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/*
 * See the NOTICE file distributed with this work for additional
 * information regarding copyright ownership.
 *
 * This 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 software 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 software; if not, write to the Free
 * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
 */
package org.xwiki.velocity.internal;

import java.io.Reader;
import java.io.StringReader;
import java.io.Writer;
import java.util.Deque;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;

import javax.inject.Inject;

import org.apache.commons.lang3.StringUtils;
import org.apache.commons.lang3.exception.ExceptionUtils;
import org.apache.commons.lang3.reflect.FieldUtils;
import org.apache.velocity.Template;
import org.apache.velocity.VelocityContext;
import org.apache.velocity.context.Context;
import org.apache.velocity.runtime.RuntimeInstance;
import org.apache.velocity.runtime.resource.Resource;
import org.slf4j.Logger;
import org.xwiki.component.annotation.Component;
import org.xwiki.component.annotation.InstantiationStrategy;
import org.xwiki.component.descriptor.ComponentInstantiationStrategy;
import org.xwiki.context.Execution;
import org.xwiki.context.ExecutionContext;
import org.xwiki.velocity.VelocityContextFactory;
import org.xwiki.velocity.VelocityEngine;
import org.xwiki.velocity.VelocityTemplate;
import org.xwiki.velocity.XWikiVelocityException;

/**
 * Default implementation of the Velocity service which initializes the Velocity system using configuration values
 * defined in the component's configuration. Note that the {@link #initialize} method has to be executed before any
 * other method can be called.
 *
 * @version $Id: dd57bc9138c47849ba7cf0a22e7b7620af953183 $
 * @since 15.9RC1
 */
@Component(roles = InternalVelocityEngine.class)
@InstantiationStrategy(ComponentInstantiationStrategy.PER_LOOKUP)
public class InternalVelocityEngine implements VelocityEngine
{
    private static final String ECONTEXT_TEMPLATES = "velocity.templates";

    private class TemplateEntry
    {
        private Template template;

        private String namespace;

        private int counter;

        /**
         * @param namespace the namespace
         */
        TemplateEntry(String namespace)
        {
            this.namespace = namespace;
            this.template = new Template();
            this.template.setName(namespace);
            this.template.setRuntimeServices(runtimeInstance);

            this.counter = 1;

            if (globalEntry != null) {
                // Inject global macros
                this.template.getMacros().putAll(globalEntry.getTemplate().getMacros());
            }
        }

        Template getTemplate()
        {
            return this.template;
        }

        String getNamespace()
        {
            return this.namespace;
        }

        int getCounter()
        {
            return this.counter;
        }

        int incrementCounter()
        {
            ++this.counter;

            return this.counter;
        }

        int decrementCounter()
        {
            --this.counter;

            return this.counter;
        }
    }

    /**
     * Used to create a new context whenever one isn't already provided to the
     * {@link #evaluate(Context, Writer, String, Reader)} method.
     */
    @Inject
    private VelocityContextFactory velocityContextFactory;

    @Inject
    private Execution execution;

    /**
     * The logger to use for logging.
     */
    @Inject
    private Logger logger;

    /**
     * The actual Velocity runtime.
     */
    private RuntimeInstance runtimeInstance;

    private TemplateEntry globalEntry;

    /**
     * @param runtimeInstance the actual Velocity runtime
     */
    public void initialize(RuntimeInstance runtimeInstance)
    {
        this.runtimeInstance = runtimeInstance;

        this.globalEntry = new TemplateEntry("");
    }

    @Override
    public void addGlobalMacros(Map macros)
    {
        this.globalEntry.getTemplate().getMacros().putAll(macros);
    }

    @Override
    public boolean evaluate(Context context, Writer out, String namespace, String source) throws XWikiVelocityException
    {
        return evaluate(context, out, namespace, new StringReader(source));
    }

    @Override
    public boolean evaluate(Context context, Writer out, String namespace, Reader source) throws XWikiVelocityException
    {
        // Create the template
        VelocityTemplate template = DefaultVelocityManager.compile(namespace != null ? namespace : "unknown template",
            source, this.runtimeInstance);

        evaluate(context, out, namespace, template);

        return true;
    }

    private TemplateEntry pushNamespace(String namespace)
    {
        TemplateEntry templateEntry;
        if (StringUtils.isNotEmpty(namespace)) {
            templateEntry = startedUsingMacroNamespaceInternal(namespace);
        } else {
            templateEntry = this.globalEntry;
        }

        return templateEntry;
    }

    private void popNamespace(String namespace)
    {
        if (StringUtils.isNotEmpty(namespace)) {
            stoppedUsingMacroNamespace(namespace);
        }
    }

    @Override
    public void evaluate(Context context, Writer out, String namespace, VelocityTemplate template)
        throws XWikiVelocityException
    {
        // Save some contextual metadata that needs to be restored
        Resource currentResource = null;
        List