From 1f87cdbf0885f8c131652f7a0318b2cef4f63eb6 Mon Sep 17 00:00:00 2001
From: Stefan Koelle <50440224+skoelle@users.noreply.github.com>
Date: Sun, 9 Aug 2026 13:49:38 +0200
Subject: [PATCH] Add pure template-resolution logic (kctl.ResolveTemplate)
 with unit tests

---
 internal/kctl/template.go      | 16 +++++++++++++
 internal/kctl/template_test.go | 41 ++++++++++++++++++++++++++++++++++
 2 files changed, 57 insertions(+)
 create mode 100644 internal/kctl/template.go
 create mode 100644 internal/kctl/template_test.go

diff --git a/internal/kctl/template.go b/internal/kctl/template.go
new file mode 100644
index 0000000..c2fb4f5
--- /dev/null
+++ b/internal/kctl/template.go
@@ -0,0 +1,16 @@
+package kctl
+
+import "strings"
+
+// ResolveTemplate replaces "{key}" placeholders in template with the
+// corresponding value from values. Placeholders with no matching key are
+// left untouched, so a misconfigured template is visible (e.g. a literal
+// "{typo}" in the result) instead of silently collapsing to an empty
+// string.
+func ResolveTemplate(template string, values map[string]string) string {
+	result := template
+	for k, v := range values {
+		result = strings.ReplaceAll(result, "{"+k+"}", v)
+	}
+	return result
+}
diff --git a/internal/kctl/template_test.go b/internal/kctl/template_test.go
new file mode 100644
index 0000000..1e5f3ae
--- /dev/null
+++ b/internal/kctl/template_test.go
@@ -0,0 +1,41 @@
+package kctl
+
+import "testing"
+
+func TestResolveTemplate_SinglePlaceholder(t *testing.T) {
+	got := ResolveTemplate("secret-{namespace}", map[string]string{"namespace": "example-ns"})
+	want := "secret-example-ns"
+	if got != want {
+		t.Fatalf("got %q, want %q", got, want)
+	}
+}
+
+func TestResolveTemplate_MultiplePlaceholders(t *testing.T) {
+	template := "arn:aws:eks:{region}:{account_id}:cluster/tf-{env}-{context}-1"
+	values := map[string]string{
+		"region":     "eu-central-1",
+		"account_id": "123456789012",
+		"env":        "beta",
+		"context":    "internal",
+	}
+	got := ResolveTemplate(template, values)
+	want := "arn:aws:eks:eu-central-1:123456789012:cluster/tf-beta-internal-1"
+	if got != want {
+		t.Fatalf("got %q, want %q", got, want)
+	}
+}
+
+func TestResolveTemplate_UnknownPlaceholderLeftAsIs(t *testing.T) {
+	got := ResolveTemplate("secret-{unknown}", map[string]string{"namespace": "example-ns"})
+	want := "secret-{unknown}"
+	if got != want {
+		t.Fatalf("got %q, want %q", got, want)
+	}
+}
+
+func TestResolveTemplate_EmptyTemplate(t *testing.T) {
+	got := ResolveTemplate("", map[string]string{"namespace": "example-ns"})
+	if got != "" {
+		t.Fatalf("expected empty result, got %q", got)
+	}
+}