File System Integration

interface Methods {
  /** Custom lstat implementation for getting file/directory stats */
  lstat?: (path: string, fromDir?: boolean) => Promise<Stats>;
  /** Custom realpath implementation for resolving symbolic links */
  realpath?: (path: string) => Promise<string>;
  /** Custom read stream creator for file content streaming */
  createReadStream?: (path: string, options?: object) => ReadableStream;
  /** Custom directory reader for listing directory contents */
  readdir?: (path: string) => Promise<string[]>;
  /** Custom error handler for generating error responses */
  sendError?: (absolutePath: string, response: ServerResponse, acceptsJSON: boolean, current: string, handlers: object, config: Config, spec: ErrorSpec) => Promise<void>;
}

/**
 * Custom lstat implementation for getting file/directory stats
 * @param path - Absolute path to the file or directory
 * @param fromDir - Whether the call originated from directory listing (optional)
 * @returns Promise resolving to file stats object
 */
lstat?: (path: string, fromDir?: boolean) => Promise<Stats>;

interface Stats {
  /** File size in bytes */
  size: number;
  /** Last modified time */
  mtime: Date;
  /** Whether this is a directory */
  isDirectory(): boolean;
  /** Whether this is a symbolic link */
  isSymbolicLink(): boolean;
}

const handler = require('serve-handler');

// Custom lstat for cloud storage
const methods = {
  lstat: async (path, fromDir) => {
    const cloudFile = await cloudStorage.stat(path);
    return {
      size: cloudFile.size,
      mtime: new Date(cloudFile.lastModified),
      isDirectory: () => cloudFile.type === 'directory',
      isSymbolicLink: () => false
    };
  }
};

await handler(req, res, {}, methods);

/**
 * Custom realpath implementation for resolving symbolic links
 * @param path - Path to resolve
 * @returns Promise resolving to the real path
 */
realpath?: (path: string) => Promise<string>;

const methods = {
  realpath: async (path) => {
    // Custom symlink resolution logic
    return await customResolveSymlink(path);
  }
};

/**
 * Custom read stream creator for file content streaming
 * @param path - Absolute path to the file
 * @param options - Stream options including start/end for range requests
 * @returns Readable stream of file content
 */
createReadStream?: (path: string, options?: StreamOptions) => ReadableStream;

interface StreamOptions {
  /** Start byte position for range requests */
  start?: number;
  /** End byte position for range requests */
  end?: number;
}

const methods = {
  createReadStream: (path, options = {}) => {
    // Custom stream implementation (e.g., from database or cloud storage)
    return cloudStorage.createReadStream(path, {
      start: options.start,
      end: options.end
    });
  }
};

// Example with S3
const AWS = require('aws-sdk');
const s3 = new AWS.S3();

const methods = {
  createReadStream: (path, options = {}) => {
    const params = {
      Bucket: 'my-bucket',
      Key: path.replace('/public/', '')
    };
    
    if (options.start !== undefined || options.end !== undefined) {
      params.Range = `bytes=${options.start || 0}-${options.end || ''}`;
    }
    
    return s3.getObject(params).createReadStream();
  }
};

/**
 * Custom directory reader for listing directory contents
 * @param path - Absolute path to the directory
 * @returns Promise resolving to array of file/directory names
 */
readdir?: (path: string) => Promise<string[]>;

const methods = {
  readdir: async (path) => {
    // Custom directory listing (e.g., from database)
    const files = await database.listFiles(path);
    return files.map(f => f.name);
  }
};

// Example with cloud storage
const methods = {
  readdir: async (path) => {
    const objects = await cloudStorage.listObjects({
      prefix: path.replace('/public/', ''),
      delimiter: '/'
    });
    
    return objects.map(obj => obj.name);
  }
};

