package com.atlassian.plugin.manager;
   
   import com.atlassian.plugin.Plugin;
   import com.atlassian.plugin.PluginRegistry;
   
   import java.util.ArrayList;
   import java.util.Collection;
   import java.util.Collections;
   import java.util.HashSet;
  import java.util.List;
  import java.util.Set;
  
  /**
   * A class to sort plugins in enable order
   *
   * @since v4.0
   */
  final class PluginsInEnableOrder {
      // the list of plugins sorted by requirement order.
      final List<Plugin> sortedList;
  
      public PluginsInEnableOrder(final Collection<Plugin> pluginsToEnable, PluginRegistry.ReadOnly pluginRegistry) {
          this.sortedList = new ArrayList<>();
          final Set<Plugin> visited = new HashSet<>();
  
          for (final Plugin plugin : pluginsToEnable) {
              sortPluginForEnable(plugin, visited, pluginsToEnable, pluginRegistry);
          }
      }
  
      /**
       * If currentPlugin has not been visited, recurse on to each recognized plugin that it requires, and
       * then add it to the sorted list if it is allowed.
       *
       * @param currentPlugin  the plugin we are inspecting requirements of.
       * @param visited        the list of plugins we've already recursed into.
       * @param allowedPlugins the plugins which we can accumulate into sortedList.
       */
      private void sortPluginForEnable(
              final Plugin currentPlugin,
              final Set<Plugin> visited,
              final Collection<Plugin> allowedPlugins,
              final PluginRegistry.ReadOnly pluginRegistry) {
          if (!visited.add(currentPlugin)) {
              return;
          }
  
          for (final String key : currentPlugin.getDependencies().getAll()) {
              final Plugin requiredPlugin = pluginRegistry.get(key);
  
              if (null != requiredPlugin) {
                  sortPluginForEnable(requiredPlugin, visited, allowedPlugins, pluginRegistry);
              }
          }
  
          if (allowedPlugins.contains(currentPlugin)) {
              sortedList.add(currentPlugin);
          }
      }
  
      public List<Plugin> get() {
          return Collections.unmodifiableList(sortedList);
      }
  }