osu/osu.Desktop/Beatmaps/IO/LegacyFilesystemReader.cs

using System;
using System.IO;
using System.Collections.Generic;
using System.Linq;
using osu.Game.Beatmaps.Formats;
using osu.Game.Beatmaps.IO;
using osu.Game.Beatmaps;
using osu.Game.Database;

namespace osu.Desktop.Beatmaps.IO
{
    /// <summary>
    /// Reads an extracted legacy beatmap from disk.
    /// </summary>
    public class LegacyFilesystemReader : ArchiveReader
    {
        static LegacyFilesystemReader()
        {
            AddReader<LegacyFilesystemReader>((storage, path) => Directory.Exists(path));
        }
    
        private string basePath { get; set; }
        private string[] beatmaps { get; set; }
        private Beatmap firstMap { get; set; }

        public LegacyFilesystemReader(string path)
        {
            basePath = path;
            beatmaps = Directory.GetFiles(basePath, @"*.osu").Select(f => Path.GetFileName(f)).ToArray();
            if (beatmaps.Length == 0)
                throw new FileNotFoundException(@"This directory contains no beatmaps");
            using (var stream = new StreamReader(GetStream(beatmaps[0])))
            {
                var decoder = BeatmapDecoder.GetDecoder(stream);
                firstMap = decoder.Decode(stream);
            }
        }

        public override string[] ReadBeatmaps()
        {
            return beatmaps;
        }

        public override Stream GetStream(string name)
        {
            return File.OpenRead(Path.Combine(basePath, name));
        }

        public override BeatmapMetadata ReadMetadata()
        {
            return firstMap.BeatmapInfo.Metadata;
        }
        
        public override void Dispose()
        {
            // no-op
        }
    }
}