// Copyright 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef COMPONENTS_SYNC_SESSIONS_SYNCED_SESSION_TRACKER_H_
#define COMPONENTS_SYNC_SESSIONS_SYNCED_SESSION_TRACKER_H_

#include <stddef.h>

#include <map>
#include <memory>
#include <set>
#include <string>
#include <vector>

#include "base/feature_list.h"
#include "base/macros.h"
#include "components/sessions/core/session_id.h"
#include "components/sessions/core/session_types.h"
#include "components/sync_sessions/synced_session.h"
#include "components/sync_sessions/tab_node_pool.h"

namespace sync_pb {
class SessionSpecifics;
}

namespace sync_sessions {

class SyncSessionsClient;

// TODO(crbug.com/882489): Remove feature toggle during code cleanup when a
// satisfying solution is found for closed tabs.
extern const base::Feature kDeferRecyclingOfSyncTabNodesIfUnsynced;

// Class to manage synced sessions. The tracker will own all SyncedSession
// and SyncedSessionTab objects it creates, and deletes them appropriately on
// destruction.
//
// Note: SyncedSession objects are created for all synced sessions, including
// the local session (whose tag we maintain separately).
class SyncedSessionTracker {
 public:
  // Different ways to lookup/filter tabs.
  enum SessionLookup {
    RAW,         // Return all foreign sessions.
    PRESENTABLE  // Have one window with at least one tab with syncable content.
  };

  explicit SyncedSessionTracker(SyncSessionsClient* sessions_client);
  ~SyncedSessionTracker();

  // **** Synced session/tab query methods. ****

  // Returns vector with all sessions we're tracking. SyncedSession ownership
  // remains within the SyncedSessionTracker. Lookup parameter is used to decide
  // which tabs should be included.
  std::vector<const SyncedSession*> LookupAllSessions(
      SessionLookup lookup) const;

  // Returns all foreign sessions we're tracking (skips the local session
  // object). SyncedSession ownership remains within the SyncedSessionTracker.
  // Lookup parameter is used to decide which foreign tabs should be include.
  std::vector<const SyncedSession*> LookupAllForeignSessions(
      SessionLookup lookup) const;

  // Returns the tab node ids (see GetTab) for all the tabs* associated with the
  // session having tag |session_tag|.
  std::set<int> LookupTabNodeIds(const std::string& session_tag) const;

  // Returns tabs that are unmapped for session with tag |session_tag|.
  std::vector<const sessions::SessionTab*> LookupUnmappedTabs(
      const std::string& session_tag) const;

  // Attempts to look up the session windows associatd with the session given
  // by |session_tag|. Ownership of SessionWindows stays within the
  // SyncedSessionTracker.
  // If lookup succeeds:
  // - Fills windows with the SessionWindow pointers, returns true.
  // Else
  // - Returns false.
  bool LookupSessionWindows(
      const std::string& session_tag,
      std::vector<const sessions::SessionWindow*>* windows) const;

  // Attempts to look up the tab associated with the given tag and tab id.
  // Ownership of the SessionTab remains within the SyncedSessionTracker.
  // Returns null if lookup fails.
  const sessions::SessionTab* LookupSessionTab(const std::string& session_tag,
                                               SessionID tab_id) const;

  // Allows retrieval of existing data for the local session. Unlike GetSession
  // this won't create-if-not-present and will return null instead.
  const SyncedSession* LookupLocalSession() const;

  // **** Methods for manipulating synced sessions and tabs. ****

  // Returns a pointer to the SyncedSession object associated with
  // |session_tag|. If none exists, returns nullptr. Ownership of the
  // SyncedSession remains within the SyncedSessionTracker.
  const SyncedSession* LookupSession(const std::string& session_tag) const;

  // Returns a pointer to the SyncedSession object associated with
  // |session_tag|. If none exists, creates one. Ownership of the
  // SyncedSession remains within the SyncedSessionTracker.
  SyncedSession* GetSession(const std::string& session_tag);

  // Resets the tracking information for the session specified by |session_tag|.
  // This involves clearing all the windows and tabs from the session, while
  // keeping pointers saved in the synced_window_map_ and synced_tab_map_. Once
  // reset, all calls to PutWindowInSession and PutTabInWindow will denote that
  // the requested windows and tabs are owned and add them back to their
  // session. The next call to CleanupSession(...) will delete those windows and
  // tabs not owned.
  void ResetSessionTracking(const std::string& session_tag);

