// /***************************************************************************
// Aaru Data Preservation Suite
// ----------------------------------------------------------------------------
//
// Filename       : File.cs
// Author(s)      : Natalia Portillo <claunia@claunia.com>
//
// Component      : Microsoft FAT filesystem plugin.
//
// --[ Description ] ----------------------------------------------------------
//
//     Methods to handle files.
//
// --[ License ] --------------------------------------------------------------
//
//     This library is free software; you can redistribute it and/or modify
//     it under the terms of the GNU Lesser General Public License as
//     published by the Free Software Foundation; either version 2.1 of the
//     License, or (at your option) any later version.
//
//     This library is distributed in the hope that it will be useful, but
//     WITHOUT ANY WARRANTY; without even the implied warranty of
//     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
//     Lesser General Public License for more details.
//
//     You should have received a copy of the GNU Lesser General Public
//     License along with this library; if not, see <http://www.gnu.org/licenses/>.
//
// ----------------------------------------------------------------------------
// Copyright © 2011-2021 Natalia Portillo
// ****************************************************************************/

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using Aaru.CommonTypes.Structs;
using Aaru.Helpers;
using FileAttributes = Aaru.CommonTypes.Structs.FileAttributes;

namespace Aaru.Filesystems
{
    public sealed partial class FAT
    {
        /// <inheritdoc />
        public Errno MapBlock(string path, long fileBlock, out long deviceBlock)
        {
            deviceBlock = 0;

            if(!_mounted)
                return Errno.AccessDenied;

            Errno err = Stat(path, out FileEntryInfo stat);

            if(err != Errno.NoError)
                return err;

            if(stat.Attributes.HasFlag(FileAttributes.Directory) &&
               !_debug)
                return Errno.IsDirectory;

            uint[] clusters = GetClusters((uint)stat.Inode);

            if(fileBlock >= clusters.Length)
                return Errno.InvalidArgument;

            deviceBlock = (long)(_firstClusterSector + (clusters[fileBlock] * _sectorsPerCluster));

            return Errno.NoError;
        }

        /// <inheritdoc />
        public Errno GetAttributes(string path, out FileAttributes attributes)
        {
            attributes = new FileAttributes();

            if(!_mounted)
                return Errno.AccessDenied;

            Errno err = Stat(path, out FileEntryInfo stat);

            if(err != Errno.NoError)
                return err;

            attributes = stat.Attributes;

            return Errno.NoError;
        }

        /// <inheritdoc />
        public Errno Read(string path, long offset, long size, ref byte[] buf)
        {
            if(!_mounted)
                return Errno.AccessDenied;

            Errno err = Stat(path, out FileEntryInfo stat);

            if(err != Errno.NoError)
                return err;

            if(stat.Attributes.HasFlag(FileAttributes.Directory) &&
               !_debug)
                return Errno.IsDirectory;

            if(size == 0)
            {
                buf = Array.Empty<byte>();

                return Errno.NoError;
            }

            if(offset >= stat.Length)
                return Errno.InvalidArgument;

            if(size + offset >= stat.Length)
                size = stat.Length - offset;

            uint[] clusters = GetClusters((uint)stat.Inode);

            if(clusters is null)
                return Errno.InvalidArgument;

            long firstCluster    = offset                   / _bytesPerCluster;
            long offsetInCluster = offset                   % _bytesPerCluster;
            long sizeInClusters  = (size + offsetInCluster) / _bytesPerCluster;

            if((size + offsetInCluster) % _bytesPerCluster > 0)
                sizeInClusters++;

            var ms = new MemoryStream();

            for(int i = 0; i < sizeInClusters; i++)
            {
                if(i + firstCluster >= clusters.Length)
                    return Errno.InvalidArgument;

                byte[] buffer =
                    _image.ReadSectors(_firstClusterSector + (clusters[i + firstCluster] * _sectorsPerCluster),
                                       _sectorsPerCluster);

                ms.Write(buffer, 0, buffer.Length);
            }

            ms.Position = offsetInCluster;
            buf         = new byte[size];
            ms.Read(buf, 0, (int)size);

            return Errno.NoError;
        }

        /// <inheritdoc />
        public Errno Stat(string path, out FileEntryInfo stat)
        {
            stat = null;

            if(!_mounted)
                return Errno.AccessDenied;

            Errno err = GetFileEntry(path, out CompleteDirectoryEntry completeEntry);

            if(err != Errno.NoError)
                return err;

