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// https://duplicati.com, hello@duplicati.com
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the "Software"),
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// the rights to use, copy, modify, merge, publish, distribute, sublicense,
// and/or sell copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// DEALINGS IN THE SOFTWARE.

using System;
using System.Buffers;
using System.Threading;
using Duplicati.Library.Main.Volumes;
using Duplicati.Library.Utility;

#nullable enable

namespace Duplicati.Library.Main.Operation.Restore
{

    /// <summary>
    /// Represents the type of block request.
    /// </summary>
    public enum BlockRequestType
    {
        Download, // Request to download a block
        CacheEvict, // Request to evict a block from cache
    }

    /// <summary>
    /// Represents a block of data where the byte[] buffer is returned to the ArrayPool when the DataBlock is finalized.
    /// </summary>
    public class DataBlock(byte[] data) : IDisposable
    {
        /// <summary>
        /// The data buffer for this block. This buffer is returned to the ArrayPool when the DataBlock is finalized, which will make this field null.
        /// </summary>
        public byte[]? Data = data;

        /// <summary>
        /// The reference count for this DataBlock. When the reference count reaches zero, the byte[] buffer is returned to the ArrayPool.
        /// </summary>
        private int references = 1;

        /// <summary>
        /// References this DataBlock, incrementing the reference count.
        /// </summary>
        /// <remarks>The method returns the DataBlock instance for `using` statements.</remarks>
        /// <returns>This DataBlock instance.</returns>
        public DataBlock Reference(int count = 1)
        {
            Interlocked.Add(ref references, count);
            return this;
        }

        public void Dispose()
        {
            Dereference();
            GC.SuppressFinalize(this);
        }

        /// <summary>
        /// Dereferences this DataBlock, returning the byte[] buffer to the ArrayPool if the reference count reaches zero.
        /// </summary>
        /// <returns>true if the buffer was returned to the ArrayPool; otherwise, false.</returns>
        private void Dereference()
        {
            if (Interlocked.Decrement(ref references) == 0)
            {
                if (Data != null)
                {
                    ArrayPool<byte>.Shared.Return(Data);
                    Data = null;
                }
            }
        }
    }

    /// <summary>
    /// Represents a block of data where the byte[] buffer is returned to the ArrayPool when the DataBlock is finalized.
    /// </summary>
    public class VolumeWrapper(TempFile file, BlockVolumeReader reader) : IDisposable
    {
        /// <summary>
        /// The TempFile for this volume.
        /// </summary>
        private TempFile? File = file;

        /// <summary>
        /// The BlockVolumeReader for this volume.
        /// </summary>
        public BlockVolumeReader? Reader = reader;

        /// <summary>
        /// The size of the volume file in bytes.
        /// </summary>
        public long Size { init; get; } = new System.IO.FileInfo(file).Length;

        /// <summary>
        /// The reference count for this DataBlock. When the reference count reaches zero, the byte[] buffer is returned to the ArrayPool.
        /// </summary>
        private int references = 1;

        /// <summary>
        /// References this DataBlock, incrementing the reference count.
        /// </summary>
        /// <remarks>The method returns the DataBlock instance for `using` statements.</remarks>
        /// <returns>This DataBlock instance.</returns>
        public VolumeWrapper Reference(int count = 1)
        {
            Interlocked.Add(ref references, count);
            return this;
        }

        public void Dispose()
        {
            Dereference();
            GC.SuppressFinalize(this);
        }

        /// <summary>
        /// Dereferences this DataBlock, returning the byte[] buffer to the ArrayPool if the reference count reaches zero.
        /// </summary>
        /// <returns>true if the buffer was returned to the ArrayPool; otherwise, false.</returns>
        private void Dereference()
        {
            if (Interlocked.Decrement(ref references) == 0)
            {
                Reader?.Dispose();
                Reader = null;
                File?.Dispose();
                File = null;
            }
        }
    }

    /// <summary>
    /// Represents a block request that the `VolumeDownloader` process will use to download a block from the backend.
    /// </summary>
    /// <param name="blockID">The block ID in the database.</param>
    /// <param name="blockOffset">The offset in blocks this block represents in the target file.</param>
    /// <param name="blockHash">The hash of the block.</param>
    /// <param name="blockSize">The size of the block.</param>
    /// <param name="volumeID">The ID of the volume in which the block is stored remotely.</param>
    /// <param name="cacheDecrEvict">Flag indicating that this block request should either decrement the block counter for BlockID (for BlockManager) or evict the VolumeID (for VolumeDownloader).</param>
    public class BlockRequest(long blockID, long blockOffset, string blockHash, long blockSize, long volumeID, BlockRequestType requestType)
    { // Total = 81 bytes
        public long BlockID { get; } = blockID;
        public long BlockOffset { get; } = blockOffset;
        public string BlockHash { get; } = blockHash;
        public long BlockSize { get; } = blockSize;
        public long VolumeID { get; } = volumeID;
        public BlockRequestType RequestType { get; set; } = requestType;
        public DateTime TimestampMilliseconds { get; } = DateTime.Now;
    }

    /// <summary>
    /// Represents a file request that the `FileLister` process sends to the `FileProcessor` process.
    /// </summary>
    /// <param name="ID">The File ID.</param>
    /// <param name="OriginalPath">The original path of the file.</param>
    /// <param name="TargetPath">The target path of the file.</param>
    /// <param name="Hash">The file hash.</param>
    /// <param name="Length">The length of the file.</param>
    /// <param name="BlocksetID">The BlocksetID of the file.</param>
    /// <param name="IsPriorityFile">Whether this is a priority file that should be processed before other files.</param>
    public class FileRequest(long ID, string OriginalPath, string TargetPath, string Hash, long Length, long BlocksetID, bool IsPriorityFile = false)
    {
        public long ID { get; } = ID;
        public string OriginalPath { get; } = OriginalPath;
        public string TargetPath { get; } = TargetPath;
        public string Hash { get; } = Hash;
        public long Length { get; } = Length;
        public long BlocksetID { get; } = BlocksetID;
        public bool IsPriorityFile { get; } = IsPriorityFile;
    }

}