/*
 * 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.android.contacts.common.model;

import android.accounts.Account;
import android.accounts.AccountManager;
import android.accounts.AuthenticatorDescription;
import android.accounts.OnAccountsUpdateListener;
import android.content.BroadcastReceiver;
import android.content.ContentResolver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.SyncAdapterType;
import android.content.SyncStatusObserver;
import android.content.pm.PackageManager;
import android.content.pm.ResolveInfo;
import android.net.Uri;
import android.os.AsyncTask;
import android.os.Handler;
import android.os.HandlerThread;
import android.os.Looper;
import android.os.Message;
import android.os.SystemClock;
import android.provider.ContactsContract;
import android.support.annotation.VisibleForTesting;
import android.text.TextUtils;
import android.util.ArrayMap;
import android.util.Log;
import android.util.TimingLogger;
import com.android.contacts.common.MoreContactUtils;
import com.android.contacts.common.list.ContactListFilterController;
import com.android.contacts.common.model.account.AccountType;
import com.android.contacts.common.model.account.AccountTypeWithDataSet;
import com.android.contacts.common.model.account.AccountWithDataSet;
import com.android.contacts.common.model.account.ExchangeAccountType;
import com.android.contacts.common.model.account.ExternalAccountType;
import com.android.contacts.common.model.account.FallbackAccountType;
import com.android.contacts.common.model.account.GoogleAccountType;
import com.android.contacts.common.model.account.SamsungAccountType;
import com.android.contacts.common.model.dataitem.DataKind;
import com.android.contacts.common.util.Constants;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Set;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.AtomicBoolean;

/**
 * Singleton holder for all parsed {@link AccountType} available on the system, typically filled
 * through {@link PackageManager} queries.
 */
public abstract class AccountTypeManager {

  static final String TAG = "AccountTypeManager";

  private static final Object mInitializationLock = new Object();
  private static AccountTypeManager mAccountTypeManager;

  /**
   * Requests the singleton instance of {@link AccountTypeManager} with data bound from the
   * available authenticators. This method can safely be called from the UI thread.
   */
  public static AccountTypeManager getInstance(Context context) {
    synchronized (mInitializationLock) {
      if (mAccountTypeManager == null) {
        context = context.getApplicationContext();
        mAccountTypeManager = new AccountTypeManagerImpl(context);
      }
    }
    return mAccountTypeManager;
  }

  /**
   * Set the instance of account type manager. This is only for and should only be used by unit
   * tests. While having this method is not ideal, it's simpler than the alternative of holding this
   * as a service in the ContactsApplication context class.
   *
   * @param mockManager The mock AccountTypeManager.
   */
  public static void setInstanceForTest(AccountTypeManager mockManager) {
    synchronized (mInitializationLock) {
      mAccountTypeManager = mockManager;
    }
  }

  /**
   * Returns the list of all accounts (if contactWritableOnly is false) or just the list of contact
   * writable accounts (if contactWritableOnly is true).
   */
  // TODO: Consider splitting this into getContactWritableAccounts() and getAllAccounts()
  public abstract List<AccountWithDataSet> getAccounts(boolean contactWritableOnly);

  /** Returns the list of accounts that are group writable. */
  public abstract List<AccountWithDataSet> getGroupWritableAccounts();

  public abstract AccountType getAccountType(AccountTypeWithDataSet accountTypeWithDataSet);

  public final AccountType getAccountType(String accountType, String dataSet) {
    return getAccountType(AccountTypeWithDataSet.get(accountType, dataSet));
  }

  public final AccountType getAccountTypeForAccount(AccountWithDataSet account) {
    if (account != null) {
      return getAccountType(account.getAccountTypeWithDataSet());
    }
    return getAccountType(null, null);
  }

  /**
   * @return Unmodifiable map from {@link AccountTypeWithDataSet}s to {@link AccountType}s which
   *     support the "invite" feature and have one or more account.
   *     <p>This is a filtered down and more "usable" list compared to {@link
   *     #getAllInvitableAccountTypes}, where usable is defined as: (1) making sure that the app
   *     that contributed the account type is not disabled (in order to avoid presenting the user
   *     with an option that does nothing), and (2) that there is at least one raw contact with that
   *     account type in the database (assuming that the user probably doesn't use that account
   *     type).
   *     <p>Warning: Don't use on the UI thread because this can scan the database.
   */
  public abstract Map<AccountTypeWithDataSet, AccountType> getUsableInvitableAccountTypes();

