feat(html): add context locale setters

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

context.go

@@ -87,3 +87,31 @@ func NewContextWithService(svc Translator, locale ...string) *Context {
 	applyLocaleToService(ctx.service, ctx.Locale)
 	return ctx
 }
+
+// SetService swaps the translator used by the context and reapplies the
+// current locale to it.
+// Example: ctx.SetService(svc).
+func (ctx *Context) SetService(svc Translator) *Context {
+	if ctx == nil {
+		return nil
+	}
+
+	ensureContextDefaults(ctx)
+	ctx.service = svc
+	applyLocaleToService(ctx.service, ctx.Locale)
+	return ctx
+}
+
+// SetLocale updates the context locale and reapplies it to the active
+// translator.
+// Example: ctx.SetLocale("en-US").
+func (ctx *Context) SetLocale(locale string) *Context {
+	if ctx == nil {
+		return nil
+	}
+
+	ensureContextDefaults(ctx)
+	ctx.Locale = locale
+	applyLocaleToService(ctx.service, ctx.Locale)
+	return ctx
+}

context_test.go

@@ -62,6 +62,51 @@ func TestContext_NewContextWithService_UsesLocale(t *testing.T) {
 	}
 }
 
+func TestContext_SetLocale_ReappliesToTranslator(t *testing.T) {
+	svc := &localeTranslator{}
+	ctx := NewContextWithService(svc, "en-GB")
+
+	ctx.SetLocale("fr-FR")
+
+	if ctx.Locale != "fr-FR" {
+		t.Fatalf("SetLocale should update context locale, got %q", ctx.Locale)
+	}
+	if svc.language != "fr" {
+		t.Fatalf("SetLocale should reapply locale to translator, got %q", svc.language)
+	}
+	if got := Text("prompt.yes").Render(ctx); got != "o" {
+		t.Fatalf("SetLocale translation = %q, want %q", got, "o")
+	}
+}
+
+func TestContext_SetService_ReappliesCurrentLocale(t *testing.T) {
+	ctx := NewContext("fr-FR")
+	svc := &localeTranslator{}
+
+	ctx.SetService(svc)
+
+	if ctx.service != svc {
+		t.Fatalf("SetService should replace the active translator")
+	}
+	if svc.language != "fr" {
+		t.Fatalf("SetService should apply the existing locale to the new translator, got %q", svc.language)
+	}
+	if got := Text("prompt.yes").Render(ctx); got != "o" {
+		t.Fatalf("SetService translation = %q, want %q", got, "o")
+	}
+}
+
+func TestContext_Setters_NilReceiver(t *testing.T) {
+	var ctx *Context
+
+	if got := ctx.SetLocale("en-GB"); got != nil {
+		t.Fatalf("nil Context.SetLocale should return nil, got %v", got)
+	}
+	if got := ctx.SetService(&localeTranslator{}); got != nil {
+		t.Fatalf("nil Context.SetService should return nil, got %v", got)
+	}
+}
+
 func TestText_RenderFallsBackToDefaultTranslator(t *testing.T) {
 	svc, _ := i18n.New()
 	i18n.SetDefault(svc)