StructureMap-based extraction

[ekigamba]

Is your feature request related to a problem? Please describe.
Partly yes.

1. Problem - Extracting complex multiple resources and performing transformations is currently not possible
2. FHIR Spec support - We need to support SDC StructureMap-based extraction mechanisms

Describe the solution you'd like
Defining a Questionnaire with the StructureMap reference and automatically getting the extracted resources when ResourceMapper#extraction is called with the Questionnaire and QuestionnaireResponse

Scoping

• Change the ResourceMapper#extraction return type to Bundle
• Move definition based extraction functionality to a different function
• Add structuremap-based extraction functionality on a different function
• Both extraction functions should return a Bundle
• StructureMap-based extraction should only be used if there is a questionnaire-targetStructureMap extension on the Questionnaire root
• Fetch the StructureMap from the DB so that it can be invoked against the QuestionnaireResponse - The url of the StructureMap is retrieved from the extension's valueCanonical. Functionality for invoking a StructureMap on a resource is already implemented in the hapi-fhir rg.hl7.fhir.r4.utils.StructureMapUtilities.

Handling of errors

• If the StructureMap execution fails, no data will be extracted from the Questionnaire
• If the StructureMap is not found, the extraction fails - We need to figure out a way to retry extraction

Describe alternatives you've considered
None

Additional context
http://build.fhir.org/ig/HL7/sdc/extraction.html#structuremap-based-extraction

Would you like to work on the issue?
Yes

[ekigamba]

@jingtang10 Could you take a look at this and see if this implementation is OK with you?

[jingtang10]

We still need a follow-up PR to convert the functions to suspend functions.

[ekigamba]

@jingtang10 I have created the issue here as discussed