// 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 Microsoft.Win32.SafeHandles;
using System.Runtime.InteropServices;

namespace System.IO
{
    public partial class FileStream : Stream
    {
        private unsafe SafeFileHandle OpenHandle(FileMode mode, FileShare share, FileOptions options)
        {
            Interop.Kernel32.SECURITY_ATTRIBUTES secAttrs = GetSecAttrs(share);

            int fAccess =
                ((_access & FileAccess.Read) == FileAccess.Read ? GENERIC_READ : 0) |
                ((_access & FileAccess.Write) == FileAccess.Write ? GENERIC_WRITE : 0);

            // Our Inheritable bit was stolen from Windows, but should be set in
            // the security attributes class.  Don't leave this bit set.
            share &= ~FileShare.Inheritable;

            // Must use a valid Win32 constant here...
            if (mode == FileMode.Append)
                mode = FileMode.OpenOrCreate;

            Interop.Kernel32.CREATEFILE2_EXTENDED_PARAMETERS parameters = new Interop.Kernel32.CREATEFILE2_EXTENDED_PARAMETERS();
            parameters.dwSize = (uint)sizeof(Interop.Kernel32.CREATEFILE2_EXTENDED_PARAMETERS);
            parameters.dwFileFlags = (uint)options;
            parameters.lpSecurityAttributes = &secAttrs;

            SafeFileHandle fileHandle = Interop.Kernel32.CreateFile2(
                lpFileName: _path,
                dwDesiredAccess: fAccess,
                dwShareMode: share,
                dwCreationDisposition: mode,
                pCreateExParams: &parameters);

            fileHandle.IsAsync = _useAsyncIO;

            if (fileHandle.IsInvalid)
            {
                // Return a meaningful exception with the full path.

                // NT5 oddity - when trying to open "C:\" as a Win32FileStream,
                // we usually get ERROR_PATH_NOT_FOUND from the OS.  We should
                // probably be consistent w/ every other directory.
                int errorCode = Marshal.GetLastWin32Error();

                if (errorCode == Interop.Errors.ERROR_PATH_NOT_FOUND && _path.Length == PathInternal.GetRootLength(_path))
                    errorCode = Interop.Errors.ERROR_ACCESS_DENIED;

                throw Win32Marshal.GetExceptionForWin32Error(errorCode, $"{_path} {options} {fAccess} {share} {mode}");
            }

            return fileHandle;
        }

#if PROJECTN
        // TODO: These internal methods should be removed once we start consuming updated CoreFX builds
        public static FileStream InternalOpen(string path, int bufferSize = 4096, bool useAsync = true)
        {
            return new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, bufferSize, useAsync);
        }

        public static FileStream InternalCreate(string path, int bufferSize = 4096, bool useAsync = true)
        {
            return new FileStream(path, FileMode.Create, FileAccess.Write, FileShare.Read, bufferSize, useAsync);
        }

        public static FileStream InternalAppend(string path, int bufferSize = 4096, bool useAsync = true)
        {
            return new FileStream(path, FileMode.Append, FileAccess.Write, FileShare.Read, bufferSize, useAsync);
        }
#endif
    }
}