tmp.js

const addSubscriber = assign({
  subscribers: (context, event) => context.subscribers + 1
});

const removeSubscriber = assign({
  subscribers: (context, event) => context.subscribers - 1
});


const subscribeParent = assign({
  subscription: 'parent subscription'
});

const unsubscribeParent = assign({
  subscription: null
});

// Guard to check if the glass is full
function noSubscribers(context, event) {
  return context.subscribers === 0;
}

const glassMachine = Machine(
  {
    id: 'cached-observable',
    context: {
      subscribers: 0,
      subscribtion: null,
    },
    initial: 'initial',
    states: {
      initial: {
        on: {
          SUBSCRIBE: {
            target: 'active',
            actions: [
              'addSubscriber',
              'subscribeParent'
            ]
          }
        }
      },
      active: {
        on: {
          // Transient transition
          '': {
            target: 'initial',
            cond: 'noSubscribers',
            actions:  ['unsubscribeParent']
          },
          NEXT: {
            target: 'active'
          },
          ERROR: {
            target: 'done'
          },
          COMPLETE: {
            target: 'done'
          },
          SUBSCRIBE: {
            target: 'active',
            actions: 'addSubscriber'
          },
          UNSUBSCRIBE: {
            target: 'active',
            actions: "removeSubscriber"
          }
        }
      },
      done: {
          on: {
            SUBSCRIBE: {
              target: 'done',
              actions: 'addSubscriber'
            },
            UNSUBSCRIBE: {
              target: 'done',
              actions: "removeSubscriber"
            }
          }
      }
    }
  },
  {
    actions: { addSubscriber, removeSubscriber },
    guards: { noSubscribers }
  }
);