path: root/projects/net.wotonomy.foundation/src/main/java/net/wotonomy/foundation/NSKeyValueCoding.java

/*
Wotonomy: OpenStep design patterns for pure Java applications.
Copyright (C) 2001 Intersect Software Corporation

This library 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 2.1 of the License, or (at your option) any later version.

This library 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 this library; if not, see http://www.gnu.org
*/

package net.wotonomy.foundation;

import net.wotonomy.foundation.internal.Introspector;
import net.wotonomy.foundation.internal.IntrospectorException;
import net.wotonomy.foundation.internal.MissingPropertyException;
import net.wotonomy.foundation.internal.NullPrimitiveException;
import net.wotonomy.foundation.internal.WotonomyException;

/**
 * NSKeyValueCoding defines an interface for classes that need to have more
 * control over the wotonomy's property introspection facilities. <br>
 * <br>
 * 
 * On an object that implements this interface, wotonomy will call these
 * methods, and otherwise use the static methods on NSKeyValueCodingSupport.
 * <br>
 * <br>
 *
 * NSKeyValueCodingSupport implements the default behaviors for each of these
 * methods, so classes implementing this interface can call those methods to
 * acheive the same behavior. <br>
 * <br>
 *
 * valueForKey and takeValueForKey are called in response to user actions, like
 * viewing an object or updating its value in a user interface. These should
 * call the public getter and setter methods on the object itself and the
 * operations should be subject to validation. <br>
 * <br>
 * 
 * storedValueForKey and takeStoredValueForKey are called in response to
 * wotonomy actions, like snapshotting, faulting, commits, and reverts. These
 * operations should bypass the public methods and directly modify the internal
 * state of the object without validation.
 *
 * @author michael@mpowers.net
 * @author $Author: cgruber $
 * @version $Revision: 893 $
 */
public interface NSKeyValueCoding {

	public static final Null NullValue = new Null();

	/**
	 * Returns the value for the specified property. If the property does not exist,
	 * this method should call handleQueryWithUnboundKey.
	 */
	Object valueForKey(String aKey);

	/**
	 * Sets the property to the specified value. If the property does not exist,
	 * this method should call handleTakeValueForUnboundKey. If the property is of a
	 * type that cannot allow null (e.g. primitive types) and aValue is null, this
	 * method should call unableToSetNullForKey.
	 */
	void takeValueForKey(Object aValue, String aKey);

	/**
	 * Returns the value for the private field that corresponds to the specified
	 * property.
	 */
	Object storedValueForKey(String aKey);

	/**
	 * Sets the the private field that corresponds to the specified property to the
	 * specified value.
	 */
	void takeStoredValueForKey(Object aValue, String aKey);

	/**
	 * Called by valueForKey when the specified key is not found on this object.
	 * Implementing classes should handle the specified value or otherwise throw an
	 * exception.
	 */
	Object handleQueryWithUnboundKey(String aKey);

	/**
	 * Called by takeValueForKey when the specified key is not found on this object.
	 * Implementing classes should handle the specified value or otherwise throw an
	 * exception.
	 */
	void handleTakeValueForUnboundKey(Object aValue, String aKey);

	/**
	 * Called by takeValueForKey when the type of the specified key is not allowed
	 * to be null, as is the case with primitive types. Implementing classes should
	 * handle this case appropriately or otherwise throw an exception.
	 */
	void unableToSetNullForKey(String aKey);

	/**
	 * Static utility methods that call the appropriate method if the object
	 * implements NSKeyValueCoding, otherwise calls the method on
	 * DefaultImplementation.
	 */
	public class Utility {
		/**
		 * Calls the appropriate method if the object implements NSKeyValueCoding,
		 * otherwise calls the method on DefaultImplementation.
		 */
		static public Object valueForKey(Object anObject, String aKey) {
			if (anObject instanceof NSKeyValueCoding) {
				return ((NSKeyValueCoding) anObject).valueForKey(aKey);
			}
			return DefaultImplementation.valueForKey(anObject, aKey);
		}

