Utility Functions

/**
 * Creates a configurable LRU cache instance
 * @param options - Cache configuration options
 * @returns LRU cache instance
 */
function createLRUCache<T extends {}>(options?: LRUCacheOptions): LRUCache<T>;

/**
 * LRU cache configuration options
 */
interface LRUCacheOptions {
  /** Maximum number of items to store (default: 1024) */
  max?: number;
  /** Time to live for items in milliseconds (default: 3600000 / 1 hour) */
  ttl?: number;
}

/**
 * LRU cache instance type
 */
type LRUCache<T extends {}> = LRU<string, T>;

import { createLRUCache } from "graphql-yoga";

// Default cache configuration
const cache = createLRUCache();

// Custom cache configuration
const customCache = createLRUCache({
  max: 5000,          // Store up to 5000 items
  ttl: 1800000        // 30 minutes TTL
});

// Use cache in resolvers
interface UserData {
  id: string;
  name: string;
  email: string;
}

const userCache = createLRUCache<UserData>({
  max: 1000,
  ttl: 600000 // 10 minutes
});

const resolvers = {
  Query: {
    user: async (_, { id }) => {
      // Check cache first
      let user = userCache.get(id);
      
      if (!user) {
        // Cache miss - fetch from database
        user = await fetchUserFromDatabase(id);
        if (user) {
          userCache.set(id, user);
        }
      }
      
      return user;
    }
  }
};

// Use cache for GraphQL parsing/validation
const parserCache = createLRUCache<any>({
  max: 2000,
  ttl: 3600000
});

const yoga = createYoga({
  plugins: [
    {
      onRequestParse({ request }) {
        const query = request.body?.query;
        if (query) {
          const cached = parserCache.get(query);
          if (cached) {
            console.log('Using cached parsed query');
            return cached;
          }
        }
      }
    }
  ]
});

/**
 * Renders GraphiQL HTML interface
 * @param opts - GraphiQL rendering options
 * @returns GraphiQL HTML string
 */
function renderGraphiQL(opts: GraphiQLRendererOptions): string;

/**
 * GraphiQL rendering configuration options
 */
interface GraphiQLRendererOptions {
  /** GraphQL endpoint path (default: "/graphql") */
  endpoint?: string;
  /** Default query to display */
  defaultQuery?: string;
  /** Initial headers in JSON string format */
  headers?: string;
  /** Request credentials mode */
  credentials?: RequestCredentials;
  /** Page title for GraphiQL */
  title?: string;
  /** Subscription protocol to use */
  subscriptionsProtocol?: 'SSE' | 'GRAPHQL_SSE' | 'WS' | 'LEGACY_WS';
  /** Additional headers to always include */
  additionalHeaders?: Record<string, string>;
}

import { renderGraphiQL } from "graphql-yoga";

// Basic GraphiQL rendering
const basicHTML = renderGraphiQL({
  endpoint: '/graphql'
});

// Custom GraphiQL with configuration
const customHTML = renderGraphiQL({
  endpoint: '/api/graphql',
  title: 'My API Explorer',
  defaultQuery: `
    query GetUsers {
      users {
        id
        name
        email
      }
    }
  `,
  headers: JSON.stringify({
    'Authorization': 'Bearer your-token-here',
    'X-Client-Version': '1.0.0'
  }),
  credentials: 'include',
  subscriptionsProtocol: 'SSE',
  additionalHeaders: {
    'X-Custom-Header': 'value'
  }
});

// Use in custom route handler
const customGraphiQLHandler = (request: Request, fetchAPI: FetchAPI) => {
  const html = renderGraphiQL({
    endpoint: '/graphql',
    title: 'Development API',
    defaultQuery: 'query { __schema { types { name } } }'
  });
  
  return new fetchAPI.Response(html, {
    headers: { 'Content-Type': 'text/html' }
  });
};

// Custom GraphiQL plugin
const customGraphiQLPlugin: Plugin = {
  onRequest({ request, endResponse, fetchAPI, url }) {
    if (url.pathname === '/explorer' && request.method === 'GET') {
      const html = renderGraphiQL({
        endpoint: '/graphql',
        title: 'GraphQL Explorer',
        subscriptionsProtocol: 'SSE'
      });
      
      endResponse(new fetchAPI.Response(html, {
        headers: { 'Content-Type': 'text/html; charset=utf-8' }
      }));
    }
  }
};

/**
 * Determines if request should receive GraphiQL interface
 * @param request - HTTP request to check
 * @returns Whether to render GraphiQL
 */
function shouldRenderGraphiQL(request: Request): boolean;

import { shouldRenderGraphiQL, renderGraphiQL } from "graphql-yoga";

// Custom GraphiQL handling
const graphiQLHandler = (request: Request, fetchAPI: FetchAPI) => {
  if (shouldRenderGraphiQL(request)) {
    const html = renderGraphiQL({ endpoint: '/graphql' });
    return new fetchAPI.Response(html, {
      headers: { 'Content-Type': 'text/html' }
    });
  }
  
  return null; // Not a GraphiQL request
};

