// Copyright 2018 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_sessions/session_sync_bridge.h"

#include <stdint.h>

#include <algorithm>
#include <set>
#include <utility>

#include "base/functional/bind.h"
#include "base/functional/callback_helpers.h"
#include "base/location.h"
#include "base/logging.h"
#include "base/memory/raw_ptr.h"
#include "base/task/sequenced_task_runner.h"
#include "base/time/time.h"
#include "components/sync/base/client_tag_hash.h"
#include "components/sync/base/deletion_origin.h"
#include "components/sync/base/time.h"
#include "components/sync/model/data_type_activation_request.h"
#include "components/sync/model/entity_change.h"
#include "components/sync/model/in_memory_metadata_change_list.h"
#include "components/sync/model/metadata_batch.h"
#include "components/sync/model/mutable_data_batch.h"
#include "components/sync/protocol/session_specifics.pb.h"
#include "components/sync_sessions/session_sync_prefs.h"
#include "components/sync_sessions/sync_sessions_client.h"
#include "components/sync_sessions/synced_window_delegate.h"
#include "components/sync_sessions/synced_window_delegates_getter.h"

namespace sync_sessions {
namespace {

using sync_pb::SessionSpecifics;
using syncer::MetadataChangeList;

// Default time without activity after which a session is considered stale and
// becomes a candidate for garbage collection.
const base::TimeDelta kStaleSessionThreshold = base::Days(28);

std::unique_ptr<syncer::EntityData> MoveToEntityData(
    const std::string& client_name,
    SessionSpecifics* specifics) {
  auto entity_data = std::make_unique<syncer::EntityData>();
  entity_data->name = client_name;
  entity_data->specifics.mutable_session()->Swap(specifics);
  return entity_data;
}

class LocalSessionWriteBatch : public LocalSessionEventHandlerImpl::WriteBatch {
 public:
  LocalSessionWriteBatch(const SessionStore::SessionInfo& session_info,
                         std::unique_ptr<SessionStore::WriteBatch> batch,
                         syncer::DataTypeLocalChangeProcessor* processor)
      : session_info_(session_info),
        batch_(std::move(batch)),
        processor_(processor) {
    DCHECK(batch_);
    DCHECK(processor_);
    DCHECK(processor_->IsTrackingMetadata());
  }

  ~LocalSessionWriteBatch() override = default;

  // WriteBatch implementation.
  void Delete(int tab_node_id) override {
    const std::string storage_key =
        batch_->DeleteLocalTabWithoutUpdatingTracker(tab_node_id);
    processor_->Delete(storage_key, syncer::DeletionOrigin::Unspecified(),
                       batch_->GetMetadataChangeList());
  }

  void Put(std::unique_ptr<sync_pb::SessionSpecifics> specifics) override {
    DCHECK(SessionStore::AreValidSpecifics(*specifics));
    const std::string storage_key =
        batch_->PutWithoutUpdatingTracker(*specifics);

    processor_->Put(
        storage_key,
        MoveToEntityData(session_info_.client_name, specifics.get()),
        batch_->GetMetadataChangeList());
  }

  void Commit() override {
    DCHECK(batch_) << "Cannot commit twice";
    SessionStore::WriteBatch::Commit(std::move(batch_));
  }

 private:
  const SessionStore::SessionInfo session_info_;
  std::unique_ptr<SessionStore::WriteBatch> batch_;
  const raw_ptr<syncer::DataTypeLocalChangeProcessor> processor_;
};

}  // namespace

SessionSyncBridge::SessionSyncBridge(
    const base::RepeatingClosure& notify_foreign_session_updated_cb,
    SyncSessionsClient* sessions_client,
    std::unique_ptr<syncer::DataTypeLocalChangeProcessor> change_processor)
    : DataTypeSyncBridge(std::move(change_processor)),
      notify_foreign_session_updated_cb_(notify_foreign_session_updated_cb),
      sessions_client_(sessions_client),
      local_session_event_router_(
          sessions_client->GetLocalSessionEventRouter()) {
  DCHECK(sessions_client_);
  DCHECK(local_session_event_router_);
}

