using System;
using System.Collections.Generic;

class Product
{
    public int ProductId { get; set; }
    public string Name { get; set; }
    public decimal Price { get; set; }
    public int Quantity { get; set; }
    public DateTime ExpirationDate { get; set; }
}

class Customer
{
    public int CustomerId { get; set; }
    public string Name { get; set; }
    public string ContactInformation { get; set; }
    public List<Product> PurchaseHistory { get; set; } = new List<Product>();
}

class GroceryManagementSystem
{
    private List<Product> products = new List<Product>();
    private List<Customer> customers = new List<Customer>();

    public void AddProduct()
    {
        Product product = new Product();

        Console.Write("Enter product name: ");
        product.Name = Console.ReadLine();

        Console.Write("Enter product price: ");
        while (!decimal.TryParse(Console.ReadLine(), out product.Price) || product.Price <= 0)
        {
            Console.Write("Invalid input. Enter a valid positive price: ");
        }

        Console.Write("Enter product quantity: ");
        while (!int.TryParse(Console.ReadLine(), out product.Quantity) || product.Quantity < 0)
        {
            Console.Write("Invalid input. Enter a valid non-negative quantity: ");
        }

        Console.Write("Enter product expiration date (yyyy-MM-dd): ");
        while (!DateTime.TryParseExact(Console.ReadLine(), "yyyy-MM-dd", null, System.Globalization.DateTimeStyles.None, out product.ExpirationDate))
        {
            Console.Write("Invalid input. Enter a valid date in the specified format: ");
        }

        product.ProductId = products.Count + 1;
        products.Add(product);

        Console.WriteLine("Product added successfully!");
    }

    public void AddCustomer()
    {
        Customer customer = new Customer();

        Console.Write("Enter customer name: ");
        customer.Name = Console.ReadLine();

        Console.Write("Enter customer contact information: ");
        customer.ContactInformation = Console.ReadLine();

        customer.CustomerId = customers.Count + 1;
        customers.Add(customer);

        Console.WriteLine("Customer added successfully!");
    }

    public void ProcessSale()
    {
        if (customers.Count == 0 || products.Count == 0)
        {
            Console.WriteLine("Error: There are no customers or products. Add customers and products before processing a sale.");
            return;
        }

        DisplayCustomers();
        Console.Write("Enter customer ID for the sale: ");

        int customerId;
        while (!int.TryParse(Console.ReadLine(), out customerId) || customerId <= 0 || customerId > customers.Count)
        {
            Console.Write($"Invalid input. Enter a valid customer ID between 1 and {customers.Count}: ");
        }

        DisplayInventory();
        Console.Write("Enter product ID for the sale: ");

        int productId;
        while (!int.TryParse(Console.ReadLine(), out productId) || productId <= 0 || productId > products.Count)
        {
            Console.Write($"Invalid input. Enter a valid product ID between 1 and {products.Count}: ");
        }

        Console.Write("Enter quantity for the sale: ");
        int quantity;
        while (!int.TryParse(Console.ReadLine(), out quantity) || quantity <= 0 || quantity > products[productId - 1].Quantity)
        {
            Console.Write($"Invalid input. Enter a valid quantity between 1 and {products[productId - 1].Quantity}: ");
        }

        Customer customer = customers.Find(c => c.CustomerId == customerId);
        Product product = products.Find(p => p.ProductId == productId);

        if (customer != null && product != null)
        {
            // Update product quantity
            product.Quantity -= quantity;

            // Update customer purchase history
            customer.PurchaseHistory.Add(new Product
            {
                ProductId = product.ProductId,
                Name = product.Name,
                Price = product.Price,
                Quantity = quantity,
                ExpirationDate = product.ExpirationDate
            });

            Console.WriteLine("Sale processed successfully!");
        }
        else
        {
            Console.WriteLine("Error processing sale. Please check customer and product information.");
        }
    }

    public void DisplayInventory()
    {
        Console.WriteLine("\nInventory:");

        foreach (var product in products)
        {
            Console.WriteLine($"{product.ProductId}. {product.Name} - Price: {product.Price:C}, Quantity: {product.Quantity}, Expiry Date: {product.ExpirationDate.ToShortDateString()}");
        }
    }

    public void DisplayCustomers()
    {
        Console.WriteLine("\nCustomers:");

        foreach (var customer in customers)
        {
            Console.WriteLine($"{customer.CustomerId}. {customer.Name} - Contact: {customer.ContactInformation}");
        }
    }
}

class Program
{
    static void Main()
    {
        GroceryManagementSystem grocerySystem = new GroceryManagementSystem();

        Console.WriteLine("Adding products and customers...");

        // Adding products and customers using user input
        grocerySystem.AddProduct();
        grocerySystem.AddProduct();

        grocerySystem.AddCustomer();
        grocerySystem.AddCustomer();

        // Display initial inventory and customers
        grocerySystem.DisplayInventory();
        grocerySystem.DisplayCustomers();

        // Process a sale using user input
        Console.WriteLine("\nProcessing a sale...");
        grocerySystem.ProcessSale();

        // Display updated inventory
        grocerySystem.DisplayInventory();
    }
}