Create new point template var template value

Previously users specify `resolution` and `pixelsPerPoint`. This has
been change and the front end will now need to specify `points` which is
the number of points it'd like to get back from the query.

influx/templates.go

@@ -58,6 +58,20 @@ func RenderTemplate(query string, t chronograf.TemplateVar, now time.Time) (stri
 		tv[t.Values[i].Type] = t.Values[i].Value
 	}
 
+	if pts, ok := tv["points"]; ok {
+		points, err := strconv.ParseInt(pts, 0, 64)
+		if err != nil {
+			return "", err
+		}
+
+		dur, err := ParseTime(query, now)
+		if err != nil {
+			return "", err
+		}
+		interval := AutoInterval(points, dur)
+		return strings.Replace(query, t.Var, interval, -1), nil
+	}
+
 	if res, ok := tv["resolution"]; ok {
 		resolution, err := strconv.ParseInt(res, 0, 64)
 		if err != nil {
@@ -82,6 +96,22 @@ func RenderTemplate(query string, t chronograf.TemplateVar, now time.Time) (stri
 	return query, nil
 }
 
+func AutoInterval(points int64, duration time.Duration) string {
+	// The function is: ((total_seconds * millisecond_converstion) / group_by) = pixels / 3
+	// Number of points given the pixels
+	pixels := float64(points)
+	msPerPixel := float64(duration/time.Millisecond) / pixels
+	secPerPixel := float64(duration/time.Second) / pixels
+	if secPerPixel < 1.0 {
+		if msPerPixel < 1.0 {
+			msPerPixel = 1.0
+		}
+		return strconv.FormatInt(int64(msPerPixel), 10) + "ms"
+	}
+	// If groupby is more than 1 second round to the second
+	return strconv.FormatInt(int64(secPerPixel), 10) + "s"
+}
+
 func AutoGroupBy(resolution, pixelsPerPoint int64, duration time.Duration) string {
 	// The function is: ((total_seconds * millisecond_converstion) / group_by) = pixels / 3
 	// Number of points given the pixels

influx/templates_test.go

@@ -125,6 +125,38 @@ func TestTemplateReplace(t *testing.T) {
 			},
 			want: `SELECT :field: FROM "cpu"`,
 		},
+		{
+			name:  "auto interval",
+			query: `SELECT mean(usage_idle) from "cpu" where time > now() - 4320h group by time(:interval:)`,
+			vars: []chronograf.TemplateVar{
+				{
+					Var: ":interval:",
+					Values: []chronograf.TemplateValue{
+						{
+							Value: "333",
+							Type:  "points",
+						},
+					},
+				},
+			},
+			want: `SELECT mean(usage_idle) from "cpu" where time > now() - 4320h group by time(46702s)`,
+		},
+		{
+			name:  "auto interval",
+			query: `SELECT derivative(mean(usage_idle),:interval:) from "cpu" where time > now() - 4320h group by time(:interval:)`,
+			vars: []chronograf.TemplateVar{
+				{
+					Var: ":interval:",
+					Values: []chronograf.TemplateValue{
+						{
+							Value: "333",
+							Type:  "points",
+						},
+					},
+				},
+			},
+			want: `SELECT derivative(mean(usage_idle),46702s) from "cpu" where time > now() - 4320h group by time(46702s)`,
+		},
 		{
 			name:  "auto group by",
 			query: `SELECT mean(usage_idle) from "cpu" where time > now() - 4320h group by :interval:`,
@@ -133,7 +165,7 @@ func TestTemplateReplace(t *testing.T) {
 					Var: ":interval:",
 					Values: []chronograf.TemplateValue{
 						{
-							Value: "1000",
+							Value: "999",
 							Type:  "resolution",
 						},
 						{
@@ -143,7 +175,7 @@ func TestTemplateReplace(t *testing.T) {
 					},
 				},
 			},
-			want: `SELECT mean(usage_idle) from "cpu" where time > now() - 4320h group by time(46655s)`,
+			want: `SELECT mean(usage_idle) from "cpu" where time > now() - 4320h group by time(46702s)`,
 		},
 		{
 			name:  "auto group by without duration",
@@ -153,7 +185,7 @@ func TestTemplateReplace(t *testing.T) {
 					Var: ":interval:",
 					Values: []chronograf.TemplateValue{
 						{
-							Value: "1000",
+							Value: "999",
 							Type:  "resolution",
 						},
 						{
@@ -163,7 +195,7 @@ func TestTemplateReplace(t *testing.T) {
 					},
 				},
 			},
-			want: `SELECT mean(usage_idle) from "cpu" WHERE time > now() - 4320h group by time(46655s)`,
+			want: `SELECT mean(usage_idle) from "cpu" WHERE time > now() - 4320h group by time(46702s)`,
 		},
 		{
 			name:  "auto group by with :dashboardTime:",