Cloud storage with user quotas and backups

Design an in-memory cloud storage service. The interview has four parts. Each part adds methods, and every earlier method must keep working. Implement a class CloudStorage.

File names are full path strings such as /photos/cat.png, compared exactly. Sizes are positive integers in bytes.

Part 1: files

• add_file(name: str, size: int) -> bool: add a file. Return False if a file with that name already exists.
• copy_file(name_from: str, name_to: str) -> bool: copy a file to a new name. Fail if name_from does not exist or name_to already exists.
• get_file_size(name: str) -> int: return the file's size, or -1 if it does not exist.

Part 2: search

• find_files(prefix: str, suffix: str) -> list[str]: return up to 10 files whose names start with prefix and end with suffix, formatted as "name(size)". Order by size descending, then by name ascending.

Part 3: users and quotas

• add_user(user_id: str, capacity: int) -> bool: create a user with a storage limit. Return False if the user exists.
• add_file_by(user_id: str, name: str, size: int) -> int | None: add a file owned by the user. Return the user's remaining capacity, or None if the user does not exist, the name is taken, or the file would exceed the limit.
• update_capacity(user_id: str, capacity: int) -> int | None: change the limit. If the user is now over it, delete their largest files (ties: smaller name first) until they fit. Return the number of files deleted, or None for an unknown user.
• Files added with add_file belong to a built-in admin user with no limit. A copy belongs to the source file's owner and counts against that owner's limit; the copy fails if it does not fit.

Part 4: merge, backup, restore

• merge_user(target_id: str, source_id: str) -> int | None: move all of the source's files and capacity to the target, then delete the source and its backup. Return the target's remaining capacity, or None if either user is unknown or they are the same.
• backup_user(user_id: str) -> int | None: save a snapshot of the user's files, replacing any earlier snapshot. Return the number of files saved.
• restore_user(user_id: str) -> int | None: delete the user's current files and re-create the files from the last snapshot (with no snapshot, the user ends up with no files). Skip any file whose name now belongs to another user. Return the number of files restored.

Example

add_file("/docs/a.txt", 100)         -> True
copy_file("/docs/a.txt", "/docs/b.txt") -> True
add_file("/img/d.txt", 300)          -> True
find_files("/", ".txt")              -> ["/img/d.txt(300)", "/docs/a.txt(100)", "/docs/b.txt(100)"]
add_user("u1", 500)                  -> True
add_file_by("u1", "/u1/x", 200)      -> 300
add_file_by("u1", "/u1/y", 250)      -> 50
add_file_by("u1", "/u1/z", 60)       -> None
update_capacity("u1", 300)           -> 1   (deletes /u1/y)
get_file_size("/u1/y")               -> -1