import random
import time
import os
import sys


invalid_input = True
filename = None
key = None

def menu():
    print("Welcome to the Encryption / Decryption program!\n-------------------------------------------")
    print("Please select a number (1-3) corresponding to the instruction you would like")
    menuInput = input("[1] Encrypt a message\n[2] Decrypt a message\n[3] Exit the program\n-------------------------------------------\n")
    if menuInput == '1':
        encrypt()
    elif menuInput == '2':
        decrypt()
    elif menuInput == '3':
        end = input("Are you sure you want to exit the program?\n[1] Yes\n[2] No\n")
        if end == '1':
            exit()
        elif end == '2':
            menu()
        else:
            print("Invalid selection. Returning to main menu.")
            time.sleep(2)
            menu()
    else:
        print("Invalid Selection")
        menu()

def encrypt():
        global filename
        global key
        print("You have chosen to Encrypt a message!")
        invalid_input = False
        encrypt = input("Please type in the name of the file containing the non-encrypted message\n")
        encrypt = encrypt.upper()
        message = open(encrypt+".txt","r")
        message = message.read()

        if encrypt == "SAMPLE":
            key = ''
            for i in range(0,8):
                random_number = (random.randint(33,126))
                key+=str(chr(random_number))
            print(key)
            print("You will need this key to decrypt your file!")
            time.sleep(1.5)
            print("Encrypting your file now...")
            time.sleep(2.5)

            calculate = []

            for x in key:
                x = ord(x)
                calculate.append(x)
            numbers = sum(calculate)
            divided = numbers / 8
            rounded = round(divided-0.5)
            finalNumber = rounded - 32

            time.sleep(1)
            encrypted = ''
            spaces = ''

            for letter in message:
                valLetter = ord(letter)
                if valLetter == 32:
                    encrypted += chr(valLetter)
                else:
                    added = finalNumber + valLetter

                    if added > 126:
                        subtracted = added - 94
                        encrypted += chr(subtracted)
                    else:
                        encrypted += chr(valLetter)
            print("Here is your encrypted message")
            time.sleep(1)
            print(encrypted)


            filename = input("Please enter the name you wish the file to be called: ")

            cipher_filename = filename + ".txt"
            f = open(cipher_filename,"w")

            f.write(encrypted)

            print("Thank you, you will be redirected to the main menu shortly where you can decrypt your message!")
            time.sleep(1)

        else:
            print("Invalid Filename!")

def decrypt():
        print("You have chosen to decrypt a message!")
        invalid_input = False
        newFile = input("What is the name of your file you stored your encrypted message in?\n")

        decrypt = open(newFile+".txt","r")
        msg = ''

        for words in decrypt:
            msg += str(words)

        if newFile == filename:
            print("Correct!")
            keyAuth = input("Please enter the key we provided you with earlier!")

            if keyAuth == key:
                print("Success! Decrypting your message now.")

                calculate = []

                for x in key:
                    x = ord(x)
                    calculate.append(x)
                numbers = sum(calculate)
                divided = numbers / 8
                rounded = round(divided-0.5)
                offset = rounded - 32

                time.sleep(1)
                decrypted = ''
                spaces = ''

                for letter in msg:
                    valLetter = ord(letter)
                    if valLetter == 32:
                        decrypted += chr(valLetter)
                    else:
                        subtracted = valLetter - offset

                        if subtracted < 33:
                            newVal = subtracted + 94
                            decrypted += chr(newVal)
                        else:
                            decrypted += chr(subtracted)
                print("Here is your decrypted message")
                print(decrypted)

            else:
                print("Invalid Key.")

        else:
            print("Invalid Input, try again!")

while invalid_input:
    menu()