            DirectoryEntry entry = completeEntry.Dirent;

            stat = new FileEntryInfo
            {
                Attributes = new FileAttributes(),
                Blocks     = entry.size / _bytesPerCluster,
                BlockSize  = _bytesPerCluster,
                Length     = entry.size,
                Inode      = (ulong)(_fat32 ? (entry.ea_handle << 16) + entry.start_cluster : entry.start_cluster),
                Links      = 1
            };

            if(entry.cdate > 0 ||
               entry.ctime > 0)
                stat.CreationTime = DateHandlers.DosToDateTime(entry.cdate, entry.ctime);

            if(_namespace != Namespace.Human)
            {
                if(entry.mdate > 0 ||
                   entry.mtime > 0)
                    stat.LastWriteTime = DateHandlers.DosToDateTime(entry.mdate, entry.mtime);

                if(entry.ctime_ms > 0)
                    stat.CreationTime = stat.CreationTime?.AddMilliseconds(entry.ctime_ms * 10);
            }

            if(entry.size % _bytesPerCluster > 0)
                stat.Blocks++;

            if(entry.attributes.HasFlag(FatAttributes.Subdirectory))
            {
                stat.Attributes |= FileAttributes.Directory;

                if((_fat32 && entry.ea_handle << 16 > 0) ||
                   entry.start_cluster > 0)
                    stat.Blocks = _fat32 ? (GetClusters((uint)((entry.ea_handle << 16) + entry.start_cluster))?.Length ?? 0)
                                      : (GetClusters(entry.start_cluster)?.Length??0);

                stat.Length = stat.Blocks * stat.BlockSize;
            }

            if(entry.attributes.HasFlag(FatAttributes.ReadOnly))
                stat.Attributes |= FileAttributes.ReadOnly;

            if(entry.attributes.HasFlag(FatAttributes.Hidden))
                stat.Attributes |= FileAttributes.Hidden;

            if(entry.attributes.HasFlag(FatAttributes.System))
                stat.Attributes |= FileAttributes.System;

            if(entry.attributes.HasFlag(FatAttributes.Archive))
                stat.Attributes |= FileAttributes.Archive;

            if(entry.attributes.HasFlag(FatAttributes.Device))
                stat.Attributes |= FileAttributes.Device;

            return Errno.NoError;
        }

        uint[] GetClusters(uint startCluster)
        {
            if(startCluster == 0)
                return Array.Empty<uint>();

            if(startCluster >= XmlFsType.Clusters)
                return null;

            List<uint> clusters = new List<uint>();

            uint nextCluster = startCluster;

            ulong nextSector = (nextCluster / _fatEntriesPerSector) + _fatFirstSector +
                               (_useFirstFat ? 0 : _sectorsPerFat);

            int nextEntry = (int)(nextCluster % _fatEntriesPerSector);

            ulong  currentSector = nextSector;
            byte[] fatData       = _image.ReadSector(currentSector);

            if(_fat32)
                while((nextCluster & FAT32_MASK) > 0 &&
                      (nextCluster & FAT32_MASK) <= FAT32_RESERVED)
                {
                    clusters.Add(nextCluster);

                    if(currentSector != nextSector)
                    {
                        fatData       = _image.ReadSector(nextSector);
                        currentSector = nextSector;
                    }

                    nextCluster = BitConverter.ToUInt32(fatData, nextEntry * 4);

                    nextSector = (nextCluster / _fatEntriesPerSector) + _fatFirstSector +
                                 (_useFirstFat ? 0 : _sectorsPerFat);

                    nextEntry = (int)(nextCluster % _fatEntriesPerSector);
                }
            else if(_fat16)
                while(nextCluster > 0 &&
                      nextCluster <= FAT16_RESERVED)
                {
                    if(nextCluster > _fatEntries.Length)
                        return null;

                    clusters.Add(nextCluster);
                    nextCluster = _fatEntries[nextCluster];
                }
            else
                while(nextCluster > 0 &&
                      nextCluster <= FAT12_RESERVED)
                {
                    if(nextCluster > _fatEntries.Length)
                        return null;

                    clusters.Add(nextCluster);
                    nextCluster = _fatEntries[nextCluster];
                }

            return clusters.ToArray();
        }

        Errno GetFileEntry(string path, out CompleteDirectoryEntry entry)
        {
            entry = null;

            string cutPath = path.StartsWith('/') ? path.Substring(1).ToLower(_cultureInfo)
                                 : path.ToLower(_cultureInfo);

            string[] pieces = cutPath.Split(new[]
            {
                '/'
            }, StringSplitOptions.RemoveEmptyEntries);

            if(pieces.Length == 0)
                return Errno.InvalidArgument;

            string parentPath = string.Join("/", pieces, 0, pieces.Length - 1);

            if(!_directoryCache.TryGetValue(parentPath, out _))
            {
                Errno err = ReadDir(parentPath, out _);

                if(err != Errno.NoError)
                    return err;
            }

            Dictionary<string, CompleteDirectoryEntry> parent;

            if(pieces.Length == 1)
                parent = _rootDirectoryCache;
            else if(!_directoryCache.TryGetValue(parentPath, out parent))
                return Errno.InvalidArgument;

            KeyValuePair<string, CompleteDirectoryEntry> dirent =
                parent.FirstOrDefault(t => t.Key.ToLower(_cultureInfo) == pieces[^1]);

            if(string.IsNullOrEmpty(dirent.Key))
                return Errno.NoSuchFile;

            entry = dirent.Value;

            return Errno.NoError;
        }

        byte LfnChecksum(byte[] name, byte[] extension)
        {
            byte sum = 0;

            for(int i = 0; i < 8; i++)
                sum = (byte)(((sum & 1) << 7) + (sum >> 1) + name[i]);

            for(int i = 0; i < 3; i++)
                sum = (byte)(((sum & 1) << 7) + (sum >> 1) + extension[i]);

            return sum;
        }
    }
}