package chatclient

type deliveryToken struct {
	_ byte
}

type ackEntry struct {
	seq   int64
	token *deliveryToken
	done  bool
}

type ackTracker struct {
	entries []ackEntry
	index   map[*deliveryToken]int
	retired map[*deliveryToken]struct{}
}

func newACKTracker() ackTracker {
	return ackTracker{
		index:   make(map[*deliveryToken]int),
		retired: make(map[*deliveryToken]struct{}),
	}
}

func (t *ackTracker) add(seq int64, token *deliveryToken) {
	t.index[token] = len(t.entries)
	t.entries = append(t.entries, ackEntry{seq: seq, token: token})
}

func (t *ackTracker) mark(token *deliveryToken) (int64, bool, bool) {
	i, ok := t.index[token]
	if !ok {
		if _, retired := t.retired[token]; retired {
			return t.safeBoundary(), true, true
		}
		return 0, false, false
	}
	if t.entries[i].done {
		return t.safeBoundary(), true, true
	}
	t.entries[i].done = true
	return t.safeBoundary(), true, true
}

func (t *ackTracker) safeBoundary() int64 {
	var boundary int64
	for i := range t.entries {
		if !t.entries[i].done {
			break
		}
		boundary = t.entries[i].seq
	}
	return boundary
}

func (t *ackTracker) removeConfirmed(lastAck int64) {
	n := 0
	for n < len(t.entries) {
		if !t.entries[n].done || t.entries[n].seq > lastAck {
			break
		}
		t.retired[t.entries[n].token] = struct{}{}
		delete(t.index, t.entries[n].token)
		n++
	}
	if n == 0 {
		return
	}
	copy(t.entries, t.entries[n:])
	t.entries = t.entries[:len(t.entries)-n]
	for i := range t.entries {
		t.index[t.entries[i].token] = i
	}
}