shotgun/lobby/lobby.go

package lobby

import (
	"context"

	"github.com/google/uuid"

	"git.sunturtle.xyz/studio/shotgun/player"
	"git.sunturtle.xyz/studio/shotgun/serve"
)

type GameID = serve.GameID

type matchMade struct {
	match chan GameID
	chall player.ID
}

type match chan matchMade

// Lobby is a matchmaking service.
type Lobby struct {
	// matches is dealers waiting for a match. It MUST be unbuffered.
	matches chan match
}

func New() *Lobby {
	return &Lobby{
		matches: make(chan match),
	}
}

// Queue waits for a match and returns a unique ID for it.
func (l *Lobby) Queue(ctx context.Context, p player.ID) (id GameID, chall player.ID, deal bool) {
	select {
	case m := <-l.matches:
		// We found a dealer waiting for a match.
		r := matchMade{
			match: make(chan GameID, 1),
			chall: p,
		}
		// We don't need to check the context here because the challenger
		// channel is buffered and we have exclusive send access on it.
		m <- r
		// We do need to check the context here in case they disappeared.
		select {
		case <-ctx.Done():
			return GameID{}, player.ID{}, false
		case id := <-r.match:
			return id, p, false
		}
	default: // do nothing
	}
	// We're a new dealer.
	m := make(match, 1)
	select {
	case <-ctx.Done():
		return GameID{}, player.ID{}, false
	case l.matches <- m:
		// Our match is submitted. Move on.
	case m := <-l.matches:
		// We might have become a dealer at the same time someone else did.
		// We created our match, but we can try to get theirs as well and
		// never send ours, since l.matches is unbuffered.
		r := matchMade{
			match: make(chan GameID, 1),
			chall: p,
		}
		m <- r
		select {
		case <-ctx.Done():
			return GameID{}, player.ID{}, false
		case id := <-r.match:
			return id, p, false
		}
	}
	select {
	case <-ctx.Done():
		return GameID{}, player.ID{}, false
	case r := <-m:
		// Got our challenger. Create the game and send the ID back.
		id := GameID(uuid.New())
		// Don't need to check context because the match channel is buffered.
		r.match <- id
		return id, r.chall, true
	}
}