games/snake/loop.go

package snake

import (
	"time"
)

const (
	targetFPS                      = 60
	tickInterval                   = time.Second / targetFPS
	snakeSpeed                     = 7 // cells per second
	moveInterval                   = time.Second / snakeSpeed
	countdownSecondsMultiplayer    = 10
	countdownSecondsSinglePlayer   = 3
	inactivityLimit                = 60 * time.Second
)

func (si *SnakeGameInstance) startOrResetCountdownLocked() {
	si.game.Status = StatusCountdown

	countdown := countdownSecondsMultiplayer
	if si.game.Mode == ModeSinglePlayer {
		countdown = countdownSecondsSinglePlayer
	}
	si.game.CountdownEnd = time.Now().Add(time.Duration(countdown) * time.Second)

	si.loopOnce.Do(func() {
		si.stopCh = make(chan struct{})
		go si.runLoop()
	})
}

func (si *SnakeGameInstance) runLoop() {
	si.countdownPhase()

	si.gameMu.RLock()
	stopped := si.game.Status != StatusInProgress
	si.gameMu.RUnlock()
	if stopped {
		return
	}

	si.gamePhase()
}

func (si *SnakeGameInstance) countdownPhase() {
	ticker := time.NewTicker(time.Second)
	defer ticker.Stop()

	for {
		select {
		case <-si.stopCh:
			return
		case <-ticker.C:
			si.gameMu.Lock()

			if si.game.Status != StatusCountdown {
				si.gameMu.Unlock()
				return
			}

			remaining := time.Until(si.game.CountdownEnd)
			if remaining <= 0 {
				si.initGame()
				si.game.Status = StatusInProgress

				if si.persister != nil {
					si.persister.SaveSnakeGame(si.game)
				}
				si.gameMu.Unlock()
				si.notify()
				return
			}

			if si.persister != nil {
				si.persister.SaveSnakeGame(si.game)
			}
			si.gameMu.Unlock()
			si.notify()
		}
	}
}

// initGame sets up snakes and food for the start of a game.
func (si *SnakeGameInstance) initGame() {
	// Collect active player slots
	var activeSlots []int
	for i, p := range si.game.Players {
		if p != nil {
			activeSlots = append(activeSlots, i)
		}
	}

	state := si.game.State
	state.Snakes = SpawnSnakes(activeSlots, state.Width, state.Height)
	SpawnFood(state, len(activeSlots), si.game.Mode)
}

func (si *SnakeGameInstance) gamePhase() {
	ticker := time.NewTicker(tickInterval)
	defer ticker.Stop()

	lastInput := time.Now()
	var moveAccum time.Duration

	for {
		select {
		case <-si.stopCh:
			return
		case <-ticker.C:
			si.gameMu.Lock()

			if si.game.Status != StatusInProgress {
				si.gameMu.Unlock()
				return
			}

			// Apply pending directions every tick for responsive input
			inputReceived := false
			for i := 0; i < 8; i++ {
				if si.pendingDir[i] != nil && i < len(si.game.State.Snakes) && si.game.State.Snakes[i] != nil {
					si.game.State.Snakes[i].Dir = *si.pendingDir[i]
					si.pendingDir[i] = nil
					inputReceived = true
				}
			}
			if inputReceived {
				lastInput = time.Now()
			}

			// Inactivity timeout
			if time.Since(lastInput) > inactivityLimit {
				si.game.Status = StatusFinished
				if si.persister != nil {
					si.persister.SaveSnakeGame(si.game)
				}
				si.gameMu.Unlock()
				si.notify()
				return
			}

			// Only advance game state at snakeSpeed
			moveAccum += tickInterval
			if moveAccum < moveInterval {
				si.gameMu.Unlock()
				continue
			}
			moveAccum -= moveInterval

			state := si.game.State

			// Advance snakes
			Tick(state)

			// Check collisions first (before food, so dead snakes don't eat)
			dead := CheckCollisions(state)
			MarkDead(state, dead)

			// Check food eaten (only by surviving snakes)
			eaten := CheckFood(state)
			RemoveFood(state, eaten)
			SpawnFood(state, si.game.PlayerCount(), si.game.Mode)

			// Track score for single player
			si.game.Score += len(eaten)

			// Check game over
			alive := AliveCount(state)
			gameOver := false
			if si.game.Mode == ModeSinglePlayer {
				// Single player ends when the player dies (alive == 0)
				if alive == 0 {
					gameOver = true
					// No winner in single player - just final score
				}
			} else {
				// Multiplayer ends when 1 or fewer alive
				if alive <= 1 {
					gameOver = true
					winnerIdx := LastAlive(state)
					if winnerIdx >= 0 && winnerIdx < len(si.game.Players) {
						si.game.Winner = si.game.Players[winnerIdx]
					}
				}
			}

			if gameOver {
				si.game.Status = StatusFinished
			}

			if si.persister != nil {
				si.persister.SaveSnakeGame(si.game)
			}

			si.gameMu.Unlock()
			si.notify()

			if gameOver {
				return
			}
		}
	}
}