  /**
   * Find the best {@link DataKind} matching the requested {@link AccountType#accountType}, {@link
   * AccountType#dataSet}, and {@link DataKind#mimeType}. If no direct match found, we try searching
   * {@link FallbackAccountType}.
   */
  public DataKind getKindOrFallback(AccountType type, String mimeType) {
    return type == null ? null : type.getKindForMimetype(mimeType);
  }

  /**
   * Returns all registered {@link AccountType}s, including extension ones.
   *
   * @param contactWritableOnly if true, it only returns ones that support writing contacts.
   */
  public abstract List<AccountType> getAccountTypes(boolean contactWritableOnly);

  /**
   * @param contactWritableOnly if true, it only returns ones that support writing contacts.
   * @return true when this instance contains the given account.
   */
  public boolean contains(AccountWithDataSet account, boolean contactWritableOnly) {
    for (AccountWithDataSet account_2 : getAccounts(false)) {
      if (account.equals(account_2)) {
        return true;
      }
    }
    return false;
  }
}

class AccountTypeManagerImpl extends AccountTypeManager
    implements OnAccountsUpdateListener, SyncStatusObserver {

  private static final Map<AccountTypeWithDataSet, AccountType>
      EMPTY_UNMODIFIABLE_ACCOUNT_TYPE_MAP =
          Collections.unmodifiableMap(new HashMap<AccountTypeWithDataSet, AccountType>());

  /**
   * A sample contact URI used to test whether any activities will respond to an invitable intent
   * with the given URI as the intent data. This doesn't need to be specific to a real contact
   * because an app that intercepts the intent should probably do so for all types of contact URIs.
   */
  private static final Uri SAMPLE_CONTACT_URI = ContactsContract.Contacts.getLookupUri(1, "xxx");

  private static final int MESSAGE_LOAD_DATA = 0;
  private static final int MESSAGE_PROCESS_BROADCAST_INTENT = 1;
  private static final Comparator<AccountWithDataSet> ACCOUNT_COMPARATOR =
      new Comparator<AccountWithDataSet>() {
        @Override
        public int compare(AccountWithDataSet a, AccountWithDataSet b) {
          if (Objects.equals(a.name, b.name)
              && Objects.equals(a.type, b.type)
              && Objects.equals(a.dataSet, b.dataSet)) {
            return 0;
          } else if (b.name == null || b.type == null) {
            return -1;
          } else if (a.name == null || a.type == null) {
            return 1;
          } else {
            int diff = a.name.compareTo(b.name);
            if (diff != 0) {
              return diff;
            }
            diff = a.type.compareTo(b.type);
            if (diff != 0) {
              return diff;
            }

            // Accounts without data sets get sorted before those that have them.
            if (a.dataSet != null) {
              return b.dataSet == null ? 1 : a.dataSet.compareTo(b.dataSet);
            } else {
              return -1;
            }
          }
        }
      };
  private final InvitableAccountTypeCache mInvitableAccountTypeCache;
  /**
   * The boolean value is equal to true if the {@link InvitableAccountTypeCache} has been
   * initialized. False otherwise.
   */
  private final AtomicBoolean mInvitablesCacheIsInitialized = new AtomicBoolean(false);
  /**
   * The boolean value is equal to true if the {@link FindInvitablesTask} is still executing. False
   * otherwise.
   */
  private final AtomicBoolean mInvitablesTaskIsRunning = new AtomicBoolean(false);

  private final Handler mMainThreadHandler = new Handler(Looper.getMainLooper());
  private Context mContext;
  private final Runnable mCheckFilterValidityRunnable =
      new Runnable() {
        @Override
        public void run() {
          ContactListFilterController.getInstance(mContext).checkFilterValidity(true);
        }
      };
  private AccountManager mAccountManager;
  private AccountType mFallbackAccountType;
  private List<AccountWithDataSet> mAccounts = new ArrayList<>();
  private List<AccountWithDataSet> mContactWritableAccounts = new ArrayList<>();
  private List<AccountWithDataSet> mGroupWritableAccounts = new ArrayList<>();
  private Map<AccountTypeWithDataSet, AccountType> mAccountTypesWithDataSets = new ArrayMap<>();
  private Map<AccountTypeWithDataSet, AccountType> mInvitableAccountTypes =
      EMPTY_UNMODIFIABLE_ACCOUNT_TYPE_MAP;
  private HandlerThread mListenerThread;
  private Handler mListenerHandler;
  private BroadcastReceiver mBroadcastReceiver =
      new BroadcastReceiver() {

