Add Document Key Retriever to Buffered Sender

[sarangan12]

This PR Contains the following changes:

1. Change @hidden to @internal values.
2. Fix the error code to statusCode.
3. One new requirement is that in the batch sender before sending in the batch we need to check if there are any duplicates (based on the id retrieval logic supplied by the user) and move them to the next batch. (It is ok if we send a batch that is less than the threshold size)
4. Change the autoflush to true by default.

@xirzec Please review and approve.

[xirzec]

Looking pretty good, just a few thoughts about how we can tighten typing and make the prune function not mutate its parameters.

[xirzec]

why do we have ts-ignore here?

[sarangan12]

If I do not add this here, I get the following error:

src/searchIndexingBufferedSender.ts:405:45 - error TS2345: Argument of type 'IndexDocumentsAction<T>' is not assignable to parameter of type 'T'.
  'T' could be instantiated with an arbitrary type which could be unrelated to 'IndexDocumentsAction<T>'.

405       const key = this.documentKeyRetriever(document);

[xirzec]

This is interesting. Since merge and delete operations don't need to specify the entire document, IndexDocumentsAction maps to a Partial plus the action property.

Since the action can be a partial document, that means the mapping function might not be getting the whole document. This should still be fine as the partial document must contain the key, but TS doesn't know that, so what it wants is for documentKeyRetriever to look like this:

documentKeyRetriever: (document: T | IndexDocumentsAction<T>) => string

I notice that buffered sender doesn't actually ever take in partial documents, so I think in this case it's safe to avoid it with

const key = this.documentKeyRetriever(document as unknown as T);

Which is still much better than ts-ignore as ts-ignore disables all checking instead of just one type check.

[xirzec]

I think I'm happy with this as long as we can take out the ts-ignore (see suggestion in comment)

[xirzec]

This is interesting. Since merge and delete operations don't need to specify the entire document, IndexDocumentsAction maps to a Partial plus the action property.

Since the action can be a partial document, that means the mapping function might not be getting the whole document. This should still be fine as the partial document must contain the key, but TS doesn't know that, so what it wants is for documentKeyRetriever to look like this:

documentKeyRetriever: (document: T | IndexDocumentsAction<T>) => string

I notice that buffered sender doesn't actually ever take in partial documents, so I think in this case it's safe to avoid it with

const key = this.documentKeyRetriever(document as unknown as T);

Which is still much better than ts-ignore as ts-ignore disables all checking instead of just one type check.