/**
 * Custom error handler for generating error responses
 * @param absolutePath - Absolute path that caused the error
 * @param response - HTTP response object
 * @param acceptsJSON - Whether client accepts JSON responses
 * @param current - Current working directory
 * @param handlers - Handler utilities object
 * @param config - Configuration object
 * @param spec - Error specification object
 * @returns Promise that resolves when error response is sent
 */
sendError?: (
  absolutePath: string,
  response: ServerResponse,
  acceptsJSON: boolean,
  current: string,
  handlers: object,
  config: Config,
  spec: ErrorSpec
) => Promise<void>;

interface ErrorSpec {
  /** HTTP status code */
  statusCode: number;
  /** Error code identifier */
  code: string;
  /** Error message */
  message: string;
  /** Original error object (optional) */
  err?: Error;
}

const methods = {
  sendError: async (absolutePath, response, acceptsJSON, current, handlers, config, spec) => {
    // Custom error handling
    if (spec.statusCode === 404) {
      response.statusCode = 404;
      response.setHeader('Content-Type', 'text/html');
      response.end(`
        <html>
          <body>
            <h1>Custom 404 Page</h1>
            <p>The file ${absolutePath} was not found.</p>
          </body>
        </html>
      `);
    } else {
      // Log error to external service
      await errorLogger.log({
        path: absolutePath,
        error: spec.err,
        statusCode: spec.statusCode
      });
      
      // Use default error handling
      await handlers.sendError(absolutePath, response, acceptsJSON, current, handlers, config, spec);
    }
  }
};

const handler = require('serve-handler');
const AWS = require('aws-sdk');
const redis = require('redis');

const s3 = new AWS.S3();
const redisClient = redis.createClient();

// Complete custom file system implementation for S3 + Redis caching
const methods = {
  lstat: async (path, fromDir) => {
    // Check cache first
    const cached = await redisClient.get(`stat:${path}`);
    if (cached) {
      return JSON.parse(cached);
    }
    
    // Get from S3
    try {
      const object = await s3.headObject({
        Bucket: 'my-static-site',
        Key: path.replace('/public/', '')
      }).promise();
      
      const stats = {
        size: object.ContentLength,
        mtime: object.LastModified,
        isDirectory: () => false,
        isSymbolicLink: () => false
      };
      
      // Cache for 5 minutes
      await redisClient.setex(`stat:${path}`, 300, JSON.stringify(stats));
      return stats;
    } catch (err) {
      if (err.code === 'NotFound') {
        // Check if it's a "directory" (prefix)
        const objects = await s3.listObjectsV2({
          Bucket: 'my-static-site',
          Prefix: path.replace('/public/', '') + '/',
          MaxKeys: 1
        }).promise();
        
        if (objects.Contents.length > 0) {
          return {
            size: 0,
            mtime: new Date(),
            isDirectory: () => true,
            isSymbolicLink: () => false
          };
        }
      }
      throw err;
    }
  },
  
  createReadStream: (path, options = {}) => {
    const params = {
      Bucket: 'my-static-site',
      Key: path.replace('/public/', '')
    };
    
    if (options.start !== undefined || options.end !== undefined) {
      params.Range = `bytes=${options.start || 0}-${options.end || ''}`;
    }
    
    return s3.getObject(params).createReadStream();
  },
  
  readdir: async (path) => {
    const objects = await s3.listObjectsV2({
      Bucket: 'my-static-site',
      Prefix: path.replace('/public/', '') + '/',
      Delimiter: '/'
    }).promise();
    
    const files = [];
    
    // Add files in this directory
    objects.Contents.forEach(obj => {
      const name = obj.Key.split('/').pop();
      if (name) files.push(name);
    });
    
    // Add subdirectories
    objects.CommonPrefixes.forEach(prefix => {
      const name = prefix.Prefix.split('/').slice(-2)[0];
      if (name) files.push(name);
    });
    
    return files;
  },
  
  sendError: async (absolutePath, response, acceptsJSON, current, handlers, config, spec) => {
    // Log to CloudWatch
    const cloudwatch = new AWS.CloudWatchLogs();
    await cloudwatch.putLogEvents({
      logGroupName: '/aws/lambda/static-site',
      logStreamName: 'errors',
      logEvents: [{
        timestamp: Date.now(),
        message: JSON.stringify({
          path: absolutePath,
          statusCode: spec.statusCode,
          message: spec.message
        })
      }]
    }).promise();
    
    // Use default error handling
    await handlers.sendError(absolutePath, response, acceptsJSON, current, handlers, config, spec);
  }
};

// Use with custom methods
await handler(request, response, { public: '/public' }, methods);