🔧 Adding

Command  Pattern

Author: raj713335

06 Behavioral Design Patterns/02 Command Design Pattern.py

@@ -0,0 +1,138 @@
+from abc import ABC, abstractmethod
+
+
+# Receiver: The actual business logic
+class Editor:
+    def __init__(self):
+        self.text = ""
+        self.clipboard = ""
+        self.selection = ""
+
+    def get_selection(self):
+        return self.selection
+
+    def delete_selection(self):
+        print("Deleting selection...")
+        self.text = self.text.replace(self.selection, "")
+        self.selection = ""
+
+    def replace_selection(self, new_text):
+        print(f"Replacing selection with: {new_text}")
+        self.text = self.text.replace(self.selection, new_text)
+        self.selection = new_text
+
+    def set_selection(self, selection):
+        self.selection = selection
+
+    def __str__(self):
+        return f"Text: '{self.text}' | Selection: '{self.selection}'"
+
+
+# Command Interface
+class Command(ABC):
+    def __init__(self, editor: Editor):
+        self.editor = editor
+        self._backup = ""
+
+    def save_backup(self):
+        self._backup = self.editor.text
+
+    def undo(self):
+        self.editor.text = self._backup
+
+    @abstractmethod
+    def execute(self) -> bool:
+        pass
+
+
+# Command History
+class CommandHistory:
+    def __init__(self):
+        self._history = []
+
+    def push(self, command: Command):
+        self._history.append(command)
+
+    def pop(self):
+        return self._history.pop() if self._history else None
+
+
+# Concrete Commands
+class CopyCommand(Command):
+    def execute(self):
+        self.editor.clipboard = self.editor.get_selection()
+        print(f"Copied: '{self.editor.clipboard}'")
+        return False  # No text modified
+
+
+class CutCommand(Command):
+    def execute(self):
+        self.save_backup()
+        self.editor.clipboard = self.editor.get_selection()
+        self.editor.delete_selection()
+        return True  # Text modified
+
+
+class PasteCommand(Command):
+    def execute(self):
+        self.save_backup()
+        self.editor.replace_selection(self.editor.clipboard)
+        return True  # Text modified
+
+
+class UndoCommand(Command):
+    def __init__(self, history: CommandHistory):
+        self.history = history
+
+    def execute(self):
+        command = self.history.pop()
+        if command:
+            print("Undoing last command...")
+            command.undo()
+        else:
+            print("Nothing to undo.")
+        return False
+
+
+# Invoker
+class Application:
+    def __init__(self):
+        self.editor = Editor()
+        self.history = CommandHistory()
+
+    def execute_command(self, command: Command):
+        if command.execute():
+            self.history.push(command)
+
+    def run(self):
+        self.editor.text = "Hello, World!"
+        self.editor.set_selection("World")
+
+        print("\nInitial Editor State:", self.editor)
+
+        # CUT
+        self.execute_command(CutCommand(self.editor))
+        print("After Cut:", self.editor)
+
+        # PASTE
+        self.editor.set_selection("Hello")
+        self.execute_command(PasteCommand(self.editor))
+        print("After Paste:", self.editor)
+
+        # COPY
+        self.editor.set_selection("Hello")
+        self.execute_command(CopyCommand(self.editor))
+        print("After Copy (Clipboard):", self.editor.clipboard)
+
+        # UNDO
+        undo = UndoCommand(self.history)
+        self.execute_command(undo)
+        print("After Undo 1:", self.editor)
+
+        self.execute_command(undo)
+        print("After Undo 2:", self.editor)
+
+
+if __name__ == "__main__":
+    app = Application()
+    app.run()