using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices;
using Vanara.PInvoke;
using static Vanara.PInvoke.BITS;

namespace Vanara.IO
{
	/// <summary>Manages the set of files for a background copy job.</summary>
	public class BackgroundCopyFileCollection : ICollection<BackgroundCopyFileInfo>, IDisposable
	{
		private IBackgroundCopyJob m_ijob;

		internal BackgroundCopyFileCollection(IBackgroundCopyJob ijob) => m_ijob = ijob;

		internal BackgroundCopyFileCollection()
		{
		}

		/// <summary>Gets the number of files in the current job.</summary>
		public int Count
		{
			get
			{
				try
				{
					return (int)m_ijob.EnumFiles().GetCount();
				}
				catch (COMException cex)
				{
					HandleCOMException(cex);
				}
				return 0;
			}
		}

		/// <summary>Gets a value indicating whether the <see cref="ICollection{T}"/> is read-only.</summary>
		bool ICollection<BackgroundCopyFileInfo>.IsReadOnly => false;

		/// <summary>Add a file to a download or an upload job. Only one file can be added to upload jobs.</summary>
		/// <param name="remoteFilePath">
		/// Contains the name of the file on the server (for example, http://[server]/[path]/file.ext). The format of the name must conform
		/// to the transfer protocol you use. You cannot use wildcards in the path or file name. The URL must contain only legal URL
		/// characters; no escape processing is performed. The URL is limited to 2,200 characters, not including the null terminator. You can
		/// use SMB to express the remote name of the file to download or upload; there is no SMB support for upload-reply jobs. You can
		/// specify the remote name as a UNC path, full path with a network drive, or use the "file://" prefix.
		/// </param>
		/// <param name="localFilePath">
		/// Contains the name of the file on the client. The file name must include the full path (for example, d:\myapp\updates\file.ext).
		/// You cannot use wildcards in the path or file name, and directories in the path must exist. The user must have permission to write
		/// to the local directory for downloads and the reply portion of an upload-reply job. BITS does not support NTFS streams. Instead of
		/// using network drives, which are session specific, use UNC paths.
		/// </param>
		/// <remarks>
		/// <para>
		/// To add more than one file at a time to a job, call the <see cref="AddRange(Uri, DirectoryInfo, IEnumerable{string})"/> method. It
		/// is more efficient to call the <c>AddRange</c> method when adding multiple files to a job than to call the <c>Add</c> method in a loop.
		/// </para>
		/// <para>
		/// To add a file to a job from which BITS downloads ranges of data from the file, call the
		/// <see cref="Add(string, string, long, long)"/> method.
		/// </para>
		/// <para>Upload jobs can only contain one file. If you add a second file, the method returns BG_E_TOO_MANY_FILES.</para>
		/// <para>
		/// For downloads, BITS guarantees that the version of a file (based on file size and date, not content) that it transfers will be
		/// consistent; however, it does not guarantee that a set of files will be consistent. For example, if BITS is in the middle of
		/// downloading the second of two files in the job at the time that the files are updated on the server, BITS restarts the download
		/// of the second file; however, the first file is not downloaded again.
		/// </para>
		/// <para>
		/// Note that if you own the file being downloaded from the server, you should create a new URL for each new version of the file. If
		/// you use the same URL for new versions of the file, some proxy servers may serve stale data from their cache because they do not
		/// verify with the original server if the file is stale.
		/// </para>
		/// <para>
		/// For uploads, BITS generates an error if the local file changes while the file is transferring. The error code is
		/// BG_E_FILE_CHANGED and the context is BG_ERROR_CONTEXT_LOCAL_FILE.
		/// </para>
		/// <para>
		/// BITS transfers the files within a job sequentially. If an error occurs while transferring a file, the job moves to an error state
		/// and no more files within the job are processed until the error is resolved.
		/// </para>
		/// <para>
		/// By default, a user can add up to 200 files to a job. This limit does not apply to administrators or service accounts. To change
		/// the default, set the <c>MaxFilesPerJob</c> group policies.
		/// </para>
		/// <para><c>Prior to Windows Vista:</c> There is no limit on the number of files that a user can add to a job.</para>
		/// </remarks>
		public void Add(string remoteFilePath, string localFilePath)
		{
			// remoteFilePath must not have a trailing backslash.
			if (!string.IsNullOrEmpty(remoteFilePath))
				remoteFilePath.TrimEnd('/');


			try
			{
				m_ijob.AddFile(remoteFilePath, localFilePath);
			}
			catch (COMException cex)
			{
				HandleCOMException(cex);
			}
		}

