Data Protection

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// Enterprise Data Masking Service
// Applies configurable masking strategies to sensitive data
 
interface MaskingRule {
  fieldPattern: string;  // Field name pattern (regex)
  dataType: DataType;
  strategy: MaskingStrategy;
  config: MaskingConfig;
}
 
enum MaskingStrategy {
  CHARACTER_MASK = 'character_mask',
  SUBSTITUTION = 'substitution',
  HASH = 'hash',
  SHUFFLE = 'shuffle',
  VARIANCE = 'variance',
  TRUNCATE = 'truncate',
  NULLIFY = 'nullify',
  FORMAT_PRESERVING = 'format_preserving',
}
 
interface MaskingConfig {
  maskChar?: string;           // Character for masking (default: *)
  revealFirst?: number;        // Characters to show at start
  revealLast?: number;         // Characters to show at end
  hashAlgorithm?: string;      // For hash strategy
  variancePercent?: number;    // For numeric variance
  substitutionSource?: string; // Data source for substitutions
  preserveFormat?: boolean;    // Maintain character types (letter→letter)
}
 
class DataMaskingService {
  private rules: Map<string, MaskingRule[]>;
  private substitutionData: SubstitutionDataProvider;
  private deterministicSeed: string;
 
  constructor(config: MaskingServiceConfig) {
    this.rules = this.loadRules(config.rulesPath);
    this.substitutionData = new SubstitutionDataProvider(config.substitutionDb);
    this.deterministicSeed = config.seed || crypto.randomBytes(32).toString('hex');
  }
 
  async maskRecord<T extends object>(
    record: T,
    context: MaskingContext
  ): Promise<T> {
    const masked = { ...record } as any;
    
    for (const [fieldPath, value] of this.traverseObject(record)) {
      const applicableRules = this.findApplicableRules(fieldPath, value);
      
      if (applicableRules.length > 0) {
        const rule = applicableRules[0]; // First matching rule
        const maskedValue = await this.applyMasking(
          value,
          rule,
          context,
          fieldPath
        );
        this.setFieldValue(masked, fieldPath, maskedValue);
      }
    }
    
    return masked;
  }
 
  private async applyMasking(
    value: any,
    rule: MaskingRule,
    context: MaskingContext,
    fieldPath: string
  ): Promise<any> {
    if (value === null || value === undefined) {
      return value;
    }
    
    switch (rule.strategy) {
      case MaskingStrategy.CHARACTER_MASK:
        return this.characterMask(String(value), rule.config);
        
      case MaskingStrategy.SUBSTITUTION:
        return this.substitute(value, rule, context);
        
      case MaskingStrategy.HASH:
        return this.hashMask(String(value), rule.config, fieldPath);
        
      case MaskingStrategy.VARIANCE:
        return this.applyVariance(Number(value), rule.config);
        
      case MaskingStrategy.TRUNCATE:
        return this.truncate(String(value), rule.config);
        
      case MaskingStrategy.NULLIFY:
        return null;
        
      case MaskingStrategy.FORMAT_PRESERVING:
        return this.formatPreservingMask(String(value), rule.config);
        
      case MaskingStrategy.SHUFFLE:
        // Shuffle is applied at dataset level, not individual record
        throw new Error('Shuffle strategy requires dataset-level masking');
        
      default:
        return this.characterMask(String(value), { maskChar: '*' });
    }
  }
 
  private characterMask(value: string, config: MaskingConfig): string {
    const maskChar = config.maskChar || '*';
    const revealFirst = config.revealFirst || 0;
    const revealLast = config.revealLast || 0;
    
    if (value.length <= revealFirst + revealLast) {
      return maskChar.repeat(value.length);
    }
    
    const start = value.substring(0, revealFirst);
    const end = value.substring(value.length - revealLast);
    const middleLength = value.length - revealFirst - revealLast;
    const masked = maskChar.repeat(middleLength);
    
