2nd/10_Wiki/Topics/Game_Design/State-Machine-and-Phase-Transition-Events.md

---
id: wiki-2026-0508-state-machine-and-phase-transiti
title: State Machine and Phase Transition Events
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [FSM, Game State Machine, Phase Events]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [game-design, fsm, simulation, architecture]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: typescript
  framework: xstate
---

# State Machine and Phase Transition Events

## 매 한 줄
> **"매 game logic 의 FSM-first 의 architecture"**. 매 boss phase, match flow, sector breach, AI behavior 의 deterministic state model — 매 transition event 의 explicit emission 으로 telemetry/animation/audio 의 synchronize. 매 2026 standard: XState v5 + actor model + visualizer.

## 매 핵심

### 매 정의
- **State**: 매 finite labeled status (idle, charging, attacking, dead).
- **Event**: external trigger (input, timer, hp_threshold).
- **Transition**: state × event → next_state + side_effects.
- **Phase event**: cross-cutting broadcast (e.g. "phase_2_started") for multiple subsystems.

### 매 핵심 패턴
- **Hierarchical states**: parent/child (combat → charging → release).
- **Parallel states**: 매 동시 sub-FSM (movement + weapon + status).
- **Guards**: 매 transition 의 conditional gate.
- **Actions**: entry/exit/transition side effects.

### 매 응용
1. Boss fight phase logic.
2. Multiplayer match flow (lobby → loading → playing → results).
3. Quest/dialogue branching.
4. Network connection lifecycle.

## 💻 패턴

### XState v5 boss FSM
```typescript
import { setup, createActor } from 'xstate';

const bossMachine = setup({
  types: { context: {} as { hp: number }, events: {} as { type: 'damage'; amount: number } | { type: 'tick' } },
  actions: {
    broadcastPhase: ({ context }) => emit('phase_event', { phase: context.hp > 5000 ? 1 : context.hp > 2000 ? 2 : 3 }),
  },
  guards: {
    phase2: ({ context }) => context.hp <= 5000 && context.hp > 2000,
    phase3: ({ context }) => context.hp <= 2000 && context.hp > 0,
    dead:   ({ context }) => context.hp <= 0,
  },
}).createMachine({
  id: 'boss',
  initial: 'phase1',
  context: { hp: 10_000 },
  states: {
    phase1: { on: { damage: { actions: 'broadcastPhase', guard: 'phase2', target: 'phase2' } } },
    phase2: { on: { damage: { actions: 'broadcastPhase', guard: 'phase3', target: 'phase3' } } },
    phase3: { on: { damage: { guard: 'dead', target: 'dead' } } },
    dead:   { type: 'final' },
  },
});

export const bossActor = createActor(bossMachine);
```

### Hand-rolled FSM (no deps)
```typescript
type State = 'idle' | 'charging' | 'attacking' | 'cooldown';
type Event = 'see_target' | 'charge_done' | 'attack_done' | 'lose_target';

const TABLE: Record<State, Partial<Record<Event, State>>> = {
  idle:      { see_target: 'charging' },
  charging:  { charge_done: 'attacking', lose_target: 'idle' },
  attacking: { attack_done: 'cooldown' },
  cooldown:  { charge_done: 'idle' },
};

export class FSM {
  state: State = 'idle';
  send(e: Event) {
    const next = TABLE[this.state][e];
    if (next) { this.exit(this.state); this.state = next; this.enter(next); }
  }
  enter(s: State) { /* hooks */ }
  exit(s: State) { /* hooks */ }
}
```

### Phase event bus
```typescript
type PhaseEvent =
  | { kind: 'phase_changed'; from: number; to: number; entityId: string }
  | { kind: 'sector_state_changed'; sectorId: string; state: string }
  | { kind: 'match_state_changed'; matchId: string; state: string };

class EventBus {
  private listeners = new Map<string, Array<(e: PhaseEvent) => void>>();
  emit(e: PhaseEvent) { for (const fn of this.listeners.get(e.kind) ?? []) fn(e); }
  on(kind: PhaseEvent['kind'], fn: (e: PhaseEvent) => void) {
    const arr = this.listeners.get(kind) ?? [];
    arr.push(fn); this.listeners.set(kind, arr);
  }
}
export const bus = new EventBus();
```

### Guard with cooldown
```typescript
export function withCooldown(ms: number) {
  let last = 0;
  return () => {
    const now = Date.now();
    if (now - last < ms) return false;
    last = now;
    return true;
  };
}
```

### Parallel states (movement + weapon)
```typescript
import { setup, createMachine } from 'xstate';

const player = createMachine({
  id: 'player',
  type: 'parallel',
  states: {
    movement: {
      initial: 'idle',
      states: {
        idle: { on: { move: 'running' } },
        running: { on: { stop: 'idle' } },
      },
    },
    weapon: {
      initial: 'unarmed',
      states: {
        unarmed: { on: { equip: 'armed' } },
        armed: { on: { fire: 'cooldown' } },
        cooldown: { after: { 500: 'armed' } },
      },
    },
  },
});
```

### FSM 의 telemetry
```typescript
export function logTransition(from: string, to: string, event: string) {
  console.log(JSON.stringify({ ts: Date.now(), kind: 'fsm.transition', from, to, event }));
}
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| 매 simple 3-state | Hand-rolled enum + switch. |
| 매 hierarchical / parallel | XState v5 + visualizer. |
| 매 networked sync | Authoritative server FSM + delta replication. |
| 매 hot path AI | Behavior Tree (FSM 의 not 적합). |

**기본값**: XState v5 for non-trivial; enum FSM for simple.

## 🔗 Graph
- 부모: [[Fixed Time Step vs Variable Time Step]] · [[Procedural-Rhetoric|Procedural Rhetoric (In Gaming)]]
- 변형: [[Stage-Director-and-World-Tension-Scaling]] · [[Staggered-Firing-Logic-and-Phase-Offset]]
- 응용: [[War-Commander-Combat-Ecosystem]] · [[Sector]]
- Adjacent: [[Player-Experience-Modeling]] · [[Roguelike Procedural Generation]]

## 🤖 LLM 활용
**언제**: FSM 의 design review, unreachable state 의 detect, transition coverage 의 audit.
**언제 X**: 매 hot loop transition (deterministic code).

## ❌ 안티패턴
- **Boolean flag soup**: 매 implicit state — combinatorial bug surface.
- **Missing exit action**: 매 leak 의 timer/listener.
- **Unbounded events**: 매 event queue 의 backlog — frame stall.

## 🧪 검증 / 중복
- Verified: XState v5 docs (2025), GDC AI Summit talks, Unreal Behavior Tree docs.
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — XState v5 boss + parallel state + bus 추가 |