/*
 * 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;

/**
 * Abstract VeloCity based GUI builder implementation.
 *
 * @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;

  /**
   * Velocity based GUI builder.
   *
   * @throws GuiBuildException In case of a error
   */
  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(final HttpServletRequest httpReq, final HttpServletResponse httpResp,
      final IGuiBuilderConfiguration config, final 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(final HttpServletRequest httpReq, final HttpServletResponse httpResp,
      final IGuiBuilderConfiguration config, final String contentType, final 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(final HttpServletRequest httpReq, final HttpServletResponse httpResp,
      final IVelocityGuiBuilderConfiguration config, final String loggerName)
      throws GuiBuildException {
    build(httpReq, httpResp, config, getInternalContentType(config), loggerName);

  }

  @Override
  public void build(final HttpServletRequest httpReq, final HttpServletResponse httpResp,
      final IVelocityGuiBuilderConfiguration config, final String contentType,
      final 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, "UTF-8")));

      // 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 GUI builder config
   * @return Context of Velocity engine
   */
  @Override
  public VelocityContext generateVelocityContextFromConfiguration(
      final IVelocityGuiBuilderConfiguration config) {
    return buildContextFromViewParams(config.getViewParameters());

  }

  /**
   * Load the template from different resources.
   *
   * @param config GUI builder config
   * @return An {@link InputStream} but never null. The {@link InputStream} had to
   *         be closed be the invoking method
   * @throws GuiBuildException In case of an error
   */
  @Override
  public InputStream getTemplateInputStream(final 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 GUI builder config
   * @return Template that should be used
   * @throws GuiBuildException in case of an error
   */
  protected abstract InputStream getInternalTemplate(IVelocityGuiBuilderConfiguration config)
      throws GuiBuildException;

  protected String getInternalClasspathTemplateDir(final IVelocityGuiBuilderConfiguration config,
      final String defaultClassPathDir) {
    String dir = config.getClasspathTemplateDir();
    if (dir != null) {
      if (!dir.endsWith("/")) {
        dir += "/";
      }

      return dir;

    } else {
      return defaultClassPathDir;
    }
  }

  private VelocityContext buildContextFromViewParams(final 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(final IGuiBuilderConfiguration config) {
    if (StringUtils.isEmpty(config.getDefaultContentType())) {
      return DEFAULT_CONTENT_TYPE;
    } else {
      return config.getDefaultContentType();
    }

  }

}