chromium/chrome/browser/sync_file_system/drive_backend/metadata_database.h

// Copyright 2013 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef CHROME_BROWSER_SYNC_FILE_SYSTEM_DRIVE_BACKEND_METADATA_DATABASE_H_
#define CHROME_BROWSER_SYNC_FILE_SYSTEM_DRIVE_BACKEND_METADATA_DATABASE_H_

#include <stddef.h>
#include <stdint.h>

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

#include "base/files/file_path.h"
#include "base/memory/raw_ptr.h"
#include "base/memory/weak_ptr.h"
#include "base/sequence_checker.h"
#include "base/values.h"
#include "chrome/browser/sync_file_system/drive_backend/tracker_id_set.h"
#include "chrome/browser/sync_file_system/sync_status_code.h"

namespace leveldb {
class Env;
}

namespace google_apis {
class ChangeResource;
class FileResource;
}

namespace base {
class Location;
}

namespace sync_file_system {
namespace drive_backend {

class FileDetails;
class FileMetadata;
class FileTracker;
class LevelDBWrapper;
class MetadataDatabaseIndexInterface;
class ServiceMetadata;

// MetadataDatabase holds and maintains a LevelDB instance and its indexes,
// which holds 1)ServiceMetadata, 2)FileMetadata and 3)FileTracker.
// 1) ServiceMetadata is a singleton in the database which holds information for
//    the backend.
// 2) FileMetadata represents a remote-side file and holds latest known
//    metadata of the remote file.
// 3) FileTracker represents a synced or to-be-synced file and maintains
//    the local-side folder tree.
//
// The term "file" includes files, folders and other resources on Drive.
//
// FileTrackers form a tree structure on the database, which represents the
// FileSystem trees of SyncFileSystem.  The tree has a FileTracker named
// sync-root as its root node, and a set of FileTracker named app-root.  An
// app-root represents a remote folder for an installed Chrome App and holds all
// synced contents for the App.
//
// One FileMetadata is created for each tracked remote file, which is identified
// by FileID.
// One FileTracker is created for every different {parent tracker, FileID} pair,
// excluding non-app-root inactive parent trackers. Multiple trackers may be
// associated to one FileID when the file has multiple parents. Multiple
// trackers may have the same {parent tracker, title} pair when the associated
// remote files have the same title.
//
// Files have following state:
//   - Unknown file
//     - Has a dirty inactive tracker and empty synced_details.
//     - Is initial state of a tracker, only file_id and parent_tracker_id field
//       are known.
//   - Folder
//     - Is either one of sync-root folder, app-root folder or a regular folder.
//     - Sync-root folder holds app-root folders as its direct children, and
//       holds entire SyncFileSystem files as its descentants.  Its tracker
//       should be stored in ServiceMetadata by its tracker_id.
//     - App-root folder holds all files for an application as its descendants.
//   - File
//   - Unsupported file
//     - Represents unsupported files such as hosted documents. Must be
//       inactive.
//
// Invariants:
//   - Any tracker in the database must either:
//     - be sync-root,
//     - have an app-root as its parent tracker, or
//     - have an active tracker as its parent.
//   That is, all trackers must be reachable from sync-root via app-root folders
//   and active trackers.
//
//   - Any active tracker must either:
//     - have |needs_folder_listing| flag and dirty flag, or
//     - have all children at the stored largest change ID.
//
//   - If multiple trackers have the same parent tracker and same title, they
//     must not have same |file_id|, and at most one of them may be active.
//   - If multiple trackers have the same |file_id|, at most one of them may be
//     active.
//
class MetadataDatabase { … };

}  // namespace drive_backend
}  // namespace sync_file_system

#endif  // CHROME_BROWSER_SYNC_FILE_SYSTEM_DRIVE_BACKEND_METADATA_DATABASE_H_