/*
 * Copyright 2002-2004 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 org.springframework.ui.freemarker;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.util.Map;
import java.util.Properties;

import freemarker.template.Configuration;
import freemarker.template.SimpleHash;
import freemarker.template.TemplateException;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.core.io.DefaultResourceLoader;
import org.springframework.core.io.Resource;
import org.springframework.core.io.ResourceLoader;

/**
 * Factory that configures a FreeMarker Configuration. Can be used standalone, but
 * typically you will either use FreeMarkerConfigurationFactoryBean for preparing a
 * Configuration as bean reference, or FreeMarkerConfigurer for web views.
 *
 * <p>The optional "configLocation" property sets the location of a FreeMarker
 * properties file, within the current application. FreeMarker properties can be
 * overridden via "freemarkerSettings". All of these properties will be set by
 * calling FreeMarker's <code>Configuration.setSettings()</code> method and are
 * subject to constraints set by FreeMarker.
 *
 * <p>The "freemarkerVariables" property can be used to specify a Map of
 * shared variables that will be applied to the Configuration via the
 * <code>setAllSharedVariables()</code> method. Like <code>setSettings()</code>,
 * these entries are subject to FreeMarker constraints.
 *
 * <p>The simplest way to use this class is to specify a "templateLoaderPath";
 * FreeMarker does not need any further configuration then.
 *
 * <p>Note: Spring's FreeMarker support requires FreeMarker 2.3 or higher.
 *
 * @author Darren Davison
 * @author Juergen Hoeller
 * @since 3/3/2004
 * @see #setConfigLocation
 * @see #setFreemarkerSettings
 * @see #setFreemarkerVariables
 * @see #setTemplateLoaderPath
 * @see #createConfiguration
 */
public class FreeMarkerConfigurationFactory {

	protected final Log logger = LogFactory.getLog(getClass());

	private Resource configLocation;

	private Properties freemarkerSettings;

	private Map freemarkerVariables;

	private String templateLoaderPath;

	private ResourceLoader resourceLoader = new DefaultResourceLoader();

	private boolean preferFileSystemAccess = true;


	/**
	 * Set the location of the FreeMarker config file.
	 * Alternatively, you can specify all setting locally.
	 * @see #setFreemarkerSettings
	 * @see #setTemplateLoaderPath
	 */
	public void setConfigLocation(Resource resource) {
		configLocation = resource;
	}

	/**
	 * Set properties that contain well-known FreeMarker keys which will be
	 * passed to FreeMarker's <code>Configuration.setSettings</code> method.
	 * @see freemarker.template.Configuration#setSettings
	 */
	public void setFreemarkerSettings(Properties settings) {
		this.freemarkerSettings = settings;
	}

	/**
	 * Set a Map that contains well-known FreeMarker objects which will be passed
	 * to FreeMarker's <code>Configuration.setAllSharedVariables()</code> method.
	 * @see freemarker.template.Configuration#setAllSharedVariables
	 */
	public void setFreemarkerVariables(Map variables) {
		this.freemarkerVariables = variables;
	}

	/**
	 * Set the Freemarker template loader path via a Spring resource location.
	 * <p>When populated via a String, standard URLs like "file:" and "classpath:"
	 * pseudo URLs are supported, as understood by ResourceEditor. Allows for
	 * relative paths when running in an ApplicationContext.
	 * <p>Will define a path for the default FreeMarker template loader.
	 * If the specified resource cannot be resolved to a java.io.File, a generic
	 * SpringTemplateLoader will be used, without modification detection.
	 * <p>To enforce the use of SpringTemplateLoader, i.e. to not resolve a path
	 * as file system resource in any case, turn off the "preferFileSystemAccess"
	 * flag. See the latter's javadoc for details.
	 * @see org.springframework.core.io.ResourceEditor
	 * @see org.springframework.context.ApplicationContext#getResource
	 * @see freemarker.template.Configuration#setDirectoryForTemplateLoading
	 * @see SpringTemplateLoader
	 */
	public void setTemplateLoaderPath(String templateLoaderPath) {
		this.templateLoaderPath = templateLoaderPath;
	}
    
	/**
	 * Set the Spring ResourceLoader to use for loading FreeMarker template files.
	 * The default is DefaultResourceLoader. Will get overridden by the
	 * ApplicationContext if running in a context.
	 * @see org.springframework.core.io.DefaultResourceLoader
	 */
	public void setResourceLoader(ResourceLoader resourceLoader) {
		this.resourceLoader = resourceLoader;
	}

