டைப்ஸ்கிரிப்ட் டெக்கரேட்டர்கள்: வலுவான பயன்பாடுகளுக்கான மெட்டாடேட்டா புரோகிராமிங் பேட்டர்ன்களில் தேர்ச்சி பெறுதல்

            @MyDecorator
class MyClass {
  @AnotherDecorator
  myMethod() {
    // ...
  }
}
            

              
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            // tsconfig.json
{
  "compilerOptions": {
    "target": "ES2017",
    "module": "commonjs",
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true,
    "outDir": "./dist",
    "strict": true,
    "esModuleInterop": true,
    "skipLibCheck": true,
    "forceConsistentCasingInFileNames": true
  }
}
            

              
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            npm install reflect-metadata --save
# or
yarn add reflect-metadata
            

              
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            import "reflect-metadata";
// Your application code follows
            

              
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            function Logger(prefix: string) {
  return function (target: Function) {
    console.log(`[${prefix}] Class ${target.name} has been defined.`);
  };
}

@Logger("APP_INIT")
class ApplicationBootstrap {
  constructor() {
    console.log("Application is starting...");
  }
}

const app = new ApplicationBootstrap();
// Output:
// [APP_INIT] Class ApplicationBootstrap has been defined.
// Application is starting...
            

              
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            function ClassDecorator(target: Function) { ... }
            

              
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            const InjectableServiceRegistry = new Map<string, Function>();

function Injectable(name?: string) {
  return function<T extends { new(...args: any[]): {} }>(constructor: T) {
    const serviceName = name || constructor.name;
    InjectableServiceRegistry.set(serviceName, constructor);
    console.log(`Registered service: ${serviceName}`);

    // Optionally, you could return a new class here to augment behavior
    return class extends constructor {
      createdAt = new Date();
      // Additional properties or methods for all injected services
    };
  };
}

@Injectable("UserService")
class UserDataService {
  getUsers() {
    return [{ id: 1, name: "Alice" }, { id: 2, name: "Bob" }];
  }
}

@Injectable()
class ProductDataService {
  getProducts() {
    return [{ id: 101, name: "Laptop" }, { id: 102, name: "Mouse" }];
  }
}

console.log("--- Services Registered ---");
console.log(Array.from(InjectableServiceRegistry.keys()));

const userServiceConstructor = InjectableServiceRegistry.get("UserService");
if (userServiceConstructor) {
  const userServiceInstance = new userServiceConstructor();
  console.log("Users:", userServiceInstance.getUsers());
  // console.log("User Service Created At:", userServiceInstance.createdAt); // If the returned class is used
}
            

              
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            function MethodDecorator(target: Object, propertyKey: string | symbol, descriptor: PropertyDescriptor) { ... }
            

              
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            function MeasurePerformance(target: Object, propertyKey: string, descriptor: PropertyDescriptor) {
  const originalMethod = descriptor.value;

  descriptor.value = function(...args: any[]) {
    const start = process.hrtime.bigint();
    const result = originalMethod.apply(this, args);
    const end = process.hrtime.bigint();
    const duration = Number(end - start) / 1_000_000;
    console.log(`Method "${propertyKey}" executed in ${duration.toFixed(2)} ms`);
    return result;
  };

  return descriptor;
}

class DataProcessor {
  @MeasurePerformance
  processData(data: number[]): number[] {
    // Simulate a complex, time-consuming operation
    for (let i = 0; i < 1_000_000; i++) {
      Math.sin(i);
    }
    return data.map(n => n * 2);
  }

  @MeasurePerformance
  fetchRemoteData(id: string): Promise<string> {
    return new Promise(resolve => {
      setTimeout(() => {
        resolve(`Data for ID: ${id}`);
      }, 500);
    });
  }
}

const processor = new DataProcessor();
processor.processData([1, 2, 3]);
processor.fetchRemoteData("abc").then(result => console.log(result));
            

