[WIP] Cluster mode example: factor out the database

[gaborfeher]

specific logic from taskstore.go into db_taskstore.go

[gemini-code-assist]

Summary of Changes

Hello @gaborfeher, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request refactors the database interaction logic within the cluster mode example. The primary goal is to separate the database-specific implementation from the generic task storage mechanism. This is achieved by introducing a Database interface and a generic DBTaskStore that operates against this interface, along with a concrete MySQL implementation. This change significantly improves the modularity and extensibility of the task persistence layer, making it easier to support different database backends in the future.

Highlights

• Database Abstraction: Introduced a new Database interface in utils/db_taskstore.go which defines the core persistence operations (Create, Update, Get) for tasks and events. This abstracts the database-specific implementation details.
• Generic DBTaskStore: Created a new DBTaskStore in utils/db_taskstore.go that implements the a2asrv.TaskStore interface using the newly defined Database interface. This centralizes the database-agnostic task storage logic.
• MySQL Implementation: Added mysql_db_adapter.go which provides a concrete implementation of the Database interface specifically for MySQL, handling SQL transactions, optimistic concurrency, and JSON (un)marshalling for task and event data.
• Refactored TaskStore: The original taskstore.go has been significantly refactored. It no longer contains the direct database interaction logic but now acts as a factory, creating and utilizing the MySQLDBAdapter and the generic DBTaskStore.

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[gemini-code-assist]

Code Review

This pull request effectively refactors the database-specific logic out of taskstore.go by introducing a Database interface and a MySQLDBAdapter implementation. This is a great improvement for modularity and prepares the ground for supporting other database backends. The code is well-structured and the abstraction is clean. I have a few suggestions to remove an unused parameter from the Update method signature across the new interface and implementation, which will make the code even clearer.

[gemini-code-assist]

The protocolVersion parameter is not used within this function. To align with the interface change and improve clarity, it should be removed from the function signature.

Suggested change

	func (a *MySQLDBAdapter) Update(ctx context.Context, task *a2a.Task, event a2a.Event, newVersion int64, prevVersion int64, protocolVersion a2a.ProtocolVersion) (bool, error) {
	func (a *MySQLDBAdapter) Update(ctx context.Context, task *a2a.Task, event a2a.Event, newVersion int64, prevVersion int64) (bool, error) {

[gemini-code-assist]

The protocolVersion parameter is unused in implementations of this Update method (e.g., MySQLDBAdapter). Since the protocol version of a task is not expected to change after creation, this parameter should be removed from the Update method signature to improve code clarity. This will require updating the method signature here, in the MySQLDBAdapter.Update implementation, and the call to s.db.Update in DBTaskStore.Save.

Suggested change

	Update(ctx context.Context, task *a2a.Task, event a2a.Event, newVersion int64, prevVersion int64, protocolVersion a2a.ProtocolVersion) (bool, error)
	Update(ctx context.Context, task *a2a.Task, event a2a.Event, newVersion int64, prevVersion int64) (bool, error)

[gemini-code-assist]

To align with the suggested change of removing the unused protocolVersion parameter from the db.Update method, this call should be updated accordingly.

Suggested change

	success, err := s.db.Update(ctx, task, event, newVersion, int64(prevVersion), s.version)
	success, err := s.db.Update(ctx, task, event, newVersion, int64(prevVersion))