//******************************************************************************************************
//  CompressionExtensions.cs - Gbtc
//
//  Copyright © 2012, Grid Protection Alliance.  All Rights Reserved.
//
//  Licensed to the Grid Protection Alliance (GPA) under one or more contributor license agreements. See
//  the NOTICE file distributed with this work for additional information regarding copyright ownership.
//  The GPA licenses this file to you under the MIT License (MIT), the "License"; you may
//  not use this file except in compliance with the License. You may obtain a copy of the License at:
//
//      http://www.opensource.org/licenses/MIT
//
//  Unless agreed to in writing, the subject software distributed under the License is distributed on an
//  "AS-IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. Refer to the
//  License for the specific language governing permissions and limitations.
//
//  Code Modification History:
//  ----------------------------------------------------------------------------------------------------
//  09/26/2008 - J. Ritchie Carroll
//       Generated original version of source code.
//  08/05/2009 - Josh L. Patterson
//       Edited Comments.
//  09/14/2009 - Stephen C. Wills
//       Added new header and license agreement.
//  12/14/2012 - Starlynn Danyelle Gilliam
//       Modified Header.
//
//******************************************************************************************************

using System;
using System.IO;
using System.IO.Compression;

namespace GSF.IO.Compression
{
    #region [ Enumerations ]

    /// <summary>
    /// Level of compression enumeration.
    /// </summary>
    /// <remarks>
    /// Compression strengths represent tradeoffs on speed of compression vs. effectiveness of compression.
    /// </remarks>
    public enum CompressionStrength
    {
        /// <summary>Disables compression.</summary>
        NoCompression = 0,
        /// <summary>Enables standard compression.</summary>
        Standard = 1,
        /// <summary>Enables multi-pass compression to continue recompressing buffer as long as size continues to shrink.</summary>
        MultiPass = 2
    }

    #endregion

    /// <summary>
    /// Defines extension functions related to compression.
    /// </summary>
    public static class CompressionExtensions
    {
        /// <summary>
        /// Default compression buffer size.
        /// </summary>
        public const int BufferSize = 262144;

        /// <summary>
        /// Needed version of this library to uncompress stream (1.0.0 stored as byte 100).
        /// </summary>
        public const byte CompressionVersion = 100;

        /// <summary>
        /// Compress a byte array using standard compression method.
        /// </summary>
        /// <param name="source">The <see cref="byte"/> array to compress.</param>
        /// <returns>A compressed version of the source <see cref="byte"/> array.</returns>
        public static byte[] Compress(this byte[] source)
        {
            return source.Compress(CompressionStrength.Standard);
        }

        /// <summary>
        /// Compress a byte array using specified compression method.
        /// </summary>
        /// <param name="source">The <see cref="byte"/> array to compress.</param>
        /// <param name="strength">The specified <see cref="CompressionStrength"/>.</param>
        /// <returns>A compressed version of the source <see cref="byte"/> array.</returns>
        public static byte[] Compress(this byte[] source, CompressionStrength strength)
        {
            return source.Compress(0, source.Length, strength, 0);
        }

        /// <summary>
        /// Compress a byte array using specified compression method.
        /// </summary>
        /// <param name="source">The <see cref="byte"/> array to compress.</param>
        /// <param name="length">The number of bytes to read into the byte array for compression.</param>
        /// <param name="startIndex">An <see cref="int"/> representing the start index of the byte array.</param>
        /// <param name="strength">The specified <see cref="CompressionStrength"/>.</param>
        /// <returns>A compressed version of the source <see cref="byte"/> array.</returns>
        public static byte[] Compress(this byte[] source, int startIndex, int length, CompressionStrength strength)
        {
            return source.Compress(startIndex, length, strength, 0);
        }

        // When user requests multi-pass compression, we allow multiple compression passes on a buffer because
        // this can often produce better compression results
        private static byte[] Compress(this byte[] source, int startIndex, int length, CompressionStrength strength, int compressionDepth)
        {
            if (strength == CompressionStrength.NoCompression)
            {
                // No compression requested, return specified portion of the buffer
                byte[] outBuffer = new byte[++length];
                outBuffer[0] = (byte)strength;

                for (int x = 1; x < length; x++)
                    outBuffer[x] = source[startIndex + x - 1];

                return outBuffer;
            }

            // Create a new compression deflater
            using (BlockAllocatedMemoryStream compressedData = new BlockAllocatedMemoryStream())
            {
                using (DeflateStream deflater = new DeflateStream(compressedData, CompressionMode.Compress, true))
                {
                    // Provide data for compression
                    deflater.Write(source, startIndex, length);
                }

                byte[] destination = compressedData.ToArray();
                int destinationLength = destination.Length;