    return start + masked + end;
  }
 
  private async substitute(
    value: any,
    rule: MaskingRule,
    context: MaskingContext
  ): Promise<any> {
    // Deterministic substitution for consistency across records
    const seed = this.generateDeterministicSeed(value, context.recordId);
    
    switch (rule.dataType) {
      case DataType.NAME:
        return this.substitutionData.getRandomName(seed);
      case DataType.EMAIL:
        return this.substitutionData.getRandomEmail(seed);
      case DataType.PHONE:
        return this.substitutionData.getRandomPhone(seed);
      case DataType.ADDRESS:
        return this.substitutionData.getRandomAddress(seed);
      case DataType.SSN:
        return this.substitutionData.getRandomSSN(seed);
      default:
        return value;
    }
  }
 
  private hashMask(
    value: string,
    config: MaskingConfig,
    fieldPath: string
  ): string {
    const algorithm = config.hashAlgorithm || 'sha256';
    // Include field path and seed to prevent cross-field rainbow attacks
    const saltedValue = `${this.deterministicSeed}:${fieldPath}:${value}`;
    return crypto
      .createHash(algorithm)
      .update(saltedValue)
      .digest('hex')
      .substring(0, 16); // Truncate for readability
  }
 
  private formatPreservingMask(value: string, config: MaskingConfig): string {
    // Replace each character with same type (letter→letter, digit→digit)
    let result = '';
    const revealFirst = config.revealFirst || 0;
    const revealLast = config.revealLast || 0;
    
    for (let i = 0; i < value.length; i++) {
      if (i < revealFirst || i >= value.length - revealLast) {
        result += value[i];
      } else {
        result += this.replacePreservingFormat(value[i]);
      }
    }
    
    return result;
  }
 
  private replacePreservingFormat(char: string): string {
    if (/[a-z]/.test(char)) return 'x';
    if (/[A-Z]/.test(char)) return 'X';
    if (/[0-9]/.test(char)) return '0';
    return char; // Preserve special characters, spaces, etc.
  }
 
  private applyVariance(value: number, config: MaskingConfig): number {
    const variancePercent = config.variancePercent || 10;
    const variance = value * (variancePercent / 100);
    const offset = (Math.random() * 2 - 1) * variance;
    return Math.round(value + offset);
  }
 
  // Dataset-level shuffling for referential consistency
  async shuffleDataset(
    records: any[],
    fieldsToShuffle: string[]
  ): Promise<any[]> {
    const shuffled = records.map(r => ({ ...r }));
    
    for (const field of fieldsToShuffle) {
      // Extract all values for this field
      const values = shuffled.map(r => this.getFieldValue(r, field));
      
      // Shuffle the values array
      for (let i = values.length - 1; i > 0; i--) {
        const j = Math.floor(Math.random() * (i + 1));
        [values[i], values[j]] = [values[j], values[i]];
      }
      
      // Apply shuffled values back
      shuffled.forEach((record, index) => {
        this.setFieldValue(record, field, values[index]);
      });
    }
    
    return shuffled;
  }
}

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// Application-Level Dynamic Data Masking
// Masks query results based on caller authorization
 
interface MaskingPolicy {
  fieldPath: string;
  defaultMask: MaskingStrategy;
  exemptRoles: string[];      // Roles that see unmasked data
  exemptPurposes: string[];   // Approved purposes for full access
}
 
interface DataAccessContext {
  userId: string;
  roles: string[];
  accessPurpose: string;
  clientType: 'internal' | 'external' | 'api';
}
 
class DynamicMaskingMiddleware {
  private policies: Map<string, MaskingPolicy>;
  private maskingService: DataMaskingService;
  private auditLogger: DataAccessAuditLogger;
 
  async processQueryResult<T>(
    results: T[],
    entityType: string,
    context: DataAccessContext
  ): Promise<T[]> {
    const entityPolicies = this.getPoliciesForEntity(entityType);
    
    if (entityPolicies.length === 0) {
      return results; // No masking policies for this entity
    }
    
    const maskedResults: T[] = [];
    const accessLog: FieldAccessLog[] = [];
    
    for (const record of results) {
      const maskedRecord = { ...record } as any;
      
      for (const policy of entityPolicies) {
        const fieldValue = this.getFieldValue(record, policy.fieldPath);
        
        if (fieldValue === undefined || fieldValue === null) {
          continue;
        }
        
