Refactor fhir-term module

[JohnTimm]

The fhir-term module should be updated as follows:

1. Add support to FHIRTermService for multiple FHIRTermServiceProvider instances:

	private FHIRTermServiceProvider findProvider(CodeSystem codeSystem) {
            return providers.stream()
			.filter(provider -> provider.isSupported(codeSystem))
			.findFirst()
			.orElse(null);
	}

2. Add methods to FHIRTermServiceProvider interface:
   boolean isSupported(CodeSystem)
Concept findConcept(CodeSystem, Code)
Concept findConcept(CodeSystem, Code, Code)

3. Remove methods from FHIRTermServiceProvider interface:
   boolean isExpandable(ValueSet)
   Consider removing validateCode(ValueSet, ...) methods
   Consider removing expand(ValueSet) method

4. Update methods in FHIRTermService class:
   boolean isExpandable(ValueSet) should be updated to call ValueSetSupport.isExpandable(ValueSet)
ValidationResult validateCode(ValueSet, ...) methods should be updated to call ValueSetSupport.validateCode(ValueSet, ...)
   Consider removing dependency on FHIRTermServiceProvider interface

5. Add implementation for new methods in DefaultTermServiceProvider:
   boolean isSupported(CodeSystem) -> CodeSystem.content = 'complete'
Concept findConcept(CodeSystem, Code) -> calls CodeSystemSupport.findConcept(...)
Concept findConcept(CodeSystem, Code, Code) -> calls CodeSystemSupport.findConcept(...)

6. Updated methods and inner classes in ValueSetSupport
   Update isExpandable to use FHIRTermService.getInstance().isSupported(CodeSystem)
   Update createDescendOfFilter, createGeneralizesFilter, createIsAFilter, createIsNotFilter to use FHIRTermService.getInstance().findConcept(...) method
   Update DescendantOfFilter, GeneralizesFilter, IsAFilter, EqualsFilter to use FHIRTermService.getInstance().findConcept(...) method

7. Centeralize code set caching: move code set caching from DefaultTermServiceProvider back into the ValueSetSupport class

[JohnTimm]

Proposed simplified FHIRTermServiceProvider interface:

public interface FHIRTermServiceProvider {
    boolean isSupported(CodeSystem codeSystem);
    Concept findConcept(CodeSystem codeSystem, Code code);
    Concept findConcept(CodeSysten codeSystem, Concept concept, Code code);
    LookupOutcome lookup(CodeSystem codeSystem, Code code, LookupParameters parameters);
    default LookupOutcome lookup(CodeSystem codeSystem, Code code) {
        return lookup(codeSystem, code, LookupParameter.EMPTY);
    }
    ConceptSubsumptionOutcome subsumes(CodeSystem codeSystem, Code codeA, Code codeB);
    ConceptMap closure(CodeSystem codeSystem, Code code);
    ValidationOutcome validateCode(CodeSystem codeSystem, Code code, String display, ValidationParameters parameters);
    default ValidationOutcome validateCode(CodeSystem codeSystem, Code code, String display) {
        return validateCode(codeSystem, code, display, ValidationParameters.EMPTY);
    }
}

[lmsurpre]

I think we need to update the javadoc for subsumes:

    /**
     * Find the concept in tree rooted by the provided concept that matches the specified code.
     *
     * @param codeSystem
     *     the code system
     * @param codeA
     *     the root of the hierarchy to search
     * @param codeB
     *     the code to match
     * @return
     *     the code system concept that matches the specified code, or null if not such concept exists
     */
    boolean subsumes(CodeSystem codeSystem, Code codeA, Code codeB);

It returns a boolean but the javadoc implies it will return a Concept

[lmsurpre]

was just reading at https://www.hl7.org/fhir/operation-codesystem-subsumes.html

The “A” Coding that is to be tested. The code system does not have to match the specified subsumption code system, but the relationships between the code systems must be well established

we don’t support subsumption testing across codesystems, right? is that a limitation of the current interface?

[lmsurpre]

I opened