🔧 Adding

Memento Pattern

Author: raj713335

06 Behavioral Design Patterns/05 Memento Design Pattern.py

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+from typing import List
+
+
+# ----------- MEMENTO -----------
+class Snapshot:
+    """The Memento that stores the state of the Editor."""
+
+    def __init__(self, text: str, cursor_position: int):
+        self._text = text
+        self._cursor_position = cursor_position
+
+    def get_state(self):
+        """Internal state is only accessible to the Editor."""
+        return self._text, self._cursor_position
+
+
+# ----------- ORIGINATOR -----------
+class Editor:
+    """Originator that creates and restores from Snapshots."""
+
+    def __init__(self):
+        self._text = ""
+        self._cursor_position = 0
+
+    def type(self, new_text: str):
+        self._text += new_text
+        self._cursor_position = len(self._text)
+
+    def get_content(self):
+        return self._text
+
+    def create_snapshot(self) -> Snapshot:
+        return Snapshot(self._text, self._cursor_position)
+
+    def restore(self, snapshot: Snapshot):
+        self._text, self._cursor_position = snapshot.get_state()
+
+
+# ----------- CARETAKER -----------
+class History:
+    """Caretaker that stores snapshots for undo functionality."""
+
+    def __init__(self):
+        self._snapshots: List[Snapshot] = []
+
+    def save(self, snapshot: Snapshot):
+        self._snapshots.append(snapshot)
+
+    def undo(self) -> Snapshot:
+        if not self._snapshots:
+            print("[Undo] No more states to undo.")
+            return None
+        snapshot = self._snapshots.pop()
+        print("[Undo] Restoring previous state.")
+        return snapshot
+
+
+# ----------- CLIENT CODE -----------
+def main():
+    editor = Editor()
+    history = History()
+
+    editor.type("Hello")
+    history.save(editor.create_snapshot())
+
+    editor.type(" World!")
+    history.save(editor.create_snapshot())
+
+    print("[Editor] Current content:", editor.get_content())  # Hello World!
+
+    editor.type(" Let's learn Memento.")
+    print("[Editor] Current content:", editor.get_content())  # Hello World! Let's learn Memento.
+
+    # Perform undo
+    snapshot = history.undo()
+    if snapshot:
+        editor.restore(snapshot)
+        print("[Editor] After undo:", editor.get_content())  # Hello World!
+
+    # Another undo
+    snapshot = history.undo()
+    if snapshot:
+        editor.restore(snapshot)
+        print("[Editor] After second undo:", editor.get_content())  # Hello
+
+    snapshot = history.undo()
+    if snapshot:
+        editor.restore(snapshot)
+        print("[Editor] After Third undo:", editor.get_content())
+
+
+
+if __name__ == "__main__":
+    main()