// Av Daniel Larsson och Martin Ekström

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace LibraryProject
{
    /// <summary>
    /// A service that handles book copies, uses singleton pattern and can only be instantiated/accessed through GetInstance().
    /// </summary>
    class BookCopyService
    {
        private static BookCopyService instance;
        private Database db;

        /// <summary>
        /// Event for when a book copy is added
        /// </summary>
        public event Action Updated = delegate { };

        /// <summary>
        /// Default constructor
        /// </summary>
        private BookCopyService()
        {
            db = Database.GetInstance();
        }

        /// <summary>
        /// Method to instantiate/access the book copy service.
        /// </summary>
        /// <returns>An instance of BookCopyService</returns>
        public static BookCopyService GetInstance()
        {
            if (instance == null)
                instance = new BookCopyService();

            return instance;
        }

        /// <summary>
        /// Method that add a single copy of a book
        /// </summary>
        /// <param name="book">Book of which the copy should be added</param>
        public void AddBookCopy(Book book)
        {
            Book_Copy copy = new Book_Copy
            {
                Fk_Books_Id = book.Id
            };

            db.Book_Copies.AddObject(copy);
            db.SaveChanges();

            Updated();
        }

        /// <summary>
        /// Method to add a number of copies of a book
        /// </summary>
        /// <param name="book">Book of which copies should be added</param>
        /// <param name="nrOfBooks">Number of copies to add</param>
        public void AddBookCopies(Book book, int nrOfBooks)
        {
            for (int i = 0; i < nrOfBooks; i++)
            {
                AddBookCopy(book);
            }
        }

        /// <summary>
        /// Method that returns the number of available copies
        /// </summary>
        /// <returns>Number of available copies</returns>
        public int GetTotalNrOfAvailableCopies()
        {
            int nrOfBookCopies = db.Book_Copies.Count();
            int nrOfLoans = db.Loans.Count();
            return nrOfBookCopies - nrOfLoans;
        }

    }
}