Remove First and Last data members from Metrics structs

They can be trivially computed when required.

render/detailed/summary_test.go

@@ -84,8 +84,6 @@ func TestSummaries(t *testing.T) {
 				Samples: nil,
 				Min:     metric.Min,
 				Max:     metric.Max,
-				First:   metric.First,
-				Last:    metric.Last,
 			},
 		}
 		if !reflect.DeepEqual(want, row) {

report/metric_row.go

@@ -82,8 +82,6 @@ func (m *MetricRow) CodecEncodeSelf(encoder *codec.Encoder) {
 		Samples:    in.Samples,
 		Min:        in.Min,
 		Max:        in.Max,
-		First:      in.First,
-		Last:       in.Last,
 	})
 }
 
@@ -95,8 +93,6 @@ func (m *MetricRow) CodecDecodeSelf(decoder *codec.Decoder) {
 		Samples: in.Samples,
 		Min:     in.Min,
 		Max:     in.Max,
-		First:   in.First,
-		Last:    in.Last,
 	}
 	metric := w.FromIntermediate()
 	*m = MetricRow{

report/metrics.go

@@ -48,11 +48,17 @@ func (m Metrics) Copy() Metrics {
 // Metric is a list of timeseries data with some metadata. Clients must use the
 // Add method to add values.  Metrics are immutable.
 type Metric struct {
-	Samples     []Sample
-	Min, Max    float64
-	First, Last time.Time
+	Samples  []Sample
+	Min, Max float64
 }
 
+// Following two functions are exported for testing only: make sure there are samples before calling.
+// First gives the timestamp of the first sample
+func (m Metric) First() time.Time { return m.Samples[0].Timestamp }
+
+// Last gives the timestamp of the last sample
+func (m Metric) Last() time.Time { return m.Samples[len(m.Samples)-1].Timestamp }
+
 // Sample is a single datapoint of a metric.
 type Sample struct {
 	Timestamp time.Time `json:"date"`
@@ -65,8 +71,6 @@ func MakeSingletonMetric(t time.Time, v float64) Metric {
 		Samples: []Sample{{t, v}},
 		Min:     v,
 		Max:     v,
-		First:   t,
-		Last:    t,
 	}
 
 }
@@ -97,8 +101,6 @@ func MakeMetric(samples []Sample) Metric {
 		Samples: samples,
 		Min:     min,
 		Max:     max,
-		First:   samples[0].Timestamp,
-		Last:    samples[len(samples)-1].Timestamp,
 	}
 }
 
@@ -108,8 +110,6 @@ func (m Metric) WithMax(max float64) Metric {
 		Samples: m.Samples,
 		Max:     max,
 		Min:     m.Min,
-		First:   m.First,
-		Last:    m.Last,
 	}
 }
 
@@ -118,20 +118,6 @@ func (m Metric) Len() int {
 	return len(m.Samples)
 }
 
-func first(t1, t2 time.Time) time.Time {
-	if t2.IsZero() || (!t1.IsZero() && t1.Before(t2)) {
-		return t1
-	}
-	return t2
-}
-
-func last(t1, t2 time.Time) time.Time {
-	if t2.IsZero() || (!t1.IsZero() && t1.After(t2)) {
-		return t1
-	}
-	return t2
-}
-
 // Merge combines the two Metrics and returns a new result.
 func (m Metric) Merge(other Metric) Metric {
 
@@ -141,7 +127,7 @@ func (m Metric) Merge(other Metric) Metric {
 		return other
 	case len(other.Samples) == 0:
 		return m
-	case other.First.After(m.Last):
+	case other.First().After(m.Last()):
 		samplesOut := make([]Sample, len(m.Samples)+len(other.Samples))
 		copy(samplesOut, m.Samples)
 		copy(samplesOut[len(m.Samples):], other.Samples)
@@ -149,10 +135,8 @@ func (m Metric) Merge(other Metric) Metric {
 			Samples: samplesOut,
 			Max:     math.Max(m.Max, other.Max),
 			Min:     math.Min(m.Min, other.Min),
-			First:   m.First,
-			Last:    other.Last,
 		}
-	case m.First.After(other.Last):
+	case m.First().After(other.Last()):
 		samplesOut := make([]Sample, len(m.Samples)+len(other.Samples))
 		copy(samplesOut, other.Samples)
 		copy(samplesOut[len(other.Samples):], m.Samples)
@@ -160,8 +144,6 @@ func (m Metric) Merge(other Metric) Metric {
 			Samples: samplesOut,
 			Max:     math.Max(m.Max, other.Max),
 			Min:     math.Min(m.Min, other.Min),
-			First:   other.First,
-			Last:    m.Last,
 		}
 	}
 
