Fixed #8

Fixed #12
Fixed #13
Fixed #14

src/core/Event.py

@@ -0,0 +1,69 @@
+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())
+