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Apache Commons BeanUtils provides an easy-to-use but flexible wrapper around reflection and introspection.
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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.beanutils2;

import java.util.Arrays;
import java.util.Objects;

/**
 * 
 * DynaClass which implements the {@code MutableDynaClass} interface.
 * 
 *
 * 
 * A {@code MutableDynaClass is a specialized extension to DynaClass}
 *    that allows properties to be added or removed dynamically.

 *
 * This implementation has one slightly unusual default behavior - calling
 *    the {@code getDynaProperty(name)} method for a property which doesn't
 *    exist returns a {@code DynaProperty rather than null}. The reason for this is that {@code BeanUtils} calls this method to check if a property
 * exists before trying to set the value. This would defeat the object of the {@code LazyDynaBean} which automatically adds missing properties when any of its
 * {@code set()} methods are called. For this reason the {@code isDynaProperty(name)} method has been added to this implementation in order to determine if a
 * property actually exists. If the more normal behavior of returning {@code null} is required, then this can be achieved by calling the
 * {@code setReturnNull(true)}.
 * 

 *
 * 
 * The {@code add(name, type, readable, writable)} method is not implemented and always throws an {@code UnsupportedOperationException}. I believe this
 * attributes need to be added to the {@code DynaProperty} class in order to control read/write facilities.
 * 
 *
 * @see LazyDynaBean
 */
public class LazyDynaClass extends BasicDynaClass implements MutableDynaClass {

    private static final long serialVersionUID = 1L;

    /**
     * Controls whether changes to this DynaClass's properties are allowed.
     */
    protected boolean restricted;

    /**
     * 
     * Controls whether the {@code getDynaProperty()} method returns null if a property doesn't exist - or creates a new one.
     * 
     *
     * 
     * Default is {@code false}.
     */
    protected boolean returnNull;

    /**
     * Constructs a new LazyDynaClass with default parameters.
     */
    public LazyDynaClass() {
        this(null, (DynaProperty[]) null);
    }

    /**
     * Constructs a new LazyDynaClass with the specified name.
     *
     * @param name Name of this DynaBean class
     */
    public LazyDynaClass(final String name) {
        this(name, (DynaProperty[]) null);
    }

    /**
     * Constructs a new LazyDynaClass with the specified name and DynaBean class.
     *
     * @param name          Name of this DynaBean class
     * @param dynaBeanClass The implementation class for new instances
     */
    public LazyDynaClass(final String name, final Class dynaBeanClass) {
        this(name, dynaBeanClass, null);
    }

    /**
     * Constructs a new LazyDynaClass with the specified name, DynaBean class and properties.
     *
     * @param name          Name of this DynaBean class
     * @param dynaBeanClass The implementation class for new instances
     * @param properties    Property descriptors for the supported properties
     */
    public LazyDynaClass(final String name, final Class dynaBeanClass, final DynaProperty[] properties) {
        super(name, dynaBeanClass, properties);
    }

    /**
     * Constructs a new LazyDynaClass with the specified name and properties.
     *
     * @param name       Name of this DynaBean class
     * @param properties Property descriptors for the supported properties
     */
    public LazyDynaClass(final String name, final DynaProperty[] properties) {
        this(name, LazyDynaBean.class, properties);
    }

    /**
     * Add a new dynamic property.
     *
     * @param property Property the new dynamic property to add.
     * @throws IllegalArgumentException if name is null
     * @throws IllegalStateException    if this DynaClass is currently restricted, so no new properties can be added
     */
    protected void add(final DynaProperty property) {
        Objects.requireNonNull(property, "property");
        Objects.requireNonNull(property.getName(), "property.getName()");
        if (isRestricted()) {
            throw new IllegalStateException("DynaClass is currently restricted. No new properties can be added.");
        }
        // Check if property already exists
        if (propertiesMap.get(property.getName()) != null) {
            return;
        }
        // Create a new property array with the specified property
        final DynaProperty[] oldProperties = getDynaProperties();
        final DynaProperty[] newProperties = Arrays.copyOf(oldProperties, oldProperties.length + 1);
        newProperties[oldProperties.length] = property;
        // Update the properties
        setProperties(newProperties);
    }

    /**
     * Add a new dynamic property with no restrictions on data type, readability, or writeability.
     *
     * @param name Name of the new dynamic property
     * @throws IllegalArgumentException if name is null
     * @throws IllegalStateException    if this DynaClass is currently restricted, so no new properties can be added
     */
    @Override
    public void add(final String name) {
        add(new DynaProperty(name));
    }

    /**
     * Add a new dynamic property with the specified data type, but with no restrictions on readability or writeability.
     *
     * @param name Name of the new dynamic property
     * @param type Data type of the new dynamic property (null for no restrictions)
     * @throws IllegalArgumentException if name is null
     * @throws IllegalStateException    if this DynaClass is currently restricted, so no new properties can be added
     */
    @Override
    public void add(final String name, final Class type) {
        if (type == null) {
            add(name);
        } else {
            add(new DynaProperty(name, type));
        }
    }

