// Copyright 2025 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/contextual_tasks/internal/contextual_tasks_service_impl.h"

#include <optional>
#include <utility>

#include "base/containers/flat_set.h"
#include "base/feature_list.h"
#include "base/functional/bind.h"
#include "base/metrics/histogram_functions.h"
#include "base/notreached.h"
#include "base/strings/string_util.h"
#include "base/task/single_thread_task_runner.h"
#include "base/uuid.h"
#include "components/contextual_search/contextual_search_service.h"
#include "components/contextual_tasks/internal/composite_context_decorator.h"
#include "components/contextual_tasks/internal/conversions.h"
#include "components/contextual_tasks/public/account_utils.h"
#include "components/contextual_tasks/public/contextual_task.h"
#include "components/contextual_tasks/public/contextual_task_context.h"
#include "components/contextual_tasks/public/contextual_tasks_service.h"
#include "components/contextual_tasks/public/features.h"
#include "components/contextual_tasks/public/utils.h"
#include "components/omnibox/common/logger.h"
#include "components/prefs/pref_service.h"
#include "components/sessions/core/session_id.h"
#include "components/signin/public/identity_manager/identity_manager.h"
#include "components/sync/base/data_type.h"
#include "components/sync/base/report_unrecoverable_error.h"
#include "components/sync/model/client_tag_based_data_type_processor.h"
#include "components/sync/protocol/gemini_thread_specifics.pb.h"
#include "net/base/url_util.h"
#include "url/gurl.h"

namespace contextual_tasks {

namespace {

struct MergeUrlResourcesResult {
  std::vector<UrlResource> final_resources;
  std::vector<UrlResource> added_or_updated_resources;
  std::vector<base::Uuid> removed_resource_ids;
  bool has_changes = false;
};

// Helper to find the index of a matching resource in existing_resources.
// Returns -1 if no match is found.
int FindMatchingResourceIndex(
    const UrlResource& incoming_res,
    const std::vector<UrlResource>& existing_resources,
    const std::vector<bool>& existing_matched) {
  for (size_t i = 0; i < existing_resources.size(); ++i) {
    if (existing_matched[i]) {
      continue;
    }

    const auto& existing_res = existing_resources[i];
    // 1. Match by url_id.
    if (incoming_res.url_id.is_valid() &&
        existing_res.url_id == incoming_res.url_id) {
      return static_cast<int>(i);
    }

    // 2. Match by context_id.
    if (incoming_res.context_id.has_value() &&
        existing_res.context_id == incoming_res.context_id) {
      return static_cast<int>(i);
    }

    // 3. Match by url.
    if (incoming_res.url.is_valid() && existing_res.url == incoming_res.url) {
      return static_cast<int>(i);
    }
  }

  return -1;
}

// Merges incoming resources with existing ones.
// Returns a result containing the final list of resources, as well as lists of
// added/updated and removed resources to be used for sync notifications.
MergeUrlResourcesResult MergeUrlResources(
    const std::vector<UrlResource>& existing_resources,
    std::vector<UrlResource> incoming_resources) {
  MergeUrlResourcesResult result;
  std::vector<bool> existing_matched(existing_resources.size(), false);
  result.has_changes = false;

  for (auto& incoming_res : incoming_resources) {
    int matched_index = FindMatchingResourceIndex(
        incoming_res, existing_resources, existing_matched);

    if (matched_index != -1) {
      existing_matched[matched_index] = true;
      const auto& existing_res = existing_resources[matched_index];

      // Copy over fields if missing.
      if (!incoming_res.url_id.is_valid()) {
        incoming_res.url_id = existing_res.url_id;
      }
      if (!incoming_res.url.is_valid()) {
        incoming_res.url = existing_res.url;
      }
      if (!incoming_res.tab_id.has_value()) {
        incoming_res.tab_id = existing_res.tab_id;
      }
      if (!incoming_res.title.has_value()) {
        incoming_res.title = existing_res.title;
      }
      if (!incoming_res.context_id.has_value()) {
        incoming_res.context_id = existing_res.context_id;
      }
      if (!incoming_res.timestamp.has_value()) {
        incoming_res.timestamp = existing_res.timestamp;
      }
      incoming_res.has_chrome_tab_data =
          incoming_res.has_chrome_tab_data || existing_res.has_chrome_tab_data;

