import java.util.Scanner;
class main
{        
    public static void main(String[] args)
    { 
        // Create scanner object
        Scanner input = new Scanner(System.in);

	    // Declare variables
        double bookPrice = 0.0;
        String bookName;
        int bookQuantity = 0;
        int menuOption = 0;
        int arrayLength = 0;
        String newBook;
        int arrayIndex=0;
        double purchasePrice = 0.0;

        // Declare empty arrays (30 spaces) - all contain NULL
        String bookNamesArray[] = new String[30];
        double bookPricesArray[] = new double[30];
        int bookQtysInStockArray[] = new int[30];
          
        //Loop until user selects 5. Exit from the menu 
        while(menuOption <5) 
        {
            // Output the menu
            System.out.println("\nMenu"); 
            System.out.println("1. Add Stock");
            System.out.println("2. Update Stock");
            System.out.println("3. Display Stock");
            System.out.println("4. Sales");
            System.out.println("5. Exit");

            //Request menu option
            menuOption = input.nextInt();        
               
            if (menuOption==5) // exit program
            {
                System.out.print("Exit Program");
                input.close(); // Close Scanner
            }
            else
            {
                if (menuOption == 1) // Add stock
                {
                    System.out.print("Please enter the new book name: ");
                    bookName = input.next();

                    // check if book already exists in stock
                    newBook = "Yes"; // set default to true
                    try
                    {
                        for(int i = 0; i < arrayLength; i++) // loop through the BookNames array
                        {
                            // compare the entered book name to the book names in the array
                            if (bookNamesArray[i].trim().equals(bookName.trim()))
                            {
                                newBook = "No";
                            }
                        } 
                        
                    } 
                    catch (Exception e) 
                    {
                        e.printStackTrace();
                    }   

                    if (newBook == "Yes") 
                    { 
                        // request entry of price and quantity to add to stock
                        System.out.print("Please enter the new book price: £");
                        bookPrice = input.nextDouble();
                        System.out.print("Please enter the new book stock quantity: ");
                        bookQuantity = input.nextInt();  
                    
                        // Store the new book name, price and quantity in arrays 
                        bookNamesArray[arrayLength] = bookName.trim();
                        bookPricesArray[arrayLength] = bookPrice;
                        bookQtysInStockArray[arrayLength] = bookQuantity;
                        arrayLength++; // Add 1 to array length
			System.out.println("Book " + bookName + " has been added to stock");
                    }
                    else
                    {
                        System.out.println("Book " + bookName + " is already a stock item");
                    }
                }
                else if (menuOption == 2)// Update Stock (quantity only) 
                {
                    System.out.print("Please enter the book name: ");
                    bookName = input.next();
                     // check if book already exists in stock
                    newBook = "Yes"; // set default to true
                    try
                    {
                        for(int i = 0; i < arrayLength; i++) // loop through the BookNames array
                        {
                            // compare the entered book name to the book names in the array
                            if (bookNamesArray[i].trim().equals(bookName.trim()))
                            {
                                newBook = "No";
                                arrayIndex = i;//store the index of book so qty can be adjusted
                                break;
                            }
                        }
                    } 
                    catch (Exception e) 
                    {
                        e.printStackTrace();
                    } 
                    if (newBook == "No") 
                    {  
                        // request entry of quantity to adjust stock
                        System.out.print("Please enter the quantity to adjust stock: ");
                        bookQuantity = input.nextInt();  
                    
                        // Update the quantity array for the book 
                        bookQtysInStockArray[arrayIndex] = bookQtysInStockArray[arrayIndex] + bookQuantity;
                        System.out.println("The stock for book " + bookName + " has been updated");
                    }
                    else
                    {
                        System.out.println("Book " + bookName + " does not exist");
                    }
                }
                else if (menuOption == 3) // Display Stock
                {
                               
                    System.out.println("\nStock List");  
                    for(int i = 0; i < arrayLength; i++) // loop through the arrays
                    {
                        System.out.println((i + 1) + ". " + bookNamesArray[i] + " - £" + bookPricesArray[i] + " (" + bookQtysInStockArray[i] + " in stock)"); 
                    }
                }
                else if (menuOption == 4) 
                {
                    System.out.print("Please enter the book name: ");
                    bookName = input.next();
                    // check if book already exists in stock
                    newBook = "Yes"; // set default to true
                    try
                    {
                        for(int i = 0; i < arrayLength; i++) // loop through the BookNames array
                        {
                            // compare the entered book name to the book names in the array
                            if (bookNamesArray[i].trim().equals(bookName.trim())) 
                            {   
                                newBook = "No";
                                arrayIndex = i;//store the index of book so qty can be checked/adjusted
                            }
                        }
                    }
                    catch (Exception e) 
                    {
                        e.printStackTrace();
                    } 

                    if (newBook == "No") // Book exists
                    {  
                        // request entry of quantity to purchase
                        System.out.print("Please enter the quantity to be purchased: ");
                        bookQuantity = input.nextInt();
                        if (bookQuantity <= bookQtysInStockArray[arrayIndex]) 
                        // check if there's enough stock
                        {
                            // calculate the purchase price by multiplying the book price (in the Book prices array) by the quantity purchasd
                            purchasePrice = ((double)bookPricesArray[arrayIndex] * bookQuantity);
                            System.out.println("Purchase price= £" + purchasePrice);
                            // Update the quantity array for the book to subtract what has been sold
                            bookQtysInStockArray[arrayIndex] = bookQtysInStockArray[arrayIndex] - bookQuantity;
                        }
                        else // not enough stock
                        {
                           System.out.println("There is not enough in stock to purchase this quantity");
                        }
                    }
                    else 
                    {
                        System.out.println("Book " + bookName + " does not exist");
                    }
                }
                else
                {
                    System.out.println("Invalid menu option. Please try again!");
                }
           }
        } 
    }
}