        // Check if user is exempt from masking
        const isExempt = this.checkExemption(policy, context);
        
        if (!isExempt) {
          // Apply masking
          const maskedValue = await this.maskingService.maskValue(
            fieldValue,
            policy.defaultMask
          );
          this.setFieldValue(maskedRecord, policy.fieldPath, maskedValue);
          
          accessLog.push({
            field: policy.fieldPath,
            masked: true,
            reason: 'policy_enforcement',
          });
        } else {
          accessLog.push({
            field: policy.fieldPath,
            masked: false,
            reason: this.getExemptionReason(policy, context),
          });
        }
      }
      
      maskedResults.push(maskedRecord);
    }
    
    // Audit log the access
    await this.auditLogger.logDataAccess({
      userId: context.userId,
      entityType,
      recordCount: results.length,
      fieldAccess: accessLog,
      timestamp: new Date(),
      purpose: context.accessPurpose,
    });
    
    return maskedResults;
  }
 
  private checkExemption(
    policy: MaskingPolicy,
    context: DataAccessContext
  ): boolean {
    // Check role-based exemption
    if (policy.exemptRoles.some(role => context.roles.includes(role))) {
      return true;
    }
    
    // Check purpose-based exemption
    if (policy.exemptPurposes.includes(context.accessPurpose)) {
      return true;
    }
    
    return false;
  }
 
  // SQL View approach for database-level DDM
  generateMaskedView(
    tableName: string,
    policies: MaskingPolicy[],
    roleVariable: string = 'CURRENT_ROLE()'
  ): string {
    const selectClauses = [];
    const columns = this.getTableColumns(tableName);
    
    for (const column of columns) {
      const policy = policies.find(p => p.fieldPath === column.name);
      
      if (!policy) {
        selectClauses.push(column.name);
        continue;
      }
      
      // Generate CASE statement for role-based masking
      const exemptRolesStr = policy.exemptRoles
        .map(r => `'${r}'`)
        .join(', ');
      
      const maskExpression = this.generateSQLMaskExpression(
        column.name,
        column.type,
        policy.defaultMask
      );
      
      selectClauses.push(`
        CASE 
          WHEN ${roleVariable} IN (${exemptRolesStr}) THEN ${column.name}
          ELSE ${maskExpression}
        END AS ${column.name}
      `);
    }
    
    return `
      CREATE OR REPLACE VIEW ${tableName}_masked AS
      SELECT 
        ${selectClauses.join(',\n        ')}
      FROM ${tableName}
    `;
  }
 
  private generateSQLMaskExpression(
    columnName: string,
    columnType: string,
    strategy: MaskingStrategy
  ): string {
    switch (strategy) {
      case MaskingStrategy.CHARACTER_MASK:
        return `CONCAT(SUBSTRING(${columnName}, 1, 1), '****')`;
        
      case MaskingStrategy.TRUNCATE:
        return `RIGHT(${columnName}, 4)`;
        
      case MaskingStrategy.NULLIFY:
        return 'NULL';
        
      case MaskingStrategy.HASH:
        return `LEFT(SHA2(${columnName}, 256), 16)`;
        
      default:
        return `'[MASKED]'`;
    }
  }
}

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// Enterprise Tokenization Vault Service
// Securely stores sensitive data and issues non-sensitive tokens
 
interface TokenRecord {
  token: string;
  vault: string;                // Logical vault (e.g., 'payment_cards', 'ssn')
  encryptedValue: Buffer;       // AES-256-GCM encrypted original
  keyVersion: number;           // For key rotation
  metadata: TokenMetadata;
  createdAt: Date;
  expiresAt?: Date;
  accessCount: number;
  lastAccessedAt?: Date;
}
 