      // Check if anything changed.
      if (incoming_res.url_id != existing_res.url_id ||
          incoming_res.url != existing_res.url ||
          incoming_res.tab_id != existing_res.tab_id ||
          incoming_res.title != existing_res.title ||
          incoming_res.context_id != existing_res.context_id ||
          incoming_res.timestamp != existing_res.timestamp ||
          incoming_res.has_chrome_tab_data !=
              existing_res.has_chrome_tab_data) {
        result.has_changes = true;
        result.added_or_updated_resources.push_back(incoming_res);
      }
    } else {
      // New resource.
      result.has_changes = true;
      if (!incoming_res.url_id.is_valid()) {
        incoming_res.url_id = base::Uuid::GenerateRandomV4();
      }
      result.added_or_updated_resources.push_back(incoming_res);
    }
  }

  // Check for removed resources.
  for (size_t i = 0; i < existing_resources.size(); ++i) {
    if (!existing_matched[i]) {
      result.has_changes = true;
      result.removed_resource_ids.push_back(existing_resources[i].url_id);
    }
  }

  // If no content changes, adds or removes were detected, check if the order
  // has changed.
  if (!result.has_changes &&
      existing_resources.size() == incoming_resources.size()) {
    for (size_t i = 0; i < existing_resources.size(); ++i) {
      if (existing_resources[i].url_id != incoming_resources[i].url_id) {
        result.has_changes = true;
        break;
      }
    }
  }

  result.final_resources = std::move(incoming_resources);
  return result;
}

void RecordNumberOfActiveTasks(int count) {
  base::UmaHistogramCounts100("ContextualTasks.ActiveTasksCount", count);
}

ContextualTask CreateTaskForThread(const Thread& thread, bool is_ephemeral) {
  ContextualTask task(base::Uuid::GenerateRandomV4(), is_ephemeral);
  task.AddThread(thread);
  task.SetTitle(thread.title);
  return task;
}

}  // namespace

ContextualTasksServiceImpl::ContextualTasksServiceImpl(
    version_info::Channel channel,
    syncer::RepeatingDataTypeStoreFactory data_type_store_factory,
    std::unique_ptr<CompositeContextDecorator> composite_context_decorator,
    signin::IdentityManager* identity_manager,
    PrefService* pref_service,
    bool supports_ephemeral_only,
    base::RepeatingCallback<size_t()> get_active_task_count_callback,
    base::RepeatingCallback<bool()> is_gemini_threads_enabled)
    : composite_context_decorator_(std::move(composite_context_decorator)),
      get_active_task_count_callback_(
          std::move(get_active_task_count_callback)),
      is_gemini_threads_enabled_callback_(is_gemini_threads_enabled),
      identity_manager_(identity_manager),
      pref_service_(pref_service),
      supports_ephemeral_only_(supports_ephemeral_only) {
  const base::RepeatingClosure& dump_stack =
      base::BindRepeating(&syncer::ReportUnrecoverableError, channel);
  auto ai_thread_processor =
      std::make_unique<syncer::ClientTagBasedDataTypeProcessor>(
          syncer::AI_THREAD, dump_stack);
  ai_thread_sync_bridge_ = std::make_unique<AiThreadSyncBridge>(
      std::move(ai_thread_processor), data_type_store_factory);
  ai_thread_observation_.Observe(ai_thread_sync_bridge_.get());

  auto gemini_thread_processor =
      std::make_unique<syncer::ClientTagBasedDataTypeProcessor>(
          syncer::GEMINI_THREAD, dump_stack);
  gemini_thread_sync_bridge_ = std::make_unique<GeminiThreadSyncBridge>(
      std::move(gemini_thread_processor), data_type_store_factory);
  gemini_thread_observation_.Observe(gemini_thread_sync_bridge_.get());

  // Wait for both AiThreadSyncBridge and GeminiThreadSyncBridge to finish
  // loading their data store.
  on_data_loaded_barrier_ = base::BarrierClosure(
      2, base::BindOnce(&ContextualTasksServiceImpl::OnDataStoresLoaded,
                        weak_ptr_factory_.GetWeakPtr()));
}

ContextualTasksServiceImpl::~ContextualTasksServiceImpl() {
  for (auto& observer : observers_) {
    observer.OnWillBeDestroyed();
  }
}

bool ContextualTasksServiceImpl::IsInitialized() {
  return is_initialized_;
}

ContextualTask ContextualTasksServiceImpl::CreateTask() {
  // Note that we are adding 1 to the number of active tasks because the
  // histogram is recorded before the task is created, but it's not
  // immediately reflected in the active tasks count.
  RecordNumberOfActiveTasks(get_active_task_count_callback_.Run() + 1);

  base::Uuid task_id = base::Uuid::GenerateRandomV4();
  ContextualTask task(task_id, supports_ephemeral_only_);
  return AddTaskAndNotify(std::move(task));
}

