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/*
 * Hibernate, Relational Persistence for Idiomatic Java
 *
 * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
 * See the lgpl.txt file in the root directory or .
 */
package org.hibernate.engine.jdbc;

import java.io.IOException;
import java.io.InputStream;
import java.io.Reader;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.sql.Clob;
import java.sql.SQLException;

import org.hibernate.engine.jdbc.internal.CharacterStreamImpl;
import org.hibernate.type.descriptor.java.DataHelper;

/**
 * Manages aspects of proxying {@link Clob Clobs} for non-contextual creation, including proxy creation and
 * handling proxy invocations.  We use proxies here solely to avoid JDBC version incompatibilities.
 *
 * @author Gavin King
 * @author Steve Ebersole
 * @author Gail Badner
 */
public class ClobProxy implements InvocationHandler {
	private static final Class[] PROXY_INTERFACES = new Class[] { Clob.class, ClobImplementer.class };

	private final CharacterStream characterStream;
	private boolean needsReset;

	/**
	 * Constructor used to build {@link Clob} from string data.
	 *
	 * @param string The byte array
	 * @see #generateProxy(String)
	 */
	protected ClobProxy(String string) {
		this.characterStream = new CharacterStreamImpl( string );
	}

	/**
	 * Constructor used to build {@link Clob} from a reader.
	 *
	 * @param reader The character reader.
	 * @param length The length of the reader stream.
	 * @see #generateProxy(java.io.Reader, long)
	 */
	protected ClobProxy(Reader reader, long length) {
		this.characterStream = new CharacterStreamImpl( reader, length );
	}

	protected long getLength() {
		return characterStream.getLength();
	}

	protected InputStream getAsciiStream() throws SQLException {
		return new ReaderInputStream( getCharacterStream() );
	}

	protected Reader getCharacterStream() throws SQLException {
		return getUnderlyingStream().asReader();
	}

	protected CharacterStream getUnderlyingStream() throws SQLException {
		resetIfNeeded();
		return characterStream;
	}

	protected String getSubString(long start, int length) {
		final String string = characterStream.asString();
		// semi-naive implementation
		final int endIndex = Math.min( ( (int) start ) + length, string.length() );
		return string.substring( (int) start, endIndex );
	}

	/**
	 * {@inheritDoc}
	 *
	 * @throws UnsupportedOperationException if any methods other than {@link Clob#length},
	 * {@link Clob#getAsciiStream}, {@link Clob#getCharacterStream},
	 * {@link ClobImplementer#getUnderlyingStream}, {@link Clob#getSubString},
	 * {@link Clob#free}, or toString/equals/hashCode are invoked.
	 */
	@Override
	public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
		final String methodName = method.getName();
		final int argCount = method.getParameterCount();

		if ( "length".equals( methodName ) && argCount == 0 ) {
			return getLength();
		}
		if ( "getUnderlyingStream".equals( methodName ) ) {
			return getUnderlyingStream(); // Reset stream if needed.
		}
		if ( "getAsciiStream".equals( methodName ) && argCount == 0 ) {
			return getAsciiStream();
		}
		if ( "getCharacterStream".equals( methodName ) ) {
			if ( argCount == 0 ) {
				return getCharacterStream();
			}
			else if ( argCount == 2 ) {
				final long start = (Long) args[0];
				if ( start < 1 ) {
					throw new SQLException( "Start position 1-based; must be 1 or more." );
				}
				if ( start > getLength() ) {
					throw new SQLException( "Start position [" + start + "] cannot exceed overall CLOB length [" + getLength() + "]" );
				}
				final int length = (Integer) args[1];
				if ( length < 0 ) {
					// java docs specifically say for getCharacterStream(long,int) that the start+length must not exceed the
					// total length, however that is at odds with the getSubString(long,int) behavior.
					throw new SQLException( "Length must be great-than-or-equal to zero." );
				}
				return DataHelper.subStream( getCharacterStream(), start-1, length );
			}
		}
		if ( "getSubString".equals( methodName ) && argCount == 2 ) {
			final long start = (Long) args[0];
			if ( start < 1 ) {
				throw new SQLException( "Start position 1-based; must be 1 or more." );
			}
			if ( start > getLength() ) {
				throw new SQLException( "Start position [" + start + "] cannot exceed overall CLOB length [" + getLength() + "]" );
			}
			final int length = (Integer) args[1];
			if ( length < 0 ) {
				throw new SQLException( "Length must be great-than-or-equal to zero." );
			}
			return getSubString( start-1, length );
		}
		if ( "free".equals( methodName ) && argCount == 0 ) {
			characterStream.release();
			return null;
		}
		if ( "toString".equals( methodName ) && argCount == 0 ) {
			return this.toString();
		}
		if ( "equals".equals( methodName ) && argCount == 1 ) {
			return proxy == args[0];
		}
		if ( "hashCode".equals( methodName ) && argCount == 0 ) {
			return this.hashCode();
		}

		throw new UnsupportedOperationException( "Clob may not be manipulated from creating session" );
	}

	protected void resetIfNeeded() throws SQLException {
		try {
			if ( needsReset ) {
				characterStream.asReader().reset();
			}
		}
		catch ( IOException ioe ) {
			throw new SQLException( "could not reset reader", ioe );
		}
		needsReset = true;
	}

	/**
	 * Generates a {@link Clob} proxy using the string data.
	 *
	 * @param string The data to be wrapped as a {@link Clob}.
	 *
	 * @return The generated proxy.
	 */
	public static Clob generateProxy(String string) {
		return (Clob) Proxy.newProxyInstance( getProxyClassLoader(), PROXY_INTERFACES, new ClobProxy( string ) );
	}

	/**
	 * Generates a {@link Clob} proxy using a character reader of given length.
	 *
	 * @param reader The character reader
	 * @param length The length of the character reader
	 *
	 * @return The generated proxy.
	 */
	public static Clob generateProxy(Reader reader, long length) {
		return (Clob) Proxy.newProxyInstance( getProxyClassLoader(), PROXY_INTERFACES, new ClobProxy( reader, length ) );
	}

	/**
	 * Determines the appropriate class loader to which the generated proxy
	 * should be scoped.
	 *
	 * @return The class loader appropriate for proxy construction.
	 */
	protected static ClassLoader getProxyClassLoader() {
		return ClobImplementer.class.getClassLoader();
	}
}