super-auto-pets-board-game/internal/server/bots.go

package server

import (
	"errors"
	"log/slog"
	"math/rand/v2"
	"time"

	"github.com/greyson/super-auto-pets-board-game/internal/ai"
	"github.com/greyson/super-auto-pets-board-game/internal/game"
)

// botDifficulty maps the API's difficulty names to a skill level and a
// table name for the bot. The levels are calibrated against a competent
// player (ai.competentLevel, ~0.60): easy loses ~95% of games to them, medium
// is an even match, and hard wins ~80% (see TestDiagWinRateCurve). Medium is
// pinned to the competent level itself; hard is the strongest bot the engine
// can field.
var botDifficulty = map[string]struct {
	level float64
	name  string
}{
	"easy":   {0.25, "Robo Rookie"},
	"medium": {0.60, "Robo Rival"},
	"hard":   {1.00, "Robo Ace"},
}

// requireHost authorizes a lobby-management action: only the host (seat 0)
// may set the pack, add or remove players, or start the game. Identity lives
// at this trust boundary, keeping the game engine free of it.
func requireHost(g *game.Game, playerID string) error {
	if len(g.Players) == 0 || g.Players[0].ID != playerID {
		return errors.New("only the host can do that")
	}
	return nil
}

// addBot seats a computer opponent for a difficulty name, translating the
// name to the engine's skill level. Capacity and phase are enforced by the
// engine's AddPlayer.
func addBot(g *game.Game, difficulty string) error {
	bot, ok := botDifficulty[difficulty]
	if !ok {
		return errors.New("unknown bot difficulty")
	}
	_, err := g.AddBot(bot.name, bot.level)
	return err
}

// commitLocked is the one path every game mutation goes through: bots update
// their memories from the new public state, the game is persisted, every
// client gets its view, and the next bot move (if any) is scheduled. Callers
// must hold r.mu.
func (s *Server) commitLocked(r *room) {
	observeBotsLocked(r.game)
	s.persist(r)
	r.broadcastLocked()
	s.scheduleBotsLocked(r)
}

// observeBotsLocked gives each bot a look at the current state through its
// own player view — the same information a human in that seat would see.
func observeBotsLocked(g *game.Game) {
	for _, p := range g.Players {
		if !p.IsBot {
			continue
		}
		mem := ai.LoadMemory(p.BotMemory)
		view := g.ViewFor(p.ID)
		ai.Observe(&view, mem)
		p.BotMemory = mem.Marshal()
	}
}

// scheduleBotsLocked arms a delayed move for the first bot that owes the
// game an action. The delay is there purely for feel — instant replies make
// the opponent seem like a vending machine. Only one timer runs per room;
// each fired move re-schedules the next.
func (s *Server) scheduleBotsLocked(r *room) {
	if r.botArmed {
		return
	}
	for _, p := range r.game.Players {
		if !p.IsBot {
			continue
		}
		view := r.game.ViewFor(p.ID)
		if !ai.Pending(&view) {
			continue
		}
		r.botArmed = true
		playerID := p.ID
		time.AfterFunc(botDelay(r.game.Phase), func() { s.runBot(r, playerID) })
		return
	}
}

// botDelay picks a humanlike pause before a bot move.
func botDelay(phase game.Phase) time.Duration {
	ms := func(base, jitter int) time.Duration {
		return time.Duration(base+rand.IntN(jitter+1)) * time.Millisecond
	}
	switch phase {
	case game.PhaseShop:
		return ms(700, 900)
	case game.PhaseArrange:
		return ms(1600, 1600)
	default: // battle acknowledgement
		return ms(500, 300)
	}
}

// runBot fires one scheduled bot move. The state may have changed while the
// timer ran, so everything is revalidated under the lock.
func (s *Server) runBot(r *room, playerID string) {
	r.mu.Lock()
	defer r.mu.Unlock()
	r.botArmed = false
	p := r.game.PlayerByID(playerID)
	if p == nil || !p.IsBot {
		return
	}
	view := r.game.ViewFor(playerID)
	if !ai.Pending(&view) {
		// Someone else moved the game on; check the other seats.
		s.scheduleBotsLocked(r)
		return
	}
	act := ai.New(p.BotLevel).Act(&view, ai.LoadMemory(p.BotMemory))
	var err error
	if act == nil {
		err = game.ErrInvalidAction
	} else {
		err = applyBotAction(r.game, playerID, act)
	}
	if err != nil {
		// A bot must never wedge the game: fall back to the simplest legal
		// move for the phase.
		slog.Warn("bot action failed; using fallback", "game", r.game.ID, "player", playerID, "err", err)
		if err := botFallback(r.game, playerID); err != nil {
			slog.Error("bot fallback failed", "game", r.game.ID, "player", playerID, "err", err)
			return
		}
	}
	s.commitLocked(r)
}

// applyBotAction maps a bot decision onto the engine, mirroring the client
// message dispatch in apply().
func applyBotAction(g *game.Game, playerID string, a *ai.Action) error {
	switch a.Type {
	case "buy":
		return g.Buy(playerID, a.Row)
	case "buyAvocado":
		return g.BuyAvocado(playerID, a.Row)
	case "sell":
		return g.Sell(playerID, a.Cards)
	case "trade":
		return g.TradeStart(playerID, a.Cards)
	case "tradeChoose":
		return g.TradeChoose(playerID, a.Pick)
	case "revealChoose":
		return g.RevealChoose(playerID, a.CardID)
	case "sacrificeChoose":
		return g.SacrificeChoose(playerID, a.CardID)
	case "pass":
		return g.Pass(playerID)
	case "arrange":
		return g.SubmitOrder(playerID, a.Order)
	case "ready":
		return g.AcknowledgeBattle(playerID)
	}
	return game.ErrInvalidAction
}

// botFallback makes the trivially legal move for whatever the game is
// waiting on: pass the shop turn (selling down to the pet limit first if
// passing would be refused), take the first trade option, submit the deck
// as-is, or acknowledge the battle.
func botFallback(g *game.Game, playerID string) error {
	p := g.PlayerByID(playerID)
	if p == nil {
		return game.ErrInvalidAction
	}
	switch g.Phase {
	case game.PhaseShop:
		if g.PendingSacrifice != nil && g.PendingSacrifice.PlayerID == playerID {
			return g.SacrificeChoose(playerID, g.PendingSacrifice.Options[0])
		}
		if g.PendingReveal != nil && g.PendingReveal.PlayerID == playerID {
			return g.RevealChoose(playerID, g.PendingReveal.Options[0])
		}
		if g.Pending != nil && g.Pending.PlayerID == playerID {
			return g.TradeChoose(playerID, 0)
		}
		if excess := p.PetCount() - game.MaxPets; excess > 0 {
			ids := make([]string, 0, excess)
			for _, c := range p.Deck {
				if c.IsPet() && len(ids) < excess {
					ids = append(ids, c.ID)
				}
			}
			return g.Sell(playerID, ids)
		}
		return g.Pass(playerID)
	case game.PhaseArrange:
		ids := make([]string, len(p.Deck))
		for i, c := range p.Deck {
			ids[i] = c.ID
		}
		return g.SubmitOrder(playerID, ids)
	case game.PhaseBattle:
		return g.AcknowledgeBattle(playerID)
	}
	return game.ErrInvalidAction
}