ContextualTask ContextualTasksServiceImpl::CreateTaskFromUrl(const GURL& url) {
  // Note that we are adding 1 to the number of active tasks because the
  // histogram is recorded before the task is created, but it's not
  // immediately reflected in the active tasks count.
  RecordNumberOfActiveTasks(get_active_task_count_callback_.Run() + 1);

  base::Uuid task_id = base::Uuid::GenerateRandomV4();
  bool is_ephemeral = supports_ephemeral_only_ ||
                      !IsUrlForPrimaryAccount(identity_manager_, url);
  ContextualTask task(task_id, is_ephemeral);
  return AddTaskAndNotify(std::move(task));
}

void ContextualTasksServiceImpl::GetTaskById(
    const base::Uuid& task_id,
    base::OnceCallback<void(std::optional<ContextualTask>)> callback) const {
  auto it = tasks_.find(task_id);
  std::optional<ContextualTask> result;
  if (it != tasks_.end()) {
    result = it->second;
  }
  base::SingleThreadTaskRunner::GetCurrentDefault()->PostTask(
      FROM_HERE, base::BindOnce(std::move(callback), std::move(result)));
}

void ContextualTasksServiceImpl::GetTasks(
    base::OnceCallback<void(std::vector<ContextualTask>)> callback) const {
  std::vector<ContextualTask> tasks;
  for (const auto& pair : tasks_) {
    ContextualTask task = pair.second;
    if (task.IsEphemeral() || supports_ephemeral_only_) {
      continue;
    }
    tasks.push_back(task);
  }
  base::SingleThreadTaskRunner::GetCurrentDefault()->PostTask(
      FROM_HERE, base::BindOnce(std::move(callback), std::move(tasks)));
}

void ContextualTasksServiceImpl::DeleteTask(const base::Uuid& task_id) {
  RemoveTaskInternal(task_id, TriggerSource::kLocal);
}

void ContextualTasksServiceImpl::UpdateThreadForTask(
    const base::Uuid& task_id,
    ThreadType thread_type,
    const std::string& server_id,
    std::optional<std::string> conversation_turn_id,
    std::optional<std::string> title) {
  auto [it, is_new_task] = FindOrCreateTask(task_id, thread_type, server_id);

  // If a thread already exists and its server ID does not match the new server
  // ID, it indicates a mismatch or an attempt to update a different thread, so
  // we return.
  std::optional<Thread> thread = it->second.GetThread();
  // If the task doesn't exist doesn't have the right thread, return early.
  if (thread.has_value() &&
      (thread->server_id != server_id || thread->type != thread_type)) {
    return;
  }

  // Determine the new title and conversation turn ID. If provided, use them;
  // otherwise, retain the existing values if a thread already exists.
  const std::string& new_title =
      title.value_or(thread.has_value() ? thread->title : "");
  std::optional<std::string> new_conversation_turn_id = std::nullopt;
  if (conversation_turn_id.has_value()) {
    new_conversation_turn_id = conversation_turn_id;
  } else if (thread.has_value()) {
    new_conversation_turn_id = thread->conversation_turn_id;
  }

  // Add or update the thread information within the task.
  it->second.AddThread(Thread(thread_type, server_id, new_title,
                              base::Time::Now().InMillisecondsSinceUnixEpoch(),
                              new_conversation_turn_id));

  if (is_new_task) {
    base::SingleThreadTaskRunner::GetCurrentDefault()->PostTask(
        FROM_HERE, base::BindOnce(&ContextualTasksServiceImpl::NotifyTaskAdded,
                                  weak_ptr_factory_.GetWeakPtr(), it->second,
                                  TriggerSource::kLocal));
  } else {
    base::SingleThreadTaskRunner::GetCurrentDefault()->PostTask(
        FROM_HERE,
        base::BindOnce(&ContextualTasksServiceImpl::NotifyTaskUpdated,
                       weak_ptr_factory_.GetWeakPtr(), it->second,
                       TriggerSource::kLocal));
  }
}

void ContextualTasksServiceImpl::RemoveThreadFromTask(
    const base::Uuid& task_id,
    ThreadType type,
    const std::string& server_id) {
  auto it = tasks_.find(task_id);
  if (it != tasks_.end()) {
    DCHECK(it->second.GetThread().has_value());
    switch (type) {
      case ThreadType::kAiMode:
        ai_thread_sync_bridge_->DeleteThread(it->second.GetThread().value());
        break;
      case ThreadType::kGemini:
        gemini_thread_sync_bridge_->DeleteThread(
            it->second.GetThread().value());
        break;
      case ThreadType::kUnknown:
      default:
        NOTREACHED();
    }
    it->second.RemoveThread(type, server_id);
    // If the task no longer has any thread, remove it.
    if (!it->second.GetThread()) {
      DeleteTask(task_id);
    }
  }
}

