const fetchMachine = Machine(
  {
    id: 'fetch',
    initial: 'idle',
    context: {
      results: [],
      retryCount: 0,
    },
    states: {
      idle: {
        on: {
          FETCH: 'loading',
        },
      },
      loading: {
        invoke: {
          src: 'loadData',
          onDone: { target: 'success', actions: 'handleData' },
          onError: 'failure',
        },
        on: {
          RESOLVE: 'success',
          REJECT: 'failure',
        },
      },
      success: {},
      failure: {
        after: {
          FETCH_DELAY: [
            { target: 'loading', actions: 'increment', cond: 'withinLimit' },
            { target: 'terminated' },
          ],
        },
      },
      terminated: {
        type: 'final',
      },
    },
  },
  {
    guards: {
      withinLimit: () => true
    },
    actions: {
      handleData: assign({ results: (_, event) => event.data }),
      increment: assign({ retryCount: context => context.retryCount + 1 }),
    },
    delays: {
      FETCH_DELAY: context => context.retryCount * 500,
    },
  }
)