/*
 * aocode-public - Reusable Java library of general tools with minimal external dependencies.
 * Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2016  AO Industries, Inc.
 *     support@aoindustries.com
 *     7262 Bull Pen Cir
 *     Mobile, AL 36695
 *
 * This file is part of aocode-public.
 *
 * aocode-public is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * aocode-public is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with aocode-public.  If not, see <http://www.gnu.org/licenses/>.
 */
package com.aoindustries.io;

import java.io.EOFException;
import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;

/**
 * A <code>NestedInputStream</code> reads data from
 * within an <code>InputStream</code> as if it were
 * a separate stream.  The underlying <code>InputStream</code>
 * is never closed, allowing it to be used for multiple
 * nested streams.
 *
 * @author  AO Industries, Inc.
 */
public final class NestedInputStream extends FilterInputStream {

	private boolean isEOF = false;
	final private byte[] buffer = new byte[32768];
	private int bufferFilled = 0;
	private int bufferRead = 0;

	public NestedInputStream(InputStream in) {
		super(in);
	}

	@Override
	public int available() {
		return bufferFilled-bufferRead;
	}

	private int readBlockSize() throws IOException {
		int ch1 = in.read();
		int ch2 = in.read();
		if ((ch1 | ch2) < 0)
			throw new EOFException();
		return (ch1 << 8) | ch2;
	}

	private void readFully(byte b[], int off, int len) throws IOException {
		if (len < 0)
			throw new IndexOutOfBoundsException();
		int n = 0;
		while (n < len) {
			int count = in.read(b, off + n, len - n);
			if (count < 0)
			throw new EOFException();
			n += count;
		}
	}

	private void loadNextBlock() throws IOException {
		// Load the next block, if needed
		if(!isEOF && bufferRead>=bufferFilled) {
			bufferFilled = readShort();
			if(bufferFilled>0) {
				readFully(buffer, 0, bufferFilled);
				bufferRead=0;
			} else {
				isEOF=true;
				bufferFilled = bufferRead = 0;
				if(code!=EOF) throw new IOException("Unexpected code: "+code);
			}
		}
	}

	@Override
	public void close() throws IOException {
		if(!isEOF) {
			// Read the rest of the underlying stream
			int code;
			while((code=in.read())==NEXT) {
				int len=in.readShort();
				while(len>0) {
					int skipped=(int)in.skip(len);
					len-=skipped;
				}
			}
			isEOF=true;
			bufferFilled=bufferRead=0;
			if(buffer!=null) {
				BufferManager.release(buffer);
				buffer=null;
			}
			if(code!=EOF) throw new IOException("Unexpected code: "+code);
		}
	}

	public int read() throws IOException {
		if(isEOF) return -1;
		loadNextBlock();
		if(isEOF) return -1;
		return ((int)buffer[bufferRead++])&0xff;
	}

	@Override
	public int read(byte[] b, int off, int len) throws IOException {
		if(isEOF) return -1;
		loadNextBlock();
		if(isEOF) return -1;
		int bufferLeft=bufferFilled-bufferRead;
		if(bufferLeft>len) bufferLeft=len;
		System.arraycopy(buffer, bufferRead, b, off, bufferLeft);
		bufferRead+=bufferLeft;
		return bufferLeft;
	}

	@Override
	public long skip(long n) throws IOException {
		if(isEOF) return -1;
		loadNextBlock();
		if(isEOF) return -1;
		int bufferLeft=bufferFilled-bufferRead;
		if(bufferLeft>n) bufferLeft=(int)n;
		bufferRead+=bufferLeft;
		return bufferLeft;
	}

	@Override
	public void finalize() throws Throwable {
		if(buffer!=null) {
			BufferManager.release(buffer);
			buffer=null;
		}
		super.finalize();
	}

	public void mark(int readlimit) {
		throw new RuntimeException("mark not supported");
	}

	@Override
	public void reset() throws IOException {
		throw new IOException("mark not supported");
	}

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