Your Task: Implement a Simple Cloud Storage System

Overview:
Your task is to implement a simple cloud storage system that maps objects (files) to their meta-information. The system should maintain files and their associated data, such as names and sizes. This system is in-memory, meaning there is no need to interact with the real filesystem.

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Requirements

Level 1: Basic File Operations

The cloud storage system should support basic file operations: adding, retrieving, and deleting files.

• add_file(self, name: str, size: int) -> bool
  Adds a new file with the specified name and size to the storage.
  • Fails if a file with the same name already exists.
  • Returns: True if the file is added successfully, False otherwise.
• get_file_size(self, name: str) -> int | None
  Retrieves the size of the file with the given name.
  • Returns: The file size if it exists, or None otherwise.
• delete_file(self, name: str) -> int | None
  Deletes the file with the specified name.
  • Returns: The size of the deleted file if the operation is successful, or None if the file does not exist.

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Level 2: File Statistics

Support for retrieving statistics about files with a specific prefix.

• get_n_largest(self, prefix: str, n: int) -> List[str]
  Returns a list of the names of the top n largest files with names starting with the specified prefix.
  • Files should be sorted by size in descending order. In case of a tie, names should be sorted lexicographically.
  • If no such files exist, return an empty list.
  • If the number of matching files is less than n, return all of them in the specified format.

Examples:

add_file("/dir/file1.txt", 5)       -> True
add_file("/dir/file2.txt", 20)      -> True
add_file("/dir/deeper/file3.mov", 9)-> True
get_n_largest("/dir", 2)            -> ["/dir/file2.txt", "/dir/file1.txt"]
get_n_largest("/dir/file", 3)       -> ["/dir/file1.txt"]
get_n_largest("/another_dir", 2)    -> []
add_file("/big_file.mp4", 20)       -> True
get_n_largest("/", 2)               -> ["/big_file.mp4", "/dir/file2.txt"]

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Level 3: User Management

Support for multiple users, each with a storage capacity limit. All users share the same cloud storage system.

• add_user(self, user_id: str, capacity: int) -> bool
  Adds a new user with the specified storage capacity (in bytes).
  • Fails if a user with the same user_id already exists.
  • Returns: True if the user is added successfully, False otherwise.
• add_file_by(self, user_id: str, name: str, size: int) -> int | None
  Adds a file owned by the specified user, following the same logic as add_file from Level 1.
  • A file cannot be added if it exceeds the user's remaining capacity.
  • Returns: The user's remaining capacity if the file is added successfully, or None otherwise.

Notes:

• All Level 1 add_file operations are performed by the "admin" user, who has unlimited storage capacity.

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Level 4: Backup and Restore

Support for backing up and restoring files for individual users.

• backup_user(self, user_id: str) -> int | None
  Backs up the current state of all files owned by the user.
  • The backup is stored separately and is not affected by subsequent file manipulations.
  • Overwrites any previous backups for the same user.
  • Returns: The number of files backed up, or None if the user does not exist.
• restore_user(self, user_id: str) -> int | None
  Restores the user’s files to their latest backup.
  • If no backup exists, all files owned by the user are deleted.
  • Files that cannot be restored (e.g., due to naming conflicts with other users) are ignored.
  • Returns: The number of files successfully restored, or None if the user does not exist.

Notes:

• The restore_user operation does not affect the user’s capacity.
• Merging users does not affect the backup of user_id1, but user_id2 is deleted along with its backup.

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