std::optional<ContextualTask> ContextualTasksServiceImpl::GetTaskFromServerId(
    ThreadType thread_type,
    const std::string& server_id) {
  for (const auto& pair : tasks_) {
    std::optional<Thread> thread = pair.second.GetThread();
    if (thread.has_value() && thread->type == thread_type &&
        thread->server_id == server_id) {
      return pair.second;
    }
  }
  return std::nullopt;
}

void ContextualTasksServiceImpl::AttachUrlToTask(const base::Uuid& task_id,
                                                 const GURL& url) {
  auto it = tasks_.find(task_id);
  if (it != tasks_.end()) {
    UrlResource url_resource(base::Uuid::GenerateRandomV4(), url);
    if (it->second.AddUrlResource(url_resource)) {
      base::SingleThreadTaskRunner::GetCurrentDefault()->PostTask(
          FROM_HERE,
          base::BindOnce(&ContextualTasksServiceImpl::NotifyTaskUpdated,
                         weak_ptr_factory_.GetWeakPtr(), it->second,
                         TriggerSource::kLocal));
    }
  }
}

void ContextualTasksServiceImpl::DetachUrlFromTask(const base::Uuid& task_id,
                                                   const GURL& url) {
  auto it = tasks_.find(task_id);
  if (it != tasks_.end()) {
    std::optional<base::Uuid> url_id = it->second.RemoveUrl(url);
    if (url_id) {
      base::SingleThreadTaskRunner::GetCurrentDefault()->PostTask(
          FROM_HERE,
          base::BindOnce(&ContextualTasksServiceImpl::NotifyTaskUpdated,
                         weak_ptr_factory_.GetWeakPtr(), it->second,
                         TriggerSource::kLocal));
    }
  }
}

void ContextualTasksServiceImpl::SetUrlResourcesFromServer(
    const base::Uuid& task_id,
    std::vector<UrlResource> url_resources) {
  auto it = tasks_.find(task_id);
  if (it == tasks_.end()) {
    return;
  }

  // Merge incoming resources with existing ones and calculate the diff.
  ContextualTask& task = it->second;
  MergeUrlResourcesResult result =
      MergeUrlResources(task.GetUrlResources(), std::move(url_resources));

  if (!result.has_changes) {
    return;
  }

  // Update the local in-memory task state.
  task.SetUrlResourcesFromServer(std::move(result.final_resources));

  base::SingleThreadTaskRunner::GetCurrentDefault()->PostTask(
      FROM_HERE, base::BindOnce(&ContextualTasksServiceImpl::NotifyTaskUpdated,
                                weak_ptr_factory_.GetWeakPtr(), task,
                                TriggerSource::kLocal));
}

void ContextualTasksServiceImpl::AssociateTabWithTask(const base::Uuid& task_id,
                                                      SessionID tab_id) {
  auto it = tasks_.find(task_id);
  if (it == tasks_.end()) {
    return;
  }

  std::optional<ContextualTask> current_task = GetContextualTaskForTab(tab_id);
  if (current_task && current_task->GetTaskId() != task_id) {
    DisassociateTabFromTask(current_task->GetTaskId(), tab_id);
  }

  tab_to_task_[tab_id] = task_id;
  it->second.AddTabId(tab_id);

  base::UmaHistogramCounts100("ContextualTasks.TabAffiliationCount",
                              GetTabsAssociatedWithTask(task_id).size());
  base::SingleThreadTaskRunner::GetCurrentDefault()->PostTask(
      FROM_HERE,
      base::BindOnce(&ContextualTasksServiceImpl::NotifyTaskAssociatedToTab,
                     weak_ptr_factory_.GetWeakPtr(), task_id, tab_id));
}

void ContextualTasksServiceImpl::DisassociateTabFromTask(
    const base::Uuid& task_id,
    SessionID tab_id) {
  tab_to_task_.erase(tab_id);
  auto it = tasks_.find(task_id);
  if (it != tasks_.end()) {
    it->second.RemoveTabId(tab_id);

    if (base::FeatureList::IsEnabled(
            kContextualTasksRemoveTasksWithoutThreadsOrTabAssociations)) {
      // If the task doesn't have a thread and tabs associated with it,
      // it can be safely removed here.
      if (!it->second.GetThread() && it->second.GetTabIds().empty()) {
        RemoveTaskInternal(task_id, TriggerSource::kLocal);
      }
    }
  }
  base::SingleThreadTaskRunner::GetCurrentDefault()->PostTask(
      FROM_HERE,
      base::BindOnce(
          &ContextualTasksServiceImpl::NotifyTaskDisassociatedFromTab,
          weak_ptr_factory_.GetWeakPtr(), task_id, tab_id));
}

