From e0dbc8c5612a4994fc10d16632641e2650a245e8 Mon Sep 17 00:00:00 2001
From: Julius Volz <julius@soundcloud.com>
Date: Sat, 16 Mar 2013 01:29:21 -0700
Subject: [PATCH] Fix edge cases in data extraction for point and interval ops.

---
 storage/metric/operation.go | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/storage/metric/operation.go b/storage/metric/operation.go
index 9abb3796a..ef7ea2dbe 100644
--- a/storage/metric/operation.go
+++ b/storage/metric/operation.go
@@ -104,13 +104,23 @@ func extractValuesAroundTime(t time.Time, in []model.SamplePair) (out []model.Sa
 	i := sort.Search(len(in), func(i int) bool {
 		return !in[i].Timestamp.Before(t)
 	})
-	switch i {
-	case len(in):
+	if i == len(in) {
+		// Target time is past the end, return only the last sample.
 		out = in[len(in)-1:]
-	case 0:
-		out = append(out, in[0:1]...)
-	default:
-		out = append(out, in[i-1:i+1]...)
+	} else {
+		if in[i].Timestamp.Equal(t) && len(in) > i+1 {
+			// We hit exactly the current sample time. Very unlikely in practice.
+			// Return only the current sample.
+			out = append(out, in[i])
+		} else {
+			if i == 0 {
+				// We hit before the first sample time. Return only the first sample.
+				out = append(out, in[0:1]...)
+			} else {
+				// We hit between two samples. Return both surrounding samples.
+				out = append(out, in[i-1:i+1]...)
+			}
+		}
 	}
 	return
 }