🔧 Adding

State Design Pattern

Author: raj713335

06 Behavioral Design Patterns/07 State Design Pattern.py

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+from abc import ABC, abstractmethod
+
+
+# -------------- STATE INTERFACE ----------------
+class State(ABC):
+    def __init__(self, document):
+        self.document = document
+
+    @abstractmethod
+    def edit(self):
+        ...
+
+    @abstractmethod
+    def publish(self, user_role: str):
+        ...
+
+
+# -------------- CONCRETE STATES ----------------
+class DraftState(State):
+    def edit(self):
+        print("[Draft] You can freely edit the document.")
+
+    def publish(self, user_role: str):
+        print("[Draft] Moving to moderation.")
+        self.document.change_state(ModerationState(self.document))
+
+
+class ModerationState(State):
+    def edit(self):
+        print("[Moderation] Document is under review. Limited editing allowed.")
+
+    def publish(self, user_role: str):
+        if user_role.lower() == "admin":
+            print("[Moderation] Approved by admin. Document is now published.")
+            self.document.change_state(PublishedState(self.document))
+        else:
+            print("[Moderation] Only admins can publish from moderation.")
+
+
+class PublishedState(State):
+    def edit(self):
+        print("[Published] Cannot edit a published document.")
+
+    def publish(self, user_role: str):
+        print("[Published] Document is already published. No action taken.")
+
+
+# -------------- CONTEXT ----------------
+class Document:
+    def __init__(self):
+        self._state: State = DraftState(self)
+        print("[Document] Initialized in Draft state.")
+
+    def change_state(self, new_state: State):
+        self._state = new_state
+        print(f"[Document] State changed to {self._state.__class__.__name__}.")
+
+    def edit(self):
+        self._state.edit()
+
+    def publish(self, user_role: str):
+        self._state.publish(user_role)
+
+
+# -------------- CLIENT CODE ----------------
+def main():
+    document = Document()
+
+    document.edit()                # Allowed
+    document.publish("writer")     # Moves to Moderation
+
+    document.edit()                # Limited edit
+    document.publish("user")       # Denied (not admin)
+
+    document.publish("admin")      # Published
+
+    document.edit()                # Not allowed
+    document.publish("admin")      # Already published
+
+
+if __name__ == "__main__":
+    main()