feat(i18n): support translation context lookup

Co-Authored-By: Virgil <virgil@lethean.io>

service.go

@@ -344,14 +344,13 @@ func (s *Service) resolveWithFallback(messageID string, data any) string {
 }
 
 func (s *Service) tryResolve(lang, key string, data any) string {
-	formality := s.getEffectiveFormality(data)
-	if formality != FormalityNeutral {
-		formalityKey := key + "._" + formality.String()
-		if text := s.resolveMessage(lang, formalityKey, data); text != "" {
+	context, formality := s.getEffectiveContextAndFormality(data)
+	for _, lookupKey := range lookupVariants(key, context, formality) {
+		if text := s.resolveMessage(lang, lookupKey, data); text != "" {
 			return text
 		}
 	}
-	return s.resolveMessage(lang, key, data)
+	return ""
 }
 
 func (s *Service) resolveMessage(lang, key string, data any) string {
@@ -374,6 +373,39 @@ func (s *Service) resolveMessage(lang, key string, data any) string {
 	return text
 }
 
+func (s *Service) getEffectiveContextAndFormality(data any) (string, Formality) {
+	if ctx, ok := data.(*TranslationContext); ok && ctx != nil {
+		formality := ctx.FormalityValue()
+		if formality == FormalityNeutral {
+			formality = s.formality
+		}
+		return ctx.ContextString(), formality
+	}
+	if m, ok := data.(map[string]any); ok {
+		var context string
+		if v, ok := m["Context"].(string); ok {
+			context = core.Trim(v)
+		}
+		if v, ok := m["Formality"]; ok {
+			switch f := v.(type) {
+			case Formality:
+				if f != FormalityNeutral {
+					return context, f
+				}
+			case string:
+				switch core.Lower(f) {
+				case "formal":
+					return context, FormalityFormal
+				case "informal":
+					return context, FormalityInformal
+				}
+			}
+		}
+		return context, s.formality
+	}
+	return "", s.getEffectiveFormality(data)
+}
+
 func (s *Service) getEffectiveFormality(data any) Formality {
 	if ctx, ok := data.(*TranslationContext); ok && ctx != nil {
 		if ctx.Formality != FormalityNeutral {
@@ -403,6 +435,21 @@ func (s *Service) getEffectiveFormality(data any) Formality {
 	return s.formality
 }
 
+func lookupVariants(key, context string, formality Formality) []string {
+	var variants []string
+	if context != "" {
+		if formality != FormalityNeutral {
+			variants = append(variants, key+"._"+context+"._"+formality.String())
+		}
+		variants = append(variants, key+"._"+context)
+	}
+	if formality != FormalityNeutral {
+		variants = append(variants, key+"._"+formality.String())
+	}
+	variants = append(variants, key)
+	return variants
+}
+
 func (s *Service) handleMissingKey(key string, args []any) string {
 	switch s.mode {
 	case ModeStrict:

service_test.go

@@ -202,6 +202,36 @@ func TestServiceFormality(t *testing.T) {
 	}
 }
 
+func TestServiceTranslationContext(t *testing.T) {
+	svc, err := New()
+	if err != nil {
+		t.Fatalf("New() failed: %v", err)
+	}
+
+	svc.AddMessages("en", map[string]string{
+		"direction.right._navigation":          "right",
+		"direction.right._navigation._formal":  "right, sir",
+		"direction.right._correctness":         "correct",
+		"direction.right._correctness._formal": "correct, sir",
+	})
+
+	if got := svc.T("direction.right", C("navigation")); got != "right" {
+		t.Errorf("T(direction.right, C(navigation)) = %q, want %q", got, "right")
+	}
+
+	if got := svc.T("direction.right", C("navigation").Formal()); got != "right, sir" {
+		t.Errorf("T(direction.right, C(navigation).Formal()) = %q, want %q", got, "right, sir")
+	}
+
+	if got := svc.T("direction.right", C("correctness")); got != "correct" {
+		t.Errorf("T(direction.right, C(correctness)) = %q, want %q", got, "correct")
+	}
+
+	if got := svc.T("direction.right", C("correctness").Formal()); got != "correct, sir" {
+		t.Errorf("T(direction.right, C(correctness).Formal()) = %q, want %q", got, "correct, sir")
+	}
+}
+
 func TestServiceDirection(t *testing.T) {
 	svc, err := New()
 	if err != nil {