using System;
using System.IO;
using System.Linq;
using System.Threading;
using NLog;
using NzbDrone.Common.EnsureThat;
using NzbDrone.Common.Extensions;

namespace NzbDrone.Common.Disk
{
    public interface IDiskTransferService
    {
        TransferMode TransferFolder(string sourcePath, string targetPath, TransferMode mode);
        TransferMode TransferFile(string sourcePath, string targetPath, TransferMode mode, bool overwrite = false);
        int MirrorFolder(string sourcePath, string targetPath);
    }
    
    public class DiskTransferService : IDiskTransferService
    {
        private readonly IDiskProvider _diskProvider;
        private readonly Logger _logger;

        public DiskTransferService(IDiskProvider diskProvider, Logger logger)
        {
            _diskProvider = diskProvider;
            _logger = logger;
        }

        private string ResolveRealParentPath(string path)
        {
            var parentPath = path.GetParentPath();
            if (!_diskProvider.FolderExists(parentPath))
            {
                return path;
            }

            var realParentPath = parentPath.GetActualCasing();

            var partialChildPath = path.Substring(parentPath.Length);

            return realParentPath + partialChildPath;
        }
        
        public TransferMode TransferFolder(string sourcePath, string targetPath, TransferMode mode)
        {
            Ensure.That(sourcePath, () => sourcePath).IsValidPath();
            Ensure.That(targetPath, () => targetPath).IsValidPath();

            sourcePath = ResolveRealParentPath(sourcePath);
            targetPath = ResolveRealParentPath(targetPath);

            _logger.Debug("{0} Directory [{1}] > [{2}]", mode, sourcePath, targetPath);

            if (sourcePath == targetPath)
            {
                throw new IOException(string.Format("Source and destination can't be the same {0}", sourcePath));
            }

            if (mode == TransferMode.Move && sourcePath.PathEquals(targetPath, StringComparison.InvariantCultureIgnoreCase) && _diskProvider.FolderExists(targetPath))
            {
                // Move folder out of the way to allow case-insensitive renames
                var tempPath = sourcePath + ".backup~";
                _logger.Trace("Rename Intermediate Directory [{0}] > [{1}]", sourcePath, tempPath);
                _diskProvider.MoveFolder(sourcePath, tempPath);

                if (!_diskProvider.FolderExists(targetPath))
                {
                    _logger.Trace("Rename Intermediate Directory [{0}] > [{1}]", tempPath, targetPath);
                    _logger.Debug("Rename Directory [{0}] > [{1}]", sourcePath, targetPath);
                    _diskProvider.MoveFolder(tempPath, targetPath);
                    return mode;
                }

                // There were two separate folders, revert the intermediate rename and let the recursion deal with it
                _logger.Trace("Rename Intermediate Directory [{0}] > [{1}]", tempPath, sourcePath);
                _diskProvider.MoveFolder(tempPath, sourcePath);
            }

            if (mode == TransferMode.Move && !_diskProvider.FolderExists(targetPath))
            {
                var sourceMount = _diskProvider.GetMount(sourcePath);
                var targetMount = _diskProvider.GetMount(targetPath);

                // If we're on the same mount, do a simple folder move.
                if (sourceMount != null && targetMount != null && sourceMount.RootDirectory == targetMount.RootDirectory)
                {
                    _logger.Debug("Rename Directory [{0}] > [{1}]", sourcePath, targetPath);
                    _diskProvider.MoveFolder(sourcePath, targetPath);
                    return mode;
                }
            }

            if (!_diskProvider.FolderExists(targetPath))
            {
                _diskProvider.CreateFolder(targetPath);

                _diskProvider.CopyPermissions(sourcePath, targetPath);
            }

            var result = mode;

            foreach (var subDir in _diskProvider.GetDirectoryInfos(sourcePath))
            {
                if (ShouldIgnore(subDir)) continue;

                result &= TransferFolder(subDir.FullName, Path.Combine(targetPath, subDir.Name), mode);
            }

            foreach (var sourceFile in _diskProvider.GetFileInfos(sourcePath))
            {
                if (ShouldIgnore(sourceFile)) continue;

                var destFile = Path.Combine(targetPath, sourceFile.Name);

                result &= TransferFile(sourceFile.FullName, destFile, mode, true);
            }

            if (mode.HasFlag(TransferMode.Move))
            {
                var totalSize = _diskProvider.GetFileInfos(sourcePath).Sum(v => v.Length);

                if (totalSize > (100 * 1024L * 1024L))
                {
                    throw new IOException($"Large files still exist in {sourcePath} after folder move, not deleting source folder");
                }