        @Override
        public void onReceive(Context context, Intent intent) {
          Message msg = mListenerHandler.obtainMessage(MESSAGE_PROCESS_BROADCAST_INTENT, intent);
          mListenerHandler.sendMessage(msg);
        }
      };
  /* A latch that ensures that asynchronous initialization completes before data is used */
  private volatile CountDownLatch mInitializationLatch = new CountDownLatch(1);

  /** Internal constructor that only performs initial parsing. */
  public AccountTypeManagerImpl(Context context) {
    mContext = context;
    mFallbackAccountType = new FallbackAccountType(context);

    mAccountManager = AccountManager.get(mContext);

    mListenerThread = new HandlerThread("AccountChangeListener");
    mListenerThread.start();
    mListenerHandler =
        new Handler(mListenerThread.getLooper()) {
          @Override
          public void handleMessage(Message msg) {
            switch (msg.what) {
              case MESSAGE_LOAD_DATA:
                loadAccountsInBackground();
                break;
              case MESSAGE_PROCESS_BROADCAST_INTENT:
                processBroadcastIntent((Intent) msg.obj);
                break;
            }
          }
        };

    mInvitableAccountTypeCache = new InvitableAccountTypeCache();

    // Request updates when packages or accounts change
    IntentFilter filter = new IntentFilter(Intent.ACTION_PACKAGE_ADDED);
    filter.addAction(Intent.ACTION_PACKAGE_REMOVED);
    filter.addAction(Intent.ACTION_PACKAGE_CHANGED);
    filter.addDataScheme("package");
    mContext.registerReceiver(mBroadcastReceiver, filter);
    IntentFilter sdFilter = new IntentFilter();
    sdFilter.addAction(Intent.ACTION_EXTERNAL_APPLICATIONS_AVAILABLE);
    sdFilter.addAction(Intent.ACTION_EXTERNAL_APPLICATIONS_UNAVAILABLE);
    mContext.registerReceiver(mBroadcastReceiver, sdFilter);

    // Request updates when locale is changed so that the order of each field will
    // be able to be changed on the locale change.
    filter = new IntentFilter(Intent.ACTION_LOCALE_CHANGED);
    mContext.registerReceiver(mBroadcastReceiver, filter);

    mAccountManager.addOnAccountsUpdatedListener(this, mListenerHandler, false);

    ContentResolver.addStatusChangeListener(ContentResolver.SYNC_OBSERVER_TYPE_SETTINGS, this);

    mListenerHandler.sendEmptyMessage(MESSAGE_LOAD_DATA);
  }

  /**
   * Find a specific {@link AuthenticatorDescription} in the provided list that matches the given
   * account type.
   */
  protected static AuthenticatorDescription findAuthenticator(
      AuthenticatorDescription[] auths, String accountType) {
    for (AuthenticatorDescription auth : auths) {
      if (accountType.equals(auth.type)) {
        return auth;
      }
    }
    return null;
  }

  /**
   * Return all {@link AccountType}s with at least one account which supports "invite", i.e. its
   * {@link AccountType#getInviteContactActivityClassName()} is not empty.
   */
  @VisibleForTesting
  static Map<AccountTypeWithDataSet, AccountType> findAllInvitableAccountTypes(
      Context context,
      Collection<AccountWithDataSet> accounts,
      Map<AccountTypeWithDataSet, AccountType> accountTypesByTypeAndDataSet) {
    Map<AccountTypeWithDataSet, AccountType> result = new ArrayMap<>();
    for (AccountWithDataSet account : accounts) {
      AccountTypeWithDataSet accountTypeWithDataSet = account.getAccountTypeWithDataSet();
      AccountType type = accountTypesByTypeAndDataSet.get(accountTypeWithDataSet);
      if (type == null) {
        continue; // just in case
      }
      if (result.containsKey(accountTypeWithDataSet)) {
        continue;
      }

      if (Log.isLoggable(TAG, Log.DEBUG)) {
        Log.d(
            TAG,
            "Type "
                + accountTypeWithDataSet
                + " inviteClass="
                + type.getInviteContactActivityClassName());
      }
      if (!TextUtils.isEmpty(type.getInviteContactActivityClassName())) {
        result.put(accountTypeWithDataSet, type);
      }
    }
    return Collections.unmodifiableMap(result);
  }