SessionSyncBridge::~SessionSyncBridge() {
  if (syncing_) {
    local_session_event_router_->Stop();
  }
}

SessionsGlobalIdMapper* SessionSyncBridge::GetGlobalIdMapper() {
  return &global_id_mapper_;
}

OpenTabsUIDelegate* SessionSyncBridge::GetOpenTabsUIDelegate() {
  if (!syncing_) {
    return nullptr;
  }
  return syncing_->open_tabs_ui_delegate.get();
}

bool SessionSyncBridge::IsLocalDataOutOfSyncForTest() const {
  return sessions_client_ &&
         sessions_client_->GetSessionSyncPrefs()->GetLocalDataOutOfSync();
}

std::unique_ptr<MetadataChangeList>
SessionSyncBridge::CreateMetadataChangeList() {
  return std::make_unique<syncer::InMemoryMetadataChangeList>();
}

std::optional<syncer::ModelError> SessionSyncBridge::MergeFullSyncData(
    std::unique_ptr<MetadataChangeList> metadata_change_list,
    syncer::EntityChangeList entity_data) {
  DCHECK(!syncing_);
  DCHECK(change_processor()->IsTrackingMetadata());

  StartLocalSessionEventHandler(/*is_new_session=*/true);

  return ApplyIncrementalSyncChanges(std::move(metadata_change_list),
                                     std::move(entity_data));
}

void SessionSyncBridge::StartLocalSessionEventHandler(bool is_new_session) {
  // We should be ready to propagate local state to sync.
  DCHECK(change_processor()->IsTrackingMetadata());
  DCHECK(!syncing_);

  syncing_.emplace();

  // Constructing LocalSessionEventHandlerImpl takes care of the "merge" logic,
  // that is, associating the local windows and tabs with the state in the
  // store.
  syncing_->local_session_event_handler =
      std::make_unique<LocalSessionEventHandlerImpl>(
          /*delegate=*/this, sessions_client_, store_->mutable_tracker(),
          is_new_session);

  syncing_->open_tabs_ui_delegate = std::make_unique<OpenTabsUIDelegateImpl>(
      sessions_client_, store_->tracker(),
      base::BindRepeating(&SessionSyncBridge::DeleteForeignSessionFromUI,
                          base::Unretained(this)));

  // Start processing local changes, which will be propagated to the store as
  // well as the processor.
  local_session_event_router_->StartRoutingTo(
      syncing_->local_session_event_handler.get());

  // Initializing |syncing_| influences the behavior of the public API, because
  // GetOpenTabsUIDelegate() transitions from returning nullptr to returning an
  // actual delegate. The nullptr has specifics semantics documented in the
  // SessionSyncService API, so interested parties (subscribed to changes)
  // should be notified that the value changed. https://crbug.com/1422634.
  notify_foreign_session_updated_cb_.Run();
}

std::optional<syncer::ModelError>
SessionSyncBridge::ApplyIncrementalSyncChanges(
    std::unique_ptr<MetadataChangeList> metadata_change_list,
    syncer::EntityChangeList entity_changes) {
  DCHECK(change_processor()->IsTrackingMetadata());
  DCHECK(syncing_);
  DCHECK(sessions_client_);

  // Merging sessions is simple: remote entities are expected to be foreign
  // sessions (identified by the session tag)  and hence must simply be
  // stored (server wins, including undeletion). For local sessions, remote
  // information is ignored (local wins).
  std::unique_ptr<SessionStore::WriteBatch> batch =
      CreateSessionStoreWriteBatch();

