// Copyright (C) 2009 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.account;

import com.google.gerrit.common.Nullable;
import com.google.gerrit.entities.Account;
import java.util.Map;
import java.util.Optional;
import java.util.Set;

/** Caches important (but small) account state to avoid database hits. */
public interface AccountCache {
  /**
   * Returns an {@code AccountState} instance for the given account ID. If not cached yet the
   * account is loaded. Returns {@link Optional#empty()} if the account is missing.
   *
   * @param accountId ID of the account that should be retrieved
   * @return {@code AccountState} instance for the given account ID, if no account with this ID
   *     exists {@link Optional#empty()} is returned
   */
  Optional<AccountState> get(Account.Id accountId);

  /**
   * Returns a {@code Map} of {@code Account.Id} to {@code AccountState} for the given account IDs.
   * If not cached yet the accounts are loaded. If an account can't be loaded (e.g. because it is
   * missing), the entry will be missing from the result.
   *
   * <p>Loads accounts in parallel if applicable.
   *
   * @param accountIds IDs of the account that should be retrieved
   * @return {@code Map} of {@code Account.Id} to {@code AccountState} instances for the given
   *     account IDs, if an account can't be loaded (e.g. because it is missing), the entry will be
   *     missing from the result
   */
  Map<Account.Id, AccountState> get(Set<Account.Id> accountIds);

  /**
   * Returns an {@code AccountState} instance for the given account ID. If not cached yet the
   * account is loaded. Returns an empty {@code AccountState} instance to represent a missing
   * account.
   *
   * <p>This method should only be used in exceptional cases where it is required to get an account
   * state even if the account is missing. Callers should leave a comment with the method invocation
   * explaining why this method is used. Most callers of {@link AccountCache} should use {@link
   * #get(Account.Id)} instead and handle the missing account case explicitly.
   *
   * @param accountId ID of the account that should be retrieved
   * @return {@code AccountState} instance for the given account ID, if no account with this ID
   *     exists an empty {@code AccountState} instance is returned to represent the missing account
   */
  AccountState getEvenIfMissing(Account.Id accountId);

  /**
   * Returns an {@code AccountState} instance for the given username.
   *
   * <p>This method first loads the external ID for the username and then uses the account ID of the
   * external ID to lookup the account from the cache.
   *
   * @param username username of the account that should be retrieved
   * @return {@code AccountState} instance for the given username, if no account with this username
   *     exists or if loading the external ID fails {@link Optional#empty()} is returned
   */
  Optional<AccountState> getByUsername(String username);

  /**
   * Evicts the account from the cache.
   *
   * @param accountId account ID of the account that should be evicted
   */
  void evict(@Nullable Account.Id accountId);

  /** Evict all accounts from the cache. */
  void evictAll();
}