// Copyright 2020 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "components/sync/invalidations/fcm_handler.h"

#include <map>
#include <utility>

#include "base/feature_list.h"
#include "base/functional/callback_helpers.h"
#include "base/logging.h"
#include "base/metrics/histogram_functions.h"
#include "base/observer_list.h"
#include "components/gcm_driver/gcm_driver.h"
#include "components/gcm_driver/instance_id/instance_id_driver.h"
#include "components/sync/base/features.h"
#include "components/sync/invalidations/fcm_registration_token_observer.h"
#include "components/sync/invalidations/invalidations_listener.h"

namespace syncer {

// Lower bound time between two token validations when listening.
constexpr int kTokenValidationPeriodMinutesDefault = 60 * 24;

constexpr int kInstanceIDTokenTTLSeconds = 14 * 24 * 60 * 60;  // 2 weeks.

// Limits the number of last received buffered messages.
constexpr size_t kMaxBufferedLastFcmMessages = 20;

FCMHandler::FCMHandler(gcm::GCMDriver* gcm_driver,
                       instance_id::InstanceIDDriver* instance_id_driver,
                       const std::string& sender_id,
                       const std::string& app_id)
    : gcm_driver_(gcm_driver),
      instance_id_driver_(instance_id_driver),
      sender_id_(sender_id),
      app_id_(app_id) {}

FCMHandler::~FCMHandler() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  StopListening();
}

void FCMHandler::StartListening() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  DCHECK(!IsListening());
  DCHECK(last_received_messages_.empty());
  DCHECK(!fcm_registration_token_.has_value());
  // Note that AddAppHandler() causes an immediate replay of all received
  // messages in background on Android. Those messages will be stored in
  // `last_received_messages_` and delivered to listeners once they have been
  // added.
  gcm_driver_->AddAppHandler(app_id_, this);
  StartTokenFetch();
}

void FCMHandler::StopListening() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  // StopListening() may be called after StartListening() right away and
  // DidRetrieveToken() won't be called.
  if (IsListening()) {
    gcm_driver_->RemoveAppHandler(app_id_);
    fcm_registration_token_ = std::nullopt;
    token_validation_timer_.Stop();
    last_received_messages_.clear();
  }
}

void FCMHandler::StopListeningPermanently() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);

  if (instance_id_driver_->ExistsInstanceID(app_id_)) {
    instance_id_driver_->GetInstanceID(app_id_)->DeleteID(
        /*callback=*/base::DoNothing());
  }

  const bool was_listening = IsListening();
  const bool had_token = fcm_registration_token_.has_value();

  StopListening();

  if (was_listening && had_token) {
    // After permanently stopping listening, the token is cleared.
    // Observers should be notified of this change.
    for (FCMRegistrationTokenObserver& token_observer : token_observers_) {
      token_observer.OnFCMRegistrationTokenChanged();
    }
  }
}

const std::optional<std::string>& FCMHandler::GetFCMRegistrationToken() const {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  return fcm_registration_token_;
}

void FCMHandler::ShutdownHandler() {
  // Shutdown() should come before and it removes us from the list of app
  // handlers of gcm::GCMDriver so this shouldn't ever been called.
  NOTREACHED();
}

void FCMHandler::AddListener(InvalidationsListener* listener) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  if (listeners_.HasObserver(listener)) {
    return;
  }
  listeners_.AddObserver(listener);

  // Immediately replay any buffered messages received before the `listener`
  // was added.
  for (const std::string& message : last_received_messages_) {
    listener->OnInvalidationReceived(message);
  }
}

bool FCMHandler::HasListener(InvalidationsListener* listener) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  return listeners_.HasObserver(listener);
}

void FCMHandler::RemoveListener(InvalidationsListener* listener) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  listeners_.RemoveObserver(listener);
}

void FCMHandler::OnStoreReset() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  // The FCM registration token is not stored by FCMHandler.
}

void FCMHandler::AddTokenObserver(FCMRegistrationTokenObserver* observer) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  token_observers_.AddObserver(observer);
}

void FCMHandler::RemoveTokenObserver(FCMRegistrationTokenObserver* observer) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  token_observers_.RemoveObserver(observer);
}

void FCMHandler::OnMessage(const std::string& app_id,
                           const gcm::IncomingMessage& message) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  DCHECK_EQ(app_id, app_id_);

  if (last_received_messages_.size() >= kMaxBufferedLastFcmMessages) {
    last_received_messages_.pop_front();
  }
  last_received_messages_.push_back(message.raw_data);
  for (InvalidationsListener& listener : listeners_) {
    listener.OnInvalidationReceived(message.raw_data);
  }
}

void FCMHandler::OnMessagesDeleted(const std::string& app_id) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  DCHECK_EQ(app_id, app_id_);

  base::UmaHistogramBoolean("Sync.Invalidations.OnMessagesDeleted", true);
}

void FCMHandler::OnSendError(const std::string& app_id,
                             const gcm::GCMClient::SendErrorDetails& details) {
  // Should never be called because the invalidation service doesn't send GCM
  // messages to the server.
  NOTREACHED() << "FCMHandler doesn't send GCM messages.";
}

void FCMHandler::OnSendAcknowledged(const std::string& app_id,
                                    const std::string& message_id) {
  // Should never be called because the invalidation service doesn't send GCM
  // messages to the server.
  NOTREACHED() << "FCMHandler doesn't send GCM messages.";
}

bool FCMHandler::IsListening() const {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  return gcm_driver_->GetAppHandler(app_id_) != nullptr;
}

void FCMHandler::DidRetrieveToken(const std::string& subscription_token,
                                  instance_id::InstanceID::Result result) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);

  if (!IsListening()) {
    // After we requested the token, `StopListening` has been called. Thus,
    // ignore the token.
    return;
  }

  if (result != instance_id::InstanceID::SUCCESS) {
    DLOG(WARNING) << "Messaging subscription failed: " << result;
  } else if (fcm_registration_token_ != subscription_token) {
    // Notify observers only if the token has changed.
    fcm_registration_token_ = subscription_token;
    for (FCMRegistrationTokenObserver& token_observer : token_observers_) {
      token_observer.OnFCMRegistrationTokenChanged();
    }
  }

  ScheduleNextTokenValidation();
}

void FCMHandler::ScheduleNextTokenValidation() {
  DCHECK(IsListening());

  token_validation_timer_.Start(
      FROM_HERE, base::Minutes(kTokenValidationPeriodMinutesDefault),
      base::BindOnce(&FCMHandler::StartTokenValidation,
                     weak_ptr_factory_.GetWeakPtr()));
}

void FCMHandler::StartTokenValidation() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  DCHECK(IsListening());
  StartTokenFetch();
}

void FCMHandler::StartTokenFetch() {
  std::set<instance_id::InstanceID::Flags> flags = {
      instance_id::InstanceID::Flags::kIsLazy};
  if (base::FeatureList::IsEnabled(kSyncInvalidationsBypassScheduler)) {
    flags.insert(instance_id::InstanceID::Flags::kBypassScheduler);
  }

  instance_id_driver_->GetInstanceID(app_id_)->GetToken(
      sender_id_, instance_id::kGCMScope,
      /*time_to_live=*/base::Seconds(kInstanceIDTokenTTLSeconds), flags,
      base::BindOnce(&FCMHandler::DidRetrieveToken,
                     weak_ptr_factory_.GetWeakPtr()));
}

}  // namespace syncer