using System;
using System.IO;
using System.Text;

namespace ProtoCSStruct
{
    /// <summary>
    /// Encodes and writes protocol message fields.
    /// </summary>
    /// <remarks>
    /// <para>
    /// This class is generally used by generated code to write appropriate
    /// primitives to the stream. It effectively encapsulates the lowest
    /// levels of protocol buffer format. Unlike some other implementations,
    /// this does not include combined "write tag and value" methods. Generated
    /// code knows the exact byte representations of the tags they're going to write,
    /// so there's no need to re-encode them each time. Manually-written code calling
    /// this class should just call one of the <c>WriteTag</c> overloads before each value.
    /// </para>
    /// </remarks>
    public sealed partial class CodedOutputStream : IDisposable
    {
        // "Local" copy of Encoding.UTF8, for efficiency. (Yes, it makes a difference.)
        public static readonly Encoding Utf8Encoding = Encoding.UTF8;

        /// <summary>
        /// The buffer size used by CreateInstance(Stream).
        /// </summary>
        public static readonly int DefaultBufferSize = 4096;

        private readonly bool leaveOpen;
        private readonly byte[] buffer;
        private readonly int limit;
        private int position;
        private readonly Stream output;

        #region Construction
        /// <summary>
        /// Creates a new CodedOutputStream that writes directly to the given
        /// byte array. If more bytes are written than fit in the array,
        /// OutOfSpaceException will be thrown.
        /// </summary>
        public CodedOutputStream(byte[] flatArray) : this(flatArray, 0, flatArray.Length)
        {
        }

        /// <summary>
        /// Creates a new CodedOutputStream that writes directly to the given
        /// byte array slice. If more bytes are written than fit in the array,
        /// OutOfSpaceException will be thrown.
        /// </summary>
        private CodedOutputStream(byte[] buffer, int offset, int length)
        {
            this.output = null;
            this.buffer = buffer;
            this.position = offset;
            this.limit = offset + length;
            leaveOpen = true; // Simple way of avoiding trying to dispose of a null reference
        }

        private CodedOutputStream(Stream output, byte[] buffer, bool leaveOpen)
        {
            this.output = ProtoPreconditions.CheckNotNull(output, nameof(output));
            this.buffer = buffer;
            this.position = 0;
            this.limit = buffer.Length;
            this.leaveOpen = leaveOpen;
        }

        /// <summary>
        /// Creates a new <see cref="CodedOutputStream" /> which write to the given stream, and disposes of that
        /// stream when the returned <c>CodedOutputStream</c> is disposed.
        /// </summary>
        /// <param name="output">The stream to write to. It will be disposed when the returned <c>CodedOutputStream is disposed.</c></param>
        public CodedOutputStream(Stream output) : this(output, DefaultBufferSize, false)
        {
        }

        /// <summary>
        /// Creates a new CodedOutputStream which write to the given stream and uses
        /// the specified buffer size.
        /// </summary>
        /// <param name="output">The stream to write to. It will be disposed when the returned <c>CodedOutputStream is disposed.</c></param>
        /// <param name="bufferSize">The size of buffer to use internally.</param>
        public CodedOutputStream(Stream output, int bufferSize) : this(output, new byte[bufferSize], false)
        {
        }

        /// <summary>
        /// Creates a new CodedOutputStream which write to the given stream.
        /// </summary>
        /// <param name="output">The stream to write to.</param>
        /// <param name="leaveOpen">If <c>true</c>, <paramref name="output"/> is left open when the returned <c>CodedOutputStream</c> is disposed;
        /// if <c>false</c>, the provided stream is disposed as well.</param>
        public CodedOutputStream(Stream output, bool leaveOpen) : this(output, DefaultBufferSize, leaveOpen)
        {
        }

        /// <summary>
        /// Creates a new CodedOutputStream which write to the given stream and uses
        /// the specified buffer size.
        /// </summary>
        /// <param name="output">The stream to write to.</param>
        /// <param name="bufferSize">The size of buffer to use internally.</param>
        /// <param name="leaveOpen">If <c>true</c>, <paramref name="output"/> is left open when the returned <c>CodedOutputStream</c> is disposed;
        /// if <c>false</c>, the provided stream is disposed as well.</param>
        public CodedOutputStream(Stream output, int bufferSize, bool leaveOpen) : this(output, new byte[bufferSize], leaveOpen)
        {
        }
        #endregion

        /// <summary>
        /// Returns the current position in the stream, or the position in the output buffer
        /// </summary>
        public long Position
        {
            get
            {
                if (output != null)
                {
                    return output.Position + position;
                }
                return position;
            }
        }

        #region Writing of values (not including tags)

        /// <summary>
        /// Writes a uint64 field value, without a tag, to the stream.
        /// </summary>
        /// <param name="value">The value to write</param>
        public void WriteUInt64(ulong value)
        {
            WriteRawVarint64(value);
        }

        /// <summary>
        /// Writes an int64 field value, without a tag, to the stream.
        /// </summary>
        /// <param name="value">The value to write</param>
        public void WriteInt64(long value)
        {
            WriteRawVarint64((ulong) value);
        }

