#!/bin/bash

# Function to display the calculator menu
show_menu() {
    echo "Calculator Menu:"
    echo "1) Add"
    echo "2) Subtract"
    echo "3) Multiply"
    echo "4) Divide"
    echo "5) Modulus"
    echo "6) Exit"
}

# Function to perform addition
add() {
    echo "Enter first number: "
    read num1
    echo "Enter second number: "
    read num2
    echo "Result: $(($num1 + $num2))"
}

# Function to perform subtraction
subtract() {
    echo "Enter first number: "
    read num1
    echo "Enter second number: "
    read num2
    echo "Result: $(($num1 - $num2))"
}

# Function to perform multiplication
multiply() {
    echo "Enter first number: "
    read num1
    echo "Enter second number: "
    read num2
    echo "Result: $(($num1 * $num2))"
}

# Function to perform division
divide() {
    echo "Enter first number: "
    read num1
    echo "Enter second number: "
    read num2
    if [ $num2 -eq 0 ]; then
        echo "Cannot divide by zero."
    else
        echo "Result: $(($num1 / $num2))"
    fi
}

# Function to perform modulus (remainder)
modulus() {
    echo "Enter first number: "
    read num1
    echo "Enter second number: "
    read num2
    echo "Result: $(($num1 % $num2))"
}

# Main program starts here

echo "Welcome to the Calculator Project!"
echo "Please sign in to continue."
echo -n "Username: "
read username

if [ -z "$username" ]; then
    echo "Username cannot be empty. Exiting."
    exit 1
fi

# Prompt for password (you can replace this with a more secure method)
echo -n "Password: "
read -s password
echo

# Simple password check (replace with a secure authentication system)
if [ "$password" != "secret" ]; then
    echo "Incorrect password. Access denied."
    exit 1
fi

echo "Hello, $username! Let's do some calculations."

while true; do
    show_menu
    read -p "Select an option (1-6): " option
   
    case $option in
        1) add ;;
        2) subtract ;;
        3) multiply ;;
        4) divide ;;
        5) modulus ;;
        6)
            echo "Thank you for using the calculator. Goodbye!"
            exit 0
            ;;
        *)
            echo "Invalid option. Please try again."
            ;;
    esac
done