template: add filter, ignore and join string helpers

Signed-off-by: Alexander Yastrebov <alexander.yastrebov@zalando.de>

provisioner/template.go

@@ -13,6 +13,7 @@ import (
 	"net"
 	"net/url"
 	"path"
+	"regexp"
 	"sort"
 	"strconv"
 	"strings"
@@ -107,6 +108,9 @@ func renderTemplate(context *templateContext, file string) (string, error) {
 		"azID":                 azID,
 		"azCount":              azCount,
 		"split":                split,
+		"join":                 join,
+		"filter":               filter,
+		"ignore":               ignore,
 		"mountUnitName":        mountUnitName,
 		"accountID":            accountID,
 		"portRanges":           portRanges,
@@ -274,6 +278,42 @@ func split(s string, d string) []string {
 	return strings.Split(s, d)
 }
 
+// join is a template function that returns a single string of slice elements joined with a separator.
+func join(sep string, elems []string) string {
+	// arguments in reverse order to enable piped calls
+	return strings.Join(elems, sep)
+}
+
+// filter is a template function that takes a regexp, a slice of strings and returns the slice of matching elements.
+func filter(pattern string, elems []string) ([]string, error) {
+	var result []string
+	for _, e := range elems {
+		matched, err := regexp.MatchString(pattern, e)
+		if err != nil {
+			return nil, err
+		}
+		if matched {
+			result = append(result, e)
+		}
+	}
+	return result, nil
+}
+
+// ignore is a template function that takes a regexp, a slice of strings and returns the slice of non-matching elements.
+func ignore(pattern string, elems []string) ([]string, error) {
+	var result []string
+	for _, e := range elems {
+		matched, err := regexp.MatchString(pattern, e)
+		if err != nil {
+			return nil, err
+		}
+		if !matched {
+			result = append(result, e)
+		}
+	}
+	return result, nil
+}
+
 // accountID returns just the ID part of an account
 func accountID(account string) (string, error) {
 	items := strings.Split(account, ":")

provisioner/template_test.go

@@ -943,7 +943,7 @@ CWeOoA==
 	require.Equal(t, "2022-06-10T10:06:43Z", res)
 }
 
-func TestSubQuantity(t *testing.T) {
+func TestSumQuantities(t *testing.T) {
 	for _, tc := range []struct {
 		name     string
 		template string
@@ -998,3 +998,40 @@ func TestAWSValidID(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, "aws__12345678910__eu-central-1__kube-1", result)
 }
+
+func TestJoinFilterIgnore(t *testing.T) {
+	for _, tc := range []struct {
+		name     string
+		template string
+		data     interface{}
+		expected string
+	}{
+		{
+			name:     "filter",
+			template: `{{ split "k8s.io/foo,zalando.org/bar,k8s.io/baz,zalando.org/qux" "," | filter "^zalando[.]org" | join "," }}`,
+			expected: "zalando.org/bar,zalando.org/qux",
+		},
+		{
+			name:     "lines to comma-separated double-quoted list",
+			template: `{{ split .Values.data.lines "\n" | ignore "^#" | ignore "^\\s*$" | join "\", \"" | printf "\"%s\"" }}`,
+			data: map[string]interface{}{
+				"lines": `
+# comments like this are ignored
+foo
+bar
+
+# empty line above and white spaces below are also ignored
+	
+baz
+`,
+			},
+			expected: `"foo", "bar", "baz"`,
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			res, err := renderSingle(t, tc.template, tc.data)
+			require.NoError(t, err)
+			require.Equal(t, tc.expected, res)
+		})
+	}
+}