/*
 * Copyright (c) MuleSoft, Inc.  All rights reserved.  http://www.mulesoft.com
 * The software in this package is published under the terms of the CPAL v1.0
 * license, a copy of which has been included with this distribution in the
 * LICENSE.txt file.
 */
package org.mule.runtime.config.spring;

import org.mule.runtime.api.lifecycle.Lifecycle;
import org.mule.runtime.core.lifecycle.LifecycleObject;
import org.mule.runtime.core.lifecycle.RegistryLifecycleCallback;
import org.mule.runtime.core.lifecycle.RegistryLifecycleManager;

import com.google.common.collect.TreeTraverser;

import java.util.Collection;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;

/**
 * A {@link RegistryLifecycleCallback} to be used with instances of {@link SpringRegistry}. For each object in which a
 * {@link Lifecycle} phase is going to be applied, it detects all the dependencies for that object and applies the same phase on
 * those dependencies first (recursively).
 * <p/>
 * This guarantees that if object A depends on object B and C, necessary lifecycle phases will have been applied on B and C before
 * it is applied to A
 *
 * @since 3.7.0
 */
class SpringLifecycleCallback extends RegistryLifecycleCallback<SpringRegistry> {

  public SpringLifecycleCallback(RegistryLifecycleManager registryLifecycleManager) {
    super(registryLifecycleManager);
  }

  @Override
  protected Collection<?> lookupObjectsForLifecycle(LifecycleObject lo) {
    Map<String, Object> objects = getSpringRegistry().lookupEntriesForLifecycle(lo.getType());

    final DependencyNode root = new DependencyNode(null);

    for (Map.Entry<String, Object> entry : objects.entrySet()) {
      addDependency(root, entry.getKey(), entry.getValue());
    }

    Iterable<DependencyNode> orderedNodes = new TreeTraverser<DependencyNode>() {

      @Override
      public Iterable children(DependencyNode node) {
        return node.getChilds();
      }
    }.postOrderTraversal(root);

    List<Object> orderedObjects = new LinkedList<>();
    for (DependencyNode node : orderedNodes) {
      if (node == root) {
        break;
      }

      orderedObjects.add(node.getValue());
    }

    return orderedObjects;
  }

  private SpringRegistry getSpringRegistry() {
    return (SpringRegistry) registryLifecycleManager.getLifecycleObject();
  }


  private void addDependency(DependencyNode parent, String key, Object object) {
    addDependency(parent, key, object, new HashSet<String>());
  }

  private void addDependency(DependencyNode parent, String key, Object object, Set<String> processedKeys) {
    final DependencyNode node = new DependencyNode(object);
    parent.addChild(node);

    if (!processedKeys.contains(key)) {
      processedKeys.add(key);
      for (Map.Entry<String, Object> dependency : getSpringRegistry().getDependencies(key).entrySet()) {
        addDependency(node, dependency.getKey(), dependency.getValue(), processedKeys);
      }
    }
  }

  private class DependencyNode {

    private final Object value;
    private final List<DependencyNode> childs = new LinkedList<>();

    private DependencyNode(Object value) {
      this.value = value;
    }

    public DependencyNode addChild(DependencyNode child) {
      childs.add(child);
      return this;
    }

    public List<DependencyNode> getChilds() {
      return childs;
    }

    public Object getValue() {
      return value;
    }
  }
}