add interface in core + move groupCollector to webapp

scm-webapp/src/main/java/sonia/scm/group/DefaultGroupCollector.java

@@ -0,0 +1,70 @@
+package sonia.scm.group;
+
+import com.google.common.collect.ImmutableSet;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import sonia.scm.cache.Cache;
+import sonia.scm.cache.CacheManager;
+import sonia.scm.security.GroupCollector;
+import sonia.scm.security.GroupResolver;
+
+import java.util.Set;
+
+/**
+ * Collect groups for a certain principal.
+ * <strong>Warning</strong>: The class is only for internal use and should never used directly.
+ */
+class DefaultGroupCollector implements GroupCollector {
+
+  private static final Logger LOG = LoggerFactory.getLogger(DefaultGroupCollector.class);
+
+  /** Field description */
+  public static final String CACHE_NAME = "sonia.cache.externalGroups";
+
+  /** Field description */
+  private final Cache<String, Set<String>> cache;
+  private Set<GroupResolver> groupResolvers;
+
+  private final GroupDAO groupDAO;
+
+  DefaultGroupCollector(GroupDAO groupDAO, CacheManager cacheManager, Set<GroupResolver> groupResolvers) {
+    this.groupDAO = groupDAO;
+    this.cache  = cacheManager.getCache(CACHE_NAME);
+    this.groupResolvers = groupResolvers;
+  }
+
+  @Override
+  public Iterable<String> collect(String principal) {
+
+    Set<String> externalGroups = cache.get(principal);
+
+    if (externalGroups == null) {
+      ImmutableSet.Builder<String> newExternalGroups = ImmutableSet.builder();
+
+      for (GroupResolver groupResolver : groupResolvers) {
+       Iterable<String> groups = groupResolver.resolveGroups(principal);
+       groups.forEach(newExternalGroups::add);
+      }
+
+      cache.put(principal, newExternalGroups.build());
+    }
+
+    ImmutableSet.Builder<String> builder = ImmutableSet.builder();
+
+    builder.add(GroupNames.AUTHENTICATED);
+
+    for (String group : externalGroups) {
+      builder.add(group);
+    }
+
+    for (Group group : groupDAO.getAll()) {
+      if (group.isMember(principal)) {
+        builder.add(group.getName());
+      }
+    }
+
+    GroupNames groups = new GroupNames(builder.build());
+    LOG.debug("collected following groups for principal {}: {}", principal, groups);
+    return groups;
+  }
+}