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Google App Engine compliant variation of FreeMarker. FreeMarker is a "template engine"; a generic tool to generate text output based on templates.
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/*
 * Copyright 2014 Attila Szegedi, Daniel Dekany, Jonathan Revusky
 * 
 * Licensed 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
 * 
 * http://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 freemarker.ext.jython;

import java.util.Iterator;
import java.util.List;

import org.python.core.Py;
import org.python.core.PyException;
import org.python.core.PyObject;

import freemarker.ext.util.ModelFactory;
import freemarker.ext.util.WrapperTemplateModel;
import freemarker.template.AdapterTemplateModel;
import freemarker.template.ObjectWrapper;
import freemarker.template.TemplateBooleanModel;
import freemarker.template.TemplateHashModel;
import freemarker.template.TemplateMethodModelEx;
import freemarker.template.TemplateModel;
import freemarker.template.TemplateModelException;
import freemarker.template.TemplateScalarModel;

/**
 * Generic model for arbitrary Jython objects.
 */
public class JythonModel
implements TemplateBooleanModel, TemplateScalarModel, TemplateHashModel, 
TemplateMethodModelEx, AdapterTemplateModel, WrapperTemplateModel
{
    protected final PyObject object;
    protected final JythonWrapper wrapper;
    
    static final ModelFactory FACTORY =
        new ModelFactory()
        {
            public TemplateModel create(Object object, ObjectWrapper wrapper)
            {
                return new JythonModel((PyObject)object, (JythonWrapper)wrapper);
            }
        };
        
    public JythonModel(PyObject object, JythonWrapper wrapper)
    {
        this.object = object;
        this.wrapper = wrapper;
    }

    /**
     * Returns the value of {@link PyObject#__nonzero__()}.
     */
    public boolean getAsBoolean() throws TemplateModelException
    {
        try
        {
            return object.__nonzero__();
        }
        catch(PyException e)
        {
            throw new TemplateModelException(e);
        }
    }

    /**
     * Returns the value of {@link Object#toString()}.
     */
    public String getAsString() throws TemplateModelException
    {
        try
        {
            return object.toString();
        }
        catch(PyException e)
        {
            throw new TemplateModelException(e);
        }
    }

    /**
     * Calls {@link PyObject#__findattr__(java.lang.String)}, then if it
     * returns null calls {@link PyObject#__finditem__(java.lang.String)}.
     * If {@link JythonWrapper#setAttributesShadowItems(boolean)} was called
     * with false, the order of calls is reversed (that is, item
     * lookup takes precedence over attribute lookup).
     */
    public TemplateModel get(String key)
    throws
        TemplateModelException
    {
        if(key != null)
        {
            key = key.intern();
        }
        
        PyObject obj = null;
        
        try
        {
            if(wrapper.isAttributesShadowItems())
            {
                obj = object.__findattr__(key);
                if(obj == null)
                {
                    obj = object.__finditem__(key);
                }
            }
            else
            {
                obj = object.__finditem__(key);
                if(obj == null)
                {
                    obj = object.__findattr__(key);
                }
            }
        }
        catch(PyException e)
        {
            throw new TemplateModelException(e);
        }

        return wrapper.wrap(obj);
    }
    
    /**
     * Returns {@link PyObject#__len__()} == 0.
     */
    public boolean isEmpty() throws TemplateModelException
    {
        try
        {
            return object.__len__() == 0;
        }
        catch(PyException e)
        {
            throw new TemplateModelException(e);
        }
    }

    /**
     * @see freemarker.template.TemplateMethodModel#exec(List)
     */
    public Object exec(List arguments) throws TemplateModelException
    {
        int size = arguments.size();
        try
        {
            switch(size)
            {
                case 0:
                {
                    return wrapper.wrap(object.__call__());
                }
                case 1:
                {
                    return wrapper.wrap(object.__call__(wrapper.unwrap(
                        (TemplateModel)arguments.get(0))));
                }
                default:
                {
                    PyObject[] pyargs = new PyObject[size];
                    int i = 0;
                    for (Iterator arg = arguments.iterator(); arg.hasNext();)
                    {
                        pyargs[i++] = wrapper.unwrap(
                            (TemplateModel) arg.next());
                    }
                    return wrapper.wrap(object.__call__(pyargs));
                }
            }
        }
        catch(PyException e)
        {
            throw new TemplateModelException(e);
        }
    }

    public Object getAdaptedObject(Class hint) {
        if(object == null) {
            return null;
        }
        Object view = object.__tojava__(hint);
        if(view == Py.NoConversion) {
            view = object.__tojava__(Object.class);
        }
        return view;
    }
    
    public Object getWrappedObject() {
        return object == null ? null : object.__tojava__(Object.class);
    }
}