Finite state machine

FSM? What is this?

Now we're going to talk about perhaps the most important feature of bots: the dialogue system. Unfortunately, not all actions in a bot can be performed in one message or command. Suppose you have a dating bot where you need to indicate your name, age and send a photo with a face when registering. You can, of course, ask the user to send a photo, and indicate all the data in the signature to it, but this is inconvenient for processing and requesting re-entry. Now let's imagine a step-by-step data entry, where at the beginning the bot "turns on" the mode of waiting for certain information from a specific user, then at each stage it checks the input data and transfers the person to the required handler, moving along the chain of states.

RedisStorage

The framework already has built-in support for the Redis backend for storing states, and in addition to the states, you can store arbitrary data, for example, the above name and age for later use elsewhere.

Let's describe all the possible "states" of a particular process (user registration). In words, it can be described as follows: the user calls the /register command, the bot responds with a message with a request to enter the date of birth for a specific user and is transferred to the next step - RegisterStates.birthday. As soon as the user enters the date of birth (or any line, since we do not validate the date, this is not so important now), the user will be taken to the next step - RegisterStates.email. When the user enters some data here, the bot will send data that this particular person entered a few steps ago. (we saved the data in the state machine) and resets the state with data cleansing.

So, let's go directly to the description of the states. It is advisable to specify them exactly in the order in which the user is supposed to navigate, this will slightly simplify the code. To store states, you need to create a class that inherits from the StatesGroup class, inside it, you need to create variables by assigning instances of the BaseState or State class to them:

from waio.states import State, StatesGroup


class RegisterStates(StatesGroup):
    birthday = State()
    email = State()

Let's write a handler for the first step that responds to the /register command (we will register it later):

@dp.message_handler(commands=["register"], state="*")
async def register_name(event: Event, state: FSMContext):
    await event.answer(f"Hi, {event.sender_name}! send your date of birth")
    await state.set_state(RegisterStates.birthday)

FSMContext

Notice that we now have a second state argument of the FSMContext type. Through it, you can get data from the FSM backend, namely, set the state, get the state, set data for the user, get data for the user.

In the last line, we explicitly tell the bot to get into the birthday state from the RegisterStates group. The following function will be called only from the specified state, save the text received from the user and proceed to the next step:

@dp.message_handler(state=RegisterStates.birthday)
async def register_age(event: Event, state: FSMContext):
    await state.set_data(birthday=event.text)
    await event.answer(f"Thanks for sending you birthday!\n" f"Send you email address")
    await state.set_state(RegisterStates.email)