package agent

import "context"

type conversationLock struct {
	gate  chan struct{}
	users int
}

// Serialize turns within each conversation while allowing different chats to stream.
func (s *Service) lockConversation(ctx context.Context, id string) (func(), error) {
	s.chatMu.Lock()
	if s.chatLocks == nil {
		s.chatLocks = make(map[string]*conversationLock)
	}
	lock := s.chatLocks[id]
	if lock == nil {
		lock = &conversationLock{gate: make(chan struct{}, 1)}
		s.chatLocks[id] = lock
	}
	lock.users++
	s.chatMu.Unlock()
	releaseRef := func() {
		s.chatMu.Lock()
		lock.users--
		if lock.users == 0 {
			delete(s.chatLocks, id)
		}
		s.chatMu.Unlock()
	}
	select {
	case lock.gate <- struct{}{}:
		return func() { <-lock.gate; releaseRef() }, nil
	case <-ctx.Done():
		releaseRef()
		return nil, ctx.Err()
	}
}