games/chat/chat.go

// Package chat provides a reusable chat room backed by NATS pub/sub
// with optional database persistence.
package chat

import (
	"context"
	"encoding/json"
	"slices"
	"sync"

	"github.com/nats-io/nats.go"
	"github.com/rs/zerolog/log"

	"github.com/ryanhamamura/games/db/repository"
)

// Message is the wire format for chat messages over NATS.
type Message struct {
	Nickname string `json:"nickname"`
	Slot     int    `json:"slot"` // player slot/color index
	Message  string `json:"message"`
	Time     int64  `json:"time"` // unix millis, zero for ephemeral messages
}

const maxMessages = 50

// Room manages an in-memory message buffer and NATS pub/sub for a single
// chat room (typically one per game). When created with NewPersistentRoom,
// messages are automatically loaded from and saved to the database.
type Room struct {
	subject  string
	nc       *nats.Conn
	messages []Message
	mu       sync.Mutex

	// Optional persistence; nil for ephemeral rooms (e.g. snake).
	queries *repository.Queries
	roomID  string
}

// NewRoom creates an ephemeral chat room with no database persistence.
func NewRoom(nc *nats.Conn, subject string) *Room {
	return &Room{
		subject: subject,
		nc:      nc,
	}
}

// NewPersistentRoom creates a chat room backed by the database. It loads
// existing messages on creation and auto-saves new messages on Send.
func NewPersistentRoom(nc *nats.Conn, subject string, queries *repository.Queries, roomID string) *Room {
	r := &Room{
		subject: subject,
		nc:      nc,
		queries: queries,
		roomID:  roomID,
	}
	r.messages = r.loadMessages()
	return r
}

// Send publishes a message to the room's NATS subject and persists it
// if the room is backed by a database.
func (r *Room) Send(msg Message) {
	if r.queries != nil {
		r.saveMessage(msg)
	}

	data, err := json.Marshal(msg)
	if err != nil {
		log.Error().Err(err).Str("subject", r.subject).Msg("failed to marshal chat message")
		return
	}
	if err := r.nc.Publish(r.subject, data); err != nil {
		log.Error().Err(err).Str("subject", r.subject).Msg("failed to publish chat message")
	}
}

// receive processes an incoming NATS message, appending it to the buffer.
func (r *Room) receive(data []byte) (Message, bool) {
	var msg Message
	if err := json.Unmarshal(data, &msg); err != nil {
		return msg, false
	}

	r.mu.Lock()
	r.messages = append(r.messages, msg)
	if len(r.messages) > maxMessages {
		r.messages = r.messages[len(r.messages)-maxMessages:]
	}
	r.mu.Unlock()

	return msg, true
}

// Messages returns a snapshot of the current message buffer.
func (r *Room) Messages() []Message {
	r.mu.Lock()
	defer r.mu.Unlock()
	snapshot := make([]Message, len(r.messages))
	copy(snapshot, r.messages)
	return snapshot
}

// Subscribe returns a channel of parsed messages and a cleanup function.
// The room handles NATS subscription internally and buffers messages.
func (r *Room) Subscribe() (<-chan Message, func()) {
	natsCh := make(chan *nats.Msg, 64)
	msgCh := make(chan Message, 64)

	sub, err := r.nc.ChanSubscribe(r.subject, natsCh)
	if err != nil {
		close(msgCh)
		return msgCh, func() {}
	}

	go func() {
		for natsMsg := range natsCh {
			if msg, ok := r.receive(natsMsg.Data); ok {
				msgCh <- msg
			}
		}
		close(msgCh)
	}()

	cleanup := func() {
		_ = sub.Unsubscribe()
	}

	return msgCh, cleanup
}

func (r *Room) saveMessage(msg Message) {
	err := r.queries.CreateChatMessage(context.Background(), repository.CreateChatMessageParams{
		GameID:    r.roomID,
		Nickname:  msg.Nickname,
		Color:     int64(msg.Slot),
		Message:   msg.Message,
		CreatedAt: msg.Time,
	})
	if err != nil {
		log.Error().Err(err).Str("room_id", r.roomID).Msg("failed to save chat message")
	}
}

func (r *Room) loadMessages() []Message {
	rows, err := r.queries.GetChatMessages(context.Background(), r.roomID)
	if err != nil {
		return nil
	}
	msgs := make([]Message, len(rows))
	for i, row := range rows {
		msgs[i] = Message{
			Nickname: row.Nickname,
			Slot:     int(row.Color),
			Message:  row.Message,
			Time:     row.CreatedAt,
		}
	}
	// DB returns newest-first; reverse for chronological display
	slices.Reverse(msgs)
	return msgs
}