🔧 Adding

Chain of Responsibility Pattern

Author: raj713335

06 Behavioral Design Patterns/01 Chain of Responsibility Design Pattern.py

@@ -0,0 +1,105 @@
+from abc import ABC, abstractmethod
+
+# Request object that holds user and requested daya
+
+class Request:
+    def __init__(self, username, password, role, data):
+        self.username = username
+        self.password = password
+        self.role = role
+        self.data = data
+
+# Abstract Handler
+class Handler(ABC):
+    def __init__(self):
+        self.next_handler = None
+
+    def set_next(self, handler):
+        self._next_handler = handler
+        return handler
+
+    @abstractmethod
+    def handle(self, request: Request):
+        pass
+
+# Concreate Handler 1: Authentication
+class AuthHandler(Handler):
+    def handle(self, request: Request):
+        print("[AuthHandler] Checking authentication...")
+        if request.username == "john" and request.password == "1234":
+            print("Authenticated")
+            if self._next_handler:
+                return self._next_handler.handle(request)
+        else:
+            print("Authentication failed")
+            return "Access Denied: Invalid Credentials"
+
+
+
+# Concrete Handler 2: Authorization
+class RoleHandler(Handler):
+    def handle(self, request: Request):
+        print("[RoleHandler] Checking role...")
+        if request.role == "admin" or request.role == "user":
+            print(f"Authorized as {request.role}")
+            if self._next_handler:
+                return self._next_handler.handle(request)
+        else:
+            print("Authorization failed")
+            return "Access Denied: Unauthorized Role"
+
+
+# Concrete Handler 3: Validation
+class ValidationHandler(Handler):
+    def handle(self, request: Request):
+        print("[ValidationHandler] Validating request data...")
+        if "item" in request.data and "quantity" in request.data:
+            print("Request data is valid")
+            if self._next_handler:
+                return self._next_handler.handle(request)
+        else:
+            print("Invalid request data")
+            return "Bad Request: Missing order details"
+
+# Final Handler: Order Handler
+class OrderHandler(Handler):
+    def handle(self, request: Request):
+        print(f"[OrderHandler] Processing order...")
+        return f"Order Placed for {request.data['quantity']} x {request.data['item']} by {request.username}"
+
+# Client Code
+
+if __name__ == "__main__":
+    auth = AuthHandler()
+    role = RoleHandler()
+    validate = ValidationHandler()
+    order = OrderHandler()
+
+    auth.set_next(role).set_next(role).set_next(validate).set_next(order)
+
+    # Request Valid
+    # Request 1: Valid
+    print("\n--- Request 1: Valid Order ---")
+    request1 = Request("john", "1234", "admin", {"item": "Laptop", "quantity": 2})
+    response1 = auth.handle(request1)
+    print("Response:", response1)
+
+    # Request 2: Invalid password
+    print("\n--- Request 2: Invalid Credentials ---")
+    request2 = Request("john", "wrong", "admin", {"item": "Laptop", "quantity": 2})
+    response2 = auth.handle(request2)
+    print("Response:", response2)
+
+    # Request 3: Unauthorized Role
+    print("\n--- Request 3: Unauthorized Role ---")
+    request3 = Request("john", "1234", "guest", {"item": "Laptop", "quantity": 2})
+    response3 = auth.handle(request3)
+    print("Response:", response3)
+
+    # Request 4: Missing Data
+    print("\n--- Request 4: Missing Order Data ---")
+    request4 = Request("john", "1234", "user", {"item": "Mouse"})
+    response4 = auth.handle(request4)
+    print("Response:", response4)
+
+