created RegionChunkList

src/simpleWarBackup/BackupIO.java

@@ -156,9 +156,6 @@ public class BackupIO
 			 * private .mca file. It will return length 0 if there is an error
 			 * or there is no chunk data. Otherwise, it will return the length 
 			 * value recorded in the file.
-			 * 
-			 * below writes the backup chunk data into the target region file,
-			 * overwriting the current chunk data in use by the game.
 			 */
 			if (length > 0)
 			{

src/simpleWarBackup/ChunkAccessCache.java

@@ -0,0 +1,147 @@
+package simpleWarBackup;
+
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.lang.reflect.Field;
+import java.util.HashMap;
+import java.util.Map;
+
+import net.minecraft.server.v1_12_R1.RegionFile;
+
+/**
+ * ---------------------------------------------------------------
+ * ---------------------------------------------------------------
+ * ---------------------------------------------------------------
+ * ---------------------------------------------------------------
+ * CURRENTLY A DUPLICATE OF THE SECONDARY CACHE IN RegionFileCache
+ * ---------------------------------------------------------------
+ * ---------------------------------------------------------------
+ * ---------------------------------------------------------------
+ * ---------------------------------------------------------------
+ */
+public class ChunkAccessCache 
+{
+	private static Map<RegionFile, Access> cache = new HashMap<RegionFile,  Access>();
+	
+	/**
+	 * TODO
+	 * 
+	 * @param file
+	 * @param regionFile
+	 */
+	static void cacheChunkAccess(File file, RegionFile regionFile)
+	{
+		try
+		{
+			cache.put(regionFile, new Access(regionFile));
+		} 
+		catch (FileNotFoundException  | 
+		       IllegalAccessException | 
+		       IllegalArgumentException e) 
+		{
+			e.printStackTrace();//TODO
+		}
+	}
+	
+	
+	/**
+	 * TODO
+	 * 
+	 * @param regionFile
+	 * @param x
+	 * @param z
+	 * @return
+	 */
+	public static int getChunkLength(RegionFile regionFile, int x, int z)
+	{
+		Access access = cache.get(regionFile);
+		
+		/* "offset" refers to the location of the chunk's bytes
+		 * within the .mca file - or how many bytes into the file
+		 * to seek when reading - divided by 4096.
+		 */
+		int offset;
+		
+		/* The first four bytes at that location, the first four
+		 * bytes of the chunk's data, are an int recording the
+		 * chunk's length in bytes, not including those four.
+		 * 
+		 * The next byte represents compression scheme. This byte,
+		 * like the four previous bytes, is omitted when the game 
+		 * reads a chunk's data. 
+		 * 
+		 * This method returns the length of data actually read.
+		 */
+		if (access != null && (offset = access.offset[x + z * 32]) > 0)
+		{
+			try 
+			{
+				access.bytes.seek(offset * 4096);
+				return access.bytes.readInt() - 1;
+			} 
+			catch (IOException e) { e.printStackTrace(); }
+		}
+		return 0;
+	}
+	
+	
+	/**
+	 * Gives access to the private fields {@code int[] d}, and {@code RandomAccessFile c}, 
+	 * within a RegionFile object. The names of these fields may change in new releases of
+	 * Spigot. TODO explain what both of those fields are
+	 */
+	private static class Access
+	{
+		static final Field            offsetField;
+		       final int[]            offset;
+		       
+		static final Field            bytesField;
+		       final RandomAccessFile bytes;
+		
+		static
+		{
+			Field tmp1 = null;
+			Field tmp2 = null;
+			try 
+			{
+				tmp1 = RegionFile.class.getDeclaredField("d"); 
+				tmp1.setAccessible(true);
+				
+				tmp2 = RegionFile.class.getDeclaredField("c");
+				tmp2.setAccessible(true);
+			} 
+			catch (NoSuchFieldException | SecurityException e) 
+			{
+				/* TODO take more drastic action? Either
+				 * Field missing would mean that Minecraft 
+				 * has refactored, breaking the whole plugin
+				 */
+				e.printStackTrace();
+			}
+			offsetField = tmp1;
+			bytesField  = tmp2;
+		}
+		
+		
+		/**
+		 * Creates a new Access object to hold references to the private variables {@code int[] d} 
+		 * and {@code RandomAccessFile c} within the given RegionFile. Variables are accessed by 
+		 * reflection. TODO write more
+		 * 
+		 * @param  regionFile the RegionFile whose chunks are to be accessed
+		 * 
+		 * @throws FileNotFoundException
+		 * @throws IllegalAccessException
+		 * @throws IllegalArgumentException
+		 */
+		Access(RegionFile regionFile) throws FileNotFoundException,
+		                                     IllegalAccessException,
+		                                     IllegalArgumentException
+		{
+			offset = (int[])            offsetField.get(regionFile);
+			bytes  = (RandomAccessFile) bytesField .get(regionFile);
+		}
+	}
+}

src/simpleWarBackup/RegionChunkList.java

@@ -1,6 +1,93 @@
 package simpleWarBackup;
 
+import java.io.File;
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.util.BitSet;
+import java.util.HashMap;
+
 public class RegionChunkList 
 {
+	private final File file;
+	private final RandomAccessFile readwrite;
+	private final BitSet chunks = new BitSet(1024);
 	
+	private final HashMap<String, HashMap
+	                     <String, HashMap
+	                     <String, RegionChunkList>>> lists = 
+	                     
+	              new HashMap<String, HashMap
+	                         <String, HashMap
+	                         <String, RegionChunkList>>>();
+	
+	
+	/**
+	 * TODO
+	 * 
+	 * @param file
+	 * @throws IOException
+	 */
+	RegionChunkList(File file, String backup, String town, String world) throws IOException
+	{
+		readwrite = new RandomAccessFile((this.file = file), "rw");
+		
+		byte[] bytes = new byte[128];
+		if (readwrite.length() >= 128) 
+		{
+			readwrite.readFully(bytes);
+			
+			int i = 0, j, k;
+			for (byte b : bytes)
+				for (j = 0, k = 1; j < 8; i++, j++, k <<= 1)
+					if ((b & k) == k) chunks.set(i);
+		}
+		else readwrite.write(bytes);
+		
+		lists.get(backup)
+		     .get(town)
+		     .put(world, this);
+	}
+	
+	
+	/**
+	 * TODO
+	 * 
+	 * @param x
+	 * @param z
+	 * @return
+	 */
+	boolean isChunkStored(int x, int z)
+	{
+		x &= 31;
+		z &= 31;
+		return chunks.get(x + z * 32);
+	}
+	
+	
+	/**
+	 * TODO
+	 * 
+	 * @param x
+	 * @param z
+	 */
+	void storeChunk(int x, int z)
+	{
+		x &= 31;
+		z &= 31;
+		chunks.set(x + z * 32);
+	}
+	
+	
+	/**
+	 * TODO
+	 * 
+	 * @param x
+	 * @param z
+	 */
+	void markChunkAsRestored(int x, int z)
+	{
+		x &= 31;
+		z &= 31;
+		chunks.clear(x + z * 32);
+	}
 }

src/simpleWarBackup/RegionFileCache.java

@@ -215,7 +215,7 @@ public final class RegionFileCache
 			} 
 			catch (NoSuchFieldException | SecurityException e) 
 			{
-				/* TODO take more drastic action. Either
+				/* TODO take more drastic action? Either
 				 * Field missing would mean that Minecraft 
 				 * has refactored, breaking the whole plugin
 				 */