/*

 * Copyright 2000-2007 Sun Microsystems, Inc.  All Rights Reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Sun designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Sun in the LICENSE file that accompanied this code.

 *

 * This code 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 General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 */

package java.beans;

import java.util.Collections;

import java.util.HashMap;

import java.util.IdentityHashMap;

import java.util.Map;

/**

 * An <code>Encoder</code> is a class which can be used to create

 * files or streams that encode the state of a collection of

 * JavaBeans in terms of their public APIs. The <code>Encoder</code>,

 * in conjunction with its persistence delegates, is responsible for

 * breaking the object graph down into a series of <code>Statements</code>s

 * and <code>Expression</code>s which can be used to create it.

 * A subclass typically provides a syntax for these expressions

 * using some human readable form - like Java source code or XML.

 *

 * @since 1.4

 *

 * @author Philip Milne

 */

public class Encoder {

    private final Map<Class<?>, PersistenceDelegate> delegates

            = Collections.synchronizedMap(new HashMap<Class<?>, PersistenceDelegate>());

    private Map bindings = new IdentityHashMap();

    private ExceptionListener exceptionListener;

    boolean executeStatements = true;

    private Map attributes;

    /**

     * Write the specified object to the output stream.

     * The serialized form will denote a series of

     * expressions, the combined effect of which will create

     * an equivalent object when the input stream is read.

     * By default, the object is assumed to be a <em>JavaBean</em>

     * with a nullary constructor, whose state is defined by

     * the matching pairs of "setter" and "getter" methods

     * returned by the Introspector.

     *

     * @param o The object to be written to the stream.

     *

     * @see XMLDecoder#readObject

     */

    protected void writeObject(Object o) {

        if (o == this) {

            return;

        }

        PersistenceDelegate info = getPersistenceDelegate(o == null ? null : o.getClass());

        info.writeObject(o, this);

    }

    /**

     * Sets the exception handler for this stream to <code>exceptionListener</code>.

     * The exception handler is notified when this stream catches recoverable

     * exceptions.

     *

     * @param exceptionListener The exception handler for this stream;

     *       if <code>null</code> the default exception listener will be used.

     *

     * @see #getExceptionListener

     */

    public void setExceptionListener(ExceptionListener exceptionListener) {

        this.exceptionListener = exceptionListener;

    }

    /**

     * Gets the exception handler for this stream.

     *

     * @return The exception handler for this stream;

     *    Will return the default exception listener if this has not explicitly been set.

     *

     * @see #setExceptionListener

     */

    public ExceptionListener getExceptionListener() {

        return (exceptionListener != null) ? exceptionListener : Statement.defaultExceptionListener;

    }

    Object getValue(Expression exp) {

        try {

            return (exp == null) ? null : exp.getValue();

        }

        catch (Exception e) {

            getExceptionListener().exceptionThrown(e);

            throw new RuntimeException("failed to evaluate: " + exp.toString());

        }

    }

    /**

     * Returns the persistence delegate for the given type.

     * The persistence delegate is calculated

     * by applying the following of rules in order:

     * <ul>

     * <li>

     * If the type is an array, an internal persistence

     * delegate is returned which will instantiate an

     * array of the appropriate type and length, initializing

     * each of its elements as if they are properties.

     * <li>

     * If the type is a proxy, an internal persistence

     * delegate is returned which will instantiate a

     * new proxy instance using the static

     * "newProxyInstance" method defined in the

     * Proxy class.

     * <li>

     * If the BeanInfo for this type has a <code>BeanDescriptor</code>

     * which defined a "persistenceDelegate" property, this

     * value is returned.

     * <li>

     * In all other cases the default persistence delegate

     * is returned. The default persistence delegate assumes

     * the type is a <em>JavaBean</em>, implying that it has a default constructor

     * and that its state may be characterized by the matching pairs

     * of "setter" and "getter" methods returned by the Introspector.

     * The default constructor is the constructor with the greatest number

     * of parameters that has the {@link ConstructorProperties} annotation.

     * If none of the constructors have the {@code ConstructorProperties} annotation,

     * then the nullary constructor (constructor with no parameters) will be used.

     * For example, in the following the nullary constructor

     * for {@code Foo} will be used, while the two parameter constructor

     * for {@code Bar} will be used.

     * <code>

     *   public class Foo {

     *     public Foo() { ... }

     *     public Foo(int x) { ... }

     *   }

     *   public class Bar {

     *     public Bar() { ... }

     *     @ConstructorProperties({"x"})

     *     public Bar(int x) { ... }

     *     @ConstructorProperties({"x", "y"})

     *     public Bar(int x, int y) { ... }

     *   }

     * </code>

     * </ul>

     *

     * @param  type The type of the object.

     * @return The persistence delegate for this type of object.