  @Override
  public void onStatusChanged(int which) {
    mListenerHandler.sendEmptyMessage(MESSAGE_LOAD_DATA);
  }

  public void processBroadcastIntent(Intent intent) {
    mListenerHandler.sendEmptyMessage(MESSAGE_LOAD_DATA);
  }

  /* This notification will arrive on the background thread */
  public void onAccountsUpdated(Account[] accounts) {
    // Refresh to catch any changed accounts
    loadAccountsInBackground();
  }

  /**
   * Returns instantly if accounts and account types have already been loaded. Otherwise waits for
   * the background thread to complete the loading.
   */
  void ensureAccountsLoaded() {
    CountDownLatch latch = mInitializationLatch;
    if (latch == null) {
      return;
    }
    while (true) {
      try {
        latch.await();
        return;
      } catch (InterruptedException e) {
        Thread.currentThread().interrupt();
      }
    }
  }

  /**
   * Loads account list and corresponding account types (potentially with data sets). Always called
   * on a background thread.
   */
  protected void loadAccountsInBackground() {
    if (Log.isLoggable(Constants.PERFORMANCE_TAG, Log.DEBUG)) {
      Log.d(Constants.PERFORMANCE_TAG, "AccountTypeManager.loadAccountsInBackground start");
    }
    TimingLogger timings = new TimingLogger(TAG, "loadAccountsInBackground");
    final long startTime = SystemClock.currentThreadTimeMillis();
    final long startTimeWall = SystemClock.elapsedRealtime();

    // Account types, keyed off the account type and data set concatenation.
    final Map<AccountTypeWithDataSet, AccountType> accountTypesByTypeAndDataSet = new ArrayMap<>();

    // The same AccountTypes, but keyed off {@link RawContacts#ACCOUNT_TYPE}.  Since there can
    // be multiple account types (with different data sets) for the same type of account, each
    // type string may have multiple AccountType entries.
    final Map<String, List<AccountType>> accountTypesByType = new ArrayMap<>();

    final List<AccountWithDataSet> allAccounts = new ArrayList<>();
    final List<AccountWithDataSet> contactWritableAccounts = new ArrayList<>();
    final List<AccountWithDataSet> groupWritableAccounts = new ArrayList<>();
    final Set<String> extensionPackages = new HashSet<>();

    final AccountManager am = mAccountManager;

    final SyncAdapterType[] syncs = ContentResolver.getSyncAdapterTypes();
    final AuthenticatorDescription[] auths = am.getAuthenticatorTypes();

    // First process sync adapters to find any that provide contact data.
    for (SyncAdapterType sync : syncs) {
      if (!ContactsContract.AUTHORITY.equals(sync.authority)) {
        // Skip sync adapters that don't provide contact data.
        continue;
      }

      // Look for the formatting details provided by each sync
      // adapter, using the authenticator to find general resources.
      final String type = sync.accountType;
      final AuthenticatorDescription auth = findAuthenticator(auths, type);
      if (auth == null) {
        Log.w(TAG, "No authenticator found for type=" + type + ", ignoring it.");
        continue;
      }

      AccountType accountType;
      if (GoogleAccountType.ACCOUNT_TYPE.equals(type)) {
        accountType = new GoogleAccountType(mContext, auth.packageName);
      } else if (ExchangeAccountType.isExchangeType(type)) {
        accountType = new ExchangeAccountType(mContext, auth.packageName, type);
      } else if (SamsungAccountType.isSamsungAccountType(mContext, type, auth.packageName)) {
        accountType = new SamsungAccountType(mContext, auth.packageName, type);
      } else {
        Log.d(
            TAG, "Registering external account type=" + type + ", packageName=" + auth.packageName);
        accountType = new ExternalAccountType(mContext, auth.packageName, false);
      }
      if (!accountType.isInitialized()) {
        if (accountType.isEmbedded()) {
          throw new IllegalStateException(
              "Problem initializing embedded type " + accountType.getClass().getCanonicalName());
        } else {
          // Skip external account types that couldn't be initialized.
          continue;
        }
      }

      accountType.accountType = auth.type;
      accountType.titleRes = auth.labelId;
      accountType.iconRes = auth.iconId;

      addAccountType(accountType, accountTypesByTypeAndDataSet, accountTypesByType);

