/*
 * Copyright (C) 2010 The Guava Authors
 *
 * 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.common.util.concurrent;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static java.util.Objects.requireNonNull;

import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.lang.Thread.UncaughtExceptionHandler;
import java.util.Locale;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.atomic.AtomicLong;
import javax.annotation.CheckForNull;

/**
 * A ThreadFactory builder, providing any combination of these features:
 *
 * <ul>
 *   <li>whether threads should be marked as {@linkplain Thread#setDaemon daemon} threads
 *   <li>a {@linkplain ThreadFactoryBuilder#setNameFormat naming format}
 *   <li>a {@linkplain Thread#setPriority thread priority}
 *   <li>an {@linkplain Thread#setUncaughtExceptionHandler uncaught exception handler}
 *   <li>a {@linkplain ThreadFactory#newThread backing thread factory}
 * </ul>
 *
 * <p>If no backing thread factory is provided, a default backing thread factory is used as if by
 * calling {@code setThreadFactory(}{@link Executors#defaultThreadFactory()}{@code )}.
 *
 * @author Kurt Alfred Kluever
 * @since 4.0
 */
@J2ktIncompatible
@GwtIncompatible
@ElementTypesAreNonnullByDefault
public final class ThreadFactoryBuilder {
  @CheckForNull private String nameFormat = null;
  @CheckForNull private Boolean daemon = null;
  @CheckForNull private Integer priority = null;
  @CheckForNull private UncaughtExceptionHandler uncaughtExceptionHandler = null;
  @CheckForNull private ThreadFactory backingThreadFactory = null;

  /** Creates a new {@link ThreadFactory} builder. */
  public ThreadFactoryBuilder() {}

  /**
   * Sets the naming format to use when naming threads ({@link Thread#setName}) which are created
   * with this ThreadFactory.
   *
   * @param nameFormat a {@link String#format(String, Object...)}-compatible format String, to which
   *     a unique integer (0, 1, etc.) will be supplied as the single parameter. This integer will
   *     be unique to the built instance of the ThreadFactory and will be assigned sequentially. For
   *     example, {@code "rpc-pool-%d"} will generate thread names like {@code "rpc-pool-0"}, {@code
   *     "rpc-pool-1"}, {@code "rpc-pool-2"}, etc.
   * @return this for the builder pattern
   */
  @CanIgnoreReturnValue
  public ThreadFactoryBuilder setNameFormat(String nameFormat) {
    String unused = format(nameFormat, 0); // fail fast if the format is bad or null
    this.nameFormat = nameFormat;
    return this;
  }

  /**
   * Sets daemon or not for new threads created with this ThreadFactory.
   *
   * @param daemon whether or not new Threads created with this ThreadFactory will be daemon threads
   * @return this for the builder pattern
   */
  @CanIgnoreReturnValue
  public ThreadFactoryBuilder setDaemon(boolean daemon) {
    this.daemon = daemon;
    return this;
  }

  /**
   * Sets the priority for new threads created with this ThreadFactory.
   *
   * <p><b>Warning:</b> relying on the thread scheduler is <a
   * href="http://errorprone.info/bugpattern/ThreadPriorityCheck">discouraged</a>.
   *
   * @param priority the priority for new Threads created with this ThreadFactory
   * @return this for the builder pattern
   */
  @CanIgnoreReturnValue
  public ThreadFactoryBuilder setPriority(int priority) {
    // Thread#setPriority() already checks for validity. These error messages
    // are nicer though and will fail-fast.
    checkArgument(
        priority >= Thread.MIN_PRIORITY,
        "Thread priority (%s) must be >= %s",
        priority,
        Thread.MIN_PRIORITY);
    checkArgument(
        priority <= Thread.MAX_PRIORITY,
        "Thread priority (%s) must be <= %s",
        priority,
        Thread.MAX_PRIORITY);
    this.priority = priority;
    return this;
  }

  /**
   * Sets the {@link UncaughtExceptionHandler} for new threads created with this ThreadFactory.
   *
   * @param uncaughtExceptionHandler the uncaught exception handler for new Threads created with
   *     this ThreadFactory
   * @return this for the builder pattern
   */
  @CanIgnoreReturnValue
  public ThreadFactoryBuilder setUncaughtExceptionHandler(
      UncaughtExceptionHandler uncaughtExceptionHandler) {
    this.uncaughtExceptionHandler = checkNotNull(uncaughtExceptionHandler);
    return this;
  }

  /**
   * Sets the backing {@link ThreadFactory} for new threads created with this ThreadFactory. Threads
   * will be created by invoking #newThread(Runnable) on this backing {@link ThreadFactory}.
   *
   * @param backingThreadFactory the backing {@link ThreadFactory} which will be delegated to during
   *     thread creation.
   * @return this for the builder pattern
   * @see MoreExecutors
   */
  @CanIgnoreReturnValue
  public ThreadFactoryBuilder setThreadFactory(ThreadFactory backingThreadFactory) {
    this.backingThreadFactory = checkNotNull(backingThreadFactory);
    return this;
  }

  /**
   * Returns a new thread factory using the options supplied during the building process. After
   * building, it is still possible to change the options used to build the ThreadFactory and/or
   * build again. State is not shared amongst built instances.
   *
   * @return the fully constructed {@link ThreadFactory}
   */
  public ThreadFactory build() {
    return doBuild(this);
  }

  // Split out so that the anonymous ThreadFactory can't contain a reference back to the builder.
  // At least, I assume that's why. TODO(cpovirk): Check, and maybe add a test for this.
  private static ThreadFactory doBuild(ThreadFactoryBuilder builder) {
    String nameFormat = builder.nameFormat;
    Boolean daemon = builder.daemon;
    Integer priority = builder.priority;
    UncaughtExceptionHandler uncaughtExceptionHandler = builder.uncaughtExceptionHandler;
    ThreadFactory backingThreadFactory =
        (builder.backingThreadFactory != null)
            ? builder.backingThreadFactory
            : Executors.defaultThreadFactory();
    AtomicLong count = (nameFormat != null) ? new AtomicLong(0) : null;
    return new ThreadFactory() {
      @Override
      public Thread newThread(Runnable runnable) {
        Thread thread = backingThreadFactory.newThread(runnable);
        // TODO(b/139735208): Figure out what to do when the factory returns null.
        requireNonNull(thread);
        if (nameFormat != null) {
          // requireNonNull is safe because we create `count` if (and only if) we have a nameFormat.
          thread.setName(format(nameFormat, requireNonNull(count).getAndIncrement()));
        }
        if (daemon != null) {
          thread.setDaemon(daemon);
        }
        if (priority != null) {
          thread.setPriority(priority);
        }
        if (uncaughtExceptionHandler != null) {
          thread.setUncaughtExceptionHandler(uncaughtExceptionHandler);
        }
        return thread;
      }
    };
  }

  private static String format(String format, Object... args) {
    return String.format(Locale.ROOT, format, args);
  }
}