                _diskProvider.DeleteFolder(sourcePath, true);
            }

            return result;
        }

        public int MirrorFolder(string sourcePath, string targetPath)
        {
            var filesCopied = 0;

            Ensure.That(sourcePath, () => sourcePath).IsValidPath();
            Ensure.That(targetPath, () => targetPath).IsValidPath();

            sourcePath = ResolveRealParentPath(sourcePath);
            targetPath = ResolveRealParentPath(targetPath);

            _logger.Debug("Mirror Folder [{0}] > [{1}]", sourcePath, targetPath);

            if (!_diskProvider.FolderExists(targetPath))
            {
                _diskProvider.CreateFolder(targetPath);
            }

            var sourceFolders = _diskProvider.GetDirectoryInfos(sourcePath);
            var targetFolders = _diskProvider.GetDirectoryInfos(targetPath);

            foreach (var subDir in targetFolders.Where(v => !sourceFolders.Any(d => d.Name == v.Name)))
            {
                if (ShouldIgnore(subDir)) continue;

                _diskProvider.DeleteFolder(subDir.FullName, true);
            }

            foreach (var subDir in sourceFolders)
            {
                if (ShouldIgnore(subDir)) continue;

                filesCopied += MirrorFolder(subDir.FullName, Path.Combine(targetPath, subDir.Name));
            }

            var sourceFiles = _diskProvider.GetFileInfos(sourcePath);
            var targetFiles = _diskProvider.GetFileInfos(targetPath);

            foreach (var targetFile in targetFiles.Where(v => !sourceFiles.Any(d => d.Name == v.Name)))
            {
                if (ShouldIgnore(targetFile)) continue;

                _diskProvider.DeleteFile(targetFile.FullName);
            }

            foreach (var sourceFile in sourceFiles)
            {
                if (ShouldIgnore(sourceFile)) continue;

                var targetFile = Path.Combine(targetPath, sourceFile.Name);

                if (CompareFiles(sourceFile.FullName, targetFile))
                {
                    continue;
                }

                TransferFile(sourceFile.FullName, targetFile, TransferMode.Copy, true);
                filesCopied++;
            }

            return filesCopied;
        }

        private bool CompareFiles(string sourceFile, string targetFile)
        {
            if (!_diskProvider.FileExists(sourceFile) || !_diskProvider.FileExists(targetFile))
            {
                return false;
            }

            if (_diskProvider.GetFileSize(sourceFile) != _diskProvider.GetFileSize(targetFile))
            {
                return false;
            }

            var sourceBuffer = new byte[64 * 1024];
            var targetBuffer = new byte[64 * 1024];
            using (var sourceStream = _diskProvider.OpenReadStream(sourceFile))
            using (var targetStream = _diskProvider.OpenReadStream(targetFile))
            {
                while (true)
                {
                    var sourceLength = sourceStream.Read(sourceBuffer, 0, sourceBuffer.Length);
                    var targetLength = targetStream.Read(targetBuffer, 0, targetBuffer.Length);

                    if (sourceLength != targetLength)
                    {
                        return false;
                    }

                    if (sourceLength == 0)
                    {
                        return true;
                    }

                    for (var i = 0; i < sourceLength; i++)
                    {
                        if (sourceBuffer[i] != targetBuffer[i])
                        {
                            return false;
                        }
                    }
                }
            }
        }

        public TransferMode TransferFile(string sourcePath, string targetPath, TransferMode mode, bool overwrite = false)
        {
            Ensure.That(sourcePath, () => sourcePath).IsValidPath();
            Ensure.That(targetPath, () => targetPath).IsValidPath();

            sourcePath = ResolveRealParentPath(sourcePath);
            targetPath = ResolveRealParentPath(targetPath);

