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diff --git a/dom/fs/parent/datamodel/FileSystemFileManager.h b/dom/fs/parent/datamodel/FileSystemFileManager.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef DOM_FS_PARENT_DATAMODEL_FILESYSTEMFILEMANAGER_H_
+#define DOM_FS_PARENT_DATAMODEL_FILESYSTEMFILEMANAGER_H_
+
+#include "ErrorList.h"
+#include "mozilla/dom/FileSystemTypes.h"
+#include "mozilla/dom/QMResult.h"
+#include "nsIFile.h"
+#include "nsString.h"
+
+template <class T>
+class nsCOMPtr;
+
+class nsIFileURL;
+
+namespace mozilla::dom {
+
+namespace quota {
+
+struct OriginMetadata;
+
+}  // namespace quota
+
+namespace fs::data {
+
+/**
+ * @brief Get the directory for file system items of specified origin.
+ * Use this instead of constructing the path from quota manager's storage path.
+ *
+ * @param aOrigin Specified origin
+ * @return Result<nsCOMPtr<nsIFile>, QMResult> Top file system directory
+ */
+Result<nsCOMPtr<nsIFile>, QMResult> GetFileSystemDirectory(
+    const Origin& aOrigin);
+
+/**
+ * @brief Ensure that the origin-specific directory for file system exists.
+ *
+ * @param aOriginMetadata Specified origin metadata
+ * @return nsresult Error if operation failed
+ */
+nsresult EnsureFileSystemDirectory(
+    const quota::OriginMetadata& aOriginMetadata);
+
+/**
+ * @brief Get file system's database path for specified origin.
+ * Use this to get the database path instead of constructing it from
+ * quota manager's storage path - without the side effect of potentially
+ * creating it.
+ *
+ * @param aOrigin Specified origin
+ * @return Result<nsCOMPtr<nsIFile>, QMResult> Database file object
+ */
+Result<nsCOMPtr<nsIFile>, QMResult> GetDatabaseFile(const Origin& aOrigin);
+
+/**
+ * @brief Get file system's database url with directory lock parameter for
+ * specified origin. Use this to open a database connection and have the quota
+ * manager guard against its deletion or busy errors due to other connections.
+ *
+ * @param aOrigin Specified origin
+ * @param aDirectoryLockId Directory lock id from the quota manager
+ * @return Result<nsCOMPtr<nsIFileURL>, QMResult> Database file URL object
+ */
+Result<nsCOMPtr<nsIFileURL>, QMResult> GetDatabaseFileURL(
+    const Origin& aOrigin, const int64_t aDirectoryLockId);
+
+/**
+ * @brief Creates and removes disk-backed representations of the file systems'
+ * file entries for a specified origin.
+ *
+ * Other components should not depend on how the files are organized on disk
+ * but instead rely on the entry id and have access to the local file using the
+ * GetOrCreateFile result.
+ *
+ * The local paths are not necessarily stable in the long term and if they
+ * absolutely must be cached, there should be a way to repopulate the cache
+ * after an internal reorganization of the file entry represenations on disk,
+ * for some currently unforeseen maintenance reason.
+ *
+ * Example: if GetOrCreateFile used to map entryId 'abc' to path '/c/u/1/123'
+ * and now it maps it to '/d/u/1/12/123', the cache should either update all
+ * paths at once through a migration, or purge them and save a new value
+ * whenever a call to GetOrCreateFile is made.
+ */
+class FileSystemFileManager {
+ public:
+  /**
+   * @brief Create a File System File Manager object for a specified origin.
+   *
+   * @param aOrigin
+   * @return Result<FileSystemFileManager, QMResult>
+   */
+  static Result<FileSystemFileManager, QMResult> CreateFileSystemFileManager(
+      const Origin& aOrigin);
+
+  /**
+   * @brief Create a File System File Manager object which keeps file entries
+   * under a specified directory instead of quota manager's storage path.
+   * This should only be used for testing and preferably removed.
+   *
+   * @param topDirectory
+   * @return Result<FileSystemFileManager, QMResult>
+   */
+  static Result<FileSystemFileManager, QMResult> CreateFileSystemFileManager(
+      nsCOMPtr<nsIFile>&& topDirectory);
+
+  /**
+   * @brief Get a file object for a specified entry id. If a file for the entry
+   * does not exist, returns an appropriate error.
+   *
+   * @param aEntryId Specified id of a file system entry
+   * @return Result<nsCOMPtr<nsIFile>, QMResult> File or error.
+   */
+  Result<nsCOMPtr<nsIFile>, QMResult> GetFile(const EntryId& aEntryId) const;
+
+  /**
+   * @brief Get or create a disk-backed file object for a specified entry id.
+   *
+   * @param aEntryId Specified id of a file system entry
+   * @return Result<nsCOMPtr<nsIFile>, QMResult> File abstraction or IO error
+   */
+  Result<nsCOMPtr<nsIFile>, QMResult> GetOrCreateFile(const EntryId& aEntryId);
+
+  /**
+   * @brief Remove the disk-backed file object for a specified entry id.
+   *
+   * @param aEntryId  Specified id of a file system entry
+   * @return Result<int64_t, QMResult> Error or file size
+   */
+  Result<int64_t, QMResult> RemoveFile(const EntryId& aEntryId);
+
+ private:
+  explicit FileSystemFileManager(nsCOMPtr<nsIFile>&& aTopDirectory);
+
+  nsCOMPtr<nsIFile> mTopDirectory;
+};
+
+}  // namespace fs::data
+}  // namespace mozilla::dom
+
+#endif  // DOM_FS_PARENT_DATAMODEL_FILESYSTEMFILEMANAGER_H_