              
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            function AccessorDecorator(target: Object, propertyKey: string | symbol, descriptor: PropertyDescriptor) { ... }
            

              
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            function CachedGetter(target: any, propertyKey: string, descriptor: PropertyDescriptor) {
  const originalGetter = descriptor.get;
  const cacheKey = `_cached_${String(propertyKey)}`;

  if (originalGetter) {
    descriptor.get = function() {
      if (this[cacheKey] === undefined) {
        console.log(`[Cache Miss] Computing value for ${String(propertyKey)}`);
        this[cacheKey] = originalGetter.apply(this);
      } else {
        console.log(`[Cache Hit] Using cached value for ${String(propertyKey)}`);
      }
      return this[cacheKey];
    };
  }
  return descriptor;
}

class ReportGenerator {
  private data: number[];

  constructor(data: number[]) {
    this.data = data;
  }

  // Simulates an expensive computation
  @CachedGetter
  get expensiveSummary(): number {
    console.log("Performing expensive summary calculation...");
    return this.data.reduce((sum, current) => sum + current, 0) / this.data.length;
  }
}

const generator = new ReportGenerator([10, 20, 30, 40, 50]);

console.log("First access:", generator.expensiveSummary);
console.log("Second access:", generator.expensiveSummary);
console.log("Third access:", generator.expensiveSummary);
            

              
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            function PropertyDecorator(target: Object, propertyKey: string | symbol) { ... }
            

              
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            interface ValidationRule {
  property: string | symbol;
  validate: (value: any) => boolean;
  message: string;
}

const validationRules: Map<Function, ValidationRule[]> = new Map();

function Required(target: Object, propertyKey: string | symbol) {
  const rules = validationRules.get(target.constructor) || [];
  rules.push({
    property: propertyKey,
    validate: (value: any) => value !== null && value !== undefined && value !== "",
    message: `${String(propertyKey)} is required.`
  });
  validationRules.set(target.constructor, rules);
}

function validate(instance: any): string[] {
  const classRules = validationRules.get(instance.constructor) || [];
  const errors: string[] = [];

  for (const rule of classRules) {
    if (!rule.validate(instance[rule.property])) {
      errors.push(rule.message);
    }
  }
  return errors;
}

class UserProfile {
  @Required
  firstName: string;

  @Required
  lastName: string;

  age?: number;

  constructor(firstName: string, lastName: string, age?: number) {
    this.firstName = firstName;
    this.lastName = lastName;
    this.age = age;
  }
}

const user1 = new UserProfile("John", "Doe", 30);
console.log("User 1 validation errors:", validate(user1)); // []

const user2 = new UserProfile("", "Smith");
console.log("User 2 validation errors:", validate(user2)); // ["firstName is required."]

const user3 = new UserProfile("Alice", "");
console.log("User 3 validation errors:", validate(user3)); // ["lastName is required."]
            

              
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            function ParameterDecorator(target: Object, propertyKey: string | symbol | undefined, parameterIndex: number) { ... }
            

              
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            interface ParameterMetadata {
  index: number;
  key: string | symbol;
  resolver: (request: any) => any;
}

const parameterResolvers: Map<Function, Map<string | symbol, ParameterMetadata[]>> = new Map();

function RequestParam(paramName: string) {
  return function (target: Object, propertyKey: string | symbol | undefined, parameterIndex: number) {
    const targetKey = propertyKey || "constructor";
    let methodResolvers = parameterResolvers.get(target.constructor);
    if (!methodResolvers) {
      methodResolvers = new Map();
      parameterResolvers.set(target.constructor, methodResolvers);
    }
    const paramMetadata = methodResolvers.get(targetKey) || [];
    paramMetadata.push({
      index: parameterIndex,
      key: targetKey,
      resolver: (request: any) => request[paramName]
    });
    methodResolvers.set(targetKey, paramMetadata);
  };
}

