package com.atlassian.plugins.rest.common.expand.resolver;
   
   import com.atlassian.annotations.tenancy.TenantAware;
   import com.atlassian.plugins.rest.common.expand.DefaultExpandContext;
   import com.atlassian.plugins.rest.common.expand.EntityCrawler;
   import com.atlassian.plugins.rest.common.expand.EntityExpander;
   import com.atlassian.plugins.rest.common.expand.ExpandContext;
   import com.google.common.collect.ImmutableMap;
   import com.google.common.collect.Lists;
  
  import java.util.Collection;
  import java.util.LinkedList;
  import java.util.List;
  import java.util.Map;
  
  import static com.atlassian.annotations.tenancy.TenancyScope.TENANTLESS;
  
  /**
   * An {@link EntityExpanderResolver} that can find {@link EntityExpander entity expanders} for:
   * <ul>
   * <li>{@link List}</li>
   * <li>{@link Collection}</li>
   * </ul>
   */
  public class CollectionEntityExpanderResolver implements EntityExpanderResolver {
      private static final List<Class<? extends Collection>> TYPES = Lists.newArrayList(List.class, Collection.class);
  
      @TenantAware(TENANTLESS)
      private static final Map<Class<?>, EntityExpander<?>> EXPANDERS = ImmutableMap.<Class<?>, EntityExpander<?>>builder()
              .put(List.class, new ListExpander())
              .put(Collection.class, new CollectionExpander())
              .build();
  
      public boolean hasExpander(Class<?> type) {
          for (Class<? extends Collection> expandableType : TYPES) {
              if (expandableType.isAssignableFrom(type)) {
                  return true;
              }
          }
          return false;
      }
  
      @SuppressWarnings("unchecked")
      public <T> EntityExpander<T> getExpander(Class<? extends T> type) {
          for (Class<? extends Collection> expandableType : TYPES) {
              if (expandableType.isAssignableFrom(type)) {
                  return (EntityExpander<T>) EXPANDERS.get(expandableType);
              }
          }
          return null;
      }
  
      private static class ListExpander implements EntityExpander<List> {
          public List expand(ExpandContext<List> context, EntityExpanderResolver expanderResolver, EntityCrawler entityCrawler) {
              final List list = new LinkedList();
              for (Object item : context.getEntity()) {
                  final ExpandContext<Object> itemContext = new DefaultExpandContext<Object>(item, context.getExpandable(), context.getEntityExpandParameter());
                  final EntityExpander<Object> entityExpander = item != null ? expanderResolver.getExpander(item.getClass()) : null;
                  list.add(entityExpander != null ? entityExpander.expand(itemContext, expanderResolver, entityCrawler) : item);
              }
              return list;
          }
      }
  
      private static class CollectionExpander implements EntityExpander<Collection> {
          public Collection expand(ExpandContext<Collection> context, EntityExpanderResolver expanderResolver, EntityCrawler entityCrawler) {
              final List list = new LinkedList();
              for (Object item : context.getEntity()) {
                  final ExpandContext<Object> itemContext = new DefaultExpandContext<Object>(item, context.getExpandable(), context.getEntityExpandParameter());
                  final EntityExpander<Object> entityExpander = item != null ? expanderResolver.getExpander(item.getClass()) : null;
                  list.add(entityExpander != null ? entityExpander.expand(itemContext, expanderResolver, entityCrawler) : item);
              }
              return list;
          }
      }
  }