	/**
	 * Set whether to prefer file system access for template loading.
	 * File system access enables hot detection of template changes.
	 * <p>If this is enabled, FreeMarkerConfigurationFactory will try to resolve
	 * the specified "templateLoaderPath" as file system resource (which will work
	 * for expanded class path resources and ServletContext resources too).
	 * <p>Default is true. Turn this off to always load via SpringTemplateLoader
	 * (i.e. as stream, without hot detection of template changes), which might
	 * be necessary if some of your templates reside in an expanded classes
	 * directory while others reside in jar files.
	 * @see #setTemplateLoaderPath
	 */
	public void setPreferFileSystemAccess(boolean preferFileSystemAccess) {
		this.preferFileSystemAccess = preferFileSystemAccess;
	}


	/**
	 * Prepare the FreeMarker Configuration and return it.
	 * @return the FreeMarker Configuration object
	 * @throws IOException if the config file wasn't found
	 * @throws TemplateException on FreeMarker initialization failure
	 */
	public Configuration createConfiguration() throws IOException, TemplateException {
		Configuration config = newConfiguration();
		Properties props = new Properties();

		// Load config file if set.
		if (this.configLocation != null) {
			if (logger.isInfoEnabled()) {
				logger.info("Loading FreeMarker config from [" + this.configLocation + "]");
			}
			InputStream is = this.configLocation.getInputStream();
			try {
				props.load(is);
			}
			finally {
				is.close();
			}
		}

		// Merge local properties if set.
		if (this.freemarkerSettings != null) {
			props.putAll(this.freemarkerSettings);
		}

		// FreeMarker will only accept known keys in its setSettings and
		// setAllSharedVariables methods.
		if (!props.isEmpty()) {
			config.setSettings(props);
		}
		if (this.freemarkerVariables != null && this.freemarkerVariables.size() > 0) {
			config.setAllSharedVariables(new SimpleHash(this.freemarkerVariables));
		}

		if (this.templateLoaderPath != null) {
			if (this.preferFileSystemAccess) {
				// Try to load via the file system, fall back to SpringTemplateLoader
				// (for hot detection of template changes, if possible).
				try {
					Resource path = this.resourceLoader.getResource(this.templateLoaderPath);
					File file = path.getFile();  // will fail if not resolvable in the file system
					if (logger.isDebugEnabled()) {
						logger.debug("Template loader path [" + path + "] resolved to file [" + file.getAbsolutePath() + "]");
					}
					config.setDirectoryForTemplateLoading(file);
				}
				catch (IOException ex) {
					if (logger.isDebugEnabled()) {
						logger.debug("Cannot resolve template loader path [" + this.templateLoaderPath +
								"] to java.io.File: using SpringTemplateLoader", ex);
					}
					else if (logger.isInfoEnabled()) {
						logger.info("Cannot resolve template loader path [" + this.templateLoaderPath +
								"] to java.io.File: using SpringTemplateLoader");
					}
					config.setTemplateLoader(
							new SpringTemplateLoader(this.resourceLoader, this.templateLoaderPath));
				}
			}
			else {
				// Always load via SpringTemplateLoader
				// (without hot detection of template changes).
				if (logger.isDebugEnabled()) {
					logger.debug("File system access not preferred: using SpringTemplateLoader");
				}
				config.setTemplateLoader(
						new SpringTemplateLoader(this.resourceLoader, this.templateLoaderPath));
			}
		}

		postProcessConfiguration(config);
		return config;
	}

	/**
	 * Return a new Configuration object. Subclasses can override this for
	 * custom initialization, or for using a mock object for testing.
	 * Called by createConfiguration.
	 * @return the Configuration object
	 * @throws IOException if a config file wasn't found
	 * @throws TemplateException on FreeMarker initialization failure
	 * @see #createConfiguration
	 */
	protected Configuration newConfiguration() throws IOException, TemplateException {
		return new Configuration();
	}

	/**
	 * To be implemented by subclasses that want to to perform custom
	 * post-processing of the Configuration object after this FactoryBean
	 * performed its default initialization.
	 * Called by createConfiguration.
	 * @param config the current Configuration object
	 * @throws IOException if a config file wasn't found
	 * @throws TemplateException on FreeMarker initialization failure
	 * @see #createConfiguration
	 */
	protected void postProcessConfiguration(Configuration config)
			throws IOException, TemplateException {
	}

}