// A hypothetical framework function to invoke a method with resolved parameters
function executeWithParams(instance: any, methodName: string, request: any) {
  const classResolvers = parameterResolvers.get(instance.constructor);
  if (!classResolvers) {
    return (instance[methodName] as Function).apply(instance, []);
  }
  const methodParamMetadata = classResolvers.get(methodName);
  if (!methodParamMetadata) {
    return (instance[methodName] as Function).apply(instance, []);
  }

  const args: any[] = Array(methodParamMetadata.length);
  for (const meta of methodParamMetadata) {
    args[meta.index] = meta.resolver(request);
  }
  return (instance[methodName] as Function).apply(instance, args);
}

class UserController {
  getUser(@RequestParam("id") userId: string, @RequestParam("token") authToken?: string) {
    console.log(`Fetching user with ID: ${userId}, Token: ${authToken || "N/A"}`);
    return { id: userId, name: "Jane Doe" };
  }

  deleteUser(@RequestParam("id") userId: string) {
    console.log(`Deleting user with ID: ${userId}`);
    return { status: "deleted", id: userId };
  }
}

const userController = new UserController();

// Simulate an incoming request
const mockRequest = {
  id: "user123",
  token: "abc-123",
  someOtherProp: "xyz"
};

console.log("\n--- Executing getUser ---");
executeWithParams(userController, "getUser", mockRequest);

console.log("\n--- Executing deleteUser ---");
executeWithParams(userController, "deleteUser", { id: "user456" });
            

              
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            @DecoratorA
@DecoratorB
class MyClass {
  // ...
}

            

              
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            function LogCall(target: any, propertyKey: string, descriptor: PropertyDescriptor) {
  const originalMethod = descriptor.value;
  descriptor.value = function (...args: any[]) {
    console.log(`[LOG] Calling ${String(propertyKey)} with args:`, args);
    const result = originalMethod.apply(this, args);
    console.log(`[LOG] Method ${String(propertyKey)} returned:`, result);
    return result;
  };
  return descriptor;
}

function Authorization(roles: string[]) {
  return function (target: any, propertyKey: string, descriptor: PropertyDescriptor) {
    const originalMethod = descriptor.value;
    descriptor.value = function (...args: any[]) {
      const currentUserRoles = ["admin"]; // Simulate fetching current user roles
      const authorized = roles.some(role => currentUserRoles.includes(role));
      if (!authorized) {
        console.warn(`[AUTH] Access denied for ${String(propertyKey)}. Required roles: ${roles.join(", ")}`);
        throw new Error("Unauthorized access");
      }
      console.log(`[AUTH] Access granted for ${String(propertyKey)}`);
      return originalMethod.apply(this, args);
    };
    return descriptor;
  };
}

class SecureService {
  @LogCall
  @Authorization(["admin"])
  deleteSensitiveData(id: string) {
    console.log(`Deleting sensitive data for ID: ${id}`);
    return `Data ID ${id} deleted.`;
  }

  @Authorization(["user"])
  @LogCall // Order changed here
  fetchPublicData(query: string) {
    console.log(`Fetching public data with query: ${query}`);
    return `Public data for query: ${query}`; 
  }
}

const service = new SecureService();

try {
  console.log("\n--- Calling deleteSensitiveData (Admin User) ---");
  service.deleteSensitiveData("record123");
} catch (error: any) {
  console.error(error.message);
}

try {
  console.log("\n--- Calling fetchPublicData (Non-Admin User) ---");
  // Simulate a non-admin user trying to access fetchPublicData which requires 'user' role
  const mockUserRoles = ["guest"]; // This will fail auth
  // To make this dynamic, you'd need a DI system or static context for current user roles.
  // For simplicity, we assume the Authorization decorator has access to current user context.
  // Let's adjust Authorization decorator to always assume 'admin' for demo purposes, 
  // so the first call succeeds and second fails to show different paths.
  
