backend

type FallbackEvent struct {
	Reason    string // "api_error", "api_empty", "api_unavailable"
	Entity    string // "messages", "chats", etc.
	Timestamp time.Time
	Error     error // original error if any
}

type FallbackOptions[T any] struct {
	// Backend is the selected backend mode (api, db, auto)
	Backend string
	// FallbackAllowed indicates if fallback is permitted for this operation
	FallbackAllowed bool
	// ProgressWriter receives fallback status messages
	ProgressWriter io.Writer
	// PreAPIError is an error that occurred before API call (e.g., client creation failed)
	// If set and fallback is allowed, DB fallback is attempted without calling APICall
	PreAPIError error
	// APICall executes the API operation
	APICall func() (T, error)
	// DBCall executes the DB operation
	DBCall func(store *db.Store) (T, error)
	// IsEmpty checks if the result should trigger fallback
	IsEmpty func(T) bool
	// OpenStore opens a DB connection
	OpenStore func() (*db.Store, error)
	// EntityName is used in progress messages (e.g., "messages", "chats")
	EntityName string
	// OnFallback is called when fallback is triggered (for metrics/logging)
	OnFallback func(FallbackEvent)
	// WarnStale adds a warning that DB data may be stale when fallback is used
	WarnStale bool
}

type FallbackResult[T any] struct {
	Data         T
	UsedFallback bool
	FallbackMsg  string
}