package net.wuenschenswert.spring;

import org.springframework.beans.factory.config.PropertyPlaceholderConfigurer;

import java.util.Properties;

/**
 * A property resource configurer that resolves placeholders with defaults in bean property values of
 * context definitions. It <i>pulls</i> values from a properties file into bean definitions,
 * using the default value if no value is given in the properties file.
 *
 * <p>The default syntax uses an equals sign ('=') to separate the placeholder name from the default value.
 * This syntax mimicks the syntax which would be used in a property file.
 *
 * <p>Example:
 * <pre>
 * &lt;bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource"&gt;
 *   &lt;property name="driverClassName" value="${driver=com.mysql.jdbc.Driver}"/&gt;
 *   &lt;property name="url" value="jdbc:${dbname=mysql:mydb}"/&gt;
 * &lt;/bean&gt;</pre>
 *
 * <p>Having a default value directly inside the bean definition file, at the place where the property
 * is set, avoids redundantly listing the placeholder names. It is most useful for properties that usually
 * keep their default value and are rarely customized outside the bean definition file.
 *
 * <p>The lookup order for properties and locations is exactly as described in {@link PropertyPlaceholderConfigurer}.
 * The default value is only used if none of the specified properties and locations contains a value for
 * the placeholder.  If no default value is specified, this class behaves exactly the same as its superclass.
 *
 * @see PropertyPlaceholderConfigurer
 * @see #setDefaultSeparator
 */
public class DefaultPropertyPlaceholderConfigurer extends PropertyPlaceholderConfigurer {
  public static final String DEFAULT_DEFAULT_SEPARATOR = "=";

  private String defaultSeparator = DEFAULT_DEFAULT_SEPARATOR;

  /**
   * Set the string that separates a placeholder name from the default value.
   * The default is "=".
   * @see #DEFAULT_DEFAULT_SEPARATOR
   */
  public void setDefaultSeparator(String defaultSeparator) {
    this.defaultSeparator = defaultSeparator;
  }

  protected String resolvePlaceholder(String placeholderWithDefault, Properties props, int systemPropertiesMode) {
    String placeholder = getPlaceholder(placeholderWithDefault);
    String resolved = super.resolvePlaceholder(placeholder, props, systemPropertiesMode);
    if(resolved == null)
      resolved = getDefault(placeholderWithDefault);
    return resolved;
  }

  /**
   * extract the placeholder name from the complete placeholder string (between prefix and separator,
   * or complete placeholder if no separator is found)
   * @see #setPlaceholderPrefix
   * @see #setDefaultSeparator
   * @see #setPlaceholderSuffix
   */
  protected String getPlaceholder(String placeholderWithDefault) {
    int separatorIdx = placeholderWithDefault.indexOf(defaultSeparator);
    if(separatorIdx == -1)
      return placeholderWithDefault;
    else
      return placeholderWithDefault.substring(0,separatorIdx);
  }

  /**
   * extract the default value from the complete placeholder (the part between separator and suffix)
   * @return the default value, or null if none is given.
   * @see #setPlaceholderPrefix
   * @see #setDefaultSeparator
   * @see #setPlaceholderSuffix
   */
  protected String getDefault(String placeholderWithDefault) {
    int separatorIdx = placeholderWithDefault.indexOf(defaultSeparator);
    if(separatorIdx == -1)
      return null;
    else
      return placeholderWithDefault.substring(separatorIdx+1);
  }
}