		/**
		 * Calls the appropriate method if the object implements NSKeyValueCoding,
		 * otherwise calls the method on DefaultImplementation.
		 */
		static public void takeValueForKey(Object anObject, Object aValue, String aKey) {
			if (anObject instanceof NSKeyValueCoding) {
				((NSKeyValueCoding) anObject).takeValueForKey(aValue, aKey);
			}
			DefaultImplementation.takeValueForKey(anObject, aValue, aKey);
		}

		/**
		 * Calls the appropriate method if the object implements NSKeyValueCoding,
		 * otherwise calls the method on DefaultImplementation.
		 */
		static public Object storedValueForKey(Object anObject, String aKey) {
			if (anObject instanceof NSKeyValueCoding) {
				return ((NSKeyValueCoding) anObject).storedValueForKey(aKey);
			}
			return DefaultImplementation.storedValueForKey(anObject, aKey);
		}

		/**
		 * Calls the appropriate method if the object implements NSKeyValueCoding,
		 * otherwise calls the method on DefaultImplementation.
		 */
		static public void takeStoredValueForKey(Object anObject, Object aValue, String aKey) {
			if (anObject instanceof NSKeyValueCoding) {
				((NSKeyValueCoding) anObject).takeStoredValueForKey(aValue, aKey);
			}
			DefaultImplementation.takeStoredValueForKey(anObject, aValue, aKey);
		}

		/**
		 * Calls the appropriate method if the object implements NSKeyValueCoding,
		 * otherwise calls the method on DefaultImplementation.
		 */
		static public Object handleQueryWithUnboundKey(Object anObject, String aKey) {
			if (anObject instanceof NSKeyValueCoding) {
				return ((NSKeyValueCoding) anObject).handleQueryWithUnboundKey(aKey);
			}
			return DefaultImplementation.handleQueryWithUnboundKey(anObject, aKey);
		}

		/**
		 * Calls the appropriate method if the object implements NSKeyValueCoding,
		 * otherwise calls the method on DefaultImplementation.
		 */
		static public void handleTakeValueForUnboundKey(Object anObject, Object aValue, String aKey) {
			if (anObject instanceof NSKeyValueCoding) {
				((NSKeyValueCoding) anObject).handleTakeValueForUnboundKey(aValue, aKey);
			}
			DefaultImplementation.handleTakeValueForUnboundKey(anObject, aValue, aKey);
		}

		/**
		 * Calls the appropriate method if the object implements NSKeyValueCoding,
		 * otherwise calls the method on DefaultImplementation.
		 */
		static public void unableToSetNullForKey(Object anObject, String aKey) {
			if (anObject instanceof NSKeyValueCoding) {
				((NSKeyValueCoding) anObject).unableToSetNullForKey(aKey);
			}
			DefaultImplementation.unableToSetNullForKey(anObject, aKey);
		}
	}

	public class DefaultImplementation {
		/**
		 * Returns the value for the specified property key on the specified object.
		 * <br>
		 * <br>
		 *
		 * If the property does not exist, this method calls handleQueryWithUnboundKey
		 * on the object if it implements NSKeyValueCoding, otherwise calls
		 * handleQueryWithUnboundKey on this class. <br>
		 * <br>
		 */
		static public Object valueForKey(Object anObject, String aKey) {
			if (anObject == null)
				return null;
			// TODO: may need to handle "." nesting here so
			// that handleQueryWithUnboundKey gets called for
			// for the nested object, not the parent object

			// Correction: need to handle key paths in
			// KeyValueCodingAdditionsSupport.

			try {
				return Introspector.get(anObject, aKey);
			} catch (IntrospectorException exc) {
				if (anObject instanceof NSKeyValueCoding) {
					return ((NSKeyValueCoding) anObject).handleQueryWithUnboundKey(aKey);
				}
				return handleQueryWithUnboundKey(anObject, aKey);
			}
		}

