using System;
using System.Linq;
using System.Threading.Tasks;
using DataLayer;
using Dinah.Core.ErrorHandling;
using FileLiberator;
using FileManager;

namespace FileLiberator
{
    /// <summary>
    /// Download DRM book and decrypt audiobook files
    /// 
    /// Processes:
    /// Download: download aax file: the DRM encrypted audiobook
    /// Decrypt: remove DRM encryption from audiobook. Store final book
    /// Backup: perform all steps (downloaded, decrypt) still needed to get final book
    /// </summary>
    public class BackupBook : IProcessable
    {
        public event EventHandler<LibraryBook> Begin;
        public event EventHandler<string> StatusUpdate;
        public event EventHandler<LibraryBook> Completed;

        public DownloadDecryptBook DecryptBook { get; } = new DownloadDecryptBook();
		public DownloadPdf DownloadPdf { get; } = new DownloadPdf();

		public bool Validate(LibraryBook libraryBook)
            => !AudibleFileStorage.Audio.Exists(libraryBook.Book.AudibleProductId);

		// do NOT use ConfigureAwait(false) on ProcessAsync()
		// often calls events which prints to forms in the UI context
		public async Task<StatusHandler> ProcessAsync(LibraryBook libraryBook)
        {
            Begin?.Invoke(this, libraryBook);

            try
			{
				{
					var statusHandler = await DecryptBook.TryProcessAsync(libraryBook);
					if (statusHandler.HasErrors)
						return statusHandler;
				}

				{
					var statusHandler = await DownloadPdf.TryProcessAsync(libraryBook);
					if (statusHandler.HasErrors)
						return statusHandler;
				}

				return new StatusHandler();
			}
			finally
            {
                Completed?.Invoke(this, libraryBook);
            }
        }
	}
}