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Contains the entire NEBA core implementation, i.e. the framework that interprets the NEBA API annotations and provides implementations for the service and lifecycle callback interfaces provided in the NEBA API. This package must not export anything as its implementation details are entirely private.
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/**
 * Copyright 2013 the original author or authors.
 * 
 * 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 io.neba.core.rendering;

import io.neba.api.Constants;
import io.neba.api.rendering.BeanRenderer;
import io.neba.core.util.FastStringWriter;
import org.apache.sling.scripting.api.BindingsValuesProvider;
import org.apache.velocity.VelocityContext;
import org.apache.velocity.app.VelocityEngine;

import java.io.Writer;
import java.util.List;
import java.util.Map;

import static io.neba.core.util.ClassHierarchyIterator.hierarchyOf;
import static org.apache.commons.lang.StringUtils.endsWith;
import static org.apache.commons.lang.StringUtils.isBlank;
import static org.springframework.util.Assert.notNull;

/**
 * Renders an object using the provided view repository path, the object's
 * {@link io.neba.core.util.ClassHierarchyIterator class hierarchy} and a provided viewHint to
 * build possible template names for the object. Supports adding additional elements to the 
 * rendering context.
 * 
 * 
 * Example: For a class io.neba.MyModel implementing the interface
 * io.neba.MyInterface, the renderer will attempt to resolve the following
 * templates (in this particular order according to the
 * {@link io.neba.core.util.ClassHierarchyIterator}), if the repositoryPath is "/apps/views/" and
 * the view hint is null:
 * 
 * 
 * 
 * /apps/views/io/neba/MyModel.vlt
 * /apps/views/io/neba/MyInterface.vlt
 * /java/lang/Object.vlt
 * 
 * 
 * 
 * The first view found is used to render the object.
 * 
 * 
 * 
 * Likewise, when rendering with a viewhint, e.g. "teaser", the following views
 * would be resolved:
 * 
 * 
 * 
 * /apps/views/io/neba/MyModel-teaser.vlt
 * /apps/views/io/neba/MyInterface-teaser.vlt
 * /java/lang/Object-teaser.vlt
 * 
 * 
 * TODO: Performance optimization: Caching of failed lookups and hierarchy iteration.
 * 
 * @author Olaf Otto
 */
public class BeanRendererImpl implements BeanRenderer {
    private final String repositoryPath;
    private final VelocityEngine engine;
    private final List bindingsValuesProviders;

    public BeanRendererImpl(String repositoryPath, VelocityEngine engine, List bindingsValuesProviders) {
        notNull(repositoryPath, "The view repository root path must not be null.");
        notNull(engine, "The velocity engine must not be null.");

        this.repositoryPath = normalize(repositoryPath);
        this.engine = engine;
        this.bindingsValuesProviders = bindingsValuesProviders;
    }

    private String normalize(String repositoryPath) {
        if (!endsWith(repositoryPath, "/")) {
            return repositoryPath + "/";
        }
        return repositoryPath;
    }

    @Override
    public String render(Object bean, String viewHint, Map additionalContextElements) {
        notNull(bean, "Method argument bean must not be null.");
        String renderedObject = null;
        for (Class type : hierarchyOf(bean.getClass())) {
            String templatePath = createTemplateName(viewHint, type);
            if (this.engine.resourceExists(templatePath)) {
                renderedObject = renderInternal(bean, templatePath, additionalContextElements);
                break;
            }
        }
        return renderedObject;
    }

    public String renderInternal(Object object, String templatePath, Map additionalContextElements) {
        final Writer writer = new FastStringWriter();
        final VelocityBindings bindings = prepareBindings(object);
        merge(additionalContextElements, bindings);
        final VelocityContext context = new VelocityContext(bindings);

        String renderedObject;
        try {
            this.engine.getTemplate(templatePath).merge(context, writer);
        } catch (Exception e) {
            throw new RuntimeException("Unable to render " + object + " with template " + templatePath + ".", e);
        }
        renderedObject = writer.toString();

        return renderedObject;
    }

    private VelocityBindings prepareBindings(Object model) {
        VelocityBindings bindings = new VelocityBindings();
        for (BindingsValuesProvider provider : this.bindingsValuesProviders) {
            provider.addBindings(bindings);
        }
        bindings.put(Constants.RENDERER, this);
        bindings.put(Constants.MODEL, model);
        return bindings;
    }

    public String createTemplateName(String viewHint, Class type) {
        StringBuilder templatePathBuilder = new StringBuilder(128);
        templatePathBuilder.append(this.repositoryPath).append(type.getName().replace('.', '/'));
        if (!isBlank(viewHint)) {
            templatePathBuilder.append('-').append(viewHint);
        }
        templatePathBuilder.append(".vlt");
        return templatePathBuilder.toString();
    }

    private void merge(Map context, final VelocityBindings bindings) {
        if (context != null) {
            for (Map.Entry entry : context.entrySet()) {
                final String key = entry.getKey();
                if (bindings.containsKey(key)) {
                    throw new IllegalArgumentException("The bindings already contain the key '" + key + "' (a " + bindings.get(key) + ").");
                } else {
                    bindings.put(key, entry.getValue());
                }
            }
        }
    }

    @Override
    public String render(Object bean) {
        return render(bean, null, null);
    }

    @Override
    public String render(Object bean, Map context) {
        return render(bean, null, context);
    }

    @Override
    public String render(Object bean, String viewHint) {
        return render(bean, viewHint, null);
    }
}