		/**
		 * Sets the property to the specified value on the specified object.
		 *
		 * If the property does not exist, this method calls
		 * handleTakeValueForUnboundKey on the object if it implements NSKeyValueCoding,
		 * otherwise calls handleTakeValueForUnboundKey on this class.
		 * 
		 * If the property is of a type that cannot allow null (e.g. primitive types)
		 * and aValue is null, this method should call unableToSetNullForKey on the
		 * object if it implements NSKeyValueCoding, otherwise calls
		 * unableToSetNullForKey on this class.
		 */
		static public void takeValueForKey(Object anObject, Object aValue, String aKey) {
			if (anObject == null)
				return;
			// TODO: may need to handle "." nesting here so
			// that handleTakeValueForUnboundKey gets called for
			// for the nested object, not the parent object
			try {
				Introspector.set(anObject, aKey, aValue);
			} catch (NullPrimitiveException exc) {
				if (anObject instanceof NSKeyValueCoding) {
					((NSKeyValueCoding) anObject).unableToSetNullForKey(aKey);
				} else {
					unableToSetNullForKey(anObject, aKey);
				}
			} catch (MissingPropertyException exc) {
				if (anObject instanceof NSKeyValueCoding) {
					((NSKeyValueCoding) anObject).handleTakeValueForUnboundKey(aValue, aKey);
				} else {
					handleTakeValueForUnboundKey(anObject, aValue, aKey);
				}
			}

		}

		/**
		 * Returns the value for the private field that corresponds to the specified
		 * property on the specified object.
		 *
		 * This implementation currently calls valueForKey, because java security
		 * currently prevents us from accessing the fields of another object.
		 */
		static public Object storedValueForKey(Object anObject, String aKey) {
			// TODO: this currently just calls valueForKey
			return valueForKey(anObject, aKey);
		}

		/**
		 * Sets the the private field that corresponds to the specified property to the
		 * specified value on the specified object.
		 *
		 * This implementation currently calls takeValueForKey, because java security
		 * currently prevents us from accessing the fields of another object.
		 */
		static public void takeStoredValueForKey(Object anObject, Object aValue, String aKey) {
			// TODO: this currently just calls takeValueForKey
			takeValueForKey(anObject, aValue, aKey);
		}

		/**
		 * Called by valueForKey when the specified key is not found on the specified
		 * object, if that object does not implement NSKeyValueCoding.
		 *
		 * This implementation throws a WotonomyException.
		 */
		static public Object handleQueryWithUnboundKey(Object anObject, String aKey) {
			throw new WotonomyException("Key not found for object: " + aKey + " : " + anObject);
		}

		/**
		 * Called by takeValueForKey when the specified key is not found on the
		 * specified object, if that object does not implement NSKeyValueCoding.
		 *
		 * This implementation throws a WotonomyException.
		 */
		static public void handleTakeValueForUnboundKey(Object anObject, Object aValue, String aKey) {
			throw new WotonomyException(
					"Key not found for object while setting value: " + aKey + " : " + anObject + " : " + aValue);
		}

		/**
		 * Called by takeValueForKey when the type of the specified key is not allowed
		 * to be null, as is the case with primitive types, if the specified object does
		 * not implement NSKeyValueCoding.
		 *
		 * This implementation throws a WotonomyException.
		 */
		static public void unableToSetNullForKey(Object anObject, String aKey) {
			throw new WotonomyException("Tried to key on object to null: " + aKey + " : " + anObject);
		}
	}

	public class Null {
		public Null() {
			super();
		}

		public String toString() {
			return "<null>";
		}
	}
}

/*
 * $Log$ Revision 1.2 2006/02/16 13:15:00 cgruber Check in all sources in
 * eclipse-friendly maven-enabled packages.
 *
 * Revision 1.3 2003/08/07 02:43:56 chochos added NullValue, which points to a
 * Null instance.
 *
 * Revision 1.2 2003/01/18 23:30:42 mpowers WODisplayGroup now compiles.
 *
 * Revision 1.1 2003/01/17 14:40:49 mpowers Adding files to fix build.
 *
 * Revision 1.2 2001/03/28 16:12:30 mpowers Documented interface.
 *
 * Revision 1.1 2001/03/27 23:25:05 mpowers Contributing interface, no docs yet.
 *
 *
 */