interface TokenMetadata {
  format: string;               // Original format for validation
  lastFour?: string;            // For display (cards, SSN)
  dataType: string;
  ownerId: string;              // Data subject ID
  createdBy: string;            // System that created token
}
 
interface TokenizationRequest {
  value: string;
  vault: string;
  ownerId: string;
  expirationDays?: number;
  preserveFormat?: boolean;
}
 
class TokenizationVaultService {
  private db: TokenDatabase;
  private keyManager: KeyManagementService;
  private auditLogger: VaultAuditLogger;
  private formatPreserver: FormatPreservingEncryptor;
 
  async tokenize(request: TokenizationRequest): Promise<TokenResult> {
    // Validate input format matches expected pattern
    this.validateFormat(request.value, request.vault);
    
    // Check for existing token (idempotency)
    const existingToken = await this.findExistingToken(
      request.value,
      request.vault,
      request.ownerId
    );
    
    if (existingToken) {
      return {
        token: existingToken.token,
        isNew: false,
        metadata: existingToken.metadata,
      };
    }
    
    // Generate token
    const token = request.preserveFormat
      ? await this.generateFormatPreservingToken(request.value, request.vault)
      : this.generateRandomToken(request.vault);
    
    // Encrypt the sensitive value
    const currentKey = await this.keyManager.getCurrentKey('tokenization');
    const encryptedValue = await this.encrypt(request.value, currentKey);
    
    // Extract safe metadata (last 4 digits, etc.)
    const metadata = this.extractSafeMetadata(request.value, request.vault);
    
    // Store token record
    const record: TokenRecord = {
      token,
      vault: request.vault,
      encryptedValue,
      keyVersion: currentKey.version,
      metadata: {
        ...metadata,
        ownerId: request.ownerId,
        createdBy: this.getCurrentSystemId(),
      },
      createdAt: new Date(),
      expiresAt: request.expirationDays
        ? new Date(Date.now() + request.expirationDays * 24 * 60 * 60 * 1000)
        : undefined,
      accessCount: 0,
    };
    
    await this.db.store(record);
    
    // Audit log
    await this.auditLogger.logTokenization({
      token,
      vault: request.vault,
      ownerId: request.ownerId,
      timestamp: new Date(),
    });
    
    return {
      token,
      isNew: true,
      metadata: record.metadata,
    };
  }
 
  async detokenize(
    token: string,
    context: DetokenizationContext
  ): Promise<string> {
    // Fetch token record
    const record = await this.db.getByToken(token);
    
    if (!record) {
      throw new TokenNotFoundError(`Token ${token} not found`);
    }
    
    // Check expiration
    if (record.expiresAt && record.expiresAt < new Date()) {
      throw new TokenExpiredError(`Token ${token} has expired`);
    }
    
    // Authorize the detokenization request
    await this.authorizeDetokenization(record, context);
    
    // Retrieve encryption key (may need old version for rotation)
    const key = await this.keyManager.getKey(
      'tokenization',
      record.keyVersion
    );
    
    // Decrypt the value
    const value = await this.decrypt(record.encryptedValue, key);
    
    // Update access metadata
    await this.db.updateAccessMetadata(token, {
      accessCount: record.accessCount + 1,
      lastAccessedAt: new Date(),
    });
    
    // Audit log
    await this.auditLogger.logDetokenization({
      token,
      vault: record.vault,
      accessedBy: context.requesterId,
      purpose: context.purpose,
      timestamp: new Date(),
    });
    
    return value;
  }
 
  async deleteToken(token: string, context: DeletionContext): Promise<void> {
    const record = await this.db.getByToken(token);
    
    if (!record) {
      return; // Idempotent deletion
    }
    
    // Verify deletion authorization
    await this.authorizeDeletion(record, context);
    
    // Delete the record (actual value is gone)
    await this.db.delete(token);
    
    // Audit log
    await this.auditLogger.logTokenDeletion({
      token,
      vault: record.vault,
      ownerId: record.metadata.ownerId,
      deletedBy: context.requesterId,
      reason: context.reason,
      timestamp: new Date(),
    });
  }
 
