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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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/*
 * 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
 *
 *   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 org.python.core.PyException;
import org.python.core.PyObject;

import freemarker.ext.util.ModelFactory;
import freemarker.template.ObjectWrapper;
import freemarker.template.TemplateCollectionModel;
import freemarker.template.TemplateHashModelEx;
import freemarker.template.TemplateModel;
import freemarker.template.TemplateModelException;

/**
 * Model for Jython dictionaries ({@link org.python.core.PyDictionary}
 * and {@link org.python.core.PyStringMap}).
 * Note that the basic {@link JythonModel} already provides access to the
 * {@link PyObject#__finditem__(String)} method. This class only adds 
 * {@link TemplateHashModelEx} functionality in a somewhat skewed way. One
 * could say it even violates TemplateHashModelEx semantics, as both the
 * returned keys and values are only those from the item mapping, while the
 * get() method works for attributes as well. However, in practice
 * when you ask for dict?keys inside a template, you'll really
 * want to retrieve only items, not attributes so this is considered OK.
 */
public class JythonHashModel
extends 
    JythonModel 
implements 
    TemplateHashModelEx {
    private static final String KEYS = "keys";
    private static final String KEYSET = "keySet";
    private static final String VALUES = "values";
    
    static final ModelFactory FACTORY =
        new ModelFactory()
        {
            @Override
            public TemplateModel create(Object object, ObjectWrapper wrapper) {
                return new JythonHashModel((PyObject) object, (JythonWrapper) wrapper);
            }
        };
        
    public JythonHashModel(PyObject object, JythonWrapper wrapper) {
        super(object, wrapper);
    }
    
    /**
     * Returns {@link PyObject#__len__()}.
     */
    @Override
    public int size() throws TemplateModelException {
        try {
            return object.__len__();
        } catch (PyException e) {
            throw new TemplateModelException(e);
        }
    }

    /**
     * Returns either object.__findattr__("keys").__call__()
     * or object.__findattr__("keySet").__call__().
     */
    @Override
    public TemplateCollectionModel keys() throws TemplateModelException {
        try {
            PyObject method = object.__findattr__(KEYS);
            if (method == null) {
                method = object.__findattr__(KEYSET);
            }
            if (method != null) {
                return (TemplateCollectionModel) wrapper.wrap(method.__call__());
            }
        } catch (PyException e) {
            throw new TemplateModelException(e);
        }
        throw new TemplateModelException(
                "'?keys' is not supported as there is no 'keys' nor 'keySet' attribute on an instance of "
                + JythonVersionAdapterHolder.INSTANCE.getPythonClassName(object));
    }

    /**
     * Returns object.__findattr__("values").__call__().
     */
    @Override
    public TemplateCollectionModel values() throws TemplateModelException {
        try {
            PyObject method = object.__findattr__(VALUES);
            if (method != null) {
                return (TemplateCollectionModel) wrapper.wrap(method.__call__());
            }
        } catch (PyException e) {
            throw new TemplateModelException(e);
        }
        throw new TemplateModelException(
                "'?values' is not supported as there is no 'values' attribute on an instance of "
                + JythonVersionAdapterHolder.INSTANCE.getPythonClassName(object));
    }
}