  // Deletes those windows and tabs associated with |session_tag| that are no
  // longer owned. See ResetSessionTracking(...)..
  void CleanupSession(const std::string& session_tag);

  // Adds the window with id |window_id| to the session specified by
  // |session_tag|. If none existed for that session, creates one. Similarly, if
  // the session did not exist yet, creates it. Ownership of the SessionWindow
  // remains within the SyncedSessionTracker.
  // Attempting to add a window to a session multiple times will have no effect.
  void PutWindowInSession(const std::string& session_tag, SessionID window_id);

  // Adds the tab with id |tab_id| to the window |window_id|. If none existed
  // for that session, creates one. Ownership of the SessionTab remains within
  // the SyncedSessionTracker.
  //
  // Note: GetSession(..) must have already been called with |session_tag| to
  // ensure we having mapping information for this session.
  void PutTabInWindow(const std::string& session_tag,
                      SessionID window_id,
                      SessionID tab_id);

  // Adds |tab_node_id| to the session specified by |session_tag|, creating that
  // session if necessary. This is necessary to ensure that each session has an
  // up to date list of tab nodes linked to it for session deletion purposes.
  // Note that this won't update the local tab pool, even if the local session
  // tag is passed. The tab pool is only updated with new tab nodes when they're
  // associated with a tab id (see ReassociateLocalTabNode or
  // GetTabNodeFromLocalTabId).
  void OnTabNodeSeen(const std::string& session_tag,
                     int tab_node_id,
                     SessionID tab_id);

  // Returns a pointer to the SessionTab object associated with
  // |tab_id| for the session specified with |session_tag|.
  // Note: Ownership of the SessionTab remains within the SyncedSessionTracker.
  sessions::SessionTab* GetTab(const std::string& session_tag,
                               SessionID tab_id);

  // **** Methods specific to foreign sessions. ****

  // Tracks the deletion of a foreign tab by removing the given |tab_node_id|
  // from the parent session. Doesn't actually remove any tab objects because
  // the header may have or may not have already been updated to no longer
  // parent this tab. Regardless, when the header is updated then cleanup will
  // remove the actual tab data. However, this method always needs to be called
  // upon foreign tab deletion, otherwise LookupTabNodeIds(...) may return
  // already deleted tab node ids.
  void DeleteForeignTab(const std::string& session_tag, int tab_node_id);

  // Deletes the session associated with |session_tag| if it exists.
  // Returns true if the session existed and was deleted, false otherwise.
  bool DeleteForeignSession(const std::string& session_tag);

  // **** Methods specific to the local session. ****

  // Set the local session information. Must be called before any other local
  // session methods are invoked.
  void InitLocalSession(const std::string& local_session_tag,
                        const std::string& local_session_name,
                        sync_pb::SyncEnums::DeviceType local_device_type);

  // Gets the session tag previously set with InitLocalSession().
  const std::string& GetLocalSessionTag() const;

  // Similar to CleanupSession() but also marks unmapped tabs (i.e. closed ones)
  // as free tab nodes (which can be reused by future tabs) and triggers garbage
  // collection (i.e. deletion) of free tab nodes. It returns the set of locally
  // free tab nodes to be deleted. |is_tab_node_unsynced_cb| allows callers to
  // prevent tab nodes from being "free" (and hence reusable), which in practice
  // is useful to avoid overriding data that hasn't been synced yet.
  std::set<int> CleanupLocalTabs(
      const base::RepeatingCallback<bool(int /*tab_node_id*/)>&
          is_tab_node_unsynced_cb);

  // Returns the tab node ID for |tab_id| if an existing tab node was found, or
  // kInvalidTabNodeID otherwise.
  int LookupTabNodeFromTabId(const std::string& session_tag,
                             SessionID tab_id) const;

  // Returns the tab ID associated to |tab_node_id| or SessionID::InvalidValue()
  // if not associated.
  SessionID LookupTabIdFromTabNodeId(const std::string& session_tag,
                                     int tab_node_id) const;

  // Returns a valid tab node for |tab_id|. Will reuse an existing tab node if
  // possible, and otherwise create a new one.
  int AssociateLocalTabWithFreeTabNode(SessionID tab_id);

  // Reassociates the tab denoted by |tab_node_id| with a new tab id, preserving
  // any previous SessionTab object the node was associated with. If
  // |new_tab_id| is already associated with a tab object, that tab will be
  // overwritten. Reassociating a tab with a node it is already mapped to will
  // have no effect.
  void ReassociateLocalTab(int tab_node_id, SessionID new_tab_id);

  // **** Methods for querying/manipulating overall state ****.

