/*
 * Copyright (C) 2016 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.android.voicemail.impl.scheduling;

import android.content.Context;
import android.os.Bundle;
import android.support.annotation.MainThread;
import android.support.annotation.WorkerThread;
import android.telecom.PhoneAccountHandle;
import java.util.Objects;

/**
 * A task for {@link TaskExecutor} to execute. Since the task is sent through a bundle to the
 * scheduler, The task must be constructable with the bundle. Specifically, It must have a
 * constructor with zero arguments, and have all relevant data packed inside the bundle. Use {@link
 * Tasks#createIntent(Context, Class)} to create a intent that will construct the Task.
 *
 * <p>Only {@link #onExecuteInBackgroundThread()} is run on the worker thread.
 */
public interface Task {
  /**
   * TaskId to indicate it has not be set. If a task does not provide a default TaskId it should be
   * set before {@link Task#onCreate(Context, Bundle)} returns
   */
  int TASK_INVALID = -1;

  /**
   * TaskId to indicate it should always be queued regardless of duplicates. {@link
   * Task#onDuplicatedTaskAdded(Task)} will never be called on tasks with this TaskId.
   */
  int TASK_ALLOW_DUPLICATES = -2;

  int TASK_UPLOAD = 1;
  int TASK_SYNC = 2;
  int TASK_ACTIVATION = 3;
  int TASK_STATUS_CHECK = 4;

  /**
   * Used to differentiate between types of tasks. If a task with the same TaskId is already in the
   * queue the new task will be rejected.
   */
  class TaskId {

    /** Indicates the operation type of the task. */
    public final int id;
    /**
     * Same operation for a different phoneAccountHandle is allowed. phoneAccountHandle is used to
     * differentiate phone accounts in multi-SIM scenario. For example, each SIM can queue a sync
     * task for their own.
     */
    public final PhoneAccountHandle phoneAccountHandle;

    public TaskId(int id, PhoneAccountHandle phoneAccountHandle) {
      this.id = id;
      this.phoneAccountHandle = phoneAccountHandle;
    }

    @Override
    public boolean equals(Object object) {
      if (!(object instanceof TaskId)) {
        return false;
      }
      TaskId other = (TaskId) object;
      return id == other.id && phoneAccountHandle.equals(other.phoneAccountHandle);
    }

    @Override
    public int hashCode() {
      return Objects.hash(id, phoneAccountHandle);
    }
  }

  TaskId getId();

  /**
   * Serializes the task into a bundle, which will be stored in a {@link android.app.job.JobInfo}
   * and used to reconstruct the task even if the app is terminated. The task will be initialized
   * with {@link #onCreate(Context, Bundle)}.
   */
  Bundle toBundle();

  /**
   * A task object is created through reflection, calling the default constructor. The actual
   * initialization is done in this method. If the task is not a new instance, but being restored
   * from a bundle, {@link #onRestore(Bundle)} will be called afterwards.
   */
  @MainThread
  void onCreate(Context context, Bundle extras);

  /**
   * Called after {@link #onCreate(Context, Bundle)} if the task is being restored from a Bundle
   * instead creating a new instance. For example, if the task is stored in {@link
   * TaskSchedulerJobService} during a long sleep, this will be called when the job is ran again and
   * the tasks are being restored from the saved state.
   */
  @MainThread
  void onRestore(Bundle extras);

  /**
   * @return number of milliSeconds the scheduler should wait before running this task. A value less
   *     than {@link TaskExecutor#READY_TOLERANCE_MILLISECONDS} will be considered ready. If no
   *     tasks are ready, the scheduler will sleep for this amount of time before doing another
   *     check (it will still wake if a new task is added). The first task in the queue that is
   *     ready will be executed.
   */
  @MainThread
  long getReadyInMilliSeconds();

  /**
   * Called on the main thread when the scheduler is about to send the task into the worker thread,
   * calling {@link #onExecuteInBackgroundThread()}
   */
  @MainThread
  void onBeforeExecute();

  /** The actual payload of the task, executed on the worker thread. */
  @WorkerThread
  void onExecuteInBackgroundThread();

  /**
   * Called on the main thread when {@link #onExecuteInBackgroundThread()} has finished or thrown an
   * uncaught exception. The task is already removed from the queue at this point, and a same task
   * can be queued again.
   */
  @MainThread
  void onCompleted();

  /**
   * Another task with the same TaskId has been added. Necessary data can be retrieved from the
   * other task, and after this returns the task will be discarded.
   */
  @MainThread
  void onDuplicatedTaskAdded(Task task);
}