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package com.github.akurilov.commons.io.util;

import java.io.IOException;
import java.io.InputStream;
import java.nio.ByteBuffer;

public class InputStreamWrapperChannel
extends BufferedByteChannelBase
implements BufferedReadableByteChannel {

	private InputStream in = null;

	public InputStreamWrapperChannel(final int buffSize) {
		super(buffSize);
	}

	@Override
	public final int read(final ByteBuffer dst)
	throws IOException {
		final var n = in.read(bb, 0, Math.min(bb.length, dst.remaining()));
		dst.put(bb, 0, n);
		return n;
	}

	private final static ThreadLocal
		REUSABLE_INPUT_CHANNELS = ThreadLocal.withInitial(
			() -> {
				final var count = (int) (
					Math.log(REUSABLE_BUFF_SIZE_MAX / REUSABLE_BUFF_SIZE_MIN) / Math.log(2) + 1
				);
				return new InputStreamWrapperChannel[count];
			}
		);

	/**
	 * Wraps the given input stream into the special stateless and reusable (thread local) byte
	 * channel
	 * @param in the input stream to wrap
	 * @param remainingSize the estimated size of the data to be read from the given input
	 * @return readable byte channel
	 * @throws IllegalStateException if negative remaining size is specified
	 */
	public static BufferedReadableByteChannel getThreadLocalInstance(
		final InputStream in, final long remainingSize
	) throws IllegalStateException {

		if(remainingSize < 0) {
			throw new IllegalArgumentException("Requested negative size: " + remainingSize);
		}

		final var threadLocalReusableChannels = REUSABLE_INPUT_CHANNELS.get();
		var currBuffSize = Long.highestOneBit(remainingSize);
		if(currBuffSize > REUSABLE_BUFF_SIZE_MAX) {
			currBuffSize = REUSABLE_BUFF_SIZE_MAX;
		} else if(currBuffSize < REUSABLE_BUFF_SIZE_MAX) {
			if(currBuffSize < REUSABLE_BUFF_SIZE_MIN) {
				currBuffSize = REUSABLE_BUFF_SIZE_MIN;
			} else if(currBuffSize < remainingSize) {
				currBuffSize <<= 1;
			}
		}
		final var i = Long.numberOfTrailingZeros(currBuffSize);
		var chan = threadLocalReusableChannels[i];

		if(chan == null) {
			chan = new InputStreamWrapperChannel((int) currBuffSize);
			threadLocalReusableChannels[i] = chan;
		}
		chan.in = in;

		return chan;
	}

	@Override
	public void close() {
		in = null;
	}
}