feat: storage, language rules and migration

internal/domain/language/languageDomain.go

@@ -0,0 +1,74 @@
+package language
+
+import (
+	"errors"
+	"regexp"
+	"slices"
+	"strings"
+)
+
+var (
+	ErrInvalidLanguage     = errors.New("invalid language tag")
+	ErrUnsupportedLanguage = errors.New("unsupported language")
+	ErrNoDefaultLanguage   = errors.New("the site has no default language")
+)
+
+const (
+	Unassigned   = ""
+	MaxTagLength = 35
+)
+
+var supported = []string{"en", "en-GB", "en-US", "fr", "fr-CA", "pt", "pt-BR", "es", "de", "ar"}
+
+var tagPattern = regexp.MustCompile(`^([A-Za-z]{2,3})(?:-([A-Za-z]{2}))?$`)
+
+func Supported() []string {
+	return slices.Clone(supported)
+}
+
+func Normalize(tag string) (string, error) {
+	parts := tagPattern.FindStringSubmatch(strings.TrimSpace(tag))
+	if parts == nil {
+		return "", ErrInvalidLanguage
+	}
+	normalized := strings.ToLower(parts[1])
+	if parts[2] != "" {
+		normalized += "-" + strings.ToUpper(parts[2])
+	}
+	if !slices.Contains(supported, normalized) {
+		return "", ErrUnsupportedLanguage
+	}
+	return normalized, nil
+}
+
+type Suggestion struct {
+	Tag         string
+	Found       bool
+	Substituted bool
+}
+
+func Suggest(locale *string) Suggestion {
+	if locale == nil {
+		return Suggestion{}
+	}
+	tag, err := Normalize(*locale)
+	if err == nil {
+		return Suggestion{Tag: tag, Found: true}
+	}
+	if !errors.Is(err, ErrUnsupportedLanguage) {
+		return Suggestion{}
+	}
+	base, _, _ := strings.Cut(strings.TrimSpace(*locale), "-")
+	if fallback, err := Normalize(base); err == nil {
+		return Suggestion{Tag: fallback, Found: true, Substituted: true}
+	}
+	return Suggestion{}
+}
+
+type SiteLanguage struct {
+	SiteID    uint32
+	Tag       string
+	IsDefault bool
+	Enabled   bool
+	Confirmed bool
+}