    /**
     * 

     * Add a new dynamic property with the specified data type, readability, and writeability.
     * 
     *
     * 
     * N.B.Support for readable/writable properties has not been implemented and this method always throws a
     * {@code UnsupportedOperationException}.
     * 
     *
     * 
     * I'm not sure the intention of the original authors for this method, but it seems to me that readable/writable should be attributes of the
     * {@code DynaProperty} class (which they are not) and is the reason this method has not been implemented.
     * 
     *
     * @param name     Name of the new dynamic property
     * @param type     Data type of the new dynamic property (null for no restrictions)
     * @param readable Set to {@code true} if this property value should be readable
     * @param writable Set to {@code true} if this property value should be writable
     * @throws UnsupportedOperationException anytime this method is called
     */
    @Override
    public void add(final String name, final Class type, final boolean readable, final boolean writable) {
        throw new java.lang.UnsupportedOperationException("readable/writable properties not supported");
    }

    /**
     * 
     * Return a property descriptor for the specified property.
     * 
     *
     * 
     * If the property is not found and the {@code returnNull} indicator is {@code true, this method always returns null}.
     * 

     *
     * 
     * If the property is not found and the {@code returnNull} indicator is {@code false} a new property descriptor is created and returned (although its not
     * actually added to the DynaClass's properties). This is the default behavior.
     * 
     *
     * 
     * The reason for not returning a {@code null} property descriptor is that {@code BeanUtils} uses this method to check if a property exists before trying to
     * set it - since these Lazy implementations automatically add any new properties when they are set, returning {@code null} from this method would
     * defeat their purpose.
     * 
     *
     * @param name Name of the dynamic property for which a descriptor is requested
     * @return The dyna property for the specified name
     * @throws IllegalArgumentException if no property name is specified
     */
    @Override
    public DynaProperty getDynaProperty(final String name) {
        Objects.requireNonNull(name, "name");
        DynaProperty dynaProperty = propertiesMap.get(name);
        // If it doesn't exist and returnNull is false
        // create a new DynaProperty
        if (dynaProperty == null && !isReturnNull() && !isRestricted()) {
            dynaProperty = new DynaProperty(name);
        }
        return dynaProperty;
    }

    /**
     * 
     * Indicate whether a property actually exists.
     * 
     *
     * 
     * N.B. Using {@code getDynaProperty(name) == null} doesn't work in this implementation because that method might return a DynaProperty if
     * it doesn't exist (depending on the {@code returnNull} indicator).
     * 
     *
     * @param name The name of the property to check
     * @return {@code true} if there is a property of the specified name, otherwise {@code false}
     * @throws IllegalArgumentException if no property name is specified
     */
    public boolean isDynaProperty(final String name) {
        return propertiesMap.get(Objects.requireNonNull(name, "name")) != null;
    }

    /**
     * 
     * Is this DynaClass currently restricted.
     * 
     * 
     * If restricted, no changes to the existing registration of property names, data types, readability, or writeability are allowed.
     * 
     *
     * @return {@code true} if this {@link MutableDynaClass} cannot be changed otherwise {@code false}
     */
    @Override
    public boolean isRestricted() {
        return restricted;
    }

    /**
     * Should this DynaClass return a {@code null} from the {@code getDynaProperty(name)} method if the property doesn't exist.
     *
     * @return {@code true if a null} {@link DynaProperty} should be returned if the property doesn't exist, otherwise {@code false} if a new
     *         {@link DynaProperty} should be created.
     */
    public boolean isReturnNull() {
        return returnNull;
    }

    /**
     * Remove the specified dynamic property, and any associated data type, readability, and writeability, from this dynamic class. NOTE - This
     * does NOT cause any corresponding property values to be removed from DynaBean instances associated with this DynaClass.
     *
     * @param name Name of the dynamic property to remove
     * @throws IllegalArgumentException if name is null
     * @throws IllegalStateException    if this DynaClass is currently restricted, so no properties can be removed
     */
    @Override
    public void remove(final String name) {
        Objects.requireNonNull(name, "name");
        if (isRestricted()) {
            throw new IllegalStateException("DynaClass is currently restricted. No properties can be removed.");
        }

        // Ignore if property doesn't exist
        if (propertiesMap.get(name) == null) {
            return;
        }

        // Create a new property array of without the specified property
        final DynaProperty[] oldProperties = getDynaProperties();
        final DynaProperty[] newProperties = new DynaProperty[oldProperties.length - 1];
        int j = 0;
        for (final DynaProperty oldProperty : oldProperties) {
            if (!name.equals(oldProperty.getName())) {
                newProperties[j] = oldProperty;
                j++;
            }
        }

        // Update the properties
        setProperties(newProperties);
    }

    /**
     * 
     * Set whether this DynaClass is currently restricted.
     * 
     * 
     * If restricted, no changes to the existing registration of property names, data types, readability, or writeability are allowed.
     * 
     *
     * @param restricted {@code true} if this {@link MutableDynaClass} cannot be changed otherwise {@code false}
     */
    @Override
    public void setRestricted(final boolean restricted) {
        this.restricted = restricted;
    }

    /**
     * Sets whether this DynaClass should return a {@code null} from the {@code getDynaProperty(name)} method if the property doesn't exist.
     *
     * @param returnNull {@code true if a null} {@link DynaProperty} should be returned if the property doesn't exist, otherwise {@code false} if a
     *                   new {@link DynaProperty} should be created.
     */
    public void setReturnNull(final boolean returnNull) {
        this.returnNull = returnNull;
    }

}