/*******************************************************************************
 * Copyright 2017 Graz University of Technology
 * EAAF-Core Components has been developed in a cooperation between EGIZ,  
 * A-SIT Plus, A-SIT, and Graz University of Technology.
 *
 * Licensed under the EUPL, Version 1.2 or - as soon they will be approved by
 * the European Commission - subsequent versions of the EUPL (the "Licence");
 * You may not use this work except in compliance with the Licence.
 * You may obtain a copy of the Licence at:
 * https://joinup.ec.europa.eu/news/understanding-eupl-v12
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the Licence is distributed on an "AS IS" basis,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the Licence for the specific language governing permissions and
 * limitations under the Licence.
 *  
 * This product combines work with different licenses. See the "NOTICE" text
 * file for details on the various modules and licenses.
 * The "NOTICE" text file is part of the distribution. Any derivative works
 * that you distribute must include a readable copy of the "NOTICE" text file.
 *******************************************************************************/
/*******************************************************************************
 *******************************************************************************/
/*******************************************************************************
 *******************************************************************************/
package at.gv.egiz.eaaf.core.impl.gui;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.StringWriter;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.lang3.StringUtils;
import org.apache.velocity.VelocityContext;
import org.apache.velocity.app.VelocityEngine;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import at.gv.egiz.eaaf.core.api.data.EAAFConstants;
import at.gv.egiz.eaaf.core.api.gui.IGUIBuilderConfiguration;
import at.gv.egiz.eaaf.core.api.gui.IVelocityGUIBuilderConfiguration;
import at.gv.egiz.eaaf.core.api.gui.IVelocityGuiFormBuilder;
import at.gv.egiz.eaaf.core.exceptions.GUIBuildException;
import at.gv.egiz.eaaf.core.impl.gui.velocity.VelocityProvider;

/**
 * @author tlenz 
 *
 */
public abstract class AbstractVelocityGUIFormBuilderImpl implements IVelocityGuiFormBuilder {
	private static final Logger log = LoggerFactory.getLogger(AbstractVelocityGUIFormBuilderImpl.class);
	private static final String DEFAULT_CONTENT_TYPE = EAAFConstants.CONTENTTYPE_HTML_UTF8;
			
	private VelocityEngine engine;
		
	public AbstractVelocityGUIFormBuilderImpl() throws GUIBuildException {
		try {
			engine = VelocityProvider.getClassPathVelocityEngine();
			
		} catch (final Exception e) {
			log.error("Initialization of Velocity-Engine to render GUI components FAILED.", e);
			throw new GUIBuildException("Initialization of Velocity-Engine to render GUI components FAILED.", e);
			
		}
		
	}

	@Override
	public final void build(HttpServletRequest httpReq, HttpServletResponse httpResp, IGUIBuilderConfiguration config,
			String loggerName) throws GUIBuildException {
		if (config instanceof IVelocityGUIBuilderConfiguration)
			build(httpReq, httpResp, (IVelocityGUIBuilderConfiguration)config, loggerName);
		else
			throw new IllegalStateException(this.getClass().getName() + " needs a " + IVelocityGUIBuilderConfiguration.class.getName());
		
		
	}

	@Override
	public final void build(HttpServletRequest httpReq, HttpServletResponse httpResp, IGUIBuilderConfiguration config,
			String contentType, String loggerName) throws GUIBuildException {
		if (config instanceof IVelocityGUIBuilderConfiguration)
			build(httpReq, httpResp, (IVelocityGUIBuilderConfiguration)config, contentType, loggerName);
		else
			throw new IllegalStateException(this.getClass().getName() + " needs a " + IVelocityGUIBuilderConfiguration.class.getName());
		
	}
	
	@Override
	public void build(HttpServletRequest httpReq, HttpServletResponse httpResp, IVelocityGUIBuilderConfiguration config, String loggerName) throws GUIBuildException {
		build(httpReq, httpResp, config, getInternalContentType(config), loggerName);
		
	}
	
	@Override
	public void build(HttpServletRequest httpReq, HttpServletResponse httpResp, IVelocityGUIBuilderConfiguration config, 
			String contentType, String loggerName) throws GUIBuildException {
		
