ts

type Address = string;
type Quantity = string;
type Hex = string;

type MethodDefinitions = [
  {
    Method: 'eth_accounts';
    Parameters?: undefined;
    ReturnType: Address[];
  },
  {
    Method: 'eth_chainId';
    Parameters?: undefined;
    ReturnType: Quantity;
  },
  {
    Method: 'eth_switchAccount';
    Parameters: [address: Hex];
    ReturnType: null;
  },
  {
    Method: 'eth_requestAccounts';
    Parameters?: undefined;
    ReturnType: Address[];
  }
];

type MethodNames = MethodDefinitions[number]['Method'];

type MethodParams<T extends MethodNames> = Extract<MethodDefinitions[number], { Method: T }>['Parameters'];
type MethodReturnType<T extends MethodNames> = Extract<MethodDefinitions[number], { Method: T }>['ReturnType'];

// Define RequestParams to make params optional if MethodParams<T> is undefined
type RequestParams<T extends MethodNames> = MethodParams<T> extends undefined
  ? { method: T; params?: MethodParams<T> }
  : { method: T; params: MethodParams<T> };

async function request<T extends MethodNames>(args: RequestParams<T>): Promise<MethodReturnType<T>> {
  const { method } = args;
  switch (method) {
    case 'eth_accounts':
      return ['0x1234567890abcdef1234567890abcdef12345678'] as MethodReturnType<T>;
    case 'eth_chainId':
      return '0x1' as MethodReturnType<T>;
    case 'eth_switchAccount':
      return null as MethodReturnType<T>;
    case 'eth_requestAccounts':
      return ['0x1234567890abcdef1234567890abcdef12345678'] as MethodReturnType<T>;
    default:
      throw new Error(`Unknown method: ${method}`);
  }
}

// Example usages:

async function exampleUsage() {
  // const accounts = await request({ method: 'eth_accounts' });
  // console.log(accounts); // Address[]
  const chainId = await request({ method: 'eth_chainId' });
  // console.log(chainId); // Quantity
  // const switchAccount = await request({ method: 'eth_switchAccount', params: ['0x1234567890abcdef1234567890abcdef12345678'] });
  // console.log(switchAccount); // null
  // const requestAccounts = await request({ method: 'eth_requestAccounts' });
  // console.log(requestAccounts); // Address[]
}

exampleUsage();