Implement an in-memory database with record locking

Implement an in-memory key–record database that supports basic CRUD on fields plus an exclusive lock per record.

You are given a sequence of queries. Each query is an array of strings. Implement a function that processes all queries in order and returns an array of strings containing the outputs of the queries that produce output.

Data model

• The database contains records identified by recordKey (string).
• Each record is a map from field (string) to value (string).

Locking model

• A record can be unlocked or locked by exactly one user ( userId , string).
• A lock applies to the whole record (all its fields).
• Reads are always allowed .
• Writes/deletes are allowed only if the record is not locked, or it is locked by the same userId performing the operation.

Query types

Each query is one of:

1. SET recordKey field value userId

• If the write is allowed, set recordKey[field] = value (creating the record if needed) and output "OK" .
• Otherwise output "LOCKED" and do not change the database.

2. GET recordKey field

• Output the value if present, otherwise output an empty string "" .

3. DELETE recordKey field userId

• If the delete is allowed and the field existed, remove it and output "true" .
• If the delete is allowed but the field did not exist, output "false" .
• If the delete is not allowed due to locking, output "LOCKED" .
• If a record becomes empty after deletion, remove the record entirely. If the record is removed, its lock (if any) is also removed.

4. LOCK recordKey userId

• If the record does not exist, output "INVALID" .
• If the record is unlocked, lock it for userId and output "ACQUIRED" .
• If the record is already locked by userId , output "ACQUIRED" (idempotent).
• If the record is locked by a different user, output "WAIT" .

5. UNLOCK recordKey userId

• If the record does not exist, output "INVALID" .
• If the record is locked by userId , unlock it and output "RELEASED" .
• If the record is unlocked, output "RELEASED" (idempotent).
• If the record is locked by a different user, output "INVALID" .

Requirements

• Process queries efficiently (aim for average O(1) per query using hash maps).
• Return outputs only for the queries above (all of them produce output in this spec).

Example

If a record A is locked by user u1, then SET A x 5 u2 must output "LOCKED", while GET A x still returns the stored value (or empty string if missing).