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        author: Christian Bender
        date: 21.12.2017
        class: XORCipher
        This class implements the XOR-cipher algorithm and provides
        some useful methods for encrypting and decrypting strings and
        files.
        Overview about methods
        - encrypt : list of char
        - decrypt : list of char
        - encrypt_string : str
        - decrypt_string : str
        - encrypt_file : boolean
        - decrypt_file : boolean
class XORCipher:
    def __init__(self, key: int = 0):
        """
        simple constructor that receives a key or uses
        default key = 0
        """
        # private field
        self.__key = key
    def encrypt(self, content: str, key: int) -> list[str]:
        """
        input: 'content' of type string and 'key' of type int
        output: encrypted string 'content' as a list of chars
        if key not passed the method uses the key by the constructor.
        otherwise key = 1
        """
        # precondition
        assert isinstance(key, int) and isinstance(content, str)
        key = key or self.__key or 1
        # make sure key can be any size
        while key > 255:
            key -= 255
        # This will be returned
        ans = []
        for ch in content:
            ans.append(chr(ord(ch) ^ key))
        return ans
    def decrypt(self, content: str, key: int) -> list[str]:
        """
        input: 'content' of type list and 'key' of type int
        output: decrypted string 'content' as a list of chars
        if key not passed the method uses the key by the constructor.
        otherwise key = 1
        """
        # precondition
        assert isinstance(key, int) and isinstance(content, list)
        key = key or self.__key or 1
        # make sure key can be any size
        while key > 255:
            key -= 255
        # This will be returned
        ans = []
        for ch in content:
            ans.append(chr(ord(ch) ^ key))
        return ans
    def encrypt_string(self, content: str, key: int = 0) -> str:
        """
        input: 'content' of type string and 'key' of type int
        output: encrypted string 'content'
        if key not passed the method uses the key by the constructor.
        otherwise key = 1
        """
        # precondition
        assert isinstance(key, int) and isinstance(content, str)
        key = key or self.__key or 1
        # make sure key can be any size
        while key > 255:
            key -= 255
        # This will be returned
        ans = ""
        for ch in content:
            ans += chr(ord(ch) ^ key)
        return ans
    def decrypt_string(self, content: str, key: int = 0) -> str:
        """
        input: 'content' of type string and 'key' of type int
        output: decrypted string 'content'
        if key not passed the method uses the key by the constructor.
        otherwise key = 1
        """
        # precondition
        assert isinstance(key, int) and isinstance(content, str)
        key = key or self.__key or 1
        # make sure key can be any size
        while key > 255:
            key -= 255
        # This will be returned
        ans = ""
        for ch in content:
            ans += chr(ord(ch) ^ key)
        return ans
    def encrypt_file(self, file: str, key: int = 0) -> bool:
        """
        input: filename (str) and a key (int)
        output: returns true if encrypt process was
        successful otherwise false
        if key not passed the method uses the key by the constructor.
        otherwise key = 1
        """
        # precondition
        assert isinstance(file, str) and isinstance(key, int)
        try:
            with open(file) as fin:
                with open("encrypt.out", "w+") as fout:
                    # actual encrypt-process
                    for line in fin:
                        fout.write(self.encrypt_string(line, key))
        except OSError:
            return False
        return True
    def decrypt_file(self, file: str, key: int) -> bool:
        """
        input: filename (str) and a key (int)
        output: returns true if decrypt process was
        successful otherwise false
        if key not passed the method uses the key by the constructor.
        otherwise key = 1
        """
        # precondition
        assert isinstance(file, str) and isinstance(key, int)
        try:
            with open(file) as fin:
                with open("decrypt.out", "w+") as fout:
                    # actual encrypt-process
                    for line in fin:
                        fout.write(self.decrypt_string(line, key))
        except OSError:
            return False
        return True
# crypt = XORCipher()
# # test encrypt
# print(crypt.encrypt("hallo welt",key))
# # test decrypt
# print(crypt.decrypt(crypt.encrypt("hallo welt",key), key))
# # test encrypt_string
# print(crypt.encrypt_string("hallo welt",key))
# # test decrypt_string
# print(crypt.decrypt_string(crypt.encrypt_string("hallo welt",key),key))
# if (crypt.encrypt_file("test.txt",key)):
#       print("encrypt successful")
#       print("encrypt unsuccessful")
# if (crypt.decrypt_file("encrypt.out",key)):
#       print("decrypt successful")
#       print("decrypt unsuccessful")
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