feat: sync message translation support

internal/domain/translation.go

@@ -0,0 +1,57 @@
+package domain
+
+import "errors"
+
+const (
+	// MaxTranslationTexts matches the largest batch currently issued by TDesktop's
+	// whole-chat translation tracker.
+	MaxTranslationTexts = 20
+	// MaxTranslationInputBytes bounds one upstream request independently of the
+	// MTProto frame limit. TDesktop starts a new batch at the same 24 KiB boundary.
+	MaxTranslationInputBytes = 24 * 1024
+	// MaxTranslationOutputBytes permits language expansion while bounding an
+	// untrusted provider response before TL encoding.
+	MaxTranslationOutputBytes = 4 * MaxTranslationInputBytes
+	MaxTranslationToneRunes   = 64
+)
+
+var (
+	ErrTranslationDisabled            = errors.New("translation disabled")
+	ErrTranslationInputEmpty          = errors.New("translation input empty")
+	ErrTranslationInputTooLong        = errors.New("translation input too long")
+	ErrTranslationLanguageInvalid     = errors.New("translation language invalid")
+	ErrTranslationMessageInvalid      = errors.New("translation message invalid")
+	ErrTranslationPeerInvalid         = errors.New("translation peer invalid")
+	ErrTranslationRateLimited         = errors.New("translation rate limited")
+	ErrTranslationProviderUnavailable = errors.New("translation provider unavailable")
+	ErrTranslationTimeout             = errors.New("translation timeout")
+)
+
+// TranslationText is protocol-neutral text accepted or returned by the
+// translation service. Providers may omit entities when they cannot preserve
+// offsets safely; they must never return stale source offsets for changed text.
+type TranslationText struct {
+	Text     string
+	Entities []MessageEntity
+}
+
+func (t TranslationText) Clone() TranslationText {
+	out := t
+	out.Entities = append([]MessageEntity(nil), t.Entities...)
+	return out
+}
+
+type TranslationRequest struct {
+	UserID int64
+	// Peer+IDs selects stored messages. Texts selects caller-supplied text.
+	// Exactly one mode must be used.
+	Peer   Peer
+	IDs    []int
+	Texts  []TranslationText
+	ToLang string
+	Tone   string
+}
+
+type TranslationResult struct {
+	Texts []TranslationText
+}