refactor backend API structure

internal/httpapi/openai/shared/handler_errors.go

@@ -0,0 +1,63 @@
+package shared
+
+import "net/http"
+
+func WriteOpenAIError(w http.ResponseWriter, status int, message string) {
+	WriteOpenAIErrorWithCode(w, status, message, "")
+}
+
+func WriteOpenAIErrorWithCode(w http.ResponseWriter, status int, message, code string) {
+	if code == "" {
+		code = OpenAIErrorCode(status)
+	}
+	WriteJSON(w, status, map[string]any{
+		"error": map[string]any{
+			"message": message,
+			"type":    OpenAIErrorType(status),
+			"code":    code,
+			"param":   nil,
+		},
+	})
+}
+
+func OpenAIErrorType(status int) string {
+	switch status {
+	case http.StatusBadRequest:
+		return "invalid_request_error"
+	case http.StatusUnauthorized:
+		return "authentication_error"
+	case http.StatusForbidden:
+		return "permission_error"
+	case http.StatusTooManyRequests:
+		return "rate_limit_error"
+	case http.StatusServiceUnavailable:
+		return "service_unavailable_error"
+	default:
+		if status >= 500 {
+			return "api_error"
+		}
+		return "invalid_request_error"
+	}
+}
+
+func OpenAIErrorCode(status int) string {
+	switch status {
+	case http.StatusBadRequest:
+		return "invalid_request"
+	case http.StatusUnauthorized:
+		return "authentication_failed"
+	case http.StatusForbidden:
+		return "forbidden"
+	case http.StatusTooManyRequests:
+		return "rate_limit_exceeded"
+	case http.StatusNotFound:
+		return "not_found"
+	case http.StatusServiceUnavailable:
+		return "service_unavailable"
+	default:
+		if status >= 500 {
+			return "internal_error"
+		}
+		return "invalid_request"
+	}
+}