  for (const std::unique_ptr<syncer::EntityChange>& change : entity_changes) {
    switch (change->type()) {
      case syncer::EntityChange::ACTION_DELETE:
        // Deletions are all or nothing (since we only ever delete entire
        // sessions). Therefore we don't care if it's a tab node or meta node,
        // and just ensure we've disassociated.
        if (store_->StorageKeyMatchesLocalSession(change->storage_key())) {
          // Another client has attempted to delete our local data (possibly by
          // error or a clock is inaccurate). Just ignore the deletion for now.
          DLOG(WARNING) << "Local session data deleted. Ignoring until next "
                        << "local navigation event.";
          sessions_client_->GetSessionSyncPrefs()->SetLocalDataOutOfSync(true);
          static_cast<syncer::InMemoryMetadataChangeList*>(
              metadata_change_list.get())
              ->DropMetadataChangeForStorageKey(change->storage_key());
        } else {
          // Deleting an entity (if it's a header entity) may cascade other
          // deletions, so let's assume that whoever initiated remote deletions
          // must have taken care of deleting them all. We don't have to commit
          // these deletions, simply delete all local sync metadata (untrack).
          for (const std::string& deleted_storage_key :
               batch->DeleteForeignEntityAndUpdateTracker(
                   change->storage_key())) {
            change_processor()->UntrackEntityForStorageKey(deleted_storage_key);
            metadata_change_list->ClearMetadata(deleted_storage_key);
          }
        }
        break;
      case syncer::EntityChange::ACTION_ADD:
      case syncer::EntityChange::ACTION_UPDATE: {
        const SessionSpecifics& specifics = change->data().specifics.session();

        if (store_->StorageKeyMatchesLocalSession(change->storage_key())) {
          // We should only ever receive a change to our own machine's session
          // info if encryption was turned on. In that case, the data is still
          // the same, so we can ignore.
          DLOG(WARNING) << "Dropping modification to local session.";
          sessions_client_->GetSessionSyncPrefs()->SetLocalDataOutOfSync(true);
          continue;
        }

        if (!SessionStore::AreValidSpecifics(specifics)) {
          continue;
        }

        // Guaranteed by the processor.
        DCHECK_EQ(change->data().client_tag_hash,
                  syncer::ClientTagHash::FromUnhashed(
                      syncer::SESSIONS, SessionStore::GetClientTag(specifics)));

        batch->PutAndUpdateTracker(specifics, change->data().modification_time);
        break;
      }
    }
  }

  static_cast<syncer::InMemoryMetadataChangeList*>(metadata_change_list.get())
      ->TransferChangesTo(batch->GetMetadataChangeList());

  DoGarbageCollection(batch.get());

  SessionStore::WriteBatch::Commit(std::move(batch));

  if (!entity_changes.empty()) {
    notify_foreign_session_updated_cb_.Run();
  }

  return std::nullopt;
}

std::unique_ptr<syncer::DataBatch> SessionSyncBridge::GetDataForCommit(
    StorageKeyList storage_keys) {
  DCHECK(syncing_);
  return store_->GetSessionDataForKeys(storage_keys);
}

std::unique_ptr<syncer::DataBatch> SessionSyncBridge::GetAllDataForDebugging() {
  DCHECK(syncing_);
  return store_->GetAllSessionData();
}

std::string SessionSyncBridge::GetClientTag(
    const syncer::EntityData& entity_data) const {
  if (!SessionStore::AreValidSpecifics(entity_data.specifics.session())) {
    return std::string();
  }
  return SessionStore::GetClientTag(entity_data.specifics.session());
}

std::string SessionSyncBridge::GetStorageKey(
    const syncer::EntityData& entity_data) const {
  if (!SessionStore::AreValidSpecifics(entity_data.specifics.session())) {
    return std::string();
  }
  return SessionStore::GetStorageKey(entity_data.specifics.session());
}

bool SessionSyncBridge::IsEntityDataValid(
    const syncer::EntityData& entity_data) const {
  return SessionStore::AreValidSpecifics(entity_data.specifics.session());
}

void SessionSyncBridge::ApplyDisableSyncChanges(
    std::unique_ptr<MetadataChangeList> delete_metadata_change_list) {
  DCHECK(store_);

  local_session_event_router_->Stop();

  syncing_.reset();

  recreate_empty_store_callback_ =
      SessionStore::DeleteAllDataAndMetadata(std::move(store_));
  CHECK(recreate_empty_store_callback_);