		InputStream is = null;
		try {
			final String viewName = config.getViewName();			
			is = getTemplateInputStream(config);
			
			//build Velocity Context from input paramters
			final VelocityContext context = buildContextFromViewParams(config.getViewParameters());

			//evaluate template
			final StringWriter writer = new StringWriter();
			engine.evaluate(context, writer, loggerName, new BufferedReader(new InputStreamReader(is)));
							
			//write template to response
			final byte[] content = writer.toString().getBytes("UTF-8");
			httpResp.setStatus(HttpServletResponse.SC_OK);
			httpResp.setContentLength(content.length);
			httpResp.setContentType(contentType);						
			httpResp.getOutputStream().write(content);
			
			if (log.isTraceEnabled()) {
				log.trace("Write Content for viewName:" + viewName 
						+ ". Contentsize:" + String.valueOf(content.length)
						+ " BufferSize:" + httpResp.getBufferSize()
						+ " ContentType:" + contentType);
				for (final String el : httpResp.getHeaderNames())
					log.trace(" * Headername:" + el + " Value:" + httpResp.getHeader(el));
				
			}
			
		} catch (final IOException e) {
			log.error("GUI form-builder has an internal error.", e);
			throw new GUIBuildException("GUI form-builder has an internal error.", e);
						
		} finally {
			if (is != null)
				try {
					is.close();
					
				} catch (final IOException e) {
					log.error("Can NOT close GUI-Template InputStream.", e);
					
				}
		}
		
	}

	/**
	 * Generate a new {@link VelocityContext} and populate it with MOA-ID GUI parameters
	 * 
	 * @param config
	 * @return
	 */
	@Override
	public VelocityContext generateVelocityContextFromConfiguration(IVelocityGUIBuilderConfiguration config) {
		return buildContextFromViewParams(config.getViewParameters());
		
	}
	
	/**
	 * Load the template from different resources
	 * 
	 * @param config
	 * @return An {@link InputStream} but never null. The {@link InputStream} had to be closed be the invoking method
	 * @throws GUIBuildException
	 */
	@Override
	public InputStream getTemplateInputStream(IVelocityGUIBuilderConfiguration config) throws GUIBuildException {
		InputStream is = config.getTemplate(config.getViewName());
		if (is == null) {
			log.trace("Loading GUI template:" + config.getViewName() + " from default resources ... ");
			is = getInternalTemplate(config);
			
			if (is == null) {
				log.warn("No GUI with viewName:" + config.getViewName() + " FOUND.");
				throw new GUIBuildException("No GUI with viewName:" + config.getViewName() + " FOUND.");
		
			}
		}		
		return is;
		
	}
	
	/**
	 * Load an internal template from default resources
	 * 
	 * @param config
	 * @return
	 * @throws GUIBuildException
	 */
	abstract protected InputStream getInternalTemplate(IVelocityGUIBuilderConfiguration config) throws GUIBuildException;

	
	/**
	 * @return
	 */ 
	protected String getInternalClasspathTemplateDir(IVelocityGUIBuilderConfiguration config, String defaultClassPathDir) {
		String dir = config.getClasspathTemplateDir();
		if (dir != null) {
			if (!dir.endsWith("/"))
				dir += "/";
			
			return dir;			
			
		} else
			return defaultClassPathDir;
	}
	
	/**
	 * @param viewParams
	 * @return
	 */
	private VelocityContext buildContextFromViewParams(Map<String, Object> viewParams) {
		final VelocityContext context = new VelocityContext();
				
		if (viewParams != null) {
			final Iterator<Entry<String, Object>> interator = viewParams.entrySet().iterator();
			while (interator.hasNext()) {
				final Entry<String, Object> el = interator.next();
				context.put(el.getKey(), el.getValue());
			}
			
		} 
		
		return context;
	}
	
	private String getInternalContentType(IGUIBuilderConfiguration config) {
		if (StringUtils.isEmpty(config.getDefaultContentType()))
			return DEFAULT_CONTENT_TYPE;
		
		else
			return config.getDefaultContentType();
		
	}

}