void ContextualTasksServiceImpl::DisassociateAllTabsFromTask(
    const base::Uuid& task_id) {
  for (const SessionID& tab_id : GetTabsAssociatedWithTask(task_id)) {
    DisassociateTabFromTask(task_id, tab_id);
  }
}

std::optional<ContextualTask>
ContextualTasksServiceImpl::GetContextualTaskForTab(SessionID tab_id) const {
  auto it = tab_to_task_.find(tab_id);
  if (it != tab_to_task_.end()) {
    auto task_it = tasks_.find(it->second);
    if (task_it != tasks_.end()) {
      return task_it->second;
    }
  }
  if (IsStickyConversationEnabled() && last_active_task_id_.has_value()) {
    auto task_it = tasks_.find(*last_active_task_id_);
    if (task_it != tasks_.end()) {
      return task_it->second;
    }
  }
  return std::nullopt;
}

std::vector<SessionID> ContextualTasksServiceImpl::GetTabsAssociatedWithTask(
    const base::Uuid& task_id) const {
  std::vector<SessionID> associated_tabs;
  for (const auto& pair : tab_to_task_) {
    if (pair.second == task_id) {
      associated_tabs.push_back(pair.first);
    }
  }
  return associated_tabs;
}

void ContextualTasksServiceImpl::SetLastActiveTask(const base::Uuid& task_id) {
  last_active_task_id_ = task_id;
}

void ContextualTasksServiceImpl::GetContextForTask(
    const base::Uuid& task_id,
    const std::set<ContextualTaskContextSource>& sources,
    std::unique_ptr<ContextDecorationParams> params,
    base::OnceCallback<void(std::unique_ptr<ContextualTaskContext>)>
        context_callback) {
  auto it = tasks_.find(task_id);
  if (it == tasks_.end()) {
    base::SingleThreadTaskRunner::GetCurrentDefault()->PostTask(
        FROM_HERE, base::BindOnce(std::move(context_callback),
                                  std::unique_ptr<ContextualTaskContext>()));
    return;
  }

  composite_context_decorator_->DecorateContext(
      std::make_unique<ContextualTaskContext>(it->second), sources,
      std::move(params), std::move(context_callback));
}

void ContextualTasksServiceImpl::GetThreadUrlFromTaskId(
    const base::Uuid& task_id,
    const std::string& locale,
    omnibox::ChromeAimEntryPoint entry_point,
    base::OnceCallback<void(GURL)> callback) {
  GetTaskById(
      task_id,
      base::BindOnce(
          [](const base::Uuid& task_id, const std::string& locale,
             omnibox::ChromeAimEntryPoint entry_point,
             base::OnceCallback<void(GURL)> callback,
             std::optional<ContextualTask> task) {
            OMNIBOX_LOG("nav_trace")
                << "ContextualTasks navigation trace: "
                   "GetThreadUrlFromTaskId callback called";

            // AIM is the default if no task or thread is found.
            GURL url = GetDefaultAimUrl(locale, entry_point);

            if (!task) {
              OMNIBOX_LOG("nav_trace")
                  << "ContextualTasks navigation trace: "
                     "GetThreadUrlFromTaskId returning early, no task. "
                     "Returning default: "
                  << url;
              std::move(callback).Run(url);
              return;
            }

            std::optional<Thread> thread = task->GetThread();
            if (!thread) {
              OMNIBOX_LOG("nav_trace")
                  << "ContextualTasks navigation trace: "
                     "GetThreadUrlFromTaskId returning early, no thread or "
                     "Gemini thread. Returning default: "
                  << url;
              std::move(callback).Run(url);
              return;
            }

            if (thread->type == ThreadType::kAiMode) {
              // Attach the thread ID and the most recent turn ID to the
              // URL. A query parameter needs to be present, but its
              // value is not used for continued threads.
              url = net::AppendQueryParameter(url, "q", thread->title);

              // There are rare cases where the mstk may not be present before
              // this url is requested. If that is the case, do not attempt to
              // include it in the url.
              if (thread->conversation_turn_id) {
                url = net::AppendQueryParameter(
                    url, "mstk", thread->conversation_turn_id.value());
              }
              url = net::AppendQueryParameter(url, "mtid", thread->server_id);

