osu/osu.Game/Beatmaps/Formats/Decoder.cs
2020-04-02 21:36:31 -04:00

106 lines
4.5 KiB
C#

// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
// See the LICENCE file in the repository root for full licence text.
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using osu.Game.IO;
namespace osu.Game.Beatmaps.Formats
{
public abstract class Decoder<TOutput> : Decoder
where TOutput : new()
{
protected virtual TOutput CreateTemplateObject() => new TOutput();
public TOutput Decode(LineBufferedReader primaryStream, params LineBufferedReader[] otherStreams)
{
var output = CreateTemplateObject();
foreach (LineBufferedReader stream in otherStreams.Prepend(primaryStream))
ParseStreamInto(stream, output);
return output;
}
protected abstract void ParseStreamInto(LineBufferedReader stream, TOutput output);
}
public abstract class Decoder
{
private static readonly Dictionary<Type, Dictionary<string, Func<string, Decoder>>> decoders = new Dictionary<Type, Dictionary<string, Func<string, Decoder>>>();
private static readonly Dictionary<Type, Func<Decoder>> fallback_decoders = new Dictionary<Type, Func<Decoder>>();
static Decoder()
{
LegacyBeatmapDecoder.Register();
JsonBeatmapDecoder.Register();
LegacyStoryboardDecoder.Register();
}
/// <summary>
/// Retrieves a <see cref="Decoder"/> to parse a <see cref="Beatmap"/>.
/// </summary>
/// <param name="stream">A stream pointing to the <see cref="Beatmap"/>.</param>
public static Decoder<T> GetDecoder<T>(LineBufferedReader stream)
where T : new()
{
if (stream == null)
throw new ArgumentNullException(nameof(stream));
if (!decoders.TryGetValue(typeof(T), out var typedDecoders))
throw new IOException(@"Unknown decoder type");
// start off with the first line of the file
string line = stream.PeekLine()?.Trim();
while (line != null && line.Length == 0)
{
// consume the previously peeked empty line and advance to the next one
stream.ReadLine();
line = stream.PeekLine()?.Trim();
}
if (line == null)
throw new IOException("Unknown file format (null)");
var decoder = typedDecoders.Where(d => line.StartsWith(d.Key, StringComparison.InvariantCulture)).Select(d => d.Value).FirstOrDefault();
// it's important the magic does NOT get consumed here, since sometimes it's part of the structure
// (see JsonBeatmapDecoder - the magic string is the opening brace)
// decoder implementations should therefore not die on receiving their own magic
if (decoder != null)
return (Decoder<T>)decoder.Invoke(line);
if (!fallback_decoders.TryGetValue(typeof(T), out var fallbackDecoder))
throw new IOException($"Unknown file format ({line})");
return (Decoder<T>)fallbackDecoder.Invoke();
}
/// <summary>
/// Registers an instantiation function for a <see cref="Decoder"/>.
/// </summary>
/// <param name="magic">A string in the file which triggers this decoder to be used.</param>
/// <param name="constructor">A function which constructs the <see cref="Decoder"/> given <paramref name="magic"/>.</param>
protected static void AddDecoder<T>(string magic, Func<string, Decoder> constructor)
{
if (!decoders.TryGetValue(typeof(T), out var typedDecoders))
decoders.Add(typeof(T), typedDecoders = new Dictionary<string, Func<string, Decoder>>());
typedDecoders[magic] = constructor;
}
/// <summary>
/// Registers a fallback decoder instantiation function.
/// The fallback will be returned if the first non-empty line of the decoded stream does not match any known magic.
/// Calling this method will overwrite any existing global fallback registration for type <typeparamref name="T"/> - use with caution.
/// </summary>
/// <typeparam name="T">Type of object being decoded.</typeparam>
/// <param name="constructor">A function that constructs the fallback<see cref="Decoder"/>.</param>
protected static void SetFallbackDecoder<T>(Func<Decoder> constructor)
{
fallback_decoders[typeof(T)] = constructor;
}
}
}