[MDS] Refactor several utility functions in data source plugin

[huyaboo]

Is your feature request related to a problem? Please describe.
Currently, there are two functions being repeated in plugins that can simply be extracted into data source plugin utility functions:

• A function that decides whether to use local cluster or remote OpenSearch client based on data source id
• A function that retrieves the data source id based on data source title/name

Describe the solution you'd like
There should be three utility functions placed in the data source plugin that will be exposed so that other plugins can consume:

• decideClient(context: RequestHandlerContext, dataSourceId?: string, withLongNumeralsSupport: boolean): return the correct client
• decideLegacyClient(context: RequestHandlerContext, dataSourceId?: string): return the correct legacy client
• fetchDataSourceNameById(client: SavedObjectsClientCommon, dataSourceTitle: string): return the data source id (if it exists)
  • SavedObjectClientWrapper should be defined in both public and server folders for passing type checks

Describe alternatives you've considered

N/A

Additional context

N/A

[bandinib-amzn]

Thank you for continuous improvement and insist on high standards.

[BionIT]

@huyaboo Should we target this for 2.16 instead?

[zhongnansu]

Unlike "decideClient" that will be used by many internal and external plugins, where plugins need to choose the correct client to talk to either local cluster, or data source cluster, for "fetchDataSourceIdByName", I don't think it's necessary to make it a util in data source plugin, because

1. it's only being used in vega and timeline plugin, I am not aware of any other internal or external plugins that needs it.
2. there's context specific logic in the existing fetchDataSourceIdByName function, see below for example. "data_source_name" is very specific to the timeline/vega expression use case. So it doesn't make sense to make it general

OpenSearch-Dashboards/src/plugins/vis_type_timeline/server/lib/fetch_data_source_id.ts

Lines 38 to 41 in 4f54049

	throw new Error(
	`Expected exactly 1 result for data_source_name "${config.data_source_name}" but got ${possibleDataSourceIds.length} results`
	);
	}

cc: @huyaboo @BionIT

[BionIT]

Hi @zhongnansu Is this complete? Can we close the issue?

[zhongnansu]

Hi @zhongnansu Is this complete? Can we close the issue?

Yes, closing