Simple but yet buggy login system.

login_system.py

"""
Simple but yet buggy login system.
You need to have a "database.txt" file.
"""

import tkinter

class AccountHandler:
    def __init__(self, file_path):
        self.file_path = file_path
        self.file_found = True
        try:
            with open(self.file_path, "r"):
                self.file_found = True
        except (FileNotFoundError, FileExistsError):
            self.file_found = False

        self._encryption_form = {"~": "%1", "!": "%2", "@": "%3",
                                 "#": "%4", "$": "%5", "%": "%6",
                                 "^": "%7", "&": "%8", "*": "%9",
                                 "(": r"%a", ")": r"%b", "_": r"%c",
                                 "+": r"%d", " ": r"%e"}
        self._decryption_form = {"%1": "~", "%2": "!", "%3": "@",
                                 "%4": "#", "%5": "$", "%6": "%",
                                 "%7": "^", "%8": "&", "%9": "*",
                                 r"%a": "(", r"%b": ")", r"%c": "_",
                                 r"%d": "%+", r"%e": " "}

    # Only for passwords; No need to encrypt usernames
    def encrypt_password(self, password):
        # ~!@#$%^&*()_+
        encrypted = ""
        encrypted = encrypted.maketrans(self._encryption_form)
        return str(password.translate(encrypted)) + r"%END"

    def decrypt_password(self, password):
        # ~!@#$%^&*()_+

        for letter in self._decryption_form:
            password = password.replace(letter, self._decryption_form[letter])
        return password.replace(r"%END", "")

    def read_account(self, username=""):
        """
        Gets the account data, username and password
        Optionally, you can get the account data by username
        """
        with open(self.file_path, "r") as file:
            if username != "":
                for line in file.readlines():
                    if line[:line.find(":")] == username:
                        return line[:line.find(":")], True
            else:
                return file.readlines()

    def check_account(self, username, password):
        password = self.encrypt_password(password)
        with open(self.file_path, "r") as file:
            for line in file.readlines():
                line = line.replace("\n", "")
                if line[:line.find(":")] == username:
                    index = line.find(r"%END") + 4
                    if line[line.find(":") + 1:index] == password:
                        return True
                    else:
                        return False

    def write_account(self, username, password):
        """
        Password is going to be encrypted
        """
        password = self.encrypt_password(password)
        with open(self.file_path, "a") as file:
            exist = self.read_account(username)
            if (exist is not None) and (exist[1]):
                return False
            else:
                file.write(f"{username}:{password}\n")

    def edit_account(self, old, new):
        """
        You can only change usernames
        """
        # Check if the new username exists already or not
        exist = self.read_account(new)
        if (exist is not None) and (exist[1]):
            return False

        """
        Firstly, open the file and copies everything to a variable
        Then replace the necessary stuff 
        Lastly write the new data again
        """
        data = ""
        with open(self.file_path, "r") as file:
            for line in file.readlines():
                data += line
                if line[:line.find(":")] == old:
                    data = data.replace(old, new, 1)

        with open(self.file_path, "w") as file:
            file.truncate()
            file.write(data)

class Window:
    def __init__(self):
        self.master = tkinter.Tk()
        self.master.geometry("500x500")
        self.master.title("Login System")
        self.master.resizable(False, False)

        self.account_handler = AccountHandler("database.txt")

        if self.account_handler.file_found:
            self.login_frame_message_notify = "Enter your accout information"
        else:
            self.login_frame_message_notify = "'database.txt' not found, please reopen"

        self.login_frame = tkinter.Frame(self.master)
        self.login_message_label = tkinter.Label(self.login_frame, text=self.login_frame_message_notify)
        self.login_username_entry = tkinter.Entry(self.login_frame)
        self.login_password_entry = tkinter.Entry(self.login_frame)
        self.login_enter_button = tkinter.Button(self.login_frame, text="Enter")

        if self.account_handler.file_found is False:
            self.login_enter_button.configure(state=tkinter.DISABLED)
        else:
            self.login_enter_button.configure(state=tkinter.NORMAL)

        self.login_message_label.place(x=250, y=220, anchor=tkinter.CENTER)
        self.login_username_entry.place(x=250, y=250, anchor=tkinter.CENTER)
        self.login_password_entry.place(x=250, y=275, anchor=tkinter.CENTER)
        self.login_enter_button.place(x=250, y=305, anchor=tkinter.CENTER)

        self.account_manager_frame = tkinter.Frame()
        self.account_manager_message_label = tkinter.Label(self.account_manager_frame, text="You need to put your password to change your username\nYou can only change usernames")
        self.account_manager_username_entry = tkinter.Entry(self.account_manager_frame)
        self.account_manager_password_entry = tkinter.Entry(self.account_manager_frame)
        self.account_manager_enter_button = tkinter.Button(self.account_manager_frame, text="Edit")

        self.account_manager_message_label.place(x=250, y=220, anchor=tkinter.CENTER)
        self.account_manager_username_entry.place(x=250, y=250, anchor=tkinter.CENTER)
        self.account_manager_password_entry.place(x=250, y=275, anchor=tkinter.CENTER)
        self.account_manager_enter_button.place(x=250, y=305, anchor=tkinter.CENTER)

        self.old_username = None
        self.old_password = None

    def change_account_username(self, old, new, password):
        if self.account_handler.check_account(old, password):
            if self.account_handler.edit_account(old, new):
                self.account_manager_message_label.configure(text=f"Changed username from {old} to {new}")
                self.master.title(f"Login System - {new}")
        else:
            self.account_manager_message_label.configure(text="Username already exists or password is incorrect")

    def account_manager_frame_manager(self):
        self.account_manager_enter_button.configure(command=lambda: self.change_account_username(self.old_username, self.account_manager_username_entry.get(), self.account_manager_password_entry.get()))

    def check_account(self, username, password):
        if self.account_handler.check_account(username, password):
            self.old_password = self.login_password_entry.get()
            self.old_username = self.login_username_entry.get()
            self.master.title(f"Login System - {self.login_username_entry.get()}")
            
            # Clear the frame
            for widget in self.login_frame.winfo_children():
                self.login_frame.destroy()
                widget.destroy()
            self.account_manager_frame.pack(fill="both", expand=True)
            self.account_manager_frame_manager()
        else:
            self.account_handler.write_account(username, password)
            self.login_message_label.configure(text="Created new account. Renter username and password to log-in")

    def login_frame_manager(self):
        self.login_frame.pack(fill="both", expand=True)
        self.login_enter_button.configure(command=lambda: self.check_account(self.login_username_entry.get(), self.login_password_entry.get()))

    def show(self):
        self.login_frame_manager()
        self.master.mainloop()

if __name__ == "__main__":
    window = Window()
    window.show()

It's a good work

kool