package com.atlassian.plugins.rest.common.expand.resolver;
   
   import com.atlassian.plugins.rest.common.expand.*;
   import com.atlassian.plugins.rest.common.expand.parameter.Indexes;
   
   import static com.google.common.base.Preconditions.checkNotNull;
   
   import java.lang.reflect.InvocationTargetException;
   import java.lang.reflect.Method;
  
  /**
   * {@link EntityExpanderResolver Entity expander resolver} that will get resolver for classes (objects) with method annotated with {@link ExpandConstraint @ExpandConstraint}.
   * Method signature should be the same as below:
   * <code>
   * {@literal @}ExpandConstraint public void expandInstance(Indexes indexes)
   * {
   * // your code to expand the object here
   * }
   * </code>
   */
  public class ExpandConstraintEntityExpanderResolver implements EntityExpanderResolver {
      public boolean hasExpander(Class<?> type) {
          return getConstrainMethod(checkNotNull(type)) != null;
      }
  
      public <T> EntityExpander<T> getExpander(Class<? extends T> type) {
          final Method method = getConstrainMethod(checkNotNull(type));
          return method != null ? (EntityExpander<T>) new ExpandConstraintEntityExpander(method) : null;
      }
  
      private <T> Method getConstrainMethod(Class<? extends T> type) {
          for (Method method : type.getDeclaredMethods()) {
              if (method.getAnnotation(ExpandConstraint.class) != null
                      && method.getParameterTypes().length == 1
                      && method.getParameterTypes()[0].equals(Indexes.class)) {
                  return method;
              }
          }
          return null;
      }
  
      private static class ExpandConstraintEntityExpander implements EntityExpander<Object> {
          private final Method method;
  
          public ExpandConstraintEntityExpander(Method method) {
              this.method = checkNotNull(method);
          }
  
          public Object expand(ExpandContext<Object> context, EntityExpanderResolver expanderResolver, EntityCrawler entityCrawler) {
              final Object entity = context.getEntity();
              try {
                  method.invoke(entity, context.getEntityExpandParameter().getIndexes(context.getExpandable()));
              } catch (IllegalAccessException e) {
                  throw new ExpandException(e);
              } catch (InvocationTargetException e) {
                  throw new ExpandException(e);
              }
  
              entityCrawler.crawl(entity, context.getEntityExpandParameter().getExpandParameter(context.getExpandable()), expanderResolver);
  
              return entity;
          }
      }
  }