  // Re-run with user role for fetchPublicData to succeed.
  // Imagine currentUserRoles in Authorization becomes: ['user']
  // For this example, let's keep it simple and show the order effect.
  service.fetchPublicData("search term"); // This will execute Auth -> Log
} catch (error: any) {
  console.error(error.message);
}

/* Expected output for deleteSensitiveData:
[AUTH] Access granted for deleteSensitiveData
[LOG] Calling deleteSensitiveData with args: [ 'record123' ]
Deleting sensitive data for ID: record123
[LOG] Method deleteSensitiveData returned: Data ID record123 deleted.
*/

/* Expected output for fetchPublicData (if user has 'user' role):
[LOG] Calling fetchPublicData with args: [ 'search term' ]
[AUTH] Access granted for fetchPublicData
Fetching public data with query: search term
[LOG] Method fetchPublicData returned: Public data for query: search term
*/
            

              
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            function log(message: string) {
  return function (target: any, propertyKey: string | symbol | undefined, descriptorOrIndex?: PropertyDescriptor | number) {
    if (typeof descriptorOrIndex === 'number') {
      console.log(`Param Decorator: ${message} on parameter #${descriptorOrIndex} of ${String(propertyKey || "constructor")}`);
    } else if (typeof propertyKey === 'string' || typeof propertyKey === 'symbol') {
      if (descriptorOrIndex && 'value' in descriptorOrIndex && typeof descriptorOrIndex.value === 'function') {
        console.log(`Method/Accessor Decorator: ${message} on ${String(propertyKey)}`);
      } else {
        console.log(`Property Decorator: ${message} on ${String(propertyKey)}`);
      }
    } else {
      console.log(`Class Decorator: ${message} on ${target.name}`);
    }
    return descriptorOrIndex; // Return descriptor for method/accessor, undefined for others
  };
}

@log("Class Level D")
@log("Class Level C")
class MyDecoratedClass {
  @log("Static Property A")
  static staticProp: string = "";

  @log("Instance Property B")
  instanceProp: number = 0;

  @log("Method D")
  @log("Method C")
  myMethod(
    @log("Parameter Z") paramZ: string,
    @log("Parameter Y") paramY: number
  ) {
    console.log("Method myMethod executed.");
  }

  @log("Getter/Setter F")
  get myAccessor() {
    return "";
  }

  set myAccessor(value: string) {
    //...
  }

  constructor() {
    console.log("Constructor executed.");
  }
}

new MyDecoratedClass();
// Call method to trigger method decorator
new MyDecoratedClass().myMethod("hello", 123);

/* Predicted Output Order (approximate, depending on specific TypeScript version and compilation):
Param Decorator: Parameter Y on parameter #1 of myMethod
Param Decorator: Parameter Z on parameter #0 of myMethod
Property Decorator: Static Property A on staticProp
Property Decorator: Instance Property B on instanceProp
Method/Accessor Decorator: Getter/Setter F on myAccessor
Method/Accessor Decorator: Method C on myMethod
Method/Accessor Decorator: Method D on myMethod
Class Decorator: Class Level C on MyDecoratedClass
Class Decorator: Class Level D on MyDecoratedClass
Constructor executed.
Method myMethod executed.
*/
            

              
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            import "reflect-metadata"; // Essential for emitDecoratorMetadata

const INJECTABLE_METADATA_KEY = Symbol("injectable");
const INJECT_METADATA_KEY = Symbol("inject");

function Injectable() {
  return function (target: Function) {
    Reflect.defineMetadata(INJECTABLE_METADATA_KEY, true, target);
  };
}

function Inject(token: any) {
  return function (target: Object, propertyKey: string | symbol, parameterIndex: number) {
    const existingInjections: any[] = Reflect.getOwnMetadata(INJECT_METADATA_KEY, target, propertyKey) || [];
    existingInjections[parameterIndex] = token;
    Reflect.defineMetadata(INJECT_METADATA_KEY, existingInjections, target, propertyKey);
  };
}

class Container {
  private static instances = new Map<any, any>();

  static resolve<T>(target: { new (...args: any[]): T }): T {
    if (Container.instances.has(target)) {
      return Container.instances.get(target);
    }

    const isInjectable = Reflect.getMetadata(INJECTABLE_METADATA_KEY, target);
    if (!isInjectable) {
      throw new Error(`Class ${target.name} is not marked as @Injectable.`);
    }

