/*
    *    Copyright 2012-2022 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
    *
    *       https://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.mybatis.scripting.velocity;
  
  import java.io.StringReader;
  import java.io.StringWriter;
  import java.util.HashMap;
  import java.util.Map;
  import java.util.Properties;
  import java.util.stream.Collectors;
  
  import org.apache.ibatis.builder.BuilderException;
  import org.apache.ibatis.io.Resources;
  import org.apache.ibatis.scripting.ScriptingException;
  import org.apache.velocity.Template;
  import org.apache.velocity.VelocityContext;
  import org.apache.velocity.runtime.RuntimeConstants;
  import org.apache.velocity.runtime.RuntimeInstance;
  import org.apache.velocity.runtime.parser.node.SimpleNode;
  
  public class VelocityFacade {
  
    private static final RuntimeInstance engine = new RuntimeInstance();
    private static final Map<String, Object> additionalCtxAttributes = new HashMap<>();
  
    private VelocityFacade() {
      // Prevent instantiation
    }
  
    /**
     * Initialize a template engine.
     *
     * @param driverConfig
     *          a language driver configuration
     *
     * @since 2.1.0
     */
    public static void initialize(VelocityLanguageDriverConfig driverConfig) {
      Properties properties = new Properties();
      driverConfig.getVelocitySettings().forEach(properties::setProperty);
      properties.setProperty(RuntimeConstants.CUSTOM_DIRECTIVES, driverConfig.generateCustomDirectivesString());
      engine.init(properties);
      additionalCtxAttributes.putAll(driverConfig.getAdditionalContextAttributes().entrySet().stream()
          .collect(Collectors.toMap(Map.Entry::getKey, v -> {
            try {
              return Resources.classForName(v.getValue()).getConstructor().newInstance();
            } catch (Exception e) {
              throw new ScriptingException("Cannot load additional context attribute class.", e);
            }
          })));
    }
  
    /**
     * Destroy a template engine.
     *
     * @since 2.1.0
     */
    public static void destroy() {
      engine.reset();
      additionalCtxAttributes.clear();
    }
  
    public static Object compile(String script, String name) {
      try {
        StringReader reader = new StringReader(script);
        Template template = new Template();
        SimpleNode node = engine.parse(reader, template);
        template.setRuntimeServices(engine);
        template.setData(node);
        template.setName(name);
        template.initDocument();
        return template;
      } catch (Exception ex) {
        throw new BuilderException("Error parsing velocity script '" + name + "'", ex);
      }
    }
  
    public static String apply(Object template, Map<String, Object> context) {
      final StringWriter out = new StringWriter();
      context.putAll(additionalCtxAttributes);
      ((Template) template).merge(new VelocityContext(context), out);
      return out.toString();
    }
  
  }