From a3092bf2252eb2c47df246210c1a48c2b01d8a5f Mon Sep 17 00:00:00 2001
From: Mateusz Hawrus <mateusz.hawrus@nobl9.com>
Date: Wed, 4 Sep 2024 22:41:16 +0200
Subject: [PATCH 1/2] add lazy loading

---
 pkg/rules/regex.go  | 34 ++++++++++++++++++++++++++++++++++
 pkg/rules/string.go |  9 ++-------
 2 files changed, 36 insertions(+), 7 deletions(-)
 create mode 100644 pkg/rules/regex.go

diff --git a/pkg/rules/regex.go b/pkg/rules/regex.go
new file mode 100644
index 0000000..ebcf9f1
--- /dev/null
+++ b/pkg/rules/regex.go
@@ -0,0 +1,34 @@
+package rules
+
+import (
+	"regexp"
+	"sync"
+)
+
+// nolint: lll
+// Define all regular expressions here:
+var (
+	validUUIDRegexp = lazyRegexCompile(`^[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{12}$`)
+	asciiRegexp     = lazyRegexCompile(`^[\x00-\x7F]*$`)
+)
+
+// lazyRegexCompile returns a function that compiles the regular expression
+// once, when the function is called for the first time.
+// If the function is never called, the regular expression is never compiled,
+// thus saving on performance.
+//
+// All regular expression literals should be compiled using this function.
+//
+// Credits: https://github.com/go-playground/validator/commit/2e1df48b5ab876bdd461bdccc51d109389e7572f
+func lazyRegexCompile(str string) func() *regexp.Regexp {
+	var (
+		regex *regexp.Regexp
+		once  sync.Once
+	)
+	return func() *regexp.Regexp {
+		once.Do(func() {
+			regex = regexp.MustCompile(str)
+		})
+		return regex
+	}
+}
diff --git a/pkg/rules/string.go b/pkg/rules/string.go
index 9354305..3a7fe45 100644
--- a/pkg/rules/string.go
+++ b/pkg/rules/string.go
@@ -73,12 +73,9 @@ func StringDNSLabel() govy.RuleSet[string] {
 	).WithErrorCode(ErrorCodeStringDNSLabel)
 }
 
-var validUUIDRegexp = regexp.
-	MustCompile("^[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{12}$")
-
 // StringUUID ensures property's value is a valid UUID string.
 func StringUUID() govy.Rule[string] {
-	return StringMatchRegexp(validUUIDRegexp,
+	return StringMatchRegexp(validUUIDRegexp(),
 		"00000000-0000-0000-0000-000000000000",
 		"e190c630-8873-11ee-b9d1-0242ac120002",
 		"79258D24-01A7-47E5-ACBB-7E762DE52298").
@@ -86,11 +83,9 @@ func StringUUID() govy.Rule[string] {
 		WithErrorCode(ErrorCodeStringUUID)
 }
 
-var asciiRegexp = regexp.MustCompile("^[\x00-\x7F]*$")
-
 // StringASCII ensures property's value contains only ASCII characters.
 func StringASCII() govy.Rule[string] {
-	return StringMatchRegexp(asciiRegexp).WithErrorCode(ErrorCodeStringASCII)
+	return StringMatchRegexp(asciiRegexp()).WithErrorCode(ErrorCodeStringASCII)
 }
 
 // StringURL ensures property's value is a valid URL as defined by [url.Parse] function.

From 5b7d57e4e8cc58ffd634fd84ca827d150b01cbe4 Mon Sep 17 00:00:00 2001
From: Mateusz Hawrus <mateusz.hawrus@nobl9.com>
Date: Thu, 19 Sep 2024 13:07:15 +0200
Subject: [PATCH 2/2] add tests

---
 pkg/rules/regex_test.go | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)
 create mode 100644 pkg/rules/regex_test.go

diff --git a/pkg/rules/regex_test.go b/pkg/rules/regex_test.go
new file mode 100644
index 0000000..1a50cd8
--- /dev/null
+++ b/pkg/rules/regex_test.go
@@ -0,0 +1,18 @@
+package rules
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestLazyRegexCompile(t *testing.T) {
+	lazyRegexp := lazyRegexCompile("^test$")
+
+	re1 := lazyRegexp()
+	assert.True(t, re1.MatchString("test"))
+	re2 := lazyRegexp()
+	assert.True(t, re2.MatchString("test"))
+
+	assert.True(t, re1 == re2, "both regular expression must be the same pointer")
+}