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package org.scijava.io.nio;

import java.nio.ByteBuffer;
import java.util.function.Function;

import org.scijava.io.ByteBank;

/**
 * A {@link ByteBank} backed by a {@link ByteBuffer}. Self-growing up to a
 * maximal capacity of {@link Integer#MAX_VALUE}
 *
 * @author Gabriel Einsdorf
 */
public class ByteBufferByteBank implements ByteBank {

	private static final int DEFAULT_CAPACITY = 10_000;

	private ByteBuffer buffer;

	private int size;

	private Function provider;

	public ByteBufferByteBank() {
		provider = ByteBuffer::allocate;
		buffer = provider.apply(DEFAULT_CAPACITY);
	}

	public ByteBufferByteBank(final Function provider) {
		this.provider = provider;
		buffer = provider.apply(DEFAULT_CAPACITY);
	}

	public ByteBufferByteBank(final Function provider,
		final int initialCapacity)
	{
		this.provider = provider;
		buffer = provider.apply(initialCapacity);
	}

	public ByteBufferByteBank(final int initialCapacity) {
		provider = ByteBuffer::allocate;
		buffer = provider.apply(initialCapacity);
	}

	@Override
	public long getMaxBufferSize() {
		return Integer.MAX_VALUE;
	}

	@Override
	public void setBytes(final long startpos, final byte[] bytes,
		final int offset, final int length)
	{
		// ensure we have space
		checkWritePos(startpos, startpos + length);
		final int neededCapacity = size + length;
		ensureCapacity(neededCapacity);

		// copy the data
		buffer.position((int) startpos);
		buffer.put(bytes, offset, length);

		// update the maxpos
		updateSize(startpos + length);
	}

	@Override
	public void setByte(final long pos, final byte b) {
		checkWritePos(pos, pos);
		if (pos == buffer.capacity()) {
			ensureCapacity((int) pos + 1);
		}
		buffer.put((int) pos, b);
		updateSize(pos + 1);
	}

	@Override
	public void clear() {
		buffer.clear();
		size = 0;
	}

	@Override
	public byte getByte(final long pos) {
		checkReadPos(pos, pos);
		// the buffer might contain bytes with negative value
		// we need to flip the sign to positive to satisfy the contract of this
		// method
		return buffer.get((int) pos);
	}

	@Override
	public int getBytes(final long startPos, final byte[] b, final int offset,
		final int length)
	{
		checkReadPos(startPos, startPos + length);
		// ensure we don't try to read data which is not in the buffer
		final int readLength = (int) Math.min(size() - startPos, length);
		buffer.position((int) startPos);
		buffer.get(b, offset, readLength);

		return readLength;
	}

	@Override
	public long size() {
		return size;
	}

	@Override
	public boolean isReadOnly() {
		// NB: Some ByteBuffers are read-only. But there is no API to check it.
		// Therefore, we make a "best effort" guess based on known read-only types.
		// Since these read-only types are not public, we compare class names rather
		// than checking for type equality or using instanceof.
		final String className = buffer.getClass().getName();
		return className.equals("java.nio.HeapByteBufferR") ||
			className.equals("java.nio.DirectByteBufferR");
	}

	// -- Helper methods --

	private void ensureCapacity(final int minCapacity) {
		final int oldCapacity = buffer.capacity();
		if (minCapacity <= oldCapacity) return; // no need to grow

		// grow the array by up to 50% (plus a small constant)
		final int growth = Math.min(oldCapacity / 2 + 16, Integer.MAX_VALUE);
		final int newCapacity;
		if (growth > Integer.MAX_VALUE - oldCapacity) {
			// growth would push array over the maximum array size
			newCapacity = Integer.MAX_VALUE;
		}
		else newCapacity = oldCapacity + growth;
		// ensure the array grows by at least the requested minimum capacity
		final int newLength = Math.max(minCapacity, newCapacity);

		// copy the data into a new array
		buffer.position(0);
		final ByteBuffer newBuffer = ByteBuffer.allocate(newLength);
		newBuffer.order(buffer.order());
		newBuffer.put(buffer);
		buffer = newBuffer;
	}

	private void updateSize(final long newSize) {
		size = (int) (newSize > size ? newSize : size);
	}

}