MVI ও ইউনিডাইরেকশনাল ডেটা ফ্লো

# ---------- REDUCE -- Intent থেকে সবসময় একটি নতুন, ইমিউটেবল State তৈরি করে ----------
def reduce(state, intent):
    intent_type = intent["type"]

    if intent_type == "INCREMENT":
        return {**state, "count": state["count"] + state["step"]}
    elif intent_type == "DECREMENT":
        return {**state, "count": state["count"] - state["step"]}
    elif intent_type == "SET_STEP":
        return {**state, "step": intent["value"]}
    elif intent_type == "RESET":
        return {**state, "count": 0}

    return state   # অচেনা Intent হলে state অপরিবর্তিত ফেরত (তবুও একই অবজেক্ট, নতুন নয়)


# ---------- STORE -- Intent গ্রহণ করে, reduce কল করে, বর্তমান State ধরে রাখে ----------
class CounterMVIStore:
    def __init__(self, initial_state):
        self.state = initial_state

    def dispatch(self, intent):
        old_state = self.state
        new_state = reduce(self.state, intent)
        self.state = new_state
        return old_state, new_state


# ---------- VIEW -- বর্তমান State রেন্ডার করে ----------
def view(state):
    print(f"[View] কাউন্ট: {state['count']}  (step={state['step']})")


store = CounterMVIStore({"count": 0, "step": 1})
print("== প্রাথমিক State ==")
view(store.state)

intents = [
    {"type": "INCREMENT"},
    {"type": "INCREMENT"},
    {"type": "DECREMENT"},
    {"type": "SET_STEP", "value": 5},
]

for i, intent in enumerate(intents, start=1):
    print(f"\n== Intent #{i}: {intent} ==")
    old_state, new_state = store.dispatch(intent)
    view(store.state)
    print(f"  old_state (অপরিবর্তিত রয়ে গেছে): {old_state}")
    print(f"  new_state: {new_state}")
    print(f"  id(old_state) != id(new_state): {id(old_state) != id(new_state)}")

print(f"\nচূড়ান্ত State: {store.state}")