// Package grpcerrors defines well-known error signals shared between backends
// (which produce them) and the router (which consumes them). Go error types do
// not survive the gRPC boundary, so these conditions are carried as gRPC status
// codes and detected via the code rather than by matching the error message.
package grpcerrors

import (
	"strings"

	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/status"
)

// ModelNotLoaded returns the canonical error a backend returns when it has no
// model loaded for the request. It carries codes.FailedPrecondition so callers
// can detect it across the gRPC boundary without matching the message string.
func ModelNotLoaded(backend string) error {
	return status.Errorf(codes.FailedPrecondition, "%s: model not loaded", backend)
}

// IsModelNotLoaded reports whether err signals that the backend has no model
// loaded. It prefers the typed gRPC status code (FailedPrecondition) and falls
// back to the message for backends that have not yet adopted ModelNotLoaded.
//
// Acting on a false positive is harmless: the only consequence upstream is that
// the model is reloaded, which is idempotent.
func IsModelNotLoaded(err error) bool {
	if err == nil {
		return false
	}
	if status.Code(err) == codes.FailedPrecondition {
		return true
	}
	return strings.Contains(strings.ToLower(err.Error()), "model not loaded")
}