        /// <summary>
        /// Writes an int32 field value, without a tag, to the stream.
        /// </summary>
        /// <param name="value">The value to write</param>
        public void WriteInt32(int value)
        {
            if (value >= 0)
            {
                WriteRawVarint32((uint) value);
            }
            else
            {
                // Must sign-extend.
                WriteRawVarint64((ulong) value);
            }
        }

        /// <summary>
        /// Writes a bool field value, without a tag, to the stream.
        /// </summary>
        /// <param name="value">The value to write</param>
        public void WriteBool(bool value)
        {
            WriteRawByte(value ? (byte) 1 : (byte) 0);
        }

        /// <summary>
        /// Writes a string field value, without a tag, to the stream.
        /// The data is length-prefixed.
        /// </summary>
        /// <param name="value"></param>
        unsafe public void WriteFixedStructString(char* pchar, int count)
        {
            // Optimise the case where we have enough space to write
            // the string directly to the buffer, which should be common.
            int length = Utf8Encoding.GetByteCount(pchar, count);
            WriteLength(length);
            if (limit - position >= length)
            {
                if (length == count) // Must be all ASCII...
                {
                    for (int i = 0; i < length; i++)
                    {
                        buffer[position + i] = (byte)pchar[i];
                    }
                }
                else
                {
                    fixed(byte* byteindex = &buffer[position])
                    {
                        Utf8Encoding.GetBytes(pchar, count, byteindex, length);
                    }
                    
                }
                position += length;
            }
            else//这种情况就不考虑效率了,实际使用很少发生
            {
                byte[] bytes = new byte[length];
                fixed (byte* byteindex = bytes)
                {
                    Utf8Encoding.GetBytes(pchar, count, byteindex, length);
                }
                WriteRawBytes(bytes);
            }
        }


        /// <summary>
        /// Writes a uint32 value, without a tag, to the stream.
        /// </summary>
        /// <param name="value">The value to write</param>
        public void WriteUInt32(uint value)
        {
            WriteRawVarint32(value);
        }

        /// <summary>
        /// Writes an enum value, without a tag, to the stream.
        /// </summary>
        /// <param name="value">The value to write</param>
        public void WriteEnum(int value)
        {
            WriteInt32(value);
        }


        /// <summary>
        /// Writes a length (in bytes) for length-delimited data.
        /// </summary>
        /// <remarks>
        /// This method simply writes a rawint, but exists for clarity in calling code.
        /// </remarks>
        /// <param name="length">Length value, in bytes.</param>
        public void WriteLength(int length)
        {
            WriteRawVarint32((uint) length);
        }

        #endregion

        #region Raw tag writing
        /// <summary>
        /// Encodes and writes a tag.
        /// </summary>
        /// <param name="fieldNumber">The number of the field to write the tag for</param>
        /// <param name="type">The wire format type of the tag to write</param>
        public void WriteTag(int fieldNumber, WireFormat.WireType type)
        {
            WriteRawVarint32(WireFormat.MakeTag(fieldNumber, type));
        }

        /// <summary>
        /// Writes an already-encoded tag.
        /// </summary>
        /// <param name="tag">The encoded tag</param>
        public void WriteTag(uint tag)
        {
            WriteRawVarint32(tag);
        }

        #endregion

        #region Underlying writing primitives
        /// <summary>
        /// Writes a 32 bit value as a varint. The fast route is taken when
        /// there's enough buffer space left to whizz through without checking
        /// for each byte; otherwise, we resort to calling WriteRawByte each time.
        /// </summary>
        internal void WriteRawVarint32(uint value)
        {
            // Optimize for the common case of a single byte value
            if (value < 128 && position < limit)
            {
                buffer[position++] = (byte)value;
                return;
            }

            while (value > 127 && position < limit)
            {
                buffer[position++] = (byte) ((value & 0x7F) | 0x80);
                value >>= 7;
            }
            while (value > 127)
            {
                WriteRawByte((byte) ((value & 0x7F) | 0x80));
                value >>= 7;
            }
            if (position < limit)
            {
                buffer[position++] = (byte) value;
            }
            else
            {
                WriteRawByte((byte) value);
            }
        }

        internal void WriteRawVarint64(ulong value)
        {
            while (value > 127 && position < limit)
            {
                buffer[position++] = (byte) ((value & 0x7F) | 0x80);
                value >>= 7;
            }
            while (value > 127)
            {
                WriteRawByte((byte) ((value & 0x7F) | 0x80));
                value >>= 7;
            }
            if (position < limit)
            {
                buffer[position++] = (byte) value;
            }
            else
            {
                WriteRawByte((byte) value);
            }
        }

        internal void WriteRawLittleEndian32(uint value)
        {
            if (position + 4 > limit)
            {
                WriteRawByte((byte) value);
                WriteRawByte((byte) (value >> 8));
                WriteRawByte((byte) (value >> 16));
                WriteRawByte((byte) (value >> 24));
            }
            else
            {
                buffer[position++] = ((byte) value);
                buffer[position++] = ((byte) (value >> 8));
                buffer[position++] = ((byte) (value >> 16));
                buffer[position++] = ((byte) (value >> 24));
            }
        }

