class Document:

    text = ""

    def __str__(self):

        return self.text



import abc

class DocumentCommand(abc.ABC):

    doc = None

    @abc.abstractmethod

    def execute(self):

        pass

    @abc.abstractmethod

    def undo(self):

        pass



class AddStrCommand(DocumentCommand):

    def __init__(self, doc, txt):

        self.text = txt

        self.doc = doc

    def execute(self):

        self.doc.text += self.text

        return self.doc

    def undo(self):

        return DeleteStrCommand(self.doc, self.text).execute()



class DeleteStrCommand(DocumentCommand):

    def __init__(self, doc, txt):

        self.text = txt

        self.doc = doc

    def execute(self):

        idx = self.doc.text.find(self.text)

        if idx == -1:

            return self.doc

        self.doc.text = self.doc.text[:idx]

        return self.doc

    def undo(self):

        return AddStrCommand(self.doc, self.text).execute()



doc = Document()

addingTexts = [AddStrCommand(doc,"hello\n"), AddStrCommand(doc,"My name is Chang\n"),  AddStrCommand(doc,"I hope you have a good day")]

for c in addingTexts:

    c.execute()

print("#"*5)

print(doc)

print("#"*5)

print(addingTexts[-1].undo())

print("#"*5)

print(addingTexts[-1].undo())

print("#"*5)

print("*"*30)

d = DeleteStrCommand(doc,"My name is Chang\n")

print(d.execute())

print("#"*5)

print(d.undo())

print("#"*5)