type Writable<T> = {
  -readonly [P in keyof T]: T[P];
};

interface ReadonlyConfig {
  readonly apiUrl: string;
  readonly timeout: number;
  readonly debugMode: boolean;
}

// Example Usage:
type MutableConfig = Writable<ReadonlyConfig>;

const appConfig: ReadonlyConfig = {
  apiUrl: 'https://api.example.com',
  timeout: 5000,
  debugMode: false
};

// appConfig.apiUrl = 'new_url'; // Error: Cannot assign to 'apiUrl' because it is a read-only property.

// To modify, you can create a mutable copy or cast for specific operations
const editableConfig: MutableConfig = { ...appConfig };
editableConfig.apiUrl = 'https://dev.api.example.com'; // OK
editableConfig.timeout = 10000; // OK
editableConfig.debugMode = true; // OK

function processConfig(config: Writable<ReadonlyConfig>) {
  // Inside this function, config properties are writable
  config.debugMode = true;
  console.log(config.debugMode);
}

// processConfig(appConfig); // Error because appConfig is ReadonlyConfig, and processConfig expects Writable<ReadonlyConfig>
// You'd typically pass a mutable version:
processConfig({ ...appConfig });

interface NestedReadonly {
  readonly id: string;
  readonly details: { readonly name: string };
}

type MutableNested = Writable<NestedReadonly>;
const data: NestedReadonly = { id: '1', details: { name: 'Test' }};
const mutableData: MutableNested = { ...data };
mutableData.id = '2'; // OK
// mutableData.details.name = 'New Name'; // Error: 'name' is still readonly (Writable only affects top level)