From dc091263e2bfcacae224de98a538ab2fb0c0ac25 Mon Sep 17 00:00:00 2001
From: Niko Kivel <niko.kivel@psi.ch>
Date: Fri, 26 Mar 2021 15:20:52 +0100
Subject: [PATCH] additional functions for templates

---
 docs/docs/about/templating.md   | 38 +++++++++++++++++++++++++++++++++
 internal/pkg/overlay/overlay.go |  8 ++++---
 2 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/docs/docs/about/templating.md b/docs/docs/about/templating.md
index edc22337..32fb6e42 100644
--- a/docs/docs/about/templating.md
+++ b/docs/docs/about/templating.md
@@ -2,3 +2,41 @@
 id: templating
 title: Templating
 ---
+
+# Templating
+
+## loops
+
+### range
+
+iterate over elements of an array
+
+```go
+{{ range $devname, $netdev := .NetDevs }}
+    # netdev = {{ $netdev.Hwaddr }}
+{{ end }}
+```
+
+#### increment variable in loop
+
+iterate over elements of an array and increment `i` each loop cycle
+
+```go
+{{ $i := 0 }}
+{{ range $devname, $netdev := .NetDevs }}
+    # netdev{{$i}} = {{ $netdev.Hwaddr }}
+    {{ $i = inc $i }}
+{{ end }}
+```
+
+#### decrement
+
+iterate over elements of an array and decrement `i` each loop cycle
+
+```go
+{{ $i := 10 }}
+{{ range $devname, $netdev := .NetDevs }}
+    # netdev{{$i}} = {{ $netdev.Hwaddr }}
+    {{ $i = dec $i }}
+{{ end }}
+```
diff --git a/internal/pkg/overlay/overlay.go b/internal/pkg/overlay/overlay.go
index d8bca3e9..4577bfa1 100644
--- a/internal/pkg/overlay/overlay.go
+++ b/internal/pkg/overlay/overlay.go
@@ -215,22 +215,24 @@ func buildOverlay(nodeList []node.NodeInfo, overlayType string) error {
 				tmpl, err := template.New(path.Base(location)).Funcs(template.FuncMap{
 					"Include":     templateFileInclude,
 					"IncludeFrom": templateContainerFileInclude,
+					"inc": func(i int) int { return i + 1 },
+					"dec": func(i int) int { return i - 1 },
 				}).ParseGlob(path.Join(OverlayDir, destFile+".ww*"))
 				if err != nil {
-					wwlog.Printf(wwlog.ERROR, "%s\n", err)
+					wwlog.Printf(wwlog.ERROR, "template.New %s\n", err)
 					return nil
 				}
 
 				w, err := os.OpenFile(path.Join(tmpDir, destFile), os.O_RDWR|os.O_CREATE, info.Mode())
 				if err != nil {
-					wwlog.Printf(wwlog.ERROR, "%s\n", err)
+					wwlog.Printf(wwlog.ERROR, "path.Join %s\n", err)
 					return err
 				}
 				defer w.Close()
 
 				err = tmpl.Execute(w, t)
 				if err != nil {
-					wwlog.Printf(wwlog.ERROR, "%s\n", err)
+					wwlog.Printf(wwlog.ERROR, "tmpl.Execute %s\n", err)
 					return nil
 				}