      // Check to see if the account type knows of any other non-sync-adapter packages
      // that may provide other data sets of contact data.
      extensionPackages.addAll(accountType.getExtensionPackageNames());
    }

    // If any extension packages were specified, process them as well.
    if (!extensionPackages.isEmpty()) {
      Log.d(TAG, "Registering " + extensionPackages.size() + " extension packages");
      for (String extensionPackage : extensionPackages) {
        ExternalAccountType accountType = new ExternalAccountType(mContext, extensionPackage, true);
        if (!accountType.isInitialized()) {
          // Skip external account types that couldn't be initialized.
          continue;
        }
        if (!accountType.hasContactsMetadata()) {
          Log.w(
              TAG,
              "Skipping extension package "
                  + extensionPackage
                  + " because"
                  + " it doesn't have the CONTACTS_STRUCTURE metadata");
          continue;
        }
        if (TextUtils.isEmpty(accountType.accountType)) {
          Log.w(
              TAG,
              "Skipping extension package "
                  + extensionPackage
                  + " because"
                  + " the CONTACTS_STRUCTURE metadata doesn't have the accountType"
                  + " attribute");
          continue;
        }
        Log.d(
            TAG,
            "Registering extension package account type="
                + accountType.accountType
                + ", dataSet="
                + accountType.dataSet
                + ", packageName="
                + extensionPackage);

        addAccountType(accountType, accountTypesByTypeAndDataSet, accountTypesByType);
      }
    }
    timings.addSplit("Loaded account types");

    // Map in accounts to associate the account names with each account type entry.
    Account[] accounts = mAccountManager.getAccounts();
    for (Account account : accounts) {
      boolean syncable = ContentResolver.getIsSyncable(account, ContactsContract.AUTHORITY) > 0;

      if (syncable) {
        List<AccountType> accountTypes = accountTypesByType.get(account.type);
        if (accountTypes != null) {
          // Add an account-with-data-set entry for each account type that is
          // authenticated by this account.
          for (AccountType accountType : accountTypes) {
            AccountWithDataSet accountWithDataSet =
                new AccountWithDataSet(account.name, account.type, accountType.dataSet);
            allAccounts.add(accountWithDataSet);
            if (accountType.areContactsWritable()) {
              contactWritableAccounts.add(accountWithDataSet);
            }
            if (accountType.isGroupMembershipEditable()) {
              groupWritableAccounts.add(accountWithDataSet);
            }
          }
        }
      }
    }

    Collections.sort(allAccounts, ACCOUNT_COMPARATOR);
    Collections.sort(contactWritableAccounts, ACCOUNT_COMPARATOR);
    Collections.sort(groupWritableAccounts, ACCOUNT_COMPARATOR);

    timings.addSplit("Loaded accounts");

    synchronized (this) {
      mAccountTypesWithDataSets = accountTypesByTypeAndDataSet;
      mAccounts = allAccounts;
      mContactWritableAccounts = contactWritableAccounts;
      mGroupWritableAccounts = groupWritableAccounts;
      mInvitableAccountTypes =
          findAllInvitableAccountTypes(mContext, allAccounts, accountTypesByTypeAndDataSet);
    }

    timings.dumpToLog();
    final long endTimeWall = SystemClock.elapsedRealtime();
    final long endTime = SystemClock.currentThreadTimeMillis();

    Log.i(
        TAG,
        "Loaded meta-data for "
            + mAccountTypesWithDataSets.size()
            + " account types, "
            + mAccounts.size()
            + " accounts in "
            + (endTimeWall - startTimeWall)
            + "ms(wall) "
            + (endTime - startTime)
            + "ms(cpu)");

    if (mInitializationLatch != null) {
      mInitializationLatch.countDown();
      mInitializationLatch = null;
    }
    if (Log.isLoggable(Constants.PERFORMANCE_TAG, Log.DEBUG)) {
      Log.d(Constants.PERFORMANCE_TAG, "AccountTypeManager.loadAccountsInBackground finish");
    }

    // Check filter validity since filter may become obsolete after account update. It must be
    // done from UI thread.
    mMainThreadHandler.post(mCheckFilterValidityRunnable);
  }

