.isObject(value)) {
-				label = me.getRightValue(value);
-			}
-			if (timeOpts.tooltipFormat) {
-				label = momentify(label, timeOpts).format(timeOpts.tooltipFormat);
+			if (!helpers.isObject(value)) {
+				return label;
 			}
 
-			return label;
+			momentDate = momentify(me.getRightValue(value), timeOpts);
+			tooltipFormat = typeof tooltipFormat === 'function'
+				? tooltipFormat.call(me, momentDate, datasetIndex, index)
+				: tooltipFormat;
+			return momentDate.format(tooltipFormat);
 		},
 
 		/**

test/specs/scale.time.tests.js

@@ -109,6 +109,7 @@ describe('Time scale tests', function() {
 				isoWeekday: false,
 				displayFormat: false,
 				minUnit: 'millisecond',
+				tooltipFormat: defaultConfig.time.tooltipFormat,
 				displayFormats: {
 					millisecond: 'h:mm:ss.SSS a', // 11:20:01.123 AM
 					second: 'h:mm:ss a', // 11:20:01 AM