source: trunk/src/ws/fugue88/jpath/Context.java

/*
 * Created on Apr 23, 2005
 *
 * $Log$
 * Revision 1.4  2005/09/21 22:00:45  dsowen
 * Split out the access stuff into accesslib.
 * New Creator interface off-loads object creation to user.
 *
 * Revision 1.3  2005/08/19 17:51:17  dsowen
 * Fixed: NPEs when using accessors from paths, &c.  Included tests.
 * Fixed: parsing exception wasn't very enlightening.
 *
 * Revision 1.2  2005/08/12 19:01:46  dsowen
 * Feature: can automatically fill missing parts of a graph.
 *
 * Revision 1.1  2005/08/03 00:35:29  dsowen
 * Initial commit.
 *
 * Revision 1.2  2005/04/25 02:45:56  dowen
 * Added type reporting to support creation.
 *
 * Revision 1.1  2005/04/25 01:39:53  dowen
 * Preliminary path support.
 *
 */
package ws.fugue88.jpath;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

import ws.fugue88.access.Accessor;
import ws.fugue88.access.ListAccessor;
import ws.fugue88.access.MapAccessor;

/**
 * @author dsowen
 */
public class Context {

        public Accessor getTargetAccessor(final Path path)
                        throws BrokenGraphException, IllegalAccessException,
                        InstantiationException, InvocationTargetException,
                        NoSuchPropertyException
        {
                Context current = this;
                for(Iterator i = path.parents().iterator(); i.hasNext();) {
                        final PathPart part = (PathPart)i.next();
                        Accessor accessor = current.getTargetAccessor(part);
                        Object obj = accessor.getValue();
                        if(obj == null)
                                        obj = _creator.create(accessor.getType(), current._root,
                                                        part);
                        if(obj == null)
                                        throw new BrokenGraphException(this, path, current._root,
                                                        part);

                        accessor.setValue(obj);
                        current = new Context(obj, _binder, _creator);
                }
                return current.getTargetAccessor(path.terminal());
        }

        public Object getTarget(final Path path) throws IllegalAccessException,
                        InstantiationException, InvocationTargetException,
                        NoSuchPropertyException
        {
                try {
                        return getTargetAccessor(path).getValue();
                } catch(BrokenGraphException e) {
                        return null;
                }
        }

        public Context navigate(final Path path) throws IllegalAccessException,
                        InstantiationException, InvocationTargetException,
                        NoSuchPropertyException
        {
                Object child = getTarget(path);
                return new Context(child, _binder, _creator);
        }

        public Object getRoot()
        {
                return _root;
        }

        Context(final Object root, final Binder binder, final GraphCreator creator)
        {
                // NPEs
                root.getClass();
                binder.getClass();
                creator.getClass();

                _root = root;
                _binder = binder;
                _creator = creator;
        }

        private Accessor getTargetAccessor(final PathPart part)
                        throws NoSuchPropertyException
        {
                if(part instanceof Identifier)
                                return getTargetAccessor((Identifier)part);
                return getTargetAccessor((Selector)part);
        }

        private Accessor getTargetAccessor(final Identifier ident)
                        throws NoSuchPropertyException
        {
                return new PropertyAccessor(_root, _binder.getProperty(
                                _root.getClass(), ident));
        }

        private Accessor getTargetAccessor(final Selector sel)
        {
                if(_root instanceof Map)
                                return new MapAccessor((Map)_root, sel.getKey());
                return new ListAccessor((List)_root, ((NumberSelector)sel).getIndex());
        }

        private Object createBlank(final Class type) throws IllegalAccessException,
                        InstantiationException, InvocationTargetException
        {
                try {
                        final Constructor ctor = type.getDeclaredConstructor(null);
                        ctor.setAccessible(true);
                        return ctor.newInstance(null);
                } catch(NoSuchMethodException e) {
                        throw new InstantiationException("Class " + type.getName()
                                        + " must have a no-argument constructor.");
                }
        }

        private final Object _root;
        private final Binder _binder;
        private final GraphCreator _creator;
}