game-engine

Game Engine

Manages the game lifecycle from lobby to completion — state transitions, question progression, answer tracking, scoring, iframe communication, and real-time coordination between host and players.

Overview

• State Machine: lobby → playing → question → results → complete
• Host Controls: Start game, next question, show results
• Player Flow: Join lobby, play AI-generated game in sandboxed iframe, see feedback, view leaderboard
• Iframe Architecture: Parent owns game state, iframe is a dumb renderer, communication via MessageChannel
• Scoring: Points based on correctness + speed (validated server-side, not in iframe)
• Real-time: All state changes sync instantly via Convex

When to Use This Skill

• Building or modifying the game state machine
• Implementing host controls (start, next, results)
• Building the iframe sandbox and MessageChannel communication
• Building the player answer flow (iframe → parent → Convex)
• Implementing scoring logic (server-side validation)
• Handling edge cases (disconnects, late joins, timeouts, iframe errors)

Key Concepts

State Machine

lobby → playing → question ←→ results → complete
                     ↑              |
                     └──────────────┘ (next question)

• lobby: Players joining, host waiting to start
• playing: Transitional state when game starts
• question: Active question, players submitting answers
• results: Showing answer results + leaderboard for current question
• complete: All questions done, final results displayed

State Transitions

From	To	Trigger
lobby	question	Host clicks "Start Game"
question	results	Host clicks "Show Results" OR timer expires
results	question	Host clicks "Next Question" (if questions remain)
results	complete	Host clicks "Next Question" on last question

Scoring Formula

Points = correctness_points + speed_bonus
correctness_points = correct ? 1000 : 0
speed_bonus = correct ? max(0, 500 * (1 - timeMs / timerDuration)) : 0

Max points per question: 1500 (correct + fastest possible)

Timer

• Default: 30 seconds per question
• Timer runs in the parent app (authoritative), not in the iframe
• iframe can display a visual countdown, but parent enforces the actual limit
• When timer expires, parent sends TIME_UP to iframe via MessageChannel

Iframe Communication

Parent and iframe communicate via a private MessageChannel:

1. Parent creates MessageChannel, transfers one port to iframe via initial postMessage
2. All subsequent communication flows through the private channel port
3. Never combine allow-scripts + allow-same-origin in sandbox

Parent as Source of Truth

• Parent owns game state — iframe is a rendering engine
• Scoring happens server-side (Convex), not in the iframe
• If iframe crashes, parent still has game state and can recover
• iframe cannot be trusted for authoritative state (it runs AI-generated code)

Related Files

• convex/games.ts — Game state mutations
• convex/answers.ts — Answer submission and scoring
• convex/players.ts — Player management and scores
• components/GameIframe.tsx — Sandboxed iframe wrapper with MessageChannel

Reference Files

• reference.md — Code patterns for state management and iframe communication