class TextEditorApp:
"""
TextEditorApp class that works as "Caretaker" that actually uses Memento
Pattern.
This class is responsible for keeping a collection of "Memento", but never
examines or operates on the contents of a "Memento".
"""
__slots__ = ['_text_editor', '_memento_list', '_prev_state_ptr']
def __init__(self):
"""
Default constructor.
"""
self._text_editor = TextEditor()
self._memento_list = []
self._prev_state_ptr = -1
def write(self, text: str) -> None:
"""
Writes the given text to the text editor.
:param text: str
:return: None
"""
self._text_editor.text = text
print(f"After writing '{text}': {self._text_editor}")
def save(self) -> None:
"""
Saves the current state of the text editor.
:return: None
"""
self._add_memento(self._text_editor.create_memento())
self._prev_state_ptr = len(self._memento_list) - 1
def _add_memento(self, memo: Memento) -> None:
"""
Private helper method to store the given memento.
:param memo: Memento
:return: None
"""
self._memento_list.append(memo)
def undo(self) -> None:
"""
Undo the most recent change in the text editor.
:return: None
"""
print('Undo operation...')
if self._text_editor.text !=\
self._memento_list[self._prev_state_ptr].text:
last_saved_state = self._memento_list[self._prev_state_ptr]
self._text_editor.restore(last_saved_state)
print(self._text_editor)
elif self._prev_state_ptr <= 0:
print('No more undo operation available!')
else:
self._prev_state_ptr -= 1
prev_state = self._get_memento(self._prev_state_ptr)
self._text_editor.restore(prev_state)
print(self._text_editor)
def _get_memento(self, idx: int) -> Memento:
"""
Private helper method to get the memento at the given index.
:param idx: int
:return: Memento
"""
return self._memento_list[idx]
def redo(self) -> None:
"""
Redoes the most recent change in the text editor.
:return: None
"""
print('Redo operation...')
if self._prev_state_ptr >= len(self._memento_list) - 1:
print('No more redo operation available!')
return
self._prev_state_ptr += 1
next_state = self._get_memento(self._prev_state_ptr)
self._text_editor.restore(next_state)
print(self._text_editor)