                // Prepend compression depth and extract only used part of compressed buffer
                byte[] outBuffer = new byte[++destinationLength];

                // First two bits are reserved for compression strength - this leaves 6 bits for a maximum of 64 compressions
                outBuffer[0] = (byte)((compressionDepth << 2) | (int)strength);

                for (int x = 1; x < destinationLength; x++)
                    outBuffer[x] = destination[x - 1];

                if (strength == CompressionStrength.MultiPass && destinationLength < length && compressionDepth < 64)
                {
                    // See if another pass would help the compression...
                    byte[] testBuffer = outBuffer.Compress(0, outBuffer.Length, strength, compressionDepth + 1);

                    if (testBuffer.Length < outBuffer.Length)
                        return testBuffer;

                    return outBuffer;
                }

                return outBuffer;
            }
        }

        /// <summary>
        /// Compress a stream using specified compression strength.
        /// </summary>
        /// <remarks>
        /// This returns a memory stream of the compressed results, if the incoming stream is
        /// very large this will consume a large amount memory.  In this case use the overload
        /// that takes the destination stream as a parameter instead.
        /// </remarks>
        /// <param name="source">The <see cref="Stream"/> to compress.</param>
        /// <param name="strength">The <see cref="CompressionStrength"/> of the compression.</param>
        /// <returns>Returns a <see cref="MemoryStream"/> of the compressed <see cref="Stream"/>.</returns>
        public static MemoryStream Compress(this Stream source, CompressionStrength strength)
        {
            MemoryStream destination = new MemoryStream();
            source.Compress(destination, strength, null);
            return destination;
        }

        /// <summary>
        /// Compress a stream onto given output stream using specified compression strength.
        /// </summary>
        /// <param name="source">The <see cref="Stream"/> to compress.</param>
        /// <param name="strength">The <see cref="CompressionStrength"/> of the compression.</param>
        /// <param name="destination">The <see cref="Stream"/> destination.</param>
        /// <param name="progressHandler">The progress handler to check progress.</param>
        public static void Compress(this Stream source, Stream destination, CompressionStrength strength, Action<ProcessProgress<long>> progressHandler)
        {
            ProcessProgressHandler<long> progress = null;
            byte[] inBuffer = new byte[BufferSize];
            byte[] outBuffer;
            byte[] lengthBuffer;
            int read;
            long total = 0, length = -1;

            // Send initial progress event
            if ((object)progressHandler != null)
            {
                try
                {
                    if (source.CanSeek)
                        length = source.Length;
                }
                catch
                {
                    length = -1;
                }

                // Create a new progress handler to track compression progress
                progress = new ProcessProgressHandler<long>(progressHandler, "Compress", length);
                progress.Complete = 0;
            }

            // Read initial buffer
            read = source.Read(inBuffer, 0, BufferSize);

            // Write compression version into stream
            byte[] version = new byte[1];
            version[0] = CompressionVersion;
            destination.Write(version, 0, 1);

            while (read > 0)
            {
                // Compress buffer - note that we are only going to compress used part of buffer,
                // we don't want any left over garbage to end up in compressed stream...
                outBuffer = inBuffer.Compress(0, read, strength);

                // The output stream is hopefully smaller than the input stream, so we prepend the final size of
                // each compressed buffer into the destination output stream so that we can safely uncompress
                // the stream in a "chunked" fashion later...
                lengthBuffer = BitConverter.GetBytes(outBuffer.Length);
                destination.Write(lengthBuffer, 0, lengthBuffer.Length);
                destination.Write(outBuffer, 0, outBuffer.Length);

                // Update compression progress
                if ((object)progressHandler != null)
                {
                    total += read;
                    progress.Complete = total;
                }

                // Read next buffer
                read = source.Read(inBuffer, 0, BufferSize);
            }
        }

        /// <summary>
        /// Decompress a byte array.
        /// </summary>
        /// <param name="source">The <see cref="Byte"/> array to decompress.</param>
        /// <returns>A decompressed version of the source <see cref="Byte"/> array.</returns>
        public static byte[] Decompress(this byte[] source)
        {
            return source.Decompress(0, source.Length);
        }

