ClassiCube/ClassicalSharp/TexturePack/TextureCache.cs

// ClassicalSharp copyright 2014-2016 UnknownShadow200 | Licensed under MIT
using System;
using System.Drawing;
using System.IO;
using System.Text;
#if ANDROID
using Android.Graphics;
#endif
using PathIO = System.IO.Path; // Android.Graphics.Path clash otherwise

namespace ClassicalSharp.Textures {
	
	/// <summary> Caches terrain atlases and texture packs to avoid making redundant downloads. </summary>
	public static class TextureCache {
		
		/// <summary> Gets whether the given url has data associated with it in the cache. </summary>
		public static bool HasUrl( string url ) {
			return File.Exists( MakePath( url ) );
		}

		/// <summary> Gets the stream of data associated with the url from the cache, returning null if the
		/// data for the url was not found in the cache. </summary>
		public static FileStream GetStream( string url ) {
			string path = MakePath( url );
			if( !File.Exists( path ) ) return null;
			
			try {
				return File.OpenRead( path );
			} catch( IOException ex ) {
				ErrorHandler.LogError( "Cache.GetData", ex );
				return null;
			}
		}
		
		/// <summary> Gets the time the data associated with the url from the cache was last modified,
		/// returning DateTime.MinValue if data for the url was not found in the cache. </summary>
		public static DateTime GetLastModified( string url, EntryList tags ) {
			string entry = GetFromTags( url, tags );
			long ticks = 0;
			if( entry != null && long.TryParse( entry, out ticks ) )
				return new DateTime( ticks, DateTimeKind.Utc );
			
			string path = MakePath( url );
			if( !File.Exists( path ) ) return DateTime.MinValue;			
			return File.GetLastWriteTimeUtc( path );
		}

		public static string GetETag( string url, EntryList tags ) {
			return GetFromTags( url, tags );
		}
		
		static string GetFromTags( string url, EntryList tags ) {
			string crc32 = CRC32( url );
			
			for( int i = 0; i < tags.Entries.Count; i++ ) {
				string entry = tags.Entries[i];
				if( !entry.StartsWith( crc32 ) ) continue;
				
				int sepIndex = entry.IndexOf( ' ' );
				if( sepIndex == -1 ) continue;
				return entry.Substring( sepIndex + 1 );
			}
			return null;
		}
		
		
		/// <summary> Adds the url and the bitmap associated with it to the cache. </summary>
		public static void Add( string url, Bitmap bmp ) {
			string path = MakePath( url );
			try {
				string basePath = PathIO.Combine( Program.AppDirectory, Folder );
				if( !Directory.Exists( basePath ) )
					Directory.CreateDirectory( basePath );
				
				using( FileStream fs = File.Create( path ) )
					Platform.WriteBmp( bmp, fs );
			} catch( IOException ex ) {
				ErrorHandler.LogError( "Cache.AddToCache", ex );
			}
		}
		
		/// <summary> Adds the url and the data associated with it to the cache. </summary>
		public static void Add( string url, byte[] data ) {
			string path = MakePath( url );
			try {
				string basePath = PathIO.Combine( Program.AppDirectory, Folder );
				if( !Directory.Exists( basePath ) )
					Directory.CreateDirectory( basePath );
				
				File.WriteAllBytes( path, data );
			} catch( IOException ex ) {
				ErrorHandler.LogError( "Cache.AddToCache", ex );
			}
		}
		
		public static void AddETag( string url, string etag, EntryList tags ) {
			if( etag == null ) return;
			AddToTags( url, etag, tags );
		}
		
		public static void AdddLastModified( string url, DateTime lastModified, EntryList tags ) {
			if( lastModified == DateTime.MinValue ) return;
			string data = lastModified.ToUniversalTime().Ticks.ToString();
			AddToTags( url, data, tags );
		}
		
		static void AddToTags( string url, string data, EntryList tags ) {
			string crc32 = CRC32( url );
			for( int i = 0; i < tags.Entries.Count; i++ ) {
				if( !tags.Entries[i].StartsWith( crc32 ) ) continue;
				tags.Entries[i] = crc32 + " " + data;
				tags.Save(); return;
			}
			tags.AddEntry( crc32 + " " + data );
		}
		
		
		const string Folder = "texturecache";
		
		static string MakePath( string url ) {
			string crc32 = CRC32( url );
			string basePath = PathIO.Combine( Program.AppDirectory, Folder );
			return PathIO.Combine( basePath, crc32 );
		}
		
		static string CRC32( string url ) {
			byte[] data = Encoding.UTF8.GetBytes( url );
			uint crc = 0xffffffffU;
			
			for( int i = 0; i < data.Length; i++ ) {
				crc ^= data[i];
				for( int j = 0; j < 8; j++ )
					crc = (crc >> 1) ^ (crc & 1) * 0xEDB88320;
			}
			
			uint result = crc ^ 0xffffffffU;
			return result.ToString();
		}
	}
}