/*
 * Copyright 2015 The gRPC 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 io.grpc;

import com.google.common.base.Preconditions;
import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.net.SocketAddress;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

/**
 * A group of {@link SocketAddress}es that are considered equivalent when channel makes connections.
 *
 * <p>Usually the addresses are addresses resolved from the same host name, and connecting to any of
 * them is equally sufficient. They do have order. An address appears earlier on the list is likely
 * to be tried earlier.
 */
@ExperimentalApi("https://github.com/grpc/grpc-java/issues/1770")
public final class EquivalentAddressGroup {

  /**
   * The authority to be used when constructing Subchannels for this EquivalentAddressGroup.
   * However, if the channel has overridden authority via
   * {@link ManagedChannelBuilder#overrideAuthority(String)}, the transport will use the channel's
   * authority override.
   *
   * <p>The authority <strong>must</strong> be from a trusted source, because if the authority is
   * tampered with, RPCs may be sent to attackers which may leak sensitive user data. If the
   * authority was acquired by doing I/O, the communication must be authenticated (e.g., via TLS).
   * Recognize that the server that provided the authority can trivially impersonate the service.
   */
  @Attr
  @ExperimentalApi("https://github.com/grpc/grpc-java/issues/6138")
  public static final Attributes.Key<String> ATTR_AUTHORITY_OVERRIDE =
      Attributes.Key.create("io.grpc.EquivalentAddressGroup.ATTR_AUTHORITY_OVERRIDE");
  private final List<SocketAddress> addrs;
  private final Attributes attrs;

  /**
   * {@link SocketAddress} docs say that the addresses are immutable, so we cache the hashCode.
   */
  private final int hashCode;

  /**
   * List constructor without {@link Attributes}.
   */
  public EquivalentAddressGroup(List<SocketAddress> addrs) {
    this(addrs, Attributes.EMPTY);
  }

  /**
   * List constructor with {@link Attributes}.
   */
  public EquivalentAddressGroup(List<SocketAddress> addrs, @Attr Attributes attrs) {
    Preconditions.checkArgument(!addrs.isEmpty(), "addrs is empty");
    this.addrs = Collections.unmodifiableList(new ArrayList<>(addrs));
    this.attrs = Preconditions.checkNotNull(attrs, "attrs");
    // Attributes may contain mutable objects, which means Attributes' hashCode may change over
    // time, thus we don't cache Attributes' hashCode.
    hashCode = this.addrs.hashCode();
  }

  /**
   * Singleton constructor without Attributes.
   */
  public EquivalentAddressGroup(SocketAddress addr) {
    this(addr, Attributes.EMPTY);
  }

  /**
   * Singleton constructor with Attributes.
   */
  public EquivalentAddressGroup(SocketAddress addr, @Attr Attributes attrs) {
    this(Collections.singletonList(addr), attrs);
  }

  /**
   * Returns an immutable list of the addresses.
   */
  public List<SocketAddress> getAddresses() {
    return addrs;
  }

  /**
   * Returns the attributes.
   */
  @Attr
  public Attributes getAttributes() {
    return attrs;
  }

  @Override
  public String toString() {
    // TODO(zpencer): Summarize return value if addr is very large
    return "[" + addrs + "/" + attrs + "]";
  }

  @Override
  public int hashCode() {
    // Avoids creating an iterator on the underlying array list.
    return hashCode;
  }

  /**
   * Returns true if the given object is also an {@link EquivalentAddressGroup} with an equal
   * address list and equal attribute values.
   *
   * <p>Note that if the attributes include mutable values, it is possible for two objects to be
   * considered equal at one point in time and not equal at another (due to concurrent mutation of
   * attribute values).
   */
  @Override
  public boolean equals(Object other) {
    if (!(other instanceof EquivalentAddressGroup)) {
      return false;
    }
    EquivalentAddressGroup that = (EquivalentAddressGroup) other;
    if (addrs.size() != that.addrs.size()) {
      return false;
    }
    // Avoids creating an iterator on the underlying array list.
    for (int i = 0; i < addrs.size(); i++) {
      if (!addrs.get(i).equals(that.addrs.get(i))) {
        return false;
      }
    }
    if (!attrs.equals(that.attrs)) {
      return false;
    }
    return true;
  }

  /**
   * Annotation for {@link EquivalentAddressGroup}'s attributes. It follows the annotation semantics
   * defined by {@link Attributes}.
   */
  @ExperimentalApi("https://github.com/grpc/grpc-java/issues/4972")
  @Retention(RetentionPolicy.SOURCE)
  @Documented
  public @interface Attr {}
}