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SciJava Common is a shared library for SciJava software. It provides a plugin framework, with an extensible mechanism for service discovery, backed by its own annotation processor, so that plugins can be loaded dynamically. It is used by downstream projects in the SciJava ecosystem, such as ImageJ and SCIFIO.
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 * Institute of Molecular Cell Biology and Genetics, University of
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 * 1. Redistributions of source code must retain the above copyright notice,
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package org.scijava.io.handle;

import java.io.EOFException;
import java.io.IOException;

import org.scijava.io.location.Location;

/**
 * Wraps a {@link DataHandle} and acts as a write buffer.
 *
 * @author Gabriel Einsdorf
 */
public class WriteBufferDataHandle extends AbstractHigherOrderHandle {

	private static final int DEFAULT_BUFFERSIZE = 10_000;
	private long offset = 0;
	private int nextPos = 0;

	private byte[] buffer;
	private final int bufferSize;

	/**
	 * Creates a {@link WriteBufferDataHandle} that wraps the given
	 * {@link DataHandle}, the default size for the buffer is used
	 * ({@value #DEFAULT_BUFFERSIZE} bytes).
	 *
	 * @param handle the handle to wrap
	 */
	public WriteBufferDataHandle(final DataHandle handle) {
		this(handle, DEFAULT_BUFFERSIZE);
	}

	/**
	 * Creates a {@link WriteBufferDataHandle} that wraps the given
	 * {@link DataHandle}
	 *
	 * @param handle the handle to wrap
	 * @param bufferSize the size of the write buffer in bytes
	 */
	public WriteBufferDataHandle(final DataHandle handle,
		final int bufferSize)
	{
		super(handle);
		this.bufferSize = bufferSize;
	}

	@Override
	public void write(final int b) throws IOException {
		ensureOpen();
		// if buffer is full flush
		if (nextPos >= buffer.length) {
			flush();
		}
		// buffer the byte
		buffer[nextPos] = (byte) b;
		nextPos++;
		offset++;
	}

	@Override
	public void write(final byte[] b, final int off, final int len)
		throws IOException
	{
		ensureOpen();
		// ensure the range is valid
		if ((off < 0) || (off > b.length) || (len < 0) || ((off +
			len) > b.length) || ((off + len) < 0))
		{
			throw new IndexOutOfBoundsException();
		}
		else if (len == 0) {
			return; // nothing to do
		}

		// skip the buffering and write directly to the handle
		if (len > buffer.length) {
			flush();
			handle().write(b, off, len);
			offset += len;
			return;
		}

		// copy to buffer / flush if necessary
		int start = off;
		final int total = off + len;
		while (start < total) {
			final int numItems = Math.min(buffer.length - nextPos, total - start);
			System.arraycopy(b, start, buffer, nextPos, numItems);
			start += numItems;
			nextPos += numItems;
			if (nextPos >= buffer.length) {
				flush();
			}
		}
	}

	/**
	 * Write the buffer content to the underlying handle
	 */
	private void flush() throws IOException {
		ensureOpen();
		if (nextPos == 0) return;

		handle().write(buffer, 0, nextPos);
		nextPos = 0;
	}

	@Override
	public long length() throws IOException {
		// data written out + data in the buffer
		return handle().length() + nextPos - 1;
	}

	@Override
	public void setLength(final long length) throws IOException {
		ensureOpen();
		handle().setLength(length);
	}

	@Override
	public boolean isReadable() {
		return false;
	}

	/**
	 * @throws IOException if this handle has been closed
	 */
	@Override
	protected void ensureOpen() throws IOException {
		super.ensureOpen();
		if (buffer == null) {
			buffer = new byte[bufferSize];
		}
	}

	@Override
	public long offset() throws IOException {
		return offset;
	}

	@Override
	public void seek(final long pos) throws IOException {
		ensureOpen();
		if (pos >= length()) {
			throw new EOFException();
		}
		flush();
		offset = pos;
		handle().seek(offset);
	}

	@Override
	public long skip(final long n) throws IOException {
		throw new IOException("Operation 'skip' is not supported!");
	}

	@Override
	public byte readByte() throws IOException {
		throw DataHandles.writeOnlyException();
	}

	@Override
	public int read(final byte[] b, final int off, final int len)
		throws IOException
	{
		throw DataHandles.writeOnlyException();
	}

	@Override
	protected void cleanup() throws IOException {
		flush();
		buffer = null;
	}
}