package audit

type Window struct {
    Last uint16
    HasLast bool
    Summary Summary
}

func (w *Window) Observe(sequence uint16) string {
    if !w.HasLast {
        w.Last, w.HasLast = sequence, true
        w.Summary.Accepted++
        w.Summary.Latest = sequence
        return "accepted"
    }
    delta := uint16(sequence - w.Last)
    if delta == 0 { w.Summary.Duplicate++; return "duplicate" }
    if delta > 32767 { w.Summary.Reordered++; return "reordered" }
    if delta > 1 { w.Summary.Lost += uint64(delta - 1) }
    w.Last, w.Summary.Latest = sequence, sequence
    w.Summary.Accepted++
    return "accepted"
}