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