import hashlib
from datetime import datetime


class Event(object):
    """
    Class that represents something that modifies the state of the system
    """

    def __init__(self, message="", user_id="", date=None, parents=None):
        self.user_id: str = user_id  # id of the user that triggers the modification
        self.date: datetime | None = date or datetime.now()  # when
        self.message: str = message  # user input or whatever that modifies the system
        self.parents: list[str] = parents  # digest(s) of the parent(s) of this event
        self._digest: str | None = None  # digest of the event

    def __str__(self):
        return f"{self.date.strftime('%d/%m/%Y %H:%M:%S')} {self.message}"

    def __repr__(self):
        return f"{self.get_digest()[:12]} {self.message}"

    def get_digest(self):
        """
        Returns the digest of the event
        :return: sha256 of the event
        """

        if self._digest:
            return self._digest

        if self.user_id == "":
            # only possible during the unit test
            # We use this little trick to speed up the unit test
            self._digest = self.message[6:] if self.message.startswith("TEST::") else "xxx"
            return self._digest

        if not isinstance(self.message, str):
            raise NotImplementedError(f"message={self.message}")

        to_hash = f"Event:{self.user_id}{self.date}{self.message}{self.parents}".encode("utf-8")
        self._digest = hashlib.sha256(to_hash).hexdigest()
        return self._digest

    def to_dict(self):
        return self.__dict__

    def from_dict(self, as_dict):
        self.user_id = as_dict["user_id"]
        self.date = datetime.fromisoformat(as_dict["date"])
        self.message = as_dict["message"]
        self.parents = as_dict["parents"]
        self._digest = as_dict["_digest"]  # freeze the digest

    def __eq__(self, other):
        if id(self) == id(other):
            return True

        if isinstance(other, Event):
            return (self.user_id == other.user_id and
                    self.date == other.date and
                    self.message == other.message and
                    self.parents == other.parents)

        return False

    def __hash__(self):
        return hash(self.get_digest())