  // Batch operations for efficient processing
  async batchTokenize(
    requests: TokenizationRequest[]
  ): Promise<Map<string, TokenResult>> {
    const results = new Map<string, TokenResult>();
    
    // Use transaction for atomicity
    await this.db.transaction(async (tx) => {
      for (const request of requests) {
        const result = await this.tokenize(request);
        results.set(request.value, result);
      }
    });
    
    return results;
  }
 
  // For data subject rights - delete all tokens for a user
  async deleteAllForOwner(ownerId: string, reason: string): Promise<number> {
    const tokens = await this.db.getByOwner(ownerId);
    
    for (const token of tokens) {
      await this.deleteToken(token.token, {
        requesterId: 'system',
        reason: reason,
      });
    }
    
    return tokens.length;
  }
 
  private generateRandomToken(vault: string): string {
    const prefix = vault.substring(0, 3).toLowerCase();
    const random = crypto.randomBytes(16).toString('hex');
    return `${prefix}_${random}`;
  }
 
  private async generateFormatPreservingToken(
    value: string,
    vault: string
  ): Promise<string> {
    // Format-preserving encryption keeps the token the same format as original
    // Useful for systems expecting specific formats (e.g., 16-digit card number)
    return this.formatPreserver.encrypt(value, vault);
  }
 
  private extractSafeMetadata(value: string, vault: string): Partial<TokenMetadata> {
    switch (vault) {
      case 'payment_cards':
        return {
          format: 'card',
          lastFour: value.slice(-4),
          dataType: 'credit_card',
        };
      case 'ssn':
        return {
          format: 'ssn',
          lastFour: value.replace(/-/g, '').slice(-4),
          dataType: 'ssn',
        };
      default:
        return {
          format: 'general',
          dataType: vault,
        };
    }
  }
}

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// Format-Preserving Encryption Implementation
// Uses FF1 algorithm per NIST SP 800-38G
 
interface FPEConfig {
  key: Buffer;           // 128, 192, or 256 bits
  tweak: Buffer;         // Context-specific tweak
  alphabet: string;      // Valid characters (e.g., '0123456789')
}
 
class FormatPreservingEncryptor {
  private ff1: FF1Algorithm;
 
  constructor() {
    this.ff1 = new FF1Algorithm();
  }
 
  async encryptPreservingFormat(
    plaintext: string,
    config: FPEConfig
  ): Promise<string> {
    // Validate input contains only alphabet characters
    this.validateAlphabet(plaintext, config.alphabet);
    
    // Extract format-relevant characters and their positions
    const { extracted, template } = this.extractCharacters(
      plaintext,
      config.alphabet
    );
    
    if (extracted.length === 0) {
      return plaintext; // No encryptable characters
    }
    
    // Convert to numeric representation
    const numericPlaintext = this.toNumeric(extracted, config.alphabet);
    
    // Apply FF1 encryption
    const numericCiphertext = await this.ff1.encrypt(
      numericPlaintext,
      config.key,
      config.tweak,
      config.alphabet.length
    );
    
    // Convert back to original alphabet
    const encryptedChars = this.fromNumeric(
      numericCiphertext,
      config.alphabet
    );
    
    // Reinsert into original format template
    return this.applyTemplate(encryptedChars, template);
  }
 
  async decryptPreservingFormat(
    ciphertext: string,
    config: FPEConfig
  ): Promise<string> {
    const { extracted, template } = this.extractCharacters(
      ciphertext,
      config.alphabet
    );
    
    const numericCiphertext = this.toNumeric(extracted, config.alphabet);
    
    const numericPlaintext = await this.ff1.decrypt(
      numericCiphertext,
      config.key,
      config.tweak,
      config.alphabet.length
    );
    
    const decryptedChars = this.fromNumeric(
      numericPlaintext,
      config.alphabet
    );
    
