From ccc2f5b90cdaeb4875371e963854e131ea44ea17 Mon Sep 17 00:00:00 2001
From: Ben McCann <ben@benmccann.com>
Date: Wed, 27 Dec 2017 17:25:07 -0800
Subject: [PATCH] Format the label in the time scale tooltip

---
 src/scales/scale.time.js | 32 +++++++++++++++++++++++++++++---
 1 file changed, 29 insertions(+), 3 deletions(-)

diff --git a/src/scales/scale.time.js b/src/scales/scale.time.js
index 90904f9e6f0..3275c72a5a0 100644
--- a/src/scales/scale.time.js
+++ b/src/scales/scale.time.js
@@ -403,6 +403,31 @@ function ticksFromTimestamps(values, majorUnit) {
 	return ticks;
 }
 
+function determineLabelFormat(data, timeOpts) {
+	var i, momentDate, hasTime;
+	var ilen = data.length;
+
+	if (timeOpts.tooltipFormat) {
+		return timeOpts.tooltipFormat;
+	}
+
+	// find the label with the most parts (milliseconds, minutes, etc.)
+	// format all labels with the same level of detail as the most specific label
+	for (i = 0; i < ilen; i++) {
+		momentDate = momentify(data[i], timeOpts);
+		if (momentDate.millisecond() !== 0) {
+			return 'MMM D, YYYY h:mm:ss.SSS a';
+		}
+		if (momentDate.second() !== 0 || momentDate.minute() !== 0 || momentDate.hour() !== 0) {
+			hasTime = true;
+		}
+	}
+	if (hasTime) {
+		return 'MMM D, YYYY h:mm:ss a';
+	}
+	return 'MMM D, YYYY';
+}
+
 module.exports = function(Chart) {
 
 	var defaultConfig = {
@@ -621,6 +646,7 @@ module.exports = function(Chart) {
 			me._majorUnit = determineMajorUnit(me._unit);
 			me._table = buildLookupTable(me._timestamps.data, min, max, options.distribution);
 			me._offsets = computeOffsets(me._table, ticks, min, max, options);
+			me._labelFormat = determineLabelFormat(me._timestamps.data, timeOpts);
 
 			return ticksFromTimestamps(ticks, me._majorUnit);
 		},
@@ -635,11 +661,11 @@ module.exports = function(Chart) {
 			if (helpers.isObject(value)) {
 				label = me.getRightValue(value);
 			}
-			if (timeOpts.tooltipFormat) {
-				label = momentify(label, timeOpts).format(timeOpts.tooltipFormat);
+			if (typeof label === 'string') {
+				return label;
 			}
 
-			return label;
+			return momentify(label, timeOpts).format(me._labelFormat);
 		},
 
 		/**