package inventory

import (
	"errors"
	"strings"

	"github.com/jackc/pgx/v5/pgconn"
)

// Unreachable says whether an error means the store could not be asked right now, rather than
// that it answered no.
//
// The difference decides whether something worth keeping is kept or lost. The store is recreated
// when the foundation is adopted (ADR 0078), and for those seconds every write fails with "the
// database system is starting up" or a refused connection; a caller that treats that like a
// refusal throws away what it was writing — a node's report of the apply that caused the restart
// was lost exactly so, and the mesh never heard from the node again (novox/hq issue 082).
//
// Unreachable is a connection that failed, and the server classes that mean "not now": 08
// (connection exception) and 57 (operator intervention — starting up, shutting down, admin
// shutdown, cannot connect now). Everything else is an answer, and asking again gets the same one.
func Unreachable(err error) bool {
	if err == nil {
		return false
	}
	var connect *pgconn.ConnectError
	if errors.As(err, &connect) {
		return true
	}
	var pg *pgconn.PgError
	if errors.As(err, &pg) {
		return strings.HasPrefix(pg.Code, "08") || strings.HasPrefix(pg.Code, "57")
	}
	return false
}