import string
import pandas


# Functions go here
def make_statement(statement, decoration):
    """Emphasises headings by adding decoration at the start and end"""

    return f"{decoration * 3} {statement} {decoration * 3}"


def string_check(question, valid_answers=('yes', 'no'), num_letters=1):
    """Checks that users enter the full word or the 'n' letters of a word from a list of valid responses"""

    while True:

        response = input(question).lower()

        for item in valid_answers:

            # check if the response is the entire word
            if response == item:
                return item

            # check if it's the first letter
            elif response == item[:num_letters]:
                return item

        print(f"Please choose an option from {valid_answers}")


def not_blank(question):
    """Checks that a user response is not blank"""

    while True:
        response = input(question)

        if response != "":
            return response

        print("Sorry, this can't be blank. Please try again.\n")


def instructions():
    make_statement("Instructions", "🎲")

    print('''Thank you for using this decoding program! First, select whether you want to encode or decode. If you 
    want to disguise a message using the Caesar Cipher, select encode. If you have an already encoded message that 
    you want to understand, select decode. Then enter your message and the number of letters you want it to be 
    shifted by. Please do not attempt to copy and paste long messages into the program as they may end the dialogue. 
    Instead, try decoding paragraph by paragraph. 
    When you are done using the program, type 'xxx' into the enter message section.

The program will record the messages you have encoded/decoded, what they were shifted by and how many times you have 
used the program. Once you have entered the exit code ('xxx'), the program will display your user history and write 
the data as a text file.''')


def encode(message_to_encode):
    encoded_message = ""
    for letter in message_to_encode:
        if letter in alphabet:
            new_position = alphabet.index(letter) + shift_number
            new_position = new_position % len(alphabet)
            encoded_message = encoded_message + alphabet[new_position]
        elif letter in upper_alphabet:
            new_position = upper_alphabet.index(letter) + shift_number
            new_position = new_position % len(upper_alphabet)
            encoded_message = encoded_message + upper_alphabet[new_position]
        else:
            encoded_message = encoded_message + letter

    print("This is your encoded message:", encoded_message)
    return encoded_message


def decode(message_to_decode):
    decoded_message = ""
    for letter in message_to_decode:
        if letter in alphabet:
            new_position = alphabet.index(letter) - shift_number
            new_position = new_position % len(alphabet)
            decoded_message = decoded_message + alphabet[new_position]
        elif letter in upper_alphabet:
            new_position = upper_alphabet.index(letter) - shift_number
            new_position = new_position % len(upper_alphabet)
            decoded_message = decoded_message + upper_alphabet[new_position]
        else:
            decoded_message = decoded_message + letter

    print("This is your decoded message:", decoded_message)
    return decoded_message


# initialise alphabet + enc_dec
alphabet = list(string.ascii_lowercase)
upper_alphabet = list(string.ascii_uppercase)
messages_encoded = 0
messages_decoded = 0
cipher_types = ('encode', 'decode', 'xxxxx')

# lists to hold message information
all_messages = []
all_shift_numbers = []
all_decoded_messages = []
all_encoded_messages = []


caesar_cipher_dict = {
    'Message': all_messages,
    'Shift Number': all_shift_numbers,
}

# Main routine goes here
make_statement("Caesar Cipher Program", "⚖")

print()
want_instructions = string_check("Do you want to see the instructions? ")

if want_instructions == "yes":
    instructions()

print()

while True:
    # ask user for their message (and check it's not blank)
    print()
    message = not_blank("What is your message? ")

    # if name is exit code, break out of loop
    if message == "xxx":
        break

    # Ask for their shift_number
    shift_number = int(input("How many letters would you like to shift your message by? "))

    # ask user for cipher type (encode / decode / enc / dec)
    cipher_type = string_check("Type of cipher (encode/decode): ", cipher_types, 3)
    if cipher_type == 'encode':
        returned_encoded_message = encode(message)
        messages_encoded += 1

    if cipher_type == 'decode':
        returned_decoded_message = decode(message)
        messages_decoded += 1

    # add message list, shift numbers, decoded and encoded messages
    all_messages.append(message)
    all_shift_numbers.append(shift_number)
    all_decoded_messages.append(returned_decoded_message)

# End of CC Loop
total_program_use = messages_encoded + messages_decoded


# print practice funct
print(f"Your messages were: {all_messages}")
print(f"You shifted these messages by: {all_shift_numbers}")
print(f"You encoded {messages_encoded} messages")
print(f"You decoded {messages_decoded} messages")
print(f"You used the program {total_program_use} times")