// Conditional GraphiQL plugin
const conditionalGraphiQLPlugin: Plugin = {
  onRequest({ request, endResponse, fetchAPI, url }) {
    if (url.pathname === '/graphql' && shouldRenderGraphiQL(request)) {
      // Only serve GraphiQL for appropriate requests (GET with HTML accept header)
      const html = renderGraphiQL({
        endpoint: '/graphql',
        title: 'API Explorer'
      });
      
      endResponse(new fetchAPI.Response(html, {
        headers: { 'Content-Type': 'text/html' }
      }));
    }
  }
};

// Environment-based GraphiQL
const productionSafeGraphiQL: Plugin = {
  onRequest({ request, endResponse, fetchAPI, url }) {
    const isDevelopment = process.env.NODE_ENV === 'development';
    const isGraphiQLRequest = shouldRenderGraphiQL(request);
    
    if (url.pathname === '/graphql' && isGraphiQLRequest) {
      if (!isDevelopment) {
        // Redirect to documentation in production
        endResponse(new fetchAPI.Response(null, {
          status: 302,
          headers: { 'Location': '/docs' }
        }));
      } else {
        // Serve GraphiQL in development
        const html = renderGraphiQL({ endpoint: '/graphql' });
        endResponse(new fetchAPI.Response(html, {
          headers: { 'Content-Type': 'text/html' }
        }));
      }
    }
  }
};

/**
 * Utility type for optional single value or array
 */
type MaybeArray<T> = T | T[];

/**
 * Utility type for synchronous or asynchronous values
 */
type PromiseOrValue<T> = T | Promise<T>;

/**
 * Utility type for optional values
 */
type Maybe<T> = T | null | undefined;

/**
 * Utility type for optional object properties
 */
type Optional<T, K extends keyof T> = Omit<T, K> & Partial<Pick<T, K>>;

/**
 * Utility type for object spread operations
 */
type Spread<T1, T2> = T1 & T2;

// Using utility types in function signatures
function processData<T>(input: MaybeArray<T>): T[] {
  return Array.isArray(input) ? input : [input];
}

async function resolveValue<T>(value: PromiseOrValue<T>): Promise<T> {
  return await value;
}

function handleOptionalUser(user: Maybe<User>): string {
  return user?.name ?? 'Anonymous';
}

// Configuration with optional properties
interface ServerConfig {
  port: number;
  host: string;
  ssl?: boolean;
  timeout?: number;
}

type MinimalConfig = Optional<ServerConfig, 'host' | 'ssl' | 'timeout'>;

const config: MinimalConfig = {
  port: 4000
  // host, ssl, timeout are optional
};

// Context merging with type safety
type BaseContext = {
  request: Request;
  timestamp: number;
};

type UserContext = {
  user: User;
  permissions: string[];
};

type MergedContext = Spread<BaseContext, UserContext>;

const createContext = (base: BaseContext, user: UserContext): MergedContext => {
  return { ...base, ...user };
};

// Performance monitoring with LRU cache
const metricsCache = createLRUCache<{
  count: number;
  totalTime: number;
  avgTime: number;
}>({
  max: 1000,
  ttl: 300000 // 5 minutes
});

const performancePlugin: Plugin = {
  onParams({ params, setParams }) {
    const startTime = Date.now();
    const operationName = params.operationName || 'anonymous';
    
    // Store start time in extensions
    setParams({
      ...params,
      extensions: {
        ...params.extensions,
        startTime
      }
    });
  },
  
  onResultProcess({ result, request }) {
    if ('extensions' in result && result.extensions?.startTime) {
      const duration = Date.now() - result.extensions.startTime;
      const operationName = 'operationName'; // Extract from result if available
      
      // Update metrics
      const existing = metricsCache.get(operationName) || { count: 0, totalTime: 0, avgTime: 0 };
      const updated = {
        count: existing.count + 1,
        totalTime: existing.totalTime + duration,
        avgTime: (existing.totalTime + duration) / (existing.count + 1)
      };
      
      metricsCache.set(operationName, updated);
      
      console.log(`Operation ${operationName} took ${duration}ms (avg: ${updated.avgTime.toFixed(2)}ms)`);
    }
  }
};

// Cache warming utility
async function warmupCache<T>(
  cache: LRUCache<T>,
  dataProvider: () => Promise<Array<{ key: string; value: T }>>
) {
  const data = await dataProvider();
  
  for (const { key, value } of data) {
    cache.set(key, value);
  }
  
  console.log(`Cache warmed up with ${data.length} items`);
}

// Usage
const userCache = createLRUCache<User>({ max: 10000, ttl: 600000 });

await warmupCache(userCache, async () => {
  const users = await fetchFrequentlyAccessedUsers();
  return users.map(user => ({ key: user.id, value: user }));
});