optimize session memory and language routing for migration

pkg/agent/language.go

@@ -0,0 +1,108 @@
+package agent
+
+import "strings"
+
+// DetectResponseLanguage returns a BCP-47 style language tag for reply policy.
+// Priority: explicit preference > current user text > last session language > default English.
+func DetectResponseLanguage(userText, preferred, last string) string {
+	if p := normalizeLang(preferred); p != "" {
+		return p
+	}
+	if detected := detectFromText(userText); detected != "" {
+		return detected
+	}
+	if l := normalizeLang(last); l != "" {
+		return l
+	}
+	return "en"
+}
+
+func detectFromText(text string) string {
+	text = strings.TrimSpace(text)
+	if text == "" {
+		return ""
+	}
+
+	var zh, ja, ko, letters int
+	for _, r := range text {
+		switch {
+		case r >= 0x4E00 && r <= 0x9FFF:
+			zh++
+		case r >= 0x3040 && r <= 0x30FF:
+			ja++
+		case r >= 0xAC00 && r <= 0xD7AF:
+			ko++
+		case (r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z'):
+			letters++
+		}
+	}
+
+	// CJK-first heuristic to match user typing language quickly.
+	if zh > 0 {
+		return "zh-CN"
+	}
+	if ja > 0 {
+		return "ja"
+	}
+	if ko > 0 {
+		return "ko"
+	}
+	if letters > 0 {
+		return "en"
+	}
+	return ""
+}
+
+func normalizeLang(lang string) string {
+	lang = strings.TrimSpace(strings.ToLower(lang))
+	switch lang {
+	case "zh", "zh-cn", "zh_hans", "chinese":
+		return "zh-CN"
+	case "en", "en-us", "english":
+		return "en"
+	case "ja", "jp", "japanese":
+		return "ja"
+	case "ko", "kr", "korean":
+		return "ko"
+	default:
+		if lang == "" {
+			return ""
+		}
+		return lang
+	}
+}
+
+// ExtractLanguagePreference detects explicit user instructions for language switch.
+func ExtractLanguagePreference(text string) string {
+	s := strings.ToLower(strings.TrimSpace(text))
+	if s == "" {
+		return ""
+	}
+
+	enHints := []string{"speak english", "reply in english", "use english", "以后用英文", "请用英文", "用英文"}
+	zhHints := []string{"说中文", "用中文", "请用中文", "reply in chinese", "speak chinese"}
+	jaHints := []string{"日本語", "reply in japanese", "speak japanese"}
+	koHints := []string{"한국어", "reply in korean", "speak korean"}
+
+	for _, h := range enHints {
+		if strings.Contains(s, strings.ToLower(h)) {
+			return "en"
+		}
+	}
+	for _, h := range zhHints {
+		if strings.Contains(s, strings.ToLower(h)) {
+			return "zh-CN"
+		}
+	}
+	for _, h := range jaHints {
+		if strings.Contains(s, strings.ToLower(h)) {
+			return "ja"
+		}
+	}
+	for _, h := range koHints {
+		if strings.Contains(s, strings.ToLower(h)) {
+			return "ko"
+		}
+	}
+	return ""
+}