using System;
using System.IO;
using System.Runtime.InteropServices;
using CC = System.Runtime.InteropServices.CallingConvention;

namespace MuPdfSharp
{
	sealed class MuStream : IDisposable
	{
		const int __CompressionBomb = 100 << 20;

		#region 非托管资源成员
		readonly StreamHandle _stream;
		readonly ContextHandle _context;
		GCHandle _data;
		#endregion

		#region 托管资源成员
		readonly int _knownDataLength;
		readonly bool _sharedContext;
		/// <summary>获取或设置游标位置。</summary>
		public int Position {
			get => NativeMethods.GetPosition(_context, _stream);
			set => Seek(value, SeekOrigin.Begin);
		}
		#endregion

		internal MuStream(byte[] data) {
			var ctx = ContextHandle.Create();
			_knownDataLength = data.Length;
			_data = GCHandle.Alloc(data, GCHandleType.Pinned);
			_stream = new StreamHandle(ctx, NativeMethods.OpenMemory(ctx, _data.AddrOfPinnedObject(), _knownDataLength));
			_context = ctx;
		}
		internal MuStream(ContextHandle ctx, string fileName) {
			_stream = new StreamHandle(ctx, fileName);
			_knownDataLength = -1;
			_sharedContext = true;
		}
		private MuStream(ContextHandle ctx, StreamHandle stream) {
			_context = ctx;
			_stream = stream;
			NativeMethods.Keep(ctx, stream);
			_sharedContext = true;
		}

		/// <summary>
		/// 读取 <paramref name="length"/> 字节到缓冲数组 <see cref="buffer"/>。（可能抛出异常）
		/// </summary>
		/// <param name="buffer">放置读取数据的数组。</param>
		/// <param name="length">要读取的数据长度。</param>
		/// <returns>实际读取的长度。</returns>
		public int Read(byte[] buffer, int length) {
			return NativeMethods.Read(_context, _stream, buffer, length);
		}

		/// <summary>
		/// 读取流的所有内容到字节数组。（可能抛出异常）
		/// </summary>
		/// <returns>包含流中所有内容的数组。</returns>
		public byte[] ReadAll(int initialSize) {
			if (_knownDataLength > 0) {
				var b = new byte[_knownDataLength];
				NativeMethods.Read(_context, _stream, b, _knownDataLength);
				return b;
			}
			else {
				var b = new byte[initialSize];
				int l;
				using (var ms = new MemoryStream(initialSize))
				using (var mw = new BinaryWriter(ms)) {
					while ((l = NativeMethods.Read(_context, _stream, b, initialSize)) > 0) {
						mw.Write(b, 0, l);
						if (ms.Length >= __CompressionBomb && ms.Length / 200 > initialSize) {
							throw new IOException("Compression bomb detected.");
						}
					}
					ms.Flush();
					return ms.ToArray();
				}
			}
		}

		/// <summary>
		/// 跳转到流的指定位置。
		/// </summary>
		/// <param name="offset">偏移位置。</param>
		/// <param name="origin">跳转方式。</param>
		public void Seek(int offset, SeekOrigin origin) {
			NativeMethods.Seek(_context, _stream, offset, origin == SeekOrigin.Begin ? 0 : origin == SeekOrigin.Current ? 1 : 2);
		}

		/// <summary>
		/// 将当前流视为以 CCITT Fax 压缩的图像来解压缩。
		/// </summary>
		/// <param name="width">图像宽度。</param>
		/// <param name="height">图像高度。</param>
		/// <param name="k"></param>
		/// <param name="endOfLine"></param>
		/// <param name="encodedByteAlign"></param>
		/// <param name="endOfBlock"></param>
		/// <param name="blackIs1"></param>
		/// <returns>解压缩后的图像数据。</returns>
		public MuStream DecodeTiffFax(int width, int height, int k, bool endOfLine, bool encodedByteAlign, bool endOfBlock, bool blackIs1) {
			return new MuStream(
				_context,
				new StreamHandle(_context, NativeMethods.DecodeCcittFax(_context, _stream, k, endOfLine ? 1 : 0, encodedByteAlign ? 1 : 0, width, height, endOfBlock ? 1 : 0, blackIs1 ? 1 : 0))
				);
		}

		#region 实现 IDisposable 接口的属性和方法
		private bool disposed;
		public void Dispose() {
			Dispose(true);
			GC.SuppressFinalize(this); // 抑制析构函数
		}

		/// <summary>释放由 MuPdfPage 占用的资源。</summary>
		/// <param name="disposing">是否手动释放托管资源。</param>
		void Dispose(bool disposing) {
			if (!disposed) {
				if (disposing) {
					#region 释放托管资源
					//_components.Dispose ();
					#endregion
				}

				#region 释放非托管资源
				// 注意这里不是线程安全的
				if (_stream.IsValid()) {
					_stream.Dispose();
				}
				if (_sharedContext == false && _context.IsValid()) {
					_context.Dispose();
				}
				if (_data.IsAllocated) {
					_data.Free();
				}
				#endregion
			}
			disposed = true;
		}

		// 析构函数只在未调用 Dispose 方法时调用
		// 派生类中不必再提供析构函数
		~MuStream() {
			Dispose(false);
		}
		#endregion
	}
}