# Jeffrey Chen
# October 26, 2018
# ICS3UR
# Discription - This program takes an input for a message, and allows the user to encrypt it into a file, as well
    # as decrypt, pull the file, and delete it.

# Imports the desired libraries
import random
import time
import ast
import os

# Creates 2 blank variables
values = []
main = 0

# This def function takes 2 inputs; one is a blank variable to store the encrypted message and the other one is the
    # is the message that is being encrypted. The def function then runs a the .randint code, which outputs a random
    # number from 1 to 14. This number is then added onto the unicode value of the first letter/variable of the message.
    # This step is repeated until the entire message has been encrypted. The numbers that were used for the encryption
    # are then put into a list called to be stored later if the user requests to do so.
def encrypt(msg, done):
    """ (str, str) -> (str, str)
    takes 2 str variables (one str is blank) modifies the input, and returns as a different variable.
    >>> input('hello world','')
    upzvx%„rusf
    """
    for letter in msg:
        y = random.randint(1,14)
        x = ord(letter)
        x += y
        done += chr(x)
        values.append(y)
    print(done)
    values.append(done)
    return values

# This function takes one input; a blank variable to store the decrypted message. The def function uses the imported
    # library called ast. This imported library allows the def function to take the string in the saved .txt file that
    # used to be the list that included the values used to encrypt the message, and return it to its list state. The
    # function does this by striping "removing" the first stored like (encrypted message) and passing the next line
    # (values used) through the ast library, which results in turning the str back into a list. The values are then
    # used to reverse the steps that were applied the message, thus decoding it.
def decrypt (done):
    """ (str) -> (str)
    Takes the inputted name of the .txt file, takes the contents of file, and uses it to decrypt the message to return
    it to its original state
    >>> input(file_One)
    hello world
    """
    msg = f.readline().strip('\n')
    values = ast.literal_eval(f.readline())
    index = 0
    for letter in msg:
        x = ord(letter)
        y = values[index]
        x -= y
        done += chr(x)
        index += 1
    print(done)
    f.close()

# This function takes one input; the encrypted message that was created from the encryption function. The function runs
# a while loop that test to see if the user wants to store the message as a file. If replied yes, it asks the user to
# create a file name as a .txt file. The code then runs os to check if the file already exists, and will force the user
# to create a new file if it does. The function then runs the second part of the code which allows the function to
# return 2 values instead of one, and turns the list into a str. The 2 strings are then put into the file.
def store (secret):
    """(str, list) -> (str, str)
        Takes the encrypted message from the encrypt function, and the values of the global list, turns the list into
        a string, and store them into a .txt file
        >>> f.write(msg + \n)
        >>> secret = str(secret)
            f.write(secret)
    """
    y = 0
    while y == 0:
        z = 0
        print(" ")
        x = input("Would you like to Store the Message?: ")
        if x == 'y':
            while z == 0:
                fileName = input("Please Enter the Name of the File: ") + ".txt"
                if os.path.isfile(fileName):
                    print("Error, File Exists.")
                else:
                    f = open(fileName, "w", encoding='utf-8')
                    z = 1
            msg = secret[-1]
            del secret[-1]
            secret = str(secret)
            f.write(msg + "\n")
            f.write(secret)
            f.close()
            print("Storing File......")
            time.sleep(2)
            print("File has Been Stored.")
            y = 1
        elif x == 'n':
            y = 1
        else:
            print("Invalid Input")

# Creates the main while loop that runs the entire code
while main == 0:
    del values[:]
    print("-----------------------")
    # Asks user for an input
    print("    ")
    options = input("What Would You Like To Do?: ")
    # kills the code
    if options == 'exit':
        exit()
    elif options == 'encrypt':
        # This runs the encryption portion of the code.
        secret = ""
        message = input("Please Enter a Message: ")
        print("Encrypting Message......")
        time.sleep(2)
        secret = encrypt(message, secret)
        store(secret)
    elif options == 'decrypt':
        msg = ""
        # This runs the decryption part of the code
        # This try catch is used to stop the code from crashing if the user inputs a file name that does not exist.
        while True:
            fileName = input("Please Enter the Name of the File: ") + ".txt"
            try:
                f = open(fileName, "r", encoding='utf-8')
                break
            except:
                print("This File Doesn't Exist.")
        print("Decrypting Stored File......")
        time.sleep(2)
        decrypt(msg)
    elif options == 'pull-file':
        # This runs the file extraction part of the code
        # This try catch is used to stop the code from crashing if the user inputs a file name that does not exist.
        while True:
            fileName = input("Please Enter the Name of the File: ") + ".txt"
            try:
                f = open(fileName, "r", encoding='utf-8')
                break
            except:
                print("This File Doesn't Exist.")
        print("Printing.....")
        time.sleep(2)
        print(f.read())
        f.close()
    elif options == 'delete-file':
        # this runs the file deleting part of the code
        # Runs a try catch with os to remove an existing file. The try catch will stop the code from crashing if the
        # name of the file does not exist.
        while True:
            remove = input("Please Enter the Name of the File: ") + ".txt"
            try:
                os.remove(remove)
                break
            except:
                print("This File Doesn't Exist.")
        print("Removing File......")
        time.sleep(2)
        print("File Has Been Removed.")
    else:
        # Prints when code receives an input other than the expected inputs.
        print("Invalid Input")