		/// <summary>Add a file to a download job and specify the ranges of the file you want to download.</summary>
		/// <param name="remoteFilePath">
		/// Contains the name of the file on the server (for example, http://[server]/[path]/file.ext). The format of the name must conform
		/// to the transfer protocol you use. You cannot use wildcards in the path or file name. The URL must contain only legal URL
		/// characters; no escape processing is performed. The URL is limited to 2,200 characters, not including the null terminator. You can
		/// use SMB to express the remote name of the file to download or upload; there is no SMB support for upload-reply jobs. You can
		/// specify the remote name as a UNC path, full path with a network drive, or use the "file://" prefix.
		/// </param>
		/// <param name="localFilePath">
		/// Contains the name of the file on the client. The file name must include the full path (for example, d:\myapp\updates\file.ext).
		/// You cannot use wildcards in the path or file name, and directories in the path must exist. The user must have permission to write
		/// to the local directory for downloads and the reply portion of an upload-reply job. BITS does not support NTFS streams. Instead of
		/// using network drives, which are session specific, use UNC paths.
		/// </param>
		/// <param name="initialOffset">Zero-based offset to the beginning of the range of bytes to download from a file.</param>
		/// <param name="length">Number of bytes in the range.</param>
		public void Add(string remoteFilePath, string localFilePath, long initialOffset, long length = -1)
		{
			IBackgroundCopyJob3 ijob3;
			try { ijob3 = (IBackgroundCopyJob3)m_ijob; }
			catch { throw new NotSupportedException(); }
			var rng = new[] { new BG_FILE_RANGE { InitialOffset = (ulong)initialOffset, Length = length == -1 ? ulong.MaxValue : (ulong)length } };
			try
			{
				ijob3.AddFileWithRanges(remoteFilePath, localFilePath, 1, rng);
			}
			catch (COMException cex)
			{
				HandleCOMException(cex);
			}
		}

		/// <summary>Add a list of files to download from a URL.</summary>
		/// <param name="remoteUrlRoot">
		/// Contains the name of the directory on the server (for example, http://[server]/[path]/). The format of the name must conform to
		/// the transfer protocol you use. You cannot use wildcards in the path or file name. The URL must contain only legal URL characters;
		/// no escape processing is performed. The URL is limited to 2,200 characters, not including the null terminator. You can use SMB to
		/// express the remote name of the file to download or upload; there is no SMB support for upload-reply jobs. You can specify the
		/// remote name as a UNC path, full path with a network drive, or use the "file://" prefix.
		/// </param>
		/// <param name="localDirectory">
		/// Contains the name of the directory on the client. The directory must exist. The user must have permission to write to the
		/// directory for downloads. BITS does not support NTFS streams. Instead of using network drives, which are session specific, use UNC paths.
		/// </param>
		/// <param name="files">
		/// List of relative file names to retrieve from the remote directory. Filename will be appended to both the remoteUrlRoot and the localDirectory.
		/// </param>
		public void AddRange(Uri remoteUrlRoot, DirectoryInfo localDirectory, IEnumerable<string> files)
		{
			var array = files.Select(s => new BG_FILE_INFO(new Uri(remoteUrlRoot, s).AbsoluteUri, Path.Combine(localDirectory.FullName, s))).ToArray();
			try
			{
				m_ijob.AddFileSet((uint)array.Length, array);
			}
			catch (COMException cex)
			{
				HandleCOMException(cex);
			}
		}


		/// <summary>Add a list of files to download from a URL.</summary>
		/// <param name="remoteUrlRoot">
		/// Contains the name of the directory on the server (for example, http://[server]/[path]/). The format of the name must conform to
		/// the transfer protocol you use. You cannot use wildcards in the path or file name. The URL must contain only legal URL characters;
		/// no escape processing is performed. The URL is limited to 2,200 characters, not including the null terminator. You can use SMB to
		/// express the remote name of the file to download or upload; there is no SMB support for upload-reply jobs. You can specify the
		/// remote name as a UNC path, full path with a network drive, or use the "file://" prefix.
		/// </param>
		/// <param name="localDirectory">
		/// Contains the name of the directory on the client. The directory must exist. The user must have permission to write to the
		/// directory for downloads. BITS does not support NTFS streams. Instead of using network drives, which are session specific, use UNC paths.
		/// </param>
		/// <param name="files">
		/// List of relative file names to retrieve from the remote directory. Filename will be appended to both the remoteUrlRoot and the localDirectory.
		/// </param>
		public void AddRange(string remoteUrlRoot, string localDirectory, IEnumerable<string> files)
		{
			// remoteUrlRoot must have a trailing backslash.
			if (!string.IsNullOrEmpty(remoteUrlRoot) && !remoteUrlRoot.EndsWith("/", StringComparison.Ordinal))
				remoteUrlRoot += "/";

