// Copyright (C) 2017 The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package com.google.gerrit.server.project;

import static java.util.stream.Collectors.toList;

import com.google.common.collect.ArrayListMultimap;
import com.google.common.collect.ListMultimap;
import com.google.common.collect.Multimap;
import com.google.gerrit.entities.Project;
import com.google.gerrit.extensions.common.ProjectInfo;
import com.google.gerrit.server.config.AllProjectsName;
import com.google.gerrit.server.permissions.PermissionBackend;
import com.google.gerrit.server.permissions.PermissionBackendException;
import com.google.gerrit.server.permissions.ProjectPermission;
import com.google.inject.Inject;
import com.google.inject.Singleton;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/** Retrieve child projects (ie. projects whose access inherits from a given parent.) */
@Singleton
public class ChildProjects {
  private final ProjectCache projectCache;
  private final PermissionBackend permissionBackend;
  private final AllProjectsName allProjects;
  private final ProjectJson json;

  @Inject
  ChildProjects(
      ProjectCache projectCache,
      PermissionBackend permissionBackend,
      AllProjectsName allProjectsName,
      ProjectJson json) {
    this.projectCache = projectCache;
    this.permissionBackend = permissionBackend;
    this.allProjects = allProjectsName;
    this.json = json;
  }

  /** Gets all child projects recursively. */
  public List<ProjectInfo> list(Project.NameKey parent) throws PermissionBackendException {
    Map<Project.NameKey, Project> projects = readAllReadableProjects();
    ListMultimap<Project.NameKey, Project.NameKey> children = parentToChildren(projects);
    PermissionBackend.WithUser perm = permissionBackend.currentUser();

    List<ProjectInfo> results = new ArrayList<>();
    depthFirstFormat(results, perm, projects, children, parent);
    return results;
  }

  private Map<Project.NameKey, Project> readAllReadableProjects() {
    Map<Project.NameKey, Project> projects = new HashMap<>();
    for (Project.NameKey name : projectCache.all()) {

      ProjectState c =
          projectCache
              .get(name)
              .orElseThrow(
                  () ->
                      new IllegalStateException(
                          "race while traversing projects. got "
                              + name
                              + " when loading all projects, but can't load it now"));
      if (c != null && c.statePermitsRead()) {
        projects.put(c.getNameKey(), c.getProject());
      }
    }
    return projects;
  }

  /** Map of parent project to direct child. */
  private ListMultimap<Project.NameKey, Project.NameKey> parentToChildren(
      Map<Project.NameKey, Project> projects) {
    ListMultimap<Project.NameKey, Project.NameKey> m = ArrayListMultimap.create();
    for (Map.Entry<Project.NameKey, Project> e : projects.entrySet()) {
      if (!allProjects.equals(e.getKey())) {
        m.put(e.getValue().getParent(allProjects), e.getKey());
      }
    }
    return m;
  }

  private void depthFirstFormat(
      List<ProjectInfo> results,
      PermissionBackend.WithUser perm,
      Map<Project.NameKey, Project> projects,
      Multimap<Project.NameKey, Project.NameKey> children,
      Project.NameKey parent)
      throws PermissionBackendException {
    List<Project.NameKey> canSee =
        perm.filter(ProjectPermission.ACCESS, children.get(parent)).stream()
            .sorted()
            .collect(toList());
    children.removeAll(parent); // removing all entries prevents cycles.

    for (Project.NameKey c : canSee) {
      results.add(json.format(projects.get(c)));
      depthFirstFormat(results, perm, projects, children, c);
    }
  }
}