shotgun/game.go

package main

import (
	"context"
	"errors"
	"log/slog"
	"time"

	"nhooyr.io/websocket"
	"nhooyr.io/websocket/wsjson"

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

// An action is a request to change the game state.
type action struct {
	Action string    `json:"action"`
	Player player.ID `json:"-"`
}

func applyAction(g *game.Match, a action) error {
	switch a.Action {
	case "quit":
		return g.Concede(a.Player)
	case "across", "self":
		return g.Shoot(a.Player, a.Action == "self")
	case "0":
		return g.Apply(a.Player, 0)
	case "1":
		return g.Apply(a.Player, 1)
	case "2":
		return g.Apply(a.Player, 2)
	case "3":
		return g.Apply(a.Player, 3)
	case "4":
		return g.Apply(a.Player, 4)
	case "5":
		return g.Apply(a.Player, 5)
	case "6":
		return g.Apply(a.Player, 6)
	case "7":
		return g.Apply(a.Player, 7)
	default:
		return errWeirdAction
	}
}

type observer struct {
	conn *websocket.Conn
	ctx  context.Context
}

// gameActor is an actor that updates a game's state and relays changes to all
// observers.
func gameActor(ctx context.Context, g *game.Match, dealer, chall person, join <-chan person) {
	// Games should generally be on the order of minutes. A four hour game is
	// definitely expired.
	ctx, stop := context.WithTimeoutCause(ctx, 4*time.Hour, errMatchExpired)
	defer stop()
	// Accept joins from the dealer and challenger. We don't care which is
	// which, but we need to get both to synchronize the socket.
	<-join
	<-join
	var obs []observer
	actions := make(chan action, 2)
	go playerActor(ctx, dealer, actions)
	go playerActor(ctx, chall, actions)

	slog.InfoContext(ctx, "start game", "dealer", dealer.id, "challenger", chall.id)
	const timeLimit = 15 * time.Second
	dl := time.Now().Add(timeLimit)
	broadcast(ctx, g, dealer, chall, obs, dl)
	tick := time.NewTicker(timeLimit)
	defer tick.Stop()
	for {
		select {
		case <-ctx.Done():
			return
		case p := <-join:
			slog.InfoContext(ctx, "observer", "id", p.id)
			// Deliver the game state just to the new observer.
			if err := wsjson.Write(ctx, p.conn, g.DTO(p.id, dl)); err != nil {
				// We don't need to track them as an observer. Just close their
				// conn and move on.
				go p.conn.Close(websocket.StatusNormalClosure, "looks like you dropped")
				continue
			}
			q := p.conn.CloseRead(ctx)
			obs = append(obs, observer{conn: p.conn, ctx: q})
		case a := <-actions:
			slog.InfoContext(ctx, "got action", "from", a.Player, "action", a.Action)
			err := applyAction(g, a)
			switch err {
			case nil:
				broadcast(ctx, g, dealer, chall, obs, dl)
			case game.ErrRoundEnded:
				broadcast(ctx, g, dealer, chall, obs, dl)
				if g.MatchWinner() != nil {
					gameOver(ctx, dealer, chall, obs)
					return
				}
				g.NextRound()
				broadcast(ctx, g, dealer, chall, obs, dl)
			case game.ErrGameEnded:
				broadcast(ctx, g, dealer, chall, obs, dl)
				g.NextGame()
				broadcast(ctx, g, dealer, chall, obs, dl)
			case game.ErrWrongTurn:
				slog.WarnContext(ctx, "action on wrong turn", "from", a.Player, "action", a.Action)
				continue
			case errWeirdAction:
				slog.WarnContext(ctx, "nonsense action", "from", a.Player, "action", a.Action)
				continue
			default:
				slog.ErrorContext(ctx, "action caused a mystery error", "from", a.Player, "action", a.Action, "err", err.Error())
				continue
			}
			dl = time.Now().Add(timeLimit)
			tick.Reset(timeLimit)
		case <-tick.C:
			slog.InfoContext(ctx, "out of time")
			g.Expire()
			broadcast(ctx, g, dealer, chall, obs, dl)
			gameOver(ctx, dealer, chall, obs)
			return
		}
		// Clear observers who have left.
		for k := len(obs) - 1; k >= 0; k-- {
			if obs[k].ctx.Err() != nil {
				obs[k], obs[len(obs)-1] = obs[len(obs)-1], observer{}
				obs = obs[:len(obs)-1]
			}
		}
	}
}

func playerActor(ctx context.Context, p person, actions chan<- action) {
	for {
		a := action{Player: p.id}
		if err := wsjson.Read(ctx, p.conn, &a); err != nil {
			// If we fail to read, then we consider them to have quit.
			a.Action = "quit"
			select {
			case <-ctx.Done():
			case actions <- a:
				slog.InfoContext(ctx, "lost connection", "player", p.id, "err", err.Error())
			}
			return
		}
		if a.Action == "ping" {
			continue
		}
		select {
		case <-ctx.Done():
			return
		case actions <- a:
		}
	}
}

func broadcast(ctx context.Context, g *game.Match, dealer, chall person, obs []observer, deadline time.Time) {
	// NOTE(zeph): If our sends to players fail, then the socket will close,
	// causing the readers to fail and send concede messages. No leak.
	if err := wsjson.Write(ctx, dealer.conn, g.DTO(dealer.id, deadline)); err != nil {
		slog.WarnContext(ctx, "lost dealer", "player", dealer.id, "err", err.Error())
	}
	if err := wsjson.Write(ctx, chall.conn, g.DTO(chall.id, deadline)); err != nil {
		slog.WarnContext(ctx, "lost challenger", "player", chall.id, "err", err.Error())
	}
	if len(obs) == 0 {
		return
	}
	d := g.DTO(player.ID{}, deadline)
	for _, p := range obs {
		if err := wsjson.Write(ctx, p.conn, &d); err != nil {
			slog.WarnContext(ctx, "lost observer", "err", err.Error())
		}
	}
}

func gameOver(ctx context.Context, dealer, chall person, obs []observer) {
	go dealer.conn.Close(websocket.StatusNormalClosure, "match ended")
	go chall.conn.Close(websocket.StatusNormalClosure, "match ended")
	for _, p := range obs {
		c := p.conn
		go c.Close(websocket.StatusNormalClosure, "match ended")
	}
}

var (
	errWeirdAction  = errors.New("unknown action")
	errMatchExpired = errors.New("there is a time limit on matches please")
)