			AddRange(new Uri(remoteUrlRoot), new DirectoryInfo(localDirectory), files);
		}


		/// <summary>
		/// Returns an object that implements the <see cref="IEnumerator"/> interface and that can iterate through the
		/// <see cref="BackgroundCopyFileInfo"/> objects within the <see cref="BackgroundCopyFileCollection"/> collection.
		/// </summary>
		/// <returns>
		/// Returns an object that implements the <see cref="IEnumerator"/> interface and that can iterate through the
		/// <see cref="BackgroundCopyFileInfo"/> objects within the <see cref="BackgroundCopyFileCollection"/> collection.
		/// </returns>
		public IEnumerator<BackgroundCopyFileInfo> GetEnumerator() => new Enumerator(m_ijob.EnumFiles());

		/// <summary>Adds an item to the <see cref="ICollection{T}"/>.</summary>
		/// <param name="item">The object to add to the <see cref="ICollection{T}"/>.</param>
		/// <exception cref="NotImplementedException"></exception>
		void ICollection<BackgroundCopyFileInfo>.Add(BackgroundCopyFileInfo item)
		{
		}

		/// <summary>Removes all items from the <see cref="ICollection{T}"/>.</summary>
		/// <exception cref="NotImplementedException"></exception>
		void ICollection<BackgroundCopyFileInfo>.Clear() => throw new NotSupportedException();

		/// <summary>Determines whether the <see cref="ICollection{T}"/> contains a specific value.</summary>
		/// <param name="item">The object to locate in the <see cref="ICollection{T}"/>.</param>
		/// <returns>true if <paramref name="item"/> is found in the <see cref="ICollection{T}"/>; otherwise, false.</returns>
		/// <exception cref="NotImplementedException"></exception>
		bool ICollection<BackgroundCopyFileInfo>.Contains(BackgroundCopyFileInfo item) => throw new NotSupportedException();

		/// <summary>
		/// Copies the elements of the <see cref="ICollection{T}"/> to an <see cref="T:System.Array"/>, starting at a particular
		/// <see cref="T:System.Array"/> index.
		/// </summary>
		/// <param name="array">
		/// The one-dimensional <see cref="T:System.Array"/> that is the destination of the elements copied from
		/// <see cref="ICollection{T}"/>. The <see cref="T:System.Array"/> must have zero-based indexing.
		/// </param>
		/// <param name="arrayIndex">The zero-based index in <paramref name="array"/> at which copying begins.</param>
		/// <exception cref="NotImplementedException"></exception>
		void ICollection<BackgroundCopyFileInfo>.CopyTo(BackgroundCopyFileInfo[] array, int arrayIndex) => throw new NotSupportedException();

		/// <summary>Disposes of the BackgroundCopyFileSet object.</summary>
		void IDisposable.Dispose() => m_ijob = null;

		/// <summary>Returns an enumerator that iterates through a collection.</summary>
		/// <returns>An <see cref="IEnumerator"/> object that can be used to iterate through the collection.</returns>
		IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();

		/// <summary>Removes the first occurrence of a specific object from the <see cref="ICollection{T}"/>.</summary>
		/// <param name="item">The object to remove from the <see cref="ICollection{T}"/>.</param>
		/// <returns>
		/// true if <paramref name="item"/> was successfully removed from the <see cref="ICollection{T}"/>; otherwise, false. This method
		/// also returns false if <paramref name="item"/> is not found in the original <see cref="ICollection{T}"/>.
		/// </returns>
		/// <exception cref="NotImplementedException"></exception>
		bool ICollection<BackgroundCopyFileInfo>.Remove(BackgroundCopyFileInfo item) => throw new NotSupportedException();

		internal BackgroundCopyFileInfo[] GetBCFIArray() => this.ToArray();

		private void HandleCOMException(COMException cex)
		{
			var state = m_ijob.GetState();
			if (state == BG_JOB_STATE.BG_JOB_STATE_ERROR || state == BG_JOB_STATE.BG_JOB_STATE_TRANSIENT_ERROR)
			{
				var pErr = m_ijob.GetError();
				throw new BackgroundCopyException(pErr);
			}
			else
				throw new BackgroundCopyException(cex);
		}

		/// <summary>
		/// An implementation the <see cref="IEnumerator"/> interface that can iterate through the <see cref="BackgroundCopyFileInfo"/>
		/// objects within the <see cref="BackgroundCopyFileCollection"/> collection.
		/// </summary>
		private sealed class Enumerator : Vanara.Collections.IEnumeratorFromNext<IEnumBackgroundCopyFiles, BackgroundCopyFileInfo>
		{
			internal Enumerator(IEnumBackgroundCopyFiles enumfiles) : base(enumfiles, TryGetNext, e => e.Reset())
			{
			}

			private static bool TryGetNext(IEnumBackgroundCopyFiles e, out BackgroundCopyFileInfo i)
			{
				var ifi = e.Next(1)?.FirstOrDefault();
				i = ifi is not null ? new BackgroundCopyFileInfo(ifi) : null;
				return i is not null;
			}
		}
	}
}