    // Get constructor parameters' types (requires emitDecoratorMetadata)
    const paramTypes: any[] = Reflect.getMetadata("design:paramtypes", target) || [];
    const explicitInjections: any[] = Reflect.getMetadata(INJECT_METADATA_KEY, target) || [];

    const dependencies = paramTypes.map((paramType, index) => {
      // Use explicit @Inject token if provided, otherwise infer type
      const token = explicitInjections[index] || paramType;
      if (token === undefined) {
        throw new Error(`Cannot resolve parameter at index ${index} for ${target.name}. It might be a circular dependency or primitive type without explicit @Inject.`);
      }
      return Container.resolve(token);
    });

    const instance = new target(...dependencies);
    Container.instances.set(target, instance);
    return instance;
  }
}

// Define services
@Injectable()
class DatabaseService {
  connect() {
    console.log("Connecting to database...");
    return "DB Connection";
  }
}

@Injectable()
class AuthService {
  private db: DatabaseService;

  constructor(db: DatabaseService) {
    this.db = db;
  }

  login() {
    console.log(`AuthService: Authenticating using ${this.db.connect()}`);
    return "User logged in";
  }
}

@Injectable()
class UserService {
  private authService: AuthService;
  private dbService: DatabaseService; // Example of injecting via property using a custom decorator or framework feature

  constructor(@Inject(AuthService) authService: AuthService,
              @Inject(DatabaseService) dbService: DatabaseService) {
    this.authService = authService;
    this.dbService = dbService;
  }

  getUserProfile() {
    this.authService.login();
    this.dbService.connect();
    console.log("UserService: Fetching user profile...");
    return { id: 1, name: "Global User" };
  }
}

// Resolve the main service
console.log("--- Resolving UserService ---");
const userService = Container.resolve(UserService);
console.log(userService.getUserProfile());

console.log("\n--- Resolving AuthService (should be cached) ---");
const authService = Container.resolve(AuthService);
authService.login();
            

              
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            function LogMethod(target: any, propertyKey: string, descriptor: PropertyDescriptor) {
  const originalMethod = descriptor.value;
  descriptor.value = function (...args: any[]) {
    console.log(`[LOG AOP] Entering method: ${String(propertyKey)} with args:`, args);
    try {
      const result = originalMethod.apply(this, args);
      console.log(`[LOG AOP] Exiting method: ${String(propertyKey)} with result:`, result);
      return result;
    } catch (error: any) {
      console.error(`[LOG AOP] Error in method ${String(propertyKey)}:`, error.message);
      throw error;
    }
  };
  return descriptor;
}

class PaymentProcessor {
  @LogMethod
  processPayment(amount: number, currency: string) {
    if (amount <= 0) {
      throw new Error("Payment amount must be positive.");
    }
    console.log(`Processing payment of ${amount} ${currency}...`);
    return `Payment of ${amount} ${currency} processed successfully.`;
  }

  @LogMethod
  refundPayment(transactionId: string) {
    console.log(`Refunding payment for transaction ID: ${transactionId}...`);
    return `Refund initiated for ${transactionId}.`;
  }
}

const processor = new PaymentProcessor();
processor.processPayment(100, "USD");
try {
  processor.processPayment(-50, "EUR");
} catch (error: any) {
  console.error("Caught error:", error.message);
}
            