        /// <summary>
        /// Decompress a byte array.
        /// </summary>
        /// <param name="source">The <see cref="Byte"/> array to decompress.</param>
        /// <param name="length">The number of bytes to read into the byte array for compression.</param>
        /// <param name="startIndex">An <see cref="Int32"/> representing the start index of the byte array.</param>
        /// <returns>A decompressed <see cref="Byte"/> array.</returns>
        public static byte[] Decompress(this byte[] source, int startIndex, int length)
        {
            const byte CompressionStrengthMask = (byte)(Bits.Bit00 | Bits.Bit01);

            // Unmask compression strength from first buffer byte
            CompressionStrength strength = (CompressionStrength)(source[startIndex] & CompressionStrengthMask);

            if (strength == CompressionStrength.NoCompression)
            {
                // No compression was applied to original buffer, return specified portion of the buffer
                return source.BlockCopy(startIndex + 1, length - 1);
            }

            // Create a new decompression deflater
            using (BlockAllocatedMemoryStream compressedData = new BlockAllocatedMemoryStream(source, startIndex + 1, length - 1))
            {
                byte[] destination;
                int compressionDepth = (source[startIndex] & ~CompressionStrengthMask) >> 2;

                using (DeflateStream inflater = new DeflateStream(compressedData, CompressionMode.Decompress))
                {
                    // Read uncompressed data
                    destination = inflater.ReadStream();
                }

                // When user requests multi-pass compression, there may be multiple compression passes on a buffer,
                // so we cycle through the needed uncompressions to get back to the original data
                if (strength == CompressionStrength.MultiPass && compressionDepth > 0)
                    return destination.Decompress();

                return destination;
            }
        }

        /// <summary>
        /// Decompress a stream.
        /// </summary>
        /// <remarks>
        /// This returns a memory stream of the uncompressed results, if the incoming stream is
        /// very large this will consume a large amount memory.  In this case use the overload
        /// that takes the destination stream as a parameter instead.
        /// </remarks>
        /// <param name="source">A <see cref="Stream"/> source to decompress.</param>
        /// <returns>A <see cref="MemoryStream"/> representing the decompressed source.</returns>
        public static MemoryStream Decompress(this Stream source)
        {
            MemoryStream destination = new MemoryStream();
            source.Decompress(destination, null);
            return destination;
        }

        /// <summary>
        /// Decompress a stream onto given output stream.
        /// </summary>
        /// <param name="source">A source <see cref="Stream"/> to decompress.</param>
        /// <param name="destination">The destination <see cref="Stream"/> to decompress to.</param>
        /// <param name="progressHandler">A <see cref="Action"/> handler to monitor the action's progress.</param>
        public static void Decompress(this Stream source, Stream destination, Action<ProcessProgress<long>> progressHandler)
        {
            ProcessProgressHandler<long> progress = null;
            byte[] inBuffer;
            byte[] outBuffer;
            byte[] lengthBuffer = BitConverter.GetBytes((int)0);
            int read, size;
            long total = 0, length = -1;

            // Send initial progress event
            if ((object)progressHandler != null)
            {
                try
                {
                    if (source.CanSeek)
                        length = source.Length;
                }
                catch
                {
                    length = -1;
                }

                // Create a new progress handler to track compression progress
                progress = new ProcessProgressHandler<long>(progressHandler, "Uncompress", length);
                progress.Complete = 0;
            }

            // Read compression version from stream
            byte[] versionBuffer = new byte[1];

            if (source.Read(versionBuffer, 0, 1) > 0)
            {
                if (versionBuffer[0] != CompressionVersion)
                    throw new InvalidOperationException("Invalid compression version encountered in compressed stream - decompression aborted");

                // Read initial buffer
                read = source.Read(lengthBuffer, 0, lengthBuffer.Length);

                while (read > 0)
                {
                    // Convert the byte array containing the buffer size into an integer
                    size = BitConverter.ToInt32(lengthBuffer, 0);

                    if (size > 0)
                    {
                        // Create and read the next buffer
                        inBuffer = new byte[size];
                        read = source.Read(inBuffer, 0, size);

                        if (read > 0)
                        {
                            // Uncompress buffer
                            outBuffer = inBuffer.Decompress();
                            destination.Write(outBuffer, 0, outBuffer.Length);
                        }

                        // Update decompression progress
                        if ((object)progressHandler != null)
                        {
                            total += (read + lengthBuffer.Length);
                            progress.Complete = total;
                        }
                    }

                    // Read the size of the next buffer from the stream
                    read = source.Read(lengthBuffer, 0, lengthBuffer.Length);
                }
            }
        }
    }
}