design-patterns/structural/flyweight/flyweight_factory.py

from typing import Dict, List

from structural.flyweight.flyweight import Flyweight


class FlyweightFactory:
    """
    The Flyweight Factory creates and manages the Flyweight objects. It ensures
    that flyweights are shared correctly. When the client requests a flyweight,
    the factory either returns an existing instance or creates a new one, if it
    doesn't exist yet.
    """

    _flyweights: Dict[str, Flyweight] = {}

    def __init__(self, initial_flyweights: List) -> None:
        for state in initial_flyweights:
            self._flyweights[self.get_key(state)] = Flyweight(state)

    def get_key(self, state: List) -> str:
        """
        Returns a Flyweight's string hash for a given state.
        """

        return "_".join(sorted(state))

    def get_flyweight(self, shared_state: List) -> Flyweight:
        """
        Returns an existing Flyweight with a given state or creates a new one.
        """
        key = self.get_key(shared_state)

        if not self._flyweights.get(key):
            print("FlyweightFactory: Can't find a flyweight, creating new one.")
            self._flyweights[key] = Flyweight(shared_state)
        else:
            print("FlyweightFactory: Reusing existing flyweight.")

        return self._flyweights[key]

    def list_flyweights(self) -> None:
        count = len(self._flyweights)
        print(f"FlyweightFactory: I have {count} flyweights:")
        print("\n".join(map(str, self._flyweights.keys())), end="")