Production Integration Patterns

interface SessionState {
  sessionId: string;
  skillId: string;
  algorithmId: 'speedrun' | 'practice';
  activeSessionTime: number; // seconds
  lives: number;
  isPaused: boolean;
  questionCount: number;
}

// Initialize
const session: SessionState = {
  sessionId: crypto.randomUUID(),
  skillId: selectedSkill.id,
  algorithmId: 'practice',
  activeSessionTime: 0,
  lives: 3,
  isPaused: false,
  questionCount: 0,
};

// Pause tracking
function pauseSession() {
  session.isPaused = true;
  stopTimer();
}

// Resume with same sessionId
function resumeSession() {
  session.isPaused = false;
  startTimer();
}

// Save after each answer
localStorage.setItem('current_session', JSON.stringify(session));

// Restore on reopen
const saved = localStorage.getItem('current_session');
if (saved) {
  const state = JSON.parse(saved);

  // Validate not stale (< 1 hour old)
  const age = Date.now() - state.startedAt;
  if (age < 60 * 60 * 1000) {
    session = state; // Resume
  }
}

async function fetchWithRetry<T>(fetchFn: () => Promise<T>, maxRetries = 3): Promise<T> {
  for (let attempt = 0; attempt < maxRetries; attempt++) {
    try {
      return await fetchFn();
    } catch (error) {
      const isLastAttempt = attempt === maxRetries - 1;

      // Don't retry client errors (4xx)
      if (error.statusCode >= 400 && error.statusCode < 500) {
        throw error;
      }

      if (isLastAttempt) throw error;

      // Exponential backoff: 1s, 2s, 4s
      await delay(Math.pow(2, attempt) * 1000);
    }
  }
}

// Usage
const { question } = await fetchWithRetry(() => api.getNextQuestion(skillId, algorithmId, sessionId));

async function makeRequest<T>(requestFn: () => Promise<T>): Promise<T> {
  try {
    return await requestFn();
  } catch (error) {
    // Token expired - refresh and retry once
    if (error.statusCode === 401) {
      await refreshToken();
      return await requestFn();
    }
    throw error;
  }
}

// With Amplify
async function refreshToken() {
  await fetchAuthSession({ forceRefresh: true });
}

// Error response formats
// Standard error:
// { statusCode: 400, message: "Bad Request", error: "sessionId is required" }

// Validation error:
// { statusCode: 400, message: "Validation failed", errors: [{ field: "timeTookToAnswerMs", message: "..." }] }

try {
  const feedback = await api.submitAnswer(/* ... */);
} catch (error) {
  if (error.statusCode === 400) {
    // Bad request - likely our bug
    console.error('Invalid request:', error.message);
    showMessage('Something went wrong. Please restart.');
  } else if (error.statusCode === 401) {
    // Auth expired
    showMessage('Session expired. Please sign in again.');
    redirectToLogin();
  } else if (error.statusCode >= 500) {
    // Server error - retryable
    showMessage('Server error. Retrying...');
    await retry();
  }
}

const { question, skillAvailability } = await api.getNextQuestion(/* ... */);

switch (skillAvailability) {
  case 'Available':
    displayQuestion(question);
    break;

  case 'OnCooldown':
    // Spaced repetition enforcing wait
    showMessage('All facts are resting. Come back later!');
    endSession('cooldown');
    break;

  case 'Completed':
    // 100% mastery
    showMessage('Skill mastered! 🎉');
    endSession('completed');
    break;

  case 'Unavailable':
    showMessage('Skill not available.');
    endSession('unavailable');
    break;
}

// ✅ Good: Track per-question timing
const start = Date.now();
const timeTookMs = Date.now() - start;

// ❌ Bad: Use fixed values
const timeTookMs = 3000; // API needs real timing

// ✅ Good: Only count learning time
onQuestionDisplay(() => startTimer());
onPauseMenu(() => stopTimer());

// ❌ Bad: Count everything including menus
const activeTime = Date.now() - sessionStart; // Wrong!

// ✅ Good: One sessionId per session
const sessionId = crypto.randomUUID();
// Use for all questions in this session

// ❌ Bad: New sessionId per question
await askQuestion(crypto.randomUUID()); // Wrong!

// ✅ Good: Save state, offer recovery
try {
  saveState(session);
  await api.submitAnswer(/* ... */);
} catch (error) {
  showDialog(['Retry', 'End Session', 'Menu']);
}

// ❌ Bad: Silent failure
catch (error) {
  console.error(error); // User sees nothing
}