            } else if (thread->type == ThreadType::kGemini) {
              url = GURL(GetContextualTasksGeminiBaseUrl());
              GURL::Replacements replacements;
              std::string path = url.GetPath();
              if (path.back() != '/') {
                path += '/';
              }
              std::string server_id = thread->server_id;
              if (base::StartsWith(server_id, "c_")) {
                server_id.erase(0, 2);
              }
              path += server_id;
              replacements.SetPathStr(path);

              url = url.ReplaceComponents(replacements);
            }

            OMNIBOX_LOG("nav_trace") << "ContextualTasks navigation trace: "
                                        "GetThreadUrlFromTaskId returning URL: "
                                     << url;
            std::move(callback).Run(url);
          },
          task_id, locale, entry_point, std::move(callback)));
}

void ContextualTasksServiceImpl::AddObserver(
    ContextualTasksService::Observer* observer) {
  observers_.AddObserver(observer);
}

void ContextualTasksServiceImpl::RemoveObserver(
    ContextualTasksService::Observer* observer) {
  observers_.RemoveObserver(observer);
}

base::WeakPtr<syncer::DataTypeControllerDelegate>
ContextualTasksServiceImpl::GetAiThreadControllerDelegate() {
  return ai_thread_sync_bridge_->change_processor()->GetControllerDelegate();
}

base::WeakPtr<syncer::DataTypeControllerDelegate>
ContextualTasksServiceImpl::GetGeminiThreadControllerDelegate() {
  return gemini_thread_sync_bridge_->change_processor()
      ->GetControllerDelegate();
}

bool ContextualTasksServiceImpl::IsGeminiThreadsEligible() {
  return is_gemini_threads_enabled_callback_ &&
         is_gemini_threads_enabled_callback_.Run();
}

void ContextualTasksServiceImpl::SetAiThreadSyncBridgeForTesting(
    std::unique_ptr<AiThreadSyncBridge> bridge) {
  // When provided a new service for testing, ensure observation of the old
  // service is removed to avoid UAF when this service is destroyed.
  ai_thread_observation_.Reset();
  ai_thread_sync_bridge_ = std::move(bridge);
}

void ContextualTasksServiceImpl::SetGeminiThreadSyncBridgeForTesting(
    std::unique_ptr<GeminiThreadSyncBridge> bridge) {
  gemini_thread_observation_.Reset();
  gemini_thread_sync_bridge_ = std::move(bridge);
}

void ContextualTasksServiceImpl::OnThreadDataStoreLoaded() {
  on_data_loaded_barrier_.Run();
}

void ContextualTasksServiceImpl::OnThreadAddedOrUpdatedRemotely(
    const std::vector<proto::AiThreadEntity>& threads) {
  std::map<std::string, const proto::AiThreadEntity&> thread_map;
  for (const auto& thread : threads) {
    thread_map.emplace(thread.specifics().server_id(), thread);
  }

  for (auto& task_entry : tasks_) {
    ContextualTask& task = task_entry.second;
    if (!task.GetThread()) {
      continue;
    }

    auto it = thread_map.find(task.GetThread()->server_id);
    if (it == thread_map.end() ||
        ToThreadType(it->second.specifics().type()) != task.GetThread()->type) {
      continue;
    }

    // Check if the thread has changed for the task.
    const proto::AiThreadEntity& new_thread_entity = it->second;
    const std::optional<Thread>& old_thread = task.GetThread();
    if (old_thread->conversation_turn_id !=
            new_thread_entity.specifics().conversation_turn_id() ||
        old_thread->title != new_thread_entity.specifics().title()) {
      task.AddThread(Thread(
          ThreadType::kAiMode, new_thread_entity.specifics().server_id(),
          new_thread_entity.specifics().title(),
          new_thread_entity.specifics().last_turn_time_unix_epoch_millis(),
          new_thread_entity.specifics().conversation_turn_id()));
      NotifyTaskUpdated(task, TriggerSource::kRemote);
    }

    // Remove the thread from the map. Any remaining threads will have tasks
    // created for them at the end of this function.
    thread_map.erase(it->first);
  }

