sheepit-shadow-nabber/src/main/java/com/sheepit/client/ChunkInputStream.java

package com.sheepit.client;

import lombok.NonNull;

import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.nio.file.Path;
import java.util.ArrayDeque;
import java.util.List;
import java.util.NoSuchElementException;

public class ChunkInputStream extends InputStream {
	
	@NonNull private final ArrayDeque<Path> chunkPaths;
	@NonNull private BufferedInputStream currentStream;
	
	/**
	 * Given a list of chunk paths, provides an InputStream that reads the contents of these files in the order they were provided in.
	 * @param chunkPaths Non-empty, ordered list of paths
	 * @throws IOException If the first chunk could not be found. Errors with other chunk will be thrown during calls to read()
	 */
	public ChunkInputStream(List<Path> chunkPaths) throws IOException {
		this.chunkPaths = new ArrayDeque<>(chunkPaths);
		
		/// Setup the first chunk for reading
		prepareNextChunk();
	}
	
	private void prepareNextChunk() throws FileNotFoundException, NoSuchElementException {
		currentStream = new BufferedInputStream(new FileInputStream(chunkPaths.removeFirst().toFile()));
	}
	
	@Override public int read() throws IOException {
		int result = currentStream.read();
		
		if (result == -1) {
			/// Finished reading from this chunk, continue with the next if possible
			try {
				prepareNextChunk();
			}
			catch (NoSuchElementException e) {
				/// This was the last chunk
				return -1;
			}
			result = currentStream.read();
		}
		
		return result;
	}
}