import json
import hashlib


class DB:
    def __init__(self):
        self.database = {}

    @staticmethod
    def hash_password(password):
        salt = "your_secret_salt"
        hashed_password = hashlib.sha256((password + salt).encode()).hexdigest()
        return hashed_password

    def add_user(self, data):
        username = data.get['username']
        password = data.get['password']
        hashed_password = self.hash_password(password)
        user_data = {"hashed_password": hashed_password}
        self.database[username] = user_data

    def update_password(self, data):
        username = data.get['username']
        old_password = data.get['old_password']
        new_password = data.get['new_password']
        if not self.check_credentials(data):
            return False

        hashed_new_password = self.hash_password(new_password)
        self.database[username].update({"hashed_password": hashed_new_password})
        return True

    def check_credentials(self, data):
        username = data.get['username']
        password = data.get['password']
        if username not in self.database:
            return False

        stored_hashed_password = self.database[username]["hashed_password"]
        entered_hashed_password = self.hash_password(password)
        return stored_hashed_password == entered_hashed_password

    def get_additional_info(self, data):
        username = data.get['username']
        password = data.get['password']
        if not self.check_credentials(data):
            return None

        send_back = self.database[username]
        del send_back['hashed_password']
        return send_back