TemplatingUtility.java

/* 
 *
 * SchemaCrawler
 * http://sourceforge.net/projects/schemacrawler
 * Copyright (c) 2000-2014, Sualeh Fatehi.
 *
 * This library is free software; you can redistribute it and/or modify it under the terms
 * of the GNU Lesser General Public License as published by the Free Software Foundation;
 * either version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
 * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License along with this
 * library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
 * Boston, MA 02111-1307, USA.
 *
 */

package sf.util;


import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Properties;
import java.util.Set;

/**
 * Configuration properties.
 * 
 * @author Sualeh Fatehi
 */
public final class TemplatingUtility
{

  private static final String DELIMITER_START = "${";
  private static final String DELIMITER_END = "}";

  /**
   * Expands a template using system properties. Variables in the
   * template are in the form of ${variable}.
   * 
   * @param template
   *        Template to expand.
   * @return Expanded template
   */
  public static String expandTemplate(final String template)
  {
    return expandTemplate(template, propertiesMap(System.getProperties()));
  }

  /**
   * Expands a template using variable values in the provided map.
   * Variables in the template are in the form of ${variable}.
   * 
   * @param template
   *        Template to expand.
   * @param variablesMap
   *        Variables and values.
   * @return Expanded template
   */
  public static String expandTemplate(final String template,
                                      final Map<String, String> variablesMap)
  {
    if (Utility.isBlank(template) || variablesMap == null)
    {
      return template;
    }

    final StringBuilder buffer = new StringBuilder();
    int currentPosition = 0;
    int delimiterStartPosition;
    int delimiterEndPosition;

    while (true)
    {
      delimiterStartPosition = template.indexOf(DELIMITER_START,
                                                currentPosition);
      if (delimiterStartPosition == -1)
      {
        if (currentPosition == 0)
        {
          // No substitutions required at all
          return template;
        }
        else
        {
          // No more substitutions
          buffer.append(template.substring(currentPosition, template.length()));
          return buffer.toString();
        }
      }
      else
      {
        buffer.append(template.substring(currentPosition,
                                         delimiterStartPosition));
        delimiterEndPosition = template.indexOf(DELIMITER_END,
                                                delimiterStartPosition);
        if (delimiterEndPosition > -1)
        {
          delimiterStartPosition = delimiterStartPosition
                                   + DELIMITER_START.length();
          final String key = template.substring(delimiterStartPosition,
                                                delimiterEndPosition);
          final String value = variablesMap.get(key);
          if (value != null)
          {
            buffer.append(value);
          }
          else
          {
            // Do not substitute
            buffer.append(DELIMITER_START).append(key).append(DELIMITER_END);
          }
          // Advance current position
          currentPosition = delimiterEndPosition + DELIMITER_END.length();
        }
        else
        {
          // End brace not found, so advance current position
          buffer.append(DELIMITER_START);
          currentPosition = delimiterStartPosition + DELIMITER_START.length();
        }
      }
    }
  }

  /**
   * Extracts variables from the template. Variables are in the form of
   * ${variable}.
   * 
   * @param template
   *        Template to extract variables from.
   * @return Extracted variables
   */
  public static Set<String> extractTemplateVariables(final String template)
  {

    if (Utility.isBlank(template))
    {
      return new HashSet<>();
    }

    String shrunkTemplate = template;
    final Set<String> keys = new HashSet<>();
    for (int left; (left = shrunkTemplate.indexOf(DELIMITER_START)) >= 0;)
    {
      final int right = shrunkTemplate.indexOf(DELIMITER_END, left + 2);
      if (right >= 0)
      {
        final String propertyKey = shrunkTemplate.substring(left + 2, right);
        keys.add(propertyKey);
        // Destroy key, so we can find the next one
        shrunkTemplate = shrunkTemplate.substring(0, left)
                         + shrunkTemplate.substring(right + 1);
      }
      else
      {
        // No ending baracket found
        break;
      }
    }

    return keys;
  }

  /**
   * Does one pass over the values in the map, and expands each as a
   * template, using the rest of the values in the same map. Variables
   * in the template are in the form of ${variable}.
   * 
   * @param variablesMap
   *        Map to expand.
   */
  public static void substituteVariables(final Map<String, String> variablesMap)
  {
    if (variablesMap != null && !variablesMap.isEmpty())
    {
      for (final Map.Entry<String, String> entry: variablesMap.entrySet())
      {
        variablesMap.put(entry.getKey(),
                         expandTemplate(entry.getValue(), variablesMap));
      }
    }
  }

  /**
   * Copies properties into a map.
   * 
   * @param properties
   *        Properties to copy
   * @return Map of properties and values
   */
  private static Map<String, String> propertiesMap(final Properties properties)
  {
    final Map<String, String> propertiesMap = new HashMap<>();
    if (properties != null)
    {
      final Set<Entry<Object, Object>> entries = properties.entrySet();
      for (final Entry<Object, Object> entry: entries)
      {
        propertiesMap.put((String) entry.getKey(), (String) entry.getValue());
      }
    }
    return propertiesMap;
  }

  private TemplatingUtility()
  {
  }

}