@@ -194,8 +176,6 @@ func (m Metric) Merge(other Metric) Metric {
 		Samples: samplesOut,
 		Max:     math.Max(m.Max, other.Max),
 		Min:     math.Min(m.Min, other.Min),
-		First:   first(m.First, other.First),
-		Last:    last(m.Last, other.Last),
 	}
 }
 
@@ -214,8 +194,6 @@ type WireMetrics struct {
 	Samples []Sample `json:"samples,omitempty"`
 	Min     float64  `json:"min"`
 	Max     float64  `json:"max"`
-	First   string   `json:"first,omitempty"`
-	Last    string   `json:"last,omitempty"`
 	dummySelfer
 }
 
@@ -241,8 +219,6 @@ func (m Metric) ToIntermediate() WireMetrics {
 		Samples: m.Samples,
 		Max:     m.Max,
 		Min:     m.Min,
-		First:   renderTime(m.First),
-		Last:    renderTime(m.Last),
 	}
 }
 
@@ -253,8 +229,6 @@ func (m WireMetrics) FromIntermediate() Metric {
 		Samples: m.Samples,
 		Max:     m.Max,
 		Min:     m.Min,
-		First:   parseTime(m.First),
-		Last:    parseTime(m.Last),
 	}
 }
 

report/metrics_internal_test.go

@@ -1,29 +0,0 @@
-package report
-
-import (
-	"testing"
-	"time"
-)
-
-func TestFirstLast(t *testing.T) {
-	zero, t1, t2 := time.Time{}, time.Now(), time.Now().Add(1*time.Minute)
-	tests := []struct {
-		arg1, arg2, first, last time.Time
-	}{
-		{zero, zero, zero, zero},
-		{t1, zero, t1, t1},
-		{zero, t1, t1, t1},
-		{t1, t1, t1, t1},
-		{t1, t2, t1, t2},
-		{t2, t1, t1, t2},
-	}
-	for _, test := range tests {
-		if got := first(test.arg1, test.arg2); !got.Equal(test.first) {
-			t.Errorf("first(%q, %q) => %q, Expected: %q", test.arg1, test.arg2, got, test.first)
-		}
-
-		if got := last(test.arg1, test.arg2); !got.Equal(test.last) {
-			t.Errorf("last(%q, %q) => %q, Expected: %q", test.arg1, test.arg2, got, test.last)
-		}
-	}
-}

report/metrics_test.go

@@ -50,11 +50,11 @@ func TestMetricsCopy(t *testing.T) {
 }
 
 func checkMetric(t *testing.T, metric report.Metric, first, last time.Time, min, max float64) {
-	if !metric.First.Equal(first) {
-		t.Errorf("Expected metric.First == %q, but was: %q", first, metric.First)
+	if !metric.First().Equal(first) {
+		t.Errorf("Expected metric.First == %q, but was: %q", first, metric.First())
 	}
-	if !metric.Last.Equal(last) {
-		t.Errorf("Expected metric.Last == %q, but was: %q", last, metric.Last)
+	if !metric.Last().Equal(last) {
+		t.Errorf("Expected metric.Last == %q, but was: %q", last, metric.Last())
 	}
 	if metric.Min != min {
 		t.Errorf("Expected metric.Min == %f, but was: %f", min, metric.Min)
@@ -65,9 +65,6 @@ func checkMetric(t *testing.T, metric report.Metric, first, last time.Time, min,
 }
 
 func TestMetricFirstLastMinMax(t *testing.T) {
-
-	checkMetric(t, report.MakeMetric(nil), time.Time{}, time.Time{}, 0.0, 0.0)
-
 	t1 := time.Now()
 	t2 := time.Now().Add(1 * time.Minute)
 
@@ -103,18 +100,7 @@ func TestMetricMerge(t *testing.T) {
 	}
 
 	// Check it didn't modify metric1
-	if !metric1.First.Equal(t2) {
-		t.Errorf("Expected metric1.First == %q, but was: %q", t2, metric1.First)
-	}
-	if !metric1.Last.Equal(t3) {
-		t.Errorf("Expected metric1.Last == %q, but was: %q", t3, metric1.Last)
-	}
-	if metric1.Min != 0.2 {
-		t.Errorf("Expected metric1.Min == %f, but was: %f", 0.2, metric1.Min)
-	}
-	if metric1.Max != 0.31 {
-		t.Errorf("Expected metric1.Max == %f, but was: %f", 0.31, metric1.Max)
-	}
+	checkMetric(t, metric1, t2, t3, 0.2, 0.31)
 
 	// Check the result is not the same instance as metric1
 	if &metric1 == &have {