/*******************************************************************************
 * Copyright (c) 2006, 2007 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 * 
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/

package org.eclipse.osgi.internal.verifier;

import java.io.*;
import java.security.MessageDigest;

/**
 * This InputStream will calculate the digest of bytes as they are read. At the
 * end of the InputStream, it will calculate the digests and throw an exception
 * if the calculated digest do not match the expected digests.
 */
class DigestedInputStream extends FilterInputStream {
	MessageDigest digest;
	byte result[];
	long remaining;

	/**
	 * Constructs an InputStream that uses another InputStream as a source and
	 * calculates the digest. At the end of the stream an exception will be
	 * thrown if the calculated digest doesn't match the passed digest.
	 * 
	 * @param in the stream to use as an input source.
	 * @param digestAlgorithm the MessageDigest algorithm to use.
	 * @param result the expected digest.
	 */
	DigestedInputStream(InputStream in, String digestAlgorithm, byte result[], long size) {
		super(in);
		this.remaining = size;
		this.digest = SignedBundleFile.getMessageDigest(digestAlgorithm);
		this.result = result;
	}

	/**
	 * Not supported.
	 */
	public synchronized void mark(int readlimit) {
		// Noop, we don't want to support this
	}

	/**
	 * Always returns false.
	 */
	public boolean markSupported() {
		return false;
	}

	/**
	 * Read a byte from the InputStream. Digests are calculated on reads. At the
	 * end of the stream the calculated digests must match the expected digests.
	 * 
	 * @return the character read or -1 at end of stream.
	 * @throws IOException if there was an problem reading the byte or at the
	 *         end of the stream the calculated digests do not match the
	 *         expected digests.
	 * @see java.io.InputStream#read()
	 */
	public int read() throws IOException {
		if (remaining <= 0)
			return -1;
		int c = super.read();
		if (c != -1) {
			digest.update((byte) c);
			remaining--;
		} else {
			// We hit eof so set remaining to zero
			remaining = 0;
		}
		if (remaining == 0)
			verifyDigests();
		return c;
	}

	private void verifyDigests() throws IOException {
		// Check the digest at end of file
		byte rc[] = digest.digest();
		if (!MessageDigest.isEqual(result, rc)) {			
			
			throw new IOException("Corrupted file: the digest is valid for " + digest.getAlgorithm()); //$NON-NLS-1$
			
		}
	}

	/**
	 * Read bytes from the InputStream. Digests are calculated on reads. At the
	 * end of the stream the calculated digests must match the expected digests.
	 * 
	 * @return the number of characters read or -1 at end of stream.
	 * @throws IOException if there was an problem reading or at the
	 *         end of the stream the calculated digests do not match the
	 *         expected digests.
	 * @see java.io.InputStream#read()
	 */
	public int read(byte[] b, int off, int len) throws IOException {
		if (remaining <= 0)
			return -1;
		int rc = super.read(b, off, len);
		if (rc != -1) {
			digest.update(b, off, rc);
			remaining -= rc;
		} else {
			// We hit eof so set remaining to zero
			remaining = 0;
		}
		if (remaining <= 0)
			verifyDigests();
		return rc;
	}

	/**
	 * Not supported.
	 * 
	 * @throws IOException always thrown if this method is called since mark/reset is not supported.
	 * @see java.io.InputStream#reset()
	 */
	public synchronized void reset() throws IOException {
		// Throw IOException, we don't want to support this
		throw new IOException("Reset not supported"); //$NON-NLS-1$
	}

	/**
	 * This method is implemented as a read into a bitbucket.
	 */
	public long skip(long n) throws IOException {
		byte buffer[] = new byte[4096];
		long count = 0;
		while (n - count > 0) {
			int rc = (n - count) > buffer.length ? buffer.length : (int) (n - count);
			rc = read(buffer, 0, rc);
			if (rc == -1)
				break;
			count += rc;
			n -= rc;
		}
		return count;
	}
}