        internal void WriteRawLittleEndian64(ulong value)
        {
            if (position + 8 > limit)
            {
                WriteRawByte((byte) value);
                WriteRawByte((byte) (value >> 8));
                WriteRawByte((byte) (value >> 16));
                WriteRawByte((byte) (value >> 24));
                WriteRawByte((byte) (value >> 32));
                WriteRawByte((byte) (value >> 40));
                WriteRawByte((byte) (value >> 48));
                WriteRawByte((byte) (value >> 56));
            }
            else
            {
                buffer[position++] = ((byte) value);
                buffer[position++] = ((byte) (value >> 8));
                buffer[position++] = ((byte) (value >> 16));
                buffer[position++] = ((byte) (value >> 24));
                buffer[position++] = ((byte) (value >> 32));
                buffer[position++] = ((byte) (value >> 40));
                buffer[position++] = ((byte) (value >> 48));
                buffer[position++] = ((byte) (value >> 56));
            }
        }

        public void WriteRawByte(byte value)
        {
            if (position == limit)
            {
                RefreshBuffer();
            }

            buffer[position++] = value;
        }

        internal void WriteRawByte(uint value)
        {
            WriteRawByte((byte) value);
        }

        /// <summary>
        /// Writes out an array of bytes.
        /// </summary>
        public void WriteRawBytes(byte[] value)
        {
            WriteRawBytes(value, 0, value.Length);
        }

        /// <summary>
        /// Writes out part of an array of bytes.
        /// </summary>
        public void WriteRawBytes(byte[] value, int offset, int length)
        {
            if (limit - position >= length)
            {
                ByteArray.Copy(value, offset, buffer, position, length);
                // We have room in the current buffer.
                position += length;
            }
            else
            {
                // Write extends past current buffer.  Fill the rest of this buffer and
                // flush.
                int bytesWritten = limit - position;
                ByteArray.Copy(value, offset, buffer, position, bytesWritten);
                offset += bytesWritten;
                length -= bytesWritten;
                position = limit;
                RefreshBuffer();

                // Now deal with the rest.
                // Since we have an output stream, this is our buffer
                // and buffer offset == 0
                if (length <= limit)
                {
                    // Fits in new buffer.
                    ByteArray.Copy(value, offset, buffer, 0, length);
                    position = length;
                }
                else
                {
                    // Write is very big.  Let's do it all at once.
                    output.Write(value, offset, length);
                }
            }
        }

        #endregion


        private void RefreshBuffer()
        {
            if (output == null)
            {
                // We're writing to a single buffer.
                throw new OutOfSpaceException();
            }

            // Since we have an output stream, this is our buffer
            // and buffer offset == 0
            output.Write(buffer, 0, position);
            position = 0;
        }

        /// <summary>
        /// Indicates that a CodedOutputStream wrapping a flat byte array
        /// ran out of space.
        /// </summary>
        public sealed class OutOfSpaceException : IOException
        {
            internal OutOfSpaceException()
                : base("CodedOutputStream was writing to a flat byte array and ran out of space.")
            {
            }
        }

        /// <summary>
        /// Flushes any buffered data and optionally closes the underlying stream, if any.
        /// </summary>
        /// <remarks>
        /// <para>
        /// By default, any underlying stream is closed by this method. To configure this behaviour,
        /// use a constructor overload with a <c>leaveOpen</c> parameter. If this instance does not
        /// have an underlying stream, this method does nothing.
        /// </para>
        /// <para>
        /// For the sake of efficiency, calling this method does not prevent future write calls - but
        /// if a later write ends up writing to a stream which has been disposed, that is likely to
        /// fail. It is recommend that you not call any other methods after this.
        /// </para>
        /// </remarks>
        public void Dispose()
        {
            Flush();
            if (!leaveOpen)
            {
                output.Dispose();
            }
        }

        /// <summary>
        /// Flushes any buffered data to the underlying stream (if there is one).
        /// </summary>
        public void Flush()
        {
            if (output != null)
            {
                RefreshBuffer();
            }
        }

        /// <summary>
        /// Verifies that SpaceLeft returns zero. It's common to create a byte array
        /// that is exactly big enough to hold a message, then write to it with
        /// a CodedOutputStream. Calling CheckNoSpaceLeft after writing verifies that
        /// the message was actually as big as expected, which can help bugs.
        /// </summary>
        public void CheckNoSpaceLeft()
        {
            if (SpaceLeft != 0)
            {
                throw new InvalidOperationException("Did not write as much data as expected.");
            }
        }

        /// <summary>
        /// If writing to a flat array, returns the space left in the array. Otherwise,
        /// throws an InvalidOperationException.
        /// </summary>
        public int SpaceLeft
        {
            get
            {
                if (output == null)
                {
                    return limit - position;
                }
                else
                {
                    throw new InvalidOperationException(
                        "SpaceLeft can only be called on CodedOutputStreams that are " +
                        "writing to a flat array.");
                }
            }
        }
    }
}