using System;
using System.Collections.Generic;
using System.IO;
using System.IO.Compression;

namespace GZipTest
{
	class DecompressionModule : ProcessingModuleBase
	{
		/// <summary>
		/// Reading compressed source file
		/// </summary>
		protected override void Read()
		{
			using FileStream input = File.OpenRead(source);                                         // Opening reading stream

			byte[] segmentMeta = new byte[8];                                                       // Reading first 8 bytes to determine total count of blocks
			input.Read(segmentMeta, 0, 8);
			segmentCount = BitConverter.ToInt64(segmentMeta, 0);                                    // segmentCount field will be used to display progress bar

			for (int i = 0; input.Position < input.Length; i++)
			{
				if (readBuffer.Count >= 5 * Environment.ProcessorCount)                             // Helping decompression thread if there's too many unprocessed blocks
				{
					ProcessOne();
					i--;
					continue;
				}

				byte[] meta = new byte[4];                                                          // Reading first 4 bytes to determine block's length
				input.Read(meta, 0, 4);
				int blockSize = BitConverter.ToInt32(meta, 0);

				byte[] block = new byte[blockSize];                                                 // Instantiating empty block
				input.Read(block, 0, blockSize);                                                    // Reading next block

				readBuffer.Enqueue(new KeyValuePair<int, byte[]>(i, block));                        // Adding read block to compression queue. Each block must contain its position number since compression is multi thread
			}
		}

		protected override void ProcessOne()
		{
			if (!readBuffer.TryDequeue(out KeyValuePair<int, byte[]> block))                        // Extracting read block
				return;

			processed.WaitOne();                                                                    // Waiting for empty place for compressed block

			using MemoryStream stream = new MemoryStream(block.Value);								// Instantiating memory stream with compressed block data
			using GZipStream compressor = new GZipStream(stream, CompressionMode.Decompress);		// Instantiating decompressor stream
			using MemoryStream destination = new MemoryStream();									// Instantiating memory stream which will contain decompressed block

			compressor.CopyTo(destination);															// Decompressing block

			processedBuffer.TryAdd(block.Key, destination.ToArray());								// Processing block and adding it to write queue keeping its position number
		}
	}
}