     *

     * @see #setPersistenceDelegate

     * @see java.beans.Introspector#getBeanInfo

     * @see java.beans.BeanInfo#getBeanDescriptor

     */

    public PersistenceDelegate getPersistenceDelegate(Class<?> type) {

        PersistenceDelegate pd = this.delegates.get(type);

        return (pd != null) ? pd : MetaData.getPersistenceDelegate(type);

    }

    /**

     * Sets the persistence delegate associated with this <code>type</code> to

     * <code>persistenceDelegate</code>.

     *

     * @param  type The class of objects that <code>persistenceDelegate</code> applies to.

     * @param  persistenceDelegate The persistence delegate for instances of <code>type</code>.

     *

     * @see #getPersistenceDelegate

     * @see java.beans.Introspector#getBeanInfo

     * @see java.beans.BeanInfo#getBeanDescriptor

     */

    public void setPersistenceDelegate(Class<?> type,

                                       PersistenceDelegate persistenceDelegate)

    {

        if (persistenceDelegate != null) {

            this.delegates.put(type, persistenceDelegate);

        } else {

            this.delegates.remove(type);

        }

    }

    /**

     * Removes the entry for this instance, returning the old entry.

     *

     * @param oldInstance The entry that should be removed.

     * @return The entry that was removed.

     *

     * @see #get

     */

    public Object remove(Object oldInstance) {

        Expression exp = (Expression)bindings.remove(oldInstance);

        return getValue(exp);

    }

    /**

     * Returns a tentative value for <code>oldInstance</code> in

     * the environment created by this stream. A persistence

     * delegate can use its <code>mutatesTo</code> method to

     * determine whether this value may be initialized to

     * form the equivalent object at the output or whether

     * a new object must be instantiated afresh. If the

     * stream has not yet seen this value, null is returned.

     *

     * @param  oldInstance The instance to be looked up.

     * @return The object, null if the object has not been seen before.

     */

    public Object get(Object oldInstance) {

        if (oldInstance == null || oldInstance == this ||

            oldInstance.getClass() == String.class) {

            return oldInstance;

        }

        Expression exp = (Expression)bindings.get(oldInstance);

        return getValue(exp);

    }

    private Object writeObject1(Object oldInstance) {

        Object o = get(oldInstance);

        if (o == null) {

            writeObject(oldInstance);

            o = get(oldInstance);

        }

        return o;

    }

    private Statement cloneStatement(Statement oldExp) {

        Object oldTarget = oldExp.getTarget();

        Object newTarget = writeObject1(oldTarget);

        Object[] oldArgs = oldExp.getArguments();

        Object[] newArgs = new Object[oldArgs.length];

        for (int i = 0; i < oldArgs.length; i++) {

            newArgs[i] = writeObject1(oldArgs[i]);

        }

        if (oldExp.getClass() == Statement.class) {

            return new Statement(newTarget, oldExp.getMethodName(), newArgs);

        }

        else {

            return new Expression(newTarget, oldExp.getMethodName(), newArgs);

        }

    }

    /**

     * Writes statement <code>oldStm</code> to the stream.

     * The <code>oldStm</code> should be written entirely

     * in terms of the callers environment, i.e. the

     * target and all arguments should be part of the

     * object graph being written. These expressions

     * represent a series of "what happened" expressions

     * which tell the output stream how to produce an

     * object graph like the original.

     * <p>

     * The implementation of this method will produce

     * a second expression to represent the same expression in

     * an environment that will exist when the stream is read.

     * This is achieved simply by calling <code>writeObject</code>

     * on the target and all the arguments and building a new

     * expression with the results.

     *

     * @param oldStm The expression to be written to the stream.

     */

    public void writeStatement(Statement oldStm) {

        // System.out.println("writeStatement: " + oldExp);

        Statement newStm = cloneStatement(oldStm);

        if (oldStm.getTarget() != this && executeStatements) {

            try {

                newStm.execute();

            } catch (Exception e) {

                getExceptionListener().exceptionThrown(new Exception("Encoder: discarding statement "

                                                                     + newStm, e));

            }

        }

    }

    /**

     * The implementation first checks to see if an

     * expression with this value has already been written.

     * If not, the expression is cloned, using

     * the same procedure as <code>writeStatement</code>,

     * and the value of this expression is reconciled

     * with the value of the cloned expression

     * by calling <code>writeObject</code>.

     *

     * @param oldExp The expression to be written to the stream.

     */

    public void writeExpression(Expression oldExp) {

        // System.out.println("Encoder::writeExpression: " + oldExp);

        Object oldValue = getValue(oldExp);

        if (get(oldValue) != null) {

            return;

        }

        bindings.put(oldValue, (Expression)cloneStatement(oldExp));

        writeObject(oldValue);

    }

    void clear() {

        bindings.clear();

    }

    // Package private method for setting an attributes table for the encoder

    void setAttribute(Object key, Object value) {

        if (attributes == null) {

            attributes = new HashMap();

        }

        attributes.put(key, value);

    }

    Object getAttribute(Object key) {

        if (attributes == null) {

            return null;

        }

        return attributes.get(key);

    }

}