            _logger.Debug("{0} [{1}] > [{2}]", mode, sourcePath, targetPath);

            var originalSize = _diskProvider.GetFileSize(sourcePath);

            if (sourcePath == targetPath)
            {
                throw new IOException(string.Format("Source and destination can't be the same {0}", sourcePath));
            }

            if (sourcePath.PathEquals(targetPath, StringComparison.InvariantCultureIgnoreCase))
            {
                if (mode.HasFlag(TransferMode.HardLink) || mode.HasFlag(TransferMode.Copy))
                {
                    throw new IOException(string.Format("Source and destination can't be the same {0}", sourcePath));
                }

                if (mode.HasFlag(TransferMode.Move))
                {
                    var tempPath = sourcePath + ".backup~";

                    _diskProvider.MoveFile(sourcePath, tempPath, true);
                    try
                    {
                        ClearTargetPath(sourcePath, targetPath, overwrite);

                        _diskProvider.MoveFile(tempPath, targetPath);

                        return TransferMode.Move;
                    }
                    catch
                    {
                        RollbackMove(sourcePath, tempPath);
                        throw;
                    }
                }

                return TransferMode.None;
            }

            if (sourcePath.GetParentPath() == targetPath.GetParentPath())
            {
                if (mode.HasFlag(TransferMode.Move))
                {
                    TryMoveFileVerified(sourcePath, targetPath, originalSize);
                    return TransferMode.Move;
                }
            }

            if (sourcePath.IsParentPath(targetPath))
            {
                throw new IOException(string.Format("Destination cannot be a child of the source [{0}] => [{1}]", sourcePath, targetPath));
            }

            ClearTargetPath(sourcePath, targetPath, overwrite);

            if (mode.HasFlag(TransferMode.HardLink))
            {
                var createdHardlink = _diskProvider.TryCreateHardLink(sourcePath, targetPath);
                if (createdHardlink)
                {
                    return TransferMode.HardLink;
                }
                if (!mode.HasFlag(TransferMode.Copy))
                {
                    throw new IOException("Hardlinking from '" + sourcePath + "' to '" + targetPath + "' failed.");
                }
            }

            // Adjust the transfer mode depending on the filesystems
            var sourceMount = _diskProvider.GetMount(sourcePath);
            var targetMount = _diskProvider.GetMount(targetPath);

            var isSameMount = (sourceMount != null && targetMount != null && sourceMount.RootDirectory == targetMount.RootDirectory);

            var sourceDriveFormat = sourceMount?.DriveFormat ?? string.Empty;
            var targetDriveFormat = targetMount?.DriveFormat ?? string.Empty;

            var isCifs = targetDriveFormat == "cifs";
            var isBtrfs = sourceDriveFormat == "btrfs" && targetDriveFormat == "btrfs";
           
            if (mode.HasFlag(TransferMode.Copy))
            {
                if (isBtrfs)
                {
                    if (_diskProvider.TryCreateRefLink(sourcePath, targetPath))
                    {
                        return TransferMode.Copy;
                    }
                }

                TryCopyFileVerified(sourcePath, targetPath, originalSize);
                return TransferMode.Copy;
            }

            if (mode.HasFlag(TransferMode.Move))
            {
                if (isBtrfs)
                {
                    if (isSameMount && _diskProvider.TryRenameFile(sourcePath, targetPath))
                    {
                        _logger.Trace("Renamed [{0}] to [{1}].", sourcePath, targetPath);
                        return TransferMode.Move;
                    }

                    if (_diskProvider.TryCreateRefLink(sourcePath, targetPath))
                    {
                        _logger.Trace("Reflink successful, deleting source [{0}].", sourcePath);
                        _diskProvider.DeleteFile(sourcePath);
                        return TransferMode.Move;
                    }
                }

                if (isCifs && !isSameMount)
                {
                    _logger.Trace("On cifs mount. Starting verified copy [{0}] to [{1}].", sourcePath, targetPath);
                    TryCopyFileVerified(sourcePath, targetPath, originalSize);
                    _logger.Trace("Copy successful, deleting source [{0}].", sourcePath);
                    _diskProvider.DeleteFile(sourcePath);
                    return TransferMode.Move;
                }
               
