package uk.org.lidalia.slf4jtest;
   
   import java.io.IOException;
   import java.io.InputStream;
   import java.util.Properties;
   
   import com.google.common.base.Function;
   import com.google.common.base.Optional;
   
  import static com.google.common.base.Optional.fromNullable;
  import static uk.org.lidalia.lang.Exceptions.throwUnchecked;
  
  class OverridableProperties {
      private static final Properties EMPTY_PROPERTIES = new Properties();
      private final String propertySourceName;
      private final Properties properties;
  
      OverridableProperties(final String propertySourceName) throws IOException {
          this.propertySourceName = propertySourceName;
          this.properties = getProperties();
      }
  
      private Properties getProperties() throws IOException {
          final Optional<InputStream> resourceAsStream = fromNullable(Thread.currentThread().getContextClassLoader()
                  .getResourceAsStream(propertySourceName + ".properties"));
          return resourceAsStream.transform(loadProperties).or(EMPTY_PROPERTIES);
      }
  
      private static final Function<InputStream, Properties> loadProperties = new Function<InputStream, Properties>() {
          @Override
          public Properties apply(final InputStream propertyResource) {
              try (InputStream closablePropertyResource = propertyResource) {
                  final Properties loadedProperties = new Properties();
                  loadedProperties.load(closablePropertyResource);
                  return loadedProperties;
              } catch (IOException ioException) {
                  return throwUnchecked(ioException, null);
              }
          }
      };
  
      String getProperty(final String propertyKey, final String defaultValue) {
          final String propertyFileProperty = properties.getProperty(propertyKey, defaultValue);
          return System.getProperty(propertySourceName + "." + propertyKey, propertyFileProperty);
      }
  }