    return this.applyTemplate(decryptedChars, template);
  }
 
  // Extract alphabet characters while preserving format template
  private extractCharacters(
    input: string,
    alphabet: string
  ): { extracted: string; template: (number | string)[] } {
    const extracted: string[] = [];
    const template: (number | string)[] = [];
    let extractedIndex = 0;
    
    for (const char of input) {
      if (alphabet.includes(char)) {
        extracted.push(char);
        template.push(extractedIndex++);
      } else {
        template.push(char); // Non-alphabet char preserved in template
      }
    }
    
    return {
      extracted: extracted.join(''),
      template,
    };
  }
 
  // Apply encrypted characters back into format template
  private applyTemplate(
    chars: string,
    template: (number | string)[]
  ): string {
    let result = '';
    
    for (const item of template) {
      if (typeof item === 'number') {
        result += chars[item];
      } else {
        result += item; // Preserved non-alphabet character
      }
    }
    
    return result;
  }
 
  // Example: Encrypt credit card preserving format
  encryptCreditCard(cardNumber: string, key: Buffer): Promise<string> {
    // Remove spaces/dashes for encryption, preserve positions
    const config: FPEConfig = {
      key,
      tweak: Buffer.from('credit_card'), // Domain-specific tweak
      alphabet: '0123456789',
    };
    
    return this.encryptPreservingFormat(cardNumber, config);
  }
 
  // Example: Encrypt SSN preserving format
  encryptSSN(ssn: string, key: Buffer): Promise<string> {
    const config: FPEConfig = {
      key,
      tweak: Buffer.from('social_security'),
      alphabet: '0123456789',
    };
    
    // Input: 123-45-6789
    // Output: xxx-xx-xxxx (different digits, same format)
    return this.encryptPreservingFormat(ssn, config);
  }
}
 
// Usage example
async function example() {
  const fpe = new FormatPreservingEncryptor();
  const key = crypto.randomBytes(32); // 256-bit key
  
  // Credit card encryption
  const card = '4532-1234-5678-9012';
  const encryptedCard = await fpe.encryptCreditCard(card, key);
  console.log(encryptedCard); // '8291-7456-3012-4567' (same format)
  
  // SSN encryption
  const ssn = '123-45-6789';
  const encryptedSSN = await fpe.encryptSSN(ssn, key);
  console.log(encryptedSSN); // '847-92-1356' (same format)
}

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// Realistic Test Data Generation Service
// Generates synthetic data that mimics production characteristics
 
import { faker } from '@faker-js/faker';
 
interface DataGenerationSchema {
  tableName: string;
  count: number;
  fields: FieldGenerator[];
  relationships?: RelationshipSpec[];
}
 
interface FieldGenerator {
  name: string;
  type: GeneratorType;
  options?: GeneratorOptions;
}
 
class TestDataGeneratorService {
  private generatedData: Map<string, any[]> = new Map();
  private relationshipResolver: RelationshipResolver;
 
  constructor() {
    this.relationshipResolver = new RelationshipResolver();
  }
 
  async generateDataset(
    schemas: DataGenerationSchema[]
  ): Promise<Map<string, any[]>> {
    // Sort by dependencies to ensure foreign keys are satisfied
    const sortedSchemas = this.topologicalSort(schemas);
    
    for (const schema of sortedSchemas) {
      const records = await this.generateTable(schema);
      this.generatedData.set(schema.tableName, records);
    }
    
    return this.generatedData;
  }
 
  private async generateTable(schema: DataGenerationSchema): Promise<any[]> {
    const records: any[] = [];
    
    for (let i = 0; i < schema.count; i++) {
      const record: any = {};
      
      for (const field of schema.fields) {
        record[field.name] = await this.generateField(field, i, schema);
      }
      