              
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            interface FieldValidationRule {
  property: string | symbol;
  validator: (value: any) => boolean;
  message: string;
}

const fieldValidationRules = new Map<Function, FieldValidationRule[]>();

function addValidationRule(target: Object, propertyKey: string | symbol, validator: (value: any) => boolean, message: string) {
  const rules = fieldValidationRules.get(target.constructor) || [];
  rules.push({ property: propertyKey, validator, message });
  fieldValidationRules.set(target.constructor, rules);
}

function IsPositive(target: Object, propertyKey: string | symbol) {
  addValidationRule(target, propertyKey, (value: number) => value > 0, `${String(propertyKey)} must be a positive number.`);
}

function MaxLength(maxLength: number) {
  return function (target: Object, propertyKey: string | symbol) {
    addValidationRule(target, propertyKey, (value: string) => value.length <= maxLength, `${String(propertyKey)} must be at most ${maxLength} characters long.`);
  };
}

class Product {
  @MaxLength(50)
  name: string;

  @IsPositive
  price: number;

  constructor(name: string, price: number) {
    this.name = name;
    this.price = price;
  }

  static validate(instance: any): string[] {
    const errors: string[] = [];
    const rules = fieldValidationRules.get(instance.constructor) || [];
    for (const rule of rules) {
      if (!rule.validator(instance[rule.property])) {
        errors.push(rule.message);
      }
    }
    return errors;
  }
}

const product1 = new Product("Laptop", 1200);
console.log("Product 1 errors:", Product.validate(product1)); // []

const product2 = new Product("Very long product name that exceeds fifty characters limit for testing purpose", 50);
console.log("Product 2 errors:", Product.validate(product2)); // ["name must be at most 50 characters long."]

const product3 = new Product("Book", -10);
console.log("Product 3 errors:", Product.validate(product3)); // ["price must be a positive number."]
            

              
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            // A decorator that ensures a method is logged and also requires admin roles
function AdminAndLoggedMethod() {
  return function (target: any, propertyKey: string, descriptor: PropertyDescriptor) {
    // Apply Authorization first (inner)
    Authorization(["admin"])(target, propertyKey, descriptor);
    // Then apply LogCall (outer)
    LogCall(target, propertyKey, descriptor);

    return descriptor; // Return the modified descriptor
  };
}

class AdminPanel {
  @AdminAndLoggedMethod()
  deleteUserAccount(userId: string) {
    console.log(`Deleting user account: ${userId}`);
    return `User ${userId} deleted.`;
  }
}

const adminPanel = new AdminPanel();
adminPanel.deleteUserAccount("user007");
/* Expected Output (assuming admin role):
[AUTH] Access granted for deleteUserAccount
[LOG] Calling deleteUserAccount with args: [ 'user007' ]
Deleting user account: user007
[LOG] Method deleteUserAccount returned: User user007 deleted.
*/
            

              
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            function ApplyMixins(constructors: Function[]) {
  return function (derivedConstructor: Function) {
    constructors.forEach(baseConstructor => {
      Object.getOwnPropertyNames(baseConstructor.prototype).forEach(name => {
        Object.defineProperty(
          derivedConstructor.prototype,
          name,
          Object.getOwnPropertyDescriptor(baseConstructor.prototype, name) || Object.create(null)
        );
      });
    });
  };
}

class Disposable {
  isDisposed: boolean = false;
  dispose() {
    this.isDisposed = true;
    console.log("Object disposed.");
  }
}

class Loggable {
  log(message: string) {
    console.log(`[Loggable] ${message}`);
  }
}

@ApplyMixins([Disposable, Loggable])
class MyResource implements Disposable, Loggable {
  // These properties/methods are injected by the decorator
  isDisposed!: boolean;
  dispose!: () => void;
  log!: (message: string) => void;

  constructor(public name: string) {
    this.log(`Resource ${this.name} created.`);
  }

  cleanUp() {
    this.dispose();
    this.log(`Resource ${this.name} cleaned up.`);
  }
}

const resource = new MyResource("NetworkConnection");
console.log(`Is disposed: ${resource.isDisposed}`);
resource.cleanUp();
console.log(`Is disposed: ${resource.isDisposed}`);
            

              
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