  // Ensure that we clear on-demand favicons that were downloaded using user
  // synced history data, especially by HistoryUiFaviconRequestHandler. We do
  // it upon disabling of sessions sync to have symmetry with the condition
  // checked inside that layer to allow downloads (sessions sync enabled).
  sessions_client_->ClearAllOnDemandFavicons();

  notify_foreign_session_updated_cb_.Run();
}

void SessionSyncBridge::OnSyncPaused() {
  DCHECK(store_);
  local_session_event_router_->Stop();
  syncing_.reset();
  notify_foreign_session_updated_cb_.Run();
}

std::unique_ptr<LocalSessionEventHandlerImpl::WriteBatch>
SessionSyncBridge::CreateLocalSessionWriteBatch() {
  DCHECK(syncing_);

  // If a remote client mangled with our local session (typically deleted
  // entities due to garbage collection), we resubmit all local entities at this
  // point (i.e. local changes observed).
  if (sessions_client_->GetSessionSyncPrefs()->GetLocalDataOutOfSync()) {
    sessions_client_->GetSessionSyncPrefs()->SetLocalDataOutOfSync(false);
    // We use PostTask() to avoid interfering with the ongoing handling of
    // local changes that triggered this function.
    base::SequencedTaskRunner::GetCurrentDefault()->PostTask(
        FROM_HERE, base::BindOnce(&SessionSyncBridge::ResubmitLocalSession,
                                  weak_ptr_factory_.GetWeakPtr()));
  }

  return std::make_unique<LocalSessionWriteBatch>(
      store_->local_session_info(), CreateSessionStoreWriteBatch(),
      change_processor());
}

bool SessionSyncBridge::IsTabNodeUnsynced(int tab_node_id) {
  const std::string storage_key = SessionStore::GetTabStorageKey(
      store_->local_session_info().session_tag, tab_node_id);
  return change_processor()->IsEntityUnsynced(storage_key);
}

void SessionSyncBridge::TrackLocalNavigationId(base::Time timestamp,
                                               int unique_id) {
  global_id_mapper_.TrackNavigationId(timestamp, unique_id);
}

void SessionSyncBridge::OnSyncStarting(
    const syncer::DataTypeActivationRequest& request) {
  DCHECK(!syncing_);

  // There are a few different scenarios to consider here:
  // 1. This is browser startup, and sessions sync was previously enabled. The
  //    store hasn't been created yet, and data will be read from it.
  // 2. The user just enabled sessions sync.
  //    a) Sessions sync wasn't previously enabled in this browser run, and the
  //       store has not been created yet (and it should be empty).
  //    b) Sessions sync was previously enabled, but has since been turned off.
  //       The store was previously created, but has since been cleared and
  //       destroyed.
  // 3. Sessions sync was previously enabled, but then paused. The store still
  //    exists and should be reused. Initial sync may or may not have been
  //    finished previously.

  if (store_) {
    CHECK(!recreate_empty_store_callback_);
    // Case 3: Store still exists.
    if (change_processor()->IsTrackingMetadata()) {
      // Initial sync has been finished previously; restart the event handler
      // immediately.
      StartLocalSessionEventHandler(/*is_new_session=*/false);
    }
    // Else: Initial sync has *not* been finished before, so MergeFullSyncData()
    // will be called later and start the event handler.
  } else if (recreate_empty_store_callback_) {
    // Case 2b: Recreate an empty store.
    store_ = std::move(recreate_empty_store_callback_)
                 .Run(request.cache_guid, sessions_client_);
    CHECK(store_);
  } else {
    // Cases 1 and 2a: Open the store and read state from disk if it exists.
    SessionStore::Open(request.cache_guid, sessions_client_,
                       base::BindOnce(&SessionSyncBridge::OnStoreInitialized,
                                      weak_ptr_factory_.GetWeakPtr()));
  }
}

void SessionSyncBridge::OnStoreInitialized(
    const std::optional<syncer::ModelError>& error,
    std::unique_ptr<SessionStore> store,
    std::unique_ptr<syncer::MetadataBatch> metadata_batch) {
  DCHECK(!syncing_);

  if (error) {
    change_processor()->ReportError(*error);
    return;
  }

  DCHECK(store);
  DCHECK(metadata_batch);

  store_ = std::move(store);

  change_processor()->ModelReadyToSync(std::move(metadata_batch));