      // Resolve foreign key relationships
      if (schema.relationships) {
        for (const rel of schema.relationships) {
          record[rel.foreignKey] = this.relationshipResolver.resolve(
            rel,
            this.generatedData,
            i
          );
        }
      }
      
      records.push(record);
    }
    
    return records;
  }
 
  private async generateField(
    field: FieldGenerator,
    index: number,
    schema: DataGenerationSchema
  ): Promise<any> {
    const options = field.options || {};
    
    switch (field.type) {
      // Personal Information (all synthetic)
      case 'firstName':
        return faker.person.firstName();
        
      case 'lastName':
        return faker.person.lastName();
        
      case 'fullName':
        return faker.person.fullName();
        
      case 'email':
        // Generate unique, testable emails
        return `user${index}@testdomain-${schema.tableName}.example.com`;
        
      case 'phone':
        // Use clearly fake patterns
        return faker.phone.number('555-###-####');
        
      // Financial Data (valid format, fake values)
      case 'creditCard':
        // Generate Luhn-valid test card numbers
        return this.generateTestCreditCard(options.cardType);
        
      case 'ssn':
        // Use reserved test SSN ranges (900-999 prefix)
        return `9${faker.string.numeric(2)}-${faker.string.numeric(2)}-${faker.string.numeric(4)}`;
        
      case 'bankAccount':
        return faker.finance.accountNumber();
        
      // Addresses (real-looking but fictional)
      case 'address':
        return {
          street: faker.location.streetAddress(),
          city: faker.location.city(),
          state: faker.location.state(),
          zip: faker.location.zipCode(),
          country: 'Test Country',
        };
        
      // Temporal Data
      case 'dateOfBirth':
        return faker.date.birthdate({
          min: options.minAge || 18,
          max: options.maxAge || 80,
          mode: 'age',
        });
        
      case 'timestamp':
        return faker.date.between({
          from: options.from || new Date('2020-01-01'),
          to: options.to || new Date(),
        });
        
      // Business Data
      case 'companyName':
        return faker.company.name();
        
      case 'jobTitle':
        return faker.person.jobTitle();
        
      case 'amount':
        return faker.number.float({
          min: options.min || 0,
          max: options.max || 10000,
          multipleOf: 0.01,
        });
        
      // Sequential/Reference Fields
      case 'uuid':
        return faker.string.uuid();
        
      case 'sequence':
        return index + (options.startAt || 1);
        
      // Custom Patterns
      case 'pattern':
        return faker.helpers.replaceSymbols(options.pattern);
        
      case 'enum':
        return faker.helpers.arrayElement(options.values);
        
      case 'weighted':
        return this.weightedRandom(options.weights);
        
      default:
        return faker.lorem.word();
    }
  }
 
  private generateTestCreditCard(type?: string): string {
    // Test card numbers that pass Luhn but are clearly fake
    const testCards: Record<string, string> = {
      visa: '4111111111111111',
      mastercard: '5500000000000004',
      amex: '340000000000009',
      discover: '6011000000000004',
    };
    
    return testCards[type || 'visa'];
  }
 
  private weightedRandom(weights: Record<string, number>): string {
    const entries = Object.entries(weights);
    const total = entries.reduce((sum, [_, w]) => sum + w, 0);
    let random = Math.random() * total;
    
    for (const [value, weight] of entries) {
      random -= weight;
      if (random <= 0) return value;
    }
    
    return entries[0][0];
  }
 
  // Generate consistent test datasets for reproducible tests
  generateDeterministic(
    schemas: DataGenerationSchema[],
    seed: number
  ): Promise<Map<string, any[]>> {
    faker.seed(seed);
    return this.generateDataset(schemas);
  }
}
 
// Usage Example
const schema: DataGenerationSchema = {
  tableName: 'customers',
  count: 1000,
  fields: [
    { name: 'id', type: 'uuid' },
    { name: 'firstName', type: 'firstName' },
    { name: 'lastName', type: 'lastName' },
    { name: 'email', type: 'email' },
    { name: 'phone', type: 'phone' },
    { name: 'ssn', type: 'ssn' },
    { name: 'createdAt', type: 'timestamp' },
    { name: 'tier', type: 'weighted', options: {
      weights: { 'free': 0.7, 'premium': 0.25, 'enterprise': 0.05 }
    }},
  ],
};