Fetch reducer state machine with typescript support

useFetchStateMachine.ts

import { Dispatch, Reducer, useReducer } from 'react';

type Nullable<T> = T | null | undefined;

type FetchMachineState<DataT, ErrorT> = {
  status: 'idle' | 'loading' | 'success' | 'failure';
  data: Nullable<DataT>;
  error: Nullable<ErrorT>;
};

type Event<DataT, ErrorT> =
  | { type: 'FETCH' }
  | { type: 'RESOLVE'; data: DataT }
  | { type: 'REJECT'; error: ErrorT };

function useFetchStateMachine<DataT, ErrorT = string>(
  initialData: Nullable<DataT>
): [FetchMachineState<DataT, ErrorT>, Dispatch<Event<DataT, ErrorT>>] {
  const initialState: FetchMachineState<DataT, ErrorT> = {
    status: 'idle',
    data: initialData,
    error: null,
  };

  function fetchReducer(
    state: FetchMachineState<DataT, ErrorT>,
    event: Event<DataT, ErrorT>
  ): FetchMachineState<DataT, ErrorT> {
    switch (event.type) {
      case 'FETCH':
        return {
          ...state,
          status: 'loading',
        };
      case 'RESOLVE':
        return {
          ...state,
          status: 'success',
          data: event.data,
        };
      case 'REJECT':
        return {
          ...state,
          status: 'failure',
          error: event.error,
        };
      default:
        return state;
    }
  }

  return useReducer<
    Reducer<FetchMachineState<DataT, ErrorT>, Event<DataT, ErrorT>>
  >(fetchReducer, initialState);
}

// USAGE EXAMPLE

// interface Person {
//   name: string;
//   age: number;
// }

// interface Error {
//   message: string;
// }

// const [state, dispatch] = useFetchStateMachine<Person, Error>(null);
// dispatch({ type: 'FETCH' });
// dispatch({
//   type: 'RESOLVE',
//   data: {
//     name: 'Pedro',
//     age: 2,
//   },
// });
// dispatch({
//   type: 'REJECT',
//   error: {
//     message: 'Server Error',
//   },
// });

export default useFetchStateMachine;