Sqlite implementation

[sligara7]

1. Backend Selection

• Added support for selecting the backend (Redis or SQLite) using the PLAN_QUEUE_BACKEND environment variable.
• Default backend is Redis.
• If PLAN_QUEUE_BACKEND=sqlite, the SQLite backend is used.

2. SQLite Database Initialization

• Added _initialize_sqlite_database to create required tables (kv_store, plan_queue, plan_history) if they do not exist.
• Tables include:
  • kv_store: For key-value pairs.
  • plan_queue: For storing the plan queue with a UNIQUE constraint on item_uid.
  • plan_history: For storing the plan history with a UNIQUE constraint on item_uid.

3. Backend-Specific Helper Methods

• Added backend-agnostic methods that encapsulate logic for both Redis and SQLite. These methods dynamically determine the backend and execute the appropriate logic.

4. SQLite Connection Management

• Added logic to manage SQLite connections:
  • Open connection during start.
  • Close connection during stop.

5. UID Management

• Ensured that item_uid uniqueness is enforced in SQLite:
  • Added item_uid as a UNIQUE column in plan_queue and plan_history tables.
  • Checked for duplicate item_uid values before inserting items into SQLite.

6. Testing and Compatibility

• Updated methods like _get_queue, _add_item_to_queue, _remove_item, etc., to work seamlessly with both Redis and SQLite backends.
• Ensured consistent behavior across both backends by using the backend-agnostic helper methods.