  // Bookkeeping method for tracking the known account types in the given maps.
  private void addAccountType(
      AccountType accountType,
      Map<AccountTypeWithDataSet, AccountType> accountTypesByTypeAndDataSet,
      Map<String, List<AccountType>> accountTypesByType) {
    accountTypesByTypeAndDataSet.put(accountType.getAccountTypeAndDataSet(), accountType);
    List<AccountType> accountsForType = accountTypesByType.get(accountType.accountType);
    if (accountsForType == null) {
      accountsForType = new ArrayList<>();
    }
    accountsForType.add(accountType);
    accountTypesByType.put(accountType.accountType, accountsForType);
  }

  /** Return list of all known, contact writable {@link AccountWithDataSet}'s. */
  @Override
  public List<AccountWithDataSet> getAccounts(boolean contactWritableOnly) {
    ensureAccountsLoaded();
    return contactWritableOnly ? mContactWritableAccounts : mAccounts;
  }

  /** Return the list of all known, group writable {@link AccountWithDataSet}'s. */
  public List<AccountWithDataSet> getGroupWritableAccounts() {
    ensureAccountsLoaded();
    return mGroupWritableAccounts;
  }

  /**
   * Find the best {@link DataKind} matching the requested {@link AccountType#accountType}, {@link
   * AccountType#dataSet}, and {@link DataKind#mimeType}. If no direct match found, we try searching
   * {@link FallbackAccountType}.
   */
  @Override
  public DataKind getKindOrFallback(AccountType type, String mimeType) {
    ensureAccountsLoaded();
    DataKind kind = null;

    // Try finding account type and kind matching request
    if (type != null) {
      kind = type.getKindForMimetype(mimeType);
    }

    if (kind == null) {
      // Nothing found, so try fallback as last resort
      kind = mFallbackAccountType.getKindForMimetype(mimeType);
    }

    if (kind == null) {
      if (Log.isLoggable(TAG, Log.DEBUG)) {
        Log.d(TAG, "Unknown type=" + type + ", mime=" + mimeType);
      }
    }

    return kind;
  }

  /** Return {@link AccountType} for the given account type and data set. */
  @Override
  public AccountType getAccountType(AccountTypeWithDataSet accountTypeWithDataSet) {
    ensureAccountsLoaded();
    synchronized (this) {
      AccountType type = mAccountTypesWithDataSets.get(accountTypeWithDataSet);
      return type != null ? type : mFallbackAccountType;
    }
  }

  /**
   * @return Unmodifiable map from {@link AccountTypeWithDataSet}s to {@link AccountType}s which
   *     support the "invite" feature and have one or more account. This is an unfiltered list. See
   *     {@link #getUsableInvitableAccountTypes()}.
   */
  private Map<AccountTypeWithDataSet, AccountType> getAllInvitableAccountTypes() {
    ensureAccountsLoaded();
    return mInvitableAccountTypes;
  }

  @Override
  public Map<AccountTypeWithDataSet, AccountType> getUsableInvitableAccountTypes() {
    ensureAccountsLoaded();
    // Since this method is not thread-safe, it's possible for multiple threads to encounter
    // the situation where (1) the cache has not been initialized yet or
    // (2) an async task to refresh the account type list in the cache has already been
    // started. Hence we use {@link AtomicBoolean}s and return cached values immediately
    // while we compute the actual result in the background. We use this approach instead of
    // using "synchronized" because computing the account type list involves a DB read, and
    // can potentially cause a deadlock situation if this method is called from code which
    // holds the DB lock. The trade-off of potentially having an incorrect list of invitable
    // account types for a short period of time seems more manageable than enforcing the
    // context in which this method is called.

    // Computing the list of usable invitable account types is done on the fly as requested.
    // If this method has never been called before, then block until the list has been computed.
    if (!mInvitablesCacheIsInitialized.get()) {
      mInvitableAccountTypeCache.setCachedValue(findUsableInvitableAccountTypes(mContext));
      mInvitablesCacheIsInitialized.set(true);
    } else {
      // Otherwise, there is a value in the cache. If the value has expired and
      // an async task has not already been started by another thread, then kick off a new
      // async task to compute the list.
      if (mInvitableAccountTypeCache.isExpired()
          && mInvitablesTaskIsRunning.compareAndSet(false, true)) {
        new FindInvitablesTask().execute();
      }
    }

