#########################################################################################
# file: greatest_common_divisor.py
# type: Python
# date: 05_OCTOBER_2024
# author: karbytes
# license: PUBLIC_DOMAIN 
#########################################################################################

# Include the module which defines output=os.sys.stdout
import os

"""
Use the Euclidean algorithm to compute the greatest common divisor of positive integers A and B.

Print each step of that iterative process to the output (i.e. console or file).
"""
def print_greatest_common_divisor_computation_steps(A, B, output):
    i = 0
    remainder = 0
    output.write("\n\nComputing the greatest common divisor of A and B using the Euclidean algorithm...")
    while B != 0:
        remainder = A % B
        output.write(f"\n\nstep_{i}: A = {A}, B = {B}, gcd(A,B) = A % B = {remainder}.")
        A = B
        B = remainder
        i += 1
    output.write(f"\n\nThe greatest common divisor of A and B is {A}\n")

def main():
    # Declare and initialize three variables for storing integer values.
    A = 1
    B = 1
    input_additional_values = 1

    """
    If the file named greatest_common_divisor.txt does not already exist 
    inside of the same file directory as the file named greatest_common_divisor.py, 
    create a new file named greatest_common_divisor_output.txt in that directory.
    
    Open the plain-text file named greatest_common_divisor_output.txt
    and set that file to be overwritten with program data.
    """
    with open("greatest_common_divisor_two_output.txt", "w") as file:

        # Print an opening message to the command line terminal.
        print("\n\n--------------------------------")
        print("Start Of Program")
        print("--------------------------------")

        # Print an opening message to the output file.
        file.write("--------------------------------\n")
        file.write("Start Of Program\n")
        file.write("--------------------------------\n")

        # Print "This Python program computes the greatest common divisor of two natural numbers and prints the steps involved." to the command line terminal.
        print("\n\nThis Python program computes the greatest common divisor of two natural numbers and prints the steps involved.")

        # Print "This Python program computes the greatest common divisor of two natural numbers and prints the steps involved." to the command line terminal and to the file output stream.
        file.write("\n\nThis Python program computes the greatest common divisor of two natural numbers and prints the steps involved.")

        # Print a horizontal divider line to the command line terminal and to the output file.
        print("\n\n--------------------------------")
        file.write("\n\n--------------------------------")

        # Continue input and computation loop until user inputs 0 for input_additional_values.
        while input_additional_values != 0:
            # Print the input prompt to the terminal only.
            A = int(input("\n\nEnter the first value (A): "))
            B = int(input("Enter the second value (B): "))

            # Print a horizontal divider line to the command line terminal and to the output file.
            print("\n\n--------------------------------")
            file.write("\n\n--------------------------------")

            # Log user inputs to the file after they are entered.
            file.write(f"\n\nEntered values: A = {A}, B = {B}")
            print(f"\n\nEntered values: A = {A}, B = {B}")

            # Print a horizontal divider line to the command line terminal and to the output file.
            print("\n\n--------------------------------")
            file.write("\n\n--------------------------------")

            # Execute the greatest common divisor function (defined by this Python program file) such that the computation steps and final result are printed to the output file.
            print_greatest_common_divisor_computation_steps(A, B, file)

            # Execute the greatest common divisor function (defined by this Python program file) such that the computation steps and final result are printed to the command line terminal.
            print_greatest_common_divisor_computation_steps(A, B, output=os.sys.stdout)

            # Ask the user whether or not to continue inputting values.
            input_additional_values = int(input("\n\nWould you like to input new values for A and B? (Enter 1 if YES. Enter 0 if NO): "))

        # Print a closing message to the command line terminal.
        print("\n\n--------------------------------")
        print("End Of Program")
        print("--------------------------------\n\n")

        # Print a closing message to the output file.
        file.write("\n\n--------------------------------\n")
        file.write("End Of Program\n")
        file.write("--------------------------------\n")

# Program entry point
if __name__ == "__main__":
    main()