content: /**
   * 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.apache.aurora.common.util.templating;
  
  import java.io.IOException;
  import java.io.Writer;
  import java.util.function.Consumer;
  
  import com.google.common.base.Preconditions;
  
  import org.antlr.stringtemplate.AutoIndentWriter;
  import org.antlr.stringtemplate.StringTemplate;
  import org.antlr.stringtemplate.StringTemplateGroup;
  import org.apache.aurora.common.base.MorePreconditions;
  
  /**
   * A class to simplify the operations required to load a stringtemplate template file from the
   * classpath and populate it.
   */
  public class StringTemplateHelper {
  
    private final StringTemplateGroup group;
    private final String templatePath;
  
    /**
     * Creates a new template helper.
     *
     * @param templateContextClass Classpath context for the location of the template file.
     * @param templateName Template file name (excluding .st suffix) relative to
     *     {@code templateContextClass}.
     * @param cacheTemplates Whether the template should be cached.
     */
    public StringTemplateHelper(
        Class<?> templateContextClass,
        String templateName,
        boolean cacheTemplates) {
  
      MorePreconditions.checkNotBlank(templateName);
      String templatePath =
          templateContextClass.getPackage().getName().replace('.', '/') + "/" + templateName;
      StringTemplateGroup group = new StringTemplateGroup(templateName);
      Preconditions.checkNotNull(group.getInstanceOf(templatePath),
          "Failed to load template at: %s", templatePath);
  
      this.group = group;
      if (!cacheTemplates) {
        group.setRefreshInterval(0);
      }
      this.templatePath = templatePath;
    }
  
    /**
     * Thrown when an exception is encountered while populating a template.
     */
    public static class TemplateException extends Exception {
      public TemplateException(String msg, Throwable cause) {
        super(msg, cause);
      }
    }
  
    /**
     * Writes the populated template to an output writer by providing a closure with access to
     * the unpopulated template object.
     *
     * @param out Template output writer.
     * @param parameterSetter Consumer to populate the template.
     * @throws TemplateException If an exception was encountered while populating the template.
     */
    public void writeTemplate(
        Writer out,
        Consumer<StringTemplate> parameterSetter) throws TemplateException {
  
      Preconditions.checkNotNull(out);
      Preconditions.checkNotNull(parameterSetter);
  
      StringTemplate stringTemplate = group.getInstanceOf(templatePath);
      try {
        parameterSetter.accept(stringTemplate);
        stringTemplate.write(new AutoIndentWriter(out));
      } catch (IOException e) {
        throw new TemplateException("Failed to write template: " + e, e);
      }
    }
  }
  