  // If initial sync was already done, MergeFullSyncData() will never be called
  // so we need to start syncing local changes.
  if (change_processor()->IsTrackingMetadata()) {
    StartLocalSessionEventHandler(/*is_new_session=*/false);
  }
}

void SessionSyncBridge::DeleteForeignSessionFromUI(const std::string& tag) {
  if (!syncing_) {
    return;
  }

  std::unique_ptr<SessionStore::WriteBatch> batch =
      CreateSessionStoreWriteBatch();
  DeleteForeignSessionWithBatch(tag, batch.get());
  SessionStore::WriteBatch::Commit(std::move(batch));
}

void SessionSyncBridge::DoGarbageCollection(SessionStore::WriteBatch* batch) {
  DCHECK(syncing_);
  DCHECK(batch);

  // Iterate through all the sessions and delete any with age older than
  // |kStaleSessionThreshold|.
  for (const sync_sessions::SyncedSession* session :
       store_->tracker()->LookupAllForeignSessions(SyncedSessionTracker::RAW)) {
    const base::TimeDelta session_age =
        base::Time::Now() - session->GetModifiedTime();
    if (session_age > kStaleSessionThreshold) {
      const std::string session_tag = session->GetSessionTag();
      DVLOG(1) << "Found stale session " << session_tag << " with age "
               << session_age.InDays() << " days, deleting.";
      DeleteForeignSessionWithBatch(session_tag, batch);
    }
  }
}

void SessionSyncBridge::DeleteForeignSessionWithBatch(
    const std::string& session_tag,
    SessionStore::WriteBatch* batch) {
  DCHECK(syncing_);
  DCHECK(change_processor()->IsTrackingMetadata());

  if (session_tag == store_->local_session_info().session_tag) {
    DLOG(ERROR) << "Attempting to delete local session. This is not currently "
                << "supported.";
    return;
  }

  // Deleting the header entity cascades the deletions of tabs as well.
  const std::string header_storage_key =
      SessionStore::GetHeaderStorageKey(session_tag);
  for (const std::string& deleted_storage_key :
       batch->DeleteForeignEntityAndUpdateTracker(header_storage_key)) {
    change_processor()->Delete(deleted_storage_key,
                               syncer::DeletionOrigin::Unspecified(),
                               batch->GetMetadataChangeList());
  }

  notify_foreign_session_updated_cb_.Run();
}

std::unique_ptr<SessionStore::WriteBatch>
SessionSyncBridge::CreateSessionStoreWriteBatch() {
  DCHECK(syncing_);

  return store_->CreateWriteBatch(base::BindOnce(
      &SessionSyncBridge::ReportError, weak_ptr_factory_.GetWeakPtr()));
}

void SessionSyncBridge::ResubmitLocalSession() {
  if (!syncing_) {
    return;
  }

  std::unique_ptr<SessionStore::WriteBatch> write_batch =
      CreateSessionStoreWriteBatch();
  std::unique_ptr<syncer::DataBatch> read_batch = store_->GetAllSessionData();
  while (read_batch->HasNext()) {
    auto [key, data] = read_batch->Next();
    if (store_->StorageKeyMatchesLocalSession(key)) {
      change_processor()->Put(key, std::move(data),
                              write_batch->GetMetadataChangeList());
    }
  }

  SessionStore::WriteBatch::Commit(std::move(write_batch));
}

void SessionSyncBridge::ReportError(const syncer::ModelError& error) {
  change_processor()->ReportError(error);
}

SessionSyncBridge::SyncingState::SyncingState() = default;

SessionSyncBridge::SyncingState::~SyncingState() = default;

}  // namespace sync_sessions