  // Free the memory for all dynamically allocated objects and clear the
  // tracking structures.
  void Clear();

  bool Empty() const { return session_map_.empty(); }

  // Includes both foreign sessions and the local session.
  size_t num_synced_sessions() const { return session_map_.size(); }

  // Returns the number of tabs associated with the specified session tag.
  size_t num_synced_tabs(const std::string& session_tag) const {
    auto iter = session_map_.find(session_tag);
    if (iter != session_map_.end()) {
      return iter->second.synced_tab_map.size();
    } else {
      return 0;
    }
  }

  // Returns whether a tab is unmapped or not.
  bool IsTabUnmappedForTesting(SessionID tab_id);

 private:
  friend class SyncedSessionTrackerTest;

  struct TrackedSession {
    TrackedSession();
    ~TrackedSession();

    // Owns the SyncedSessions, and transitively, all of the windows and tabs
    // they contain.
    SyncedSession synced_session;

    // The mapping of tab/window to their SessionTab/SessionWindow objects.
    // The SessionTab/SessionWindow objects referred to may be owned either by
    // the session in the |synced_session| or be temporarily unmapped and live
    // in the |unmapped_tabs|/|unmapped_windows| collections.
    std::map<SessionID, sessions::SessionTab*> synced_tab_map;
    std::map<SessionID, SyncedSessionWindow*> synced_window_map;

    // The collection of tabs/windows not owned by SyncedSession. This is the
    // case either because 1. (in the case of tabs) they were newly created by
    // GetTab() and not yet added to a session, or 2. they were removed from
    // their owning session by a call to ResetSessionTracking() and not yet
    // added back.
    std::map<SessionID, std::unique_ptr<sessions::SessionTab>> unmapped_tabs;
    std::map<SessionID, std::unique_ptr<SyncedSessionWindow>> unmapped_windows;

    // Mappings between tab node IDs and tab IDs. For the local session, it also
    // knows about available sync nodes associated with this session.
    TabNodePool tab_node_pool;
  };

  // LookupTrackedSession() returns null if the session tag is unknown.
  const TrackedSession* LookupTrackedSession(
      const std::string& session_tag) const;
  TrackedSession* LookupTrackedSession(const std::string& session_tag);
  // Creates tracked session if it wasn't known previously. Never returns null.
  TrackedSession* GetTrackedSession(const std::string& session_tag);

  std::vector<const SyncedSession*> LookupSessions(
      SessionLookup lookup,
      bool exclude_local_session) const;

  // Implementation of CleanupSession()/CleanupLocalTabs().
  void CleanupSessionImpl(
      const std::string& session_tag,
      const base::RepeatingCallback<bool(int /*tab_node_id*/)>&
          is_tab_node_unsynced_cb);

  // The client of the sync sessions datatype.
  SyncSessionsClient* const sessions_client_;

  // Map: session tag -> TrackedSession.
  std::map<std::string, TrackedSession> session_map_;

  // The tag for this machine's local session, so we can distinguish the foreign
  // sessions.
  std::string local_session_tag_;

  DISALLOW_COPY_AND_ASSIGN(SyncedSessionTracker);
};

// Helper function to load and add window or tab data from synced specifics to
// our internal tracking in SyncedSessionTracker.
void UpdateTrackerWithSpecifics(const sync_pb::SessionSpecifics& specifics,
                                base::Time modification_time,
                                SyncedSessionTracker* tracker);

// Generates all sync entities represented by the tracker. Instead of returning
// protos by value, |output_cb| is run for each serialized entity.
void SerializeTrackerToSpecifics(
    const SyncedSessionTracker& tracker,
    const base::RepeatingCallback<void(const std::string& session_name,
                                       sync_pb::SessionSpecifics* specifics)>&
        output_cb);

// Same as above but generates a subset of sync entities represented by the
// tracker, as selected by |session_tag_to_node_ids|. Unknown session tags or
// node IDs will be ignored. kInvalidTabNodeID can be used to request header
// entities.
void SerializePartialTrackerToSpecifics(
    const SyncedSessionTracker& tracker,
    const std::map<std::string, std::set<int>>& session_tag_to_node_ids,
    const base::RepeatingCallback<void(const std::string& session_name,
                                       sync_pb::SessionSpecifics* specifics)>&
        output_cb);

}  // namespace sync_sessions

#endif  // COMPONENTS_SYNC_SESSIONS_SYNCED_SESSION_TRACKER_H_