    return mInvitableAccountTypeCache.getCachedValue();
  }

  /**
   * Return all usable {@link AccountType}s that support the "invite" feature from the list of all
   * potential invitable account types (retrieved from {@link #getAllInvitableAccountTypes}). A
   * usable invitable account type means: (1) there is at least 1 raw contact in the database with
   * that account type, and (2) the app contributing the account type is not disabled.
   *
   * <p>Warning: Don't use on the UI thread because this can scan the database.
   */
  private Map<AccountTypeWithDataSet, AccountType> findUsableInvitableAccountTypes(
      Context context) {
    Map<AccountTypeWithDataSet, AccountType> allInvitables = getAllInvitableAccountTypes();
    if (allInvitables.isEmpty()) {
      return EMPTY_UNMODIFIABLE_ACCOUNT_TYPE_MAP;
    }

    final Map<AccountTypeWithDataSet, AccountType> result = new ArrayMap<>();
    result.putAll(allInvitables);

    final PackageManager packageManager = context.getPackageManager();
    for (AccountTypeWithDataSet accountTypeWithDataSet : allInvitables.keySet()) {
      AccountType accountType = allInvitables.get(accountTypeWithDataSet);

      // Make sure that account types don't come from apps that are disabled.
      Intent invitableIntent = MoreContactUtils.getInvitableIntent(accountType, SAMPLE_CONTACT_URI);
      if (invitableIntent == null) {
        result.remove(accountTypeWithDataSet);
        continue;
      }
      ResolveInfo resolveInfo =
          packageManager.resolveActivity(invitableIntent, PackageManager.MATCH_DEFAULT_ONLY);
      if (resolveInfo == null) {
        // If we can't find an activity to start for this intent, then there's no point in
        // showing this option to the user.
        result.remove(accountTypeWithDataSet);
        continue;
      }

      // Make sure that there is at least 1 raw contact with this account type. This check
      // is non-trivial and should not be done on the UI thread.
      if (!accountTypeWithDataSet.hasData(context)) {
        result.remove(accountTypeWithDataSet);
      }
    }

    return Collections.unmodifiableMap(result);
  }

  @Override
  public List<AccountType> getAccountTypes(boolean contactWritableOnly) {
    ensureAccountsLoaded();
    final List<AccountType> accountTypes = new ArrayList<>();
    synchronized (this) {
      for (AccountType type : mAccountTypesWithDataSets.values()) {
        if (!contactWritableOnly || type.areContactsWritable()) {
          accountTypes.add(type);
        }
      }
    }
    return accountTypes;
  }

  /**
   * This cache holds a list of invitable {@link AccountTypeWithDataSet}s, in the form of a {@link
   * Map<AccountTypeWithDataSet, AccountType>}. Note that the cached value is valid only for {@link
   * #TIME_TO_LIVE} milliseconds.
   */
  private static final class InvitableAccountTypeCache {

    /**
     * The cached {@link #mInvitableAccountTypes} list expires after this number of milliseconds has
     * elapsed.
     */
    private static final long TIME_TO_LIVE = 60000;

    private Map<AccountTypeWithDataSet, AccountType> mInvitableAccountTypes;

    private long mTimeLastSet;

    /**
     * Returns true if the data in this cache is stale and needs to be refreshed. Returns false
     * otherwise.
     */
    public boolean isExpired() {
      return SystemClock.elapsedRealtime() - mTimeLastSet > TIME_TO_LIVE;
    }

    /**
     * Returns the cached value. Note that the caller is responsible for checking {@link
     * #isExpired()} to ensure that the value is not stale.
     */
    public Map<AccountTypeWithDataSet, AccountType> getCachedValue() {
      return mInvitableAccountTypes;
    }

    public void setCachedValue(Map<AccountTypeWithDataSet, AccountType> map) {
      mInvitableAccountTypes = map;
      mTimeLastSet = SystemClock.elapsedRealtime();
    }
  }

  /**
   * Background task to find all usable {@link AccountType}s that support the "invite" feature from
   * the list of all potential invitable account types. Once the work is completed, the list of
   * account types is stored in the {@link AccountTypeManager}'s {@link InvitableAccountTypeCache}.
   */
  private class FindInvitablesTask
      extends AsyncTask<Void, Void, Map<AccountTypeWithDataSet, AccountType>> {

    @Override
    protected Map<AccountTypeWithDataSet, AccountType> doInBackground(Void... params) {
      return findUsableInvitableAccountTypes(mContext);
    }

    @Override
    protected void onPostExecute(Map<AccountTypeWithDataSet, AccountType> accountTypes) {
      mInvitableAccountTypeCache.setCachedValue(accountTypes);
      mInvitablesTaskIsRunning.set(false);
    }
  }
}