// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

using System;
using System.IO;
using System.Runtime.InteropServices;

namespace Microsoft.CodeAnalysis
{
    internal sealed class ReadOnlyUnmanagedMemoryStream : Stream
    {
        private readonly object _memoryOwner;
        private readonly IntPtr _data;
        private readonly int _length;
        private int _position;

        public ReadOnlyUnmanagedMemoryStream(object memoryOwner, IntPtr data, int length)
        {
            _memoryOwner = memoryOwner;
            _data = data;
            _length = length;
        }

        public override unsafe int ReadByte()
        {
            if (_position == _length)
            {
                return -1;
            }

            return ((byte*)_data)[_position++];
        }

        public override int Read(byte[] buffer, int offset, int count)
        {
            int bytesRead = Math.Min(count, _length - _position);
            Marshal.Copy(_data + _position, buffer, offset, bytesRead);
            _position += bytesRead;
            return bytesRead;
        }

        public override void Flush()
        {
        }

        public override bool CanRead
        {
            get
            {
                return true;
            }
        }

        public override bool CanSeek
        {
            get
            {
                return true;
            }
        }

        public override bool CanWrite
        {
            get
            {
                return false;
            }
        }

        public override long Length
        {
            get
            {
                return _length;
            }
        }

        public override long Position
        {
            get
            {
                return _position;
            }

            set
            {
                Seek(value, SeekOrigin.Begin);
            }
        }

        public override long Seek(long offset, SeekOrigin origin)
        {
            long target;
            try
            {
                switch (origin)
                {
                    case SeekOrigin.Begin:
                        target = offset;
                        break;

                    case SeekOrigin.Current:
                        target = checked(offset + _position);
                        break;

                    case SeekOrigin.End:
                        target = checked(offset + _length);
                        break;

                    default:
                        throw new ArgumentOutOfRangeException(nameof(origin));
                }
            }
            catch (OverflowException)
            {
                throw new ArgumentOutOfRangeException(nameof(offset));
            }

            if (target < 0 || target >= _length)
            {
                throw new ArgumentOutOfRangeException(nameof(offset));
            }

            _position = (int)target;
            return target;
        }

        public override void SetLength(long value)
        {
            throw new NotSupportedException();
        }

        public override void Write(byte[] buffer, int offset, int count)
        {
            throw new NotSupportedException();
        }
    }
}