Validate cookie policy link in banner description

Translations are no longer part of the version snapshot, so the
banner_description text must be validated at write time to ensure
the {{cookie_policy_link}} placeholder is present. Without it
the cookie policy URL silently disappears from the rendered banner.

Signed-off-by: Émile Ré <emile@getprobo.com>

pkg/cookiebanner/service.go

@@ -328,7 +328,12 @@ func (r *UpsertCookieBannerTranslationRequest) Validate() error {
 		if json.Unmarshal(raw, &s) != nil {
 			continue
 		}
-		v.Check(s, "translations."+key, validator.NoHTML(), validator.MaxLen(2000))
+
+		validators := []validator.ValidatorFunc{validator.NoHTML(), validator.MaxLen(2000)}
+		if key == "banner_description" {
+			validators = append(validators, validator.ContainsSubstring("{{cookie_policy_link}}"))
+		}
+		v.Check(s, "translations."+key, validators...)
 	}
 
 	return v.Error()

pkg/cookiebanner/service_test.go

@@ -126,6 +126,68 @@ func TestSnapshotsEqual(t *testing.T) {
 	})
 }
 
+func TestUpsertCookieBannerTranslationRequest_Validate(t *testing.T) {
+	t.Parallel()
+
+	bannerID := gid.New(gid.NewTenantID(), coredata.CookieBannerEntityType)
+
+	t.Run("banner_description with cookie_policy_link passes", func(t *testing.T) {
+		t.Parallel()
+
+		translations, err := json.Marshal(map[string]string{
+			"banner_title":       "Cookie Preferences",
+			"banner_description": "We use cookies. {{cookie_policy_link}}",
+		})
+		require.NoError(t, err)
+
+		req := UpsertCookieBannerTranslationRequest{
+			CookieBannerID: bannerID,
+			Language:       "en",
+			Translations:   translations,
+		}
+
+		assert.NoError(t, req.Validate())
+	})
+
+	t.Run("banner_description without cookie_policy_link fails", func(t *testing.T) {
+		t.Parallel()
+
+		translations, err := json.Marshal(map[string]string{
+			"banner_title":       "Cookie Preferences",
+			"banner_description": "We use cookies to improve your experience.",
+		})
+		require.NoError(t, err)
+
+		req := UpsertCookieBannerTranslationRequest{
+			CookieBannerID: bannerID,
+			Language:       "en",
+			Translations:   translations,
+		}
+
+		err = req.Validate()
+		require.Error(t, err)
+		assert.Contains(t, err.Error(), "translations.banner_description")
+	})
+
+	t.Run("translations without banner_description passes", func(t *testing.T) {
+		t.Parallel()
+
+		translations, err := json.Marshal(map[string]string{
+			"banner_title": "Cookie Preferences",
+			"button_save":  "Save",
+		})
+		require.NoError(t, err)
+
+		req := UpsertCookieBannerTranslationRequest{
+			CookieBannerID: bannerID,
+			Language:       "en",
+			Translations:   translations,
+		}
+
+		assert.NoError(t, req.Validate())
+	})
+}
+
 func TestBuildSnapshot_RankInvariant(t *testing.T) {
 	t.Parallel()
 

pkg/validator/validator_string.go

@@ -68,6 +68,30 @@ func MaxLen(maxLength int) ValidatorFunc {
 	}
 }
 
+// ContainsSubstring validates that a string contains the specified substring.
+func ContainsSubstring(substr string) ValidatorFunc {
+	return func(value any) *ValidationError {
+		actualValue, isNil := dereferenceValue(value)
+		if isNil {
+			return nil
+		}
+
+		str, ok := actualValue.(string)
+		if !ok {
+			return newValidationError(ErrorCodeInvalidFormat, "value must be a string")
+		}
+
+		if !strings.Contains(str, substr) {
+			return newValidationError(
+				ErrorCodeInvalidFormat,
+				fmt.Sprintf("must contain %q", substr),
+			)
+		}
+
+		return nil
+	}
+}
+
 // OneOfSlice validates that a value is one of the allowed values in the slice.
 // Accepts a slice of any type. Compares by value first, then by string representation.
 func OneOfSlice[T any](allowed []T) ValidatorFunc {

pkg/validator/validator_string_test.go

@@ -67,6 +67,31 @@ func TestMaxLen(t *testing.T) {
 	}
 }
 
+func TestContainsSubstring(t *testing.T) {
+	tests := []struct {
+		name      string
+		value     any
+		substr    string
+		wantError bool
+	}{
+		{"contains substring", "hello {{cookie_policy_link}} world", "{{cookie_policy_link}}", false},
+		{"missing substring", "hello world", "{{cookie_policy_link}}", true},
+		{"exact match", "{{cookie_policy_link}}", "{{cookie_policy_link}}", false},
+		{"empty string", "", "{{cookie_policy_link}}", true},
+		{"nil pointer", (*string)(nil), "{{cookie_policy_link}}", false},
+		{"non-string", 123, "foo", true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := ContainsSubstring(tt.substr)(tt.value)
+			if (err != nil) != tt.wantError {
+				t.Errorf("ContainsSubstring() error = %v, wantError %v", err, tt.wantError)
+			}
+		})
+	}
+}
+
 func TestOneOf(t *testing.T) {
 	tests := []struct {
 		name      string