                TryMoveFileVerified(sourcePath, targetPath, originalSize);
                return TransferMode.Move;
            }

            return TransferMode.None;
        }

        private void ClearTargetPath(string sourcePath, string targetPath, bool overwrite)
        {
            if (_diskProvider.FileExists(targetPath))
            {
                if (overwrite)
                {
                    _diskProvider.DeleteFile(targetPath);
                }
                else
                {
                    throw new DestinationAlreadyExistsException($"Destination {targetPath} already exists.");
                }
            }
        }

        private void RollbackPartialMove(string sourcePath, string targetPath)
        {
            try
            {
                _logger.Debug("Rolling back incomplete file move [{0}] to [{1}].", sourcePath, targetPath);

                WaitForIO();

                if (_diskProvider.FileExists(sourcePath))
                {
                    _diskProvider.DeleteFile(targetPath);
                }
                else
                {
                    _logger.Error("Failed to properly rollback the file move [{0}] to [{1}], incomplete file may be left in target path.", sourcePath, targetPath);
                }
            }
            catch (Exception ex)
            {
                _logger.Error(ex, "Failed to properly rollback the file move [{0}] to [{1}], incomplete file may be left in target path.", sourcePath, targetPath);
            }
        }

        private void RollbackMove(string sourcePath, string targetPath)
        {
            try
            {
                _logger.Debug("Rolling back file move [{0}] to [{1}].", sourcePath, targetPath);

                WaitForIO();

                _diskProvider.MoveFile(targetPath, sourcePath);
            }
            catch (Exception ex)
            {
                _logger.Error(ex, "Failed to properly rollback the file move [{0}] to [{1}], file may be left in target path.", sourcePath, targetPath);
            }
        }

        private void RollbackCopy(string sourcePath, string targetPath)
        {
            try
            {
                _logger.Debug("Rolling back file copy [{0}] to [{1}].", sourcePath, targetPath);

                WaitForIO();

                if (_diskProvider.FileExists(targetPath))
                {
                    _diskProvider.DeleteFile(targetPath);
                }
            }
            catch (Exception ex)
            {
                _logger.Error(ex, "Failed to properly rollback the file copy [{0}] to [{1}], file may be left in target path.", sourcePath, targetPath);
            }
        }

        private void WaitForIO()
        {
            // This delay is intended to give the IO stack a bit of time to recover, this is especially required if remote NAS devices are involved.
            Thread.Sleep(3000);
        }

        private void TryCopyFileVerified(string sourcePath, string targetPath, long originalSize)
        {
            try
            {
                _diskProvider.CopyFile(sourcePath, targetPath);

                var targetSize = _diskProvider.GetFileSize(targetPath);
                if (targetSize != originalSize)
                {
                    throw new IOException(string.Format("File copy incomplete. [{0}] was {1} bytes long instead of {2} bytes.", targetPath, targetSize, originalSize));
                }
            }
            catch
            {
                RollbackCopy(sourcePath, targetPath);
                throw;
            }
        }

        private void TryMoveFileVerified(string sourcePath, string targetPath, long originalSize)
        {
            try
            {
                _diskProvider.MoveFile(sourcePath, targetPath);

                var targetSize = _diskProvider.GetFileSize(targetPath);
                if (targetSize != originalSize)
                {
                    throw new IOException(string.Format("File move incomplete, data loss may have occurred. [{0}] was {1} bytes long instead of the expected {2}.", targetPath, targetSize, originalSize));
                }
            }
            catch
            {
                RollbackPartialMove(sourcePath, targetPath);
                throw;
            }
        }

        private bool ShouldIgnore(DirectoryInfo folder)
        {
            if (folder.Name.StartsWith(".nfs"))
            {
                _logger.Trace("Ignoring folder {0}", folder.FullName);
                return true;
            }

            return false;
        }

        private bool ShouldIgnore(FileInfo file)
        {
            if (file.Name.StartsWith(".nfs") || file.Name == "debug.log" || file.Name.EndsWith(".socket"))
            {
                _logger.Trace("Ignoring file {0}", file.FullName);
                return true;
            }

            return false;
        }
    }
}