  // Create tasks for any of the threads that were added or updated and didn't
  // have an associated task.
  for (const auto& [thread_id, thread_entity] : thread_map) {
    Thread thread(ToThreadType(thread_entity.specifics().type()),
                  thread_entity.specifics().server_id(),
                  thread_entity.specifics().title(),
                  thread_entity.specifics().last_turn_time_unix_epoch_millis(),
                  thread_entity.specifics().conversation_turn_id());
    ContextualTask new_task =
        CreateTaskForThread(thread, supports_ephemeral_only_);
    const auto it =
        tasks_.emplace(new_task.GetTaskId(), std::move(new_task)).first;
    base::SingleThreadTaskRunner::GetCurrentDefault()->PostTask(
        FROM_HERE, base::BindOnce(&ContextualTasksServiceImpl::NotifyTaskAdded,
                                  weak_ptr_factory_.GetWeakPtr(), it->second,
                                  TriggerSource::kRemote));
  }
}

void ContextualTasksServiceImpl::OnThreadRemovedRemotely(
    const std::vector<base::Uuid>& thread_ids) {
  OnThreadRemovedRemotelyInternal(ThreadType::kAiMode, thread_ids);
}

void ContextualTasksServiceImpl::OnGeminiThreadDataStoreLoaded() {
  on_data_loaded_barrier_.Run();
}

void ContextualTasksServiceImpl::OnGeminiThreadAddedOrUpdatedRemotely(
    const std::vector<sync_pb::GeminiThreadSpecifics>& thread_specifics) {
  std::map<std::string, const sync_pb::GeminiThreadSpecifics&> thread_map;
  for (const auto& specifics : thread_specifics) {
    thread_map.emplace(specifics.conversation_id(), specifics);
  }

  // Update existing tasks
  for (auto& task_entry : tasks_) {
    ContextualTask& task = task_entry.second;
    if (!task.GetThread() || task.GetThread()->type != ThreadType::kGemini) {
      continue;
    }

    auto it = thread_map.find(task.GetThread()->server_id);
    if (it == thread_map.end()) {
      continue;
    }

    // Check if the thread has changed for the task.
    const sync_pb::GeminiThreadSpecifics& new_thread_entity = it->second;
    const std::optional<Thread>& old_thread = task.GetThread();
    if (old_thread->title != new_thread_entity.title()) {
      task.AddThread(
          Thread(ThreadType::kGemini, new_thread_entity.conversation_id(),
                 new_thread_entity.title(),
                 new_thread_entity.last_turn_time_unix_epoch_millis()));
      NotifyTaskUpdated(task, TriggerSource::kRemote);
    }

    thread_map.erase(it->first);
  }

  // Create new task for specifics which didn't have an existing task.
  for (const auto& [thread_id, specifics] : thread_map) {
    Thread thread(ThreadType::kGemini, specifics.conversation_id(),
                  specifics.title(),
                  specifics.last_turn_time_unix_epoch_millis());
    ContextualTask new_task =
        CreateTaskForThread(thread, supports_ephemeral_only_);
    const auto it =
        tasks_.emplace(new_task.GetTaskId(), std::move(new_task)).first;
    base::SingleThreadTaskRunner::GetCurrentDefault()->PostTask(
        FROM_HERE, base::BindOnce(&ContextualTasksServiceImpl::NotifyTaskAdded,
                                  weak_ptr_factory_.GetWeakPtr(), it->second,
                                  TriggerSource::kRemote));
  }
}

void ContextualTasksServiceImpl::OnGeminiThreadRemovedRemotely(
    const std::vector<base::Uuid>& thread_ids) {
  OnThreadRemovedRemotelyInternal(ThreadType::kGemini, thread_ids);
}

std::pair<std::map<base::Uuid, ContextualTask>::iterator, bool>
ContextualTasksServiceImpl::FindOrCreateTask(const base::Uuid& task_id,
                                             ThreadType thread_type,
                                             const std::string& server_id) {
  auto it = tasks_.find(task_id);
  if (it != tasks_.end()) {
    return {it, /*is_new_task=*/false};
  }

  // Task not found, but we have a task ID. Create the task on the fly unless
  // we already have a task for this server ID.
  std::optional<ContextualTask> existing_task =
      GetTaskFromServerId(thread_type, server_id);
  if (existing_task.has_value()) {
    // TODO(nyquist): This is a temporary solution to avoid creating
    // duplicate tasks. We should remove this once we have a better solution
    // for handling out-of-sync tasks.
    it = tasks_.find(existing_task->GetTaskId());
    return {it, /*is_new_task=*/false};
  }

  it =
      tasks_.emplace(task_id, ContextualTask(task_id, supports_ephemeral_only_))
          .first;
  return {it, /*is_new_task=*/true};
}

void ContextualTasksServiceImpl::RemoveTaskInternal(const base::Uuid& task_id,
                                                    TriggerSource source) {
  auto task_it = tasks_.find(task_id);
  if (task_it == tasks_.end()) {
    return;
  }

  const auto& task = task_it->second;
  for (const auto& tab_id : task.GetTabIds()) {
    tab_to_task_.erase(tab_id);
  }

  if (last_active_task_id_ == task_id) {
    last_active_task_id_ = std::nullopt;
  }

  tasks_.erase(task_it);
  base::SingleThreadTaskRunner::GetCurrentDefault()->PostTask(
      FROM_HERE,
      base::BindOnce(&ContextualTasksServiceImpl::NotifyTaskRemoved,
                     weak_ptr_factory_.GetWeakPtr(), task_id, source));
}

void ContextualTasksServiceImpl::OnThreadRemovedRemotelyInternal(
    ThreadType thread_type_filter,
    const std::vector<base::Uuid>& thread_ids) {
  std::set<std::string> removed_thread_server_ids;
  for (const auto& id : thread_ids) {
    removed_thread_server_ids.insert(id.AsLowercaseString());
  }

  std::vector<base::Uuid> tasks_to_delete;
  for (const auto& task_entry : tasks_) {
    const ContextualTask& task = task_entry.second;
    if (task.GetThread() && task.GetThread()->type == thread_type_filter) {
      if (removed_thread_server_ids.count(task.GetThread()->server_id)) {
        tasks_to_delete.push_back(task.GetTaskId());
      }
    }
  }

  for (const auto& task_id : tasks_to_delete) {
    RemoveTaskInternal(task_id, TriggerSource::kRemote);
  }
}

size_t ContextualTasksServiceImpl::GetTabIdMapSizeForTesting() const {
  return tab_to_task_.size();
}

void ContextualTasksServiceImpl::NotifyTaskAdded(const ContextualTask& task,
                                                 TriggerSource source) {
  for (auto& observer : observers_) {
    observer.OnTaskAdded(task, source);
  }
}

void ContextualTasksServiceImpl::NotifyTaskUpdated(const ContextualTask& task,
                                                   TriggerSource source) {
  for (auto& observer : observers_) {
    observer.OnTaskUpdated(task, source);
  }
}

void ContextualTasksServiceImpl::NotifyTaskRemoved(const base::Uuid& task_id,
                                                   TriggerSource source) {
  for (auto& observer : observers_) {
    observer.OnTaskRemoved(task_id, source);
  }
}

void ContextualTasksServiceImpl::NotifyTaskAssociatedToTab(
    const base::Uuid& task_id,
    SessionID tab_id) {
  observers_.Notify(&ContextualTasksService::Observer::OnTaskAssociatedToTab,
                    task_id, tab_id);
}

void ContextualTasksServiceImpl::NotifyTaskDisassociatedFromTab(
    const base::Uuid& task_id,
    SessionID tab_id) {
  observers_.Notify(
      &ContextualTasksService::Observer::OnTaskDisassociatedFromTab, task_id,
      tab_id);
}

ContextualTask ContextualTasksServiceImpl::AddTaskAndNotify(
    ContextualTask task) {
  auto it = tasks_.emplace(task.GetTaskId(), task).first;
  base::SingleThreadTaskRunner::GetCurrentDefault()->PostTask(
      FROM_HERE, base::BindOnce(&ContextualTasksServiceImpl::NotifyTaskAdded,
                                weak_ptr_factory_.GetWeakPtr(), it->second,
                                TriggerSource::kLocal));
  return it->second;
}

void ContextualTasksServiceImpl::OnDataStoresLoaded() {
  is_initialized_ = true;
  std::vector<ContextualTask> tasks = BuildTasks();
  for (const auto& task : tasks) {
    tasks_.emplace(task.GetTaskId(), task);
  }
  for (auto& observer : observers_) {
    observer.OnContextualTasksServiceInitialized();
  }
}

std::vector<ContextualTask> ContextualTasksServiceImpl::BuildTasks() const {
  // First attempt to add threads to tasks that were persisted. Any threads that
  // do not have a task will have one created.
  base::flat_set<std::string> used_thread_ids;

  std::vector<Thread> threads = ai_thread_sync_bridge_->GetThreads();
  std::vector<ContextualTask> tasks;
  for (const auto& thread : threads) {
    if (used_thread_ids.contains(thread.server_id)) {
      continue;
    }
    // While these tasks are not persisted, they're also not considered
    // ephemeral since they are built using a user's threads.
    // TODO(485520978): Use a UUIDv5 based on the thread ID here so the UUID
    //                  is deterministic between restarts.
    tasks.push_back(CreateTaskForThread(thread, supports_ephemeral_only_));
  }
  for (const auto& thread : gemini_thread_sync_bridge_->GetThreads()) {
    if (used_thread_ids.contains(thread.server_id)) {
      continue;
    }
    tasks.push_back(CreateTaskForThread(thread, supports_ephemeral_only_));
  }

  return tasks;
}

}  // namespace contextual_tasks