Ryujinx/src/Ryujinx.HLE/HOS/Services/Fs/FileSystemProxy/LazyFile.cs

using LibHac;
using LibHac.Common;
using LibHac.Fs;
using System;
using System.IO;

namespace Ryujinx.HLE.HOS.Services.Fs.FileSystemProxy
{
    class LazyFile : LibHac.Fs.Fsa.IFile
    {
        private readonly LibHac.Fs.Fsa.IFileSystem _fs;
        private readonly string _filePath;
        private readonly UniqueRef<LibHac.Fs.Fsa.IFile> _fileReference = new();
        private readonly FileInfo _fileInfo;

        public LazyFile(string filePath, string prefix, LibHac.Fs.Fsa.IFileSystem fs)
        {
            _fs = fs;
            _filePath = filePath;
            _fileInfo = new FileInfo(prefix + "/" + filePath);
        }

        private void PrepareFile()
        {
            if (_fileReference.Get == null)
            {
                _fs.OpenFile(ref _fileReference.Ref, _filePath.ToU8Span(), OpenMode.Read).ThrowIfFailure();
            }
        }

        protected override Result DoRead(out long bytesRead, long offset, Span<byte> destination, in ReadOption option)
        {
            PrepareFile();

            return _fileReference.Get!.Read(out bytesRead, offset, destination);
        }

        protected override Result DoWrite(long offset, ReadOnlySpan<byte> source, in WriteOption option)
        {
            throw new NotSupportedException();
        }

        protected override Result DoFlush()
        {
            throw new NotSupportedException();
        }

        protected override Result DoSetSize(long size)
        {
            throw new NotSupportedException();
        }

        protected override Result DoGetSize(out long size)
        {
            size = _fileInfo.Length;

            return Result.Success;
        }

        protected override Result DoOperateRange(Span<byte> outBuffer, OperationId operationId, long offset, long size, ReadOnlySpan<byte> inBuffer)
        {
            throw new NotSupportedException();
        }
    }
}