From a9fd130980269c132f0d23bc4b7ea7a336fa1a31 Mon Sep 17 00:00:00 2001
From: Aliaksandr Valialkin <valyala@victoriametrics.com>
Date: Tue, 16 Jan 2024 21:02:31 +0200
Subject: [PATCH] app/vmselect/graphite: properly handle -N index for the array
 of N items

This is a follow-up for 70cd09e736752d8b22697b57e24d600bcf358fee
Updates https://github.com/VictoriaMetrics/VictoriaMetrics/pull/5581
---
 app/vmselect/graphite/transform.go      |  8 ++++----
 app/vmselect/graphite/transform_test.go | 14 ++++++++++++++
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/app/vmselect/graphite/transform.go b/app/vmselect/graphite/transform.go
index 7047edf85..9232cca8c 100644
--- a/app/vmselect/graphite/transform.go
+++ b/app/vmselect/graphite/transform.go
@@ -3600,11 +3600,11 @@ func groupSeriesByNodes(ss []*series, nodes []graphiteql.Expr) map[string][]*ser
 }
 
 func getAbsoluteNodeIndex(index, size int) int {
-	// handling the negative index case
-	if index < 0 && index+size > 0 {
-		index = index + size
+	// Handle the negative index case as Python does
+	if index < 0 {
+		index = size + index
 	}
-	if index >= size || index < 0 {
+	if index < 0 || index >= size {
 		return -1
 	}
 	return index
diff --git a/app/vmselect/graphite/transform_test.go b/app/vmselect/graphite/transform_test.go
index 22b918010..ae54e4ed7 100644
--- a/app/vmselect/graphite/transform_test.go
+++ b/app/vmselect/graphite/transform_test.go
@@ -92,4 +92,18 @@ func TestGetAbsoluteNodeIndex(t *testing.T) {
 	f(0, 1, 0)
 	f(-1, 3, 2)
 	f(-3, 1, -1)
+	f(-1, 1, 0)
+	f(-2, 1, -1)
+	f(3, 2, -1)
+	f(2, 2, -1)
+	f(1, 2, 1)
+	f(0, 2, 0)
+	f(-1, 2, 1)
+	f(-2, 2, 0)
+	f(-3, 2, -1)
+	f(-5, 2, -1)
+	f(-1, 100, 99)
+	f(-99, 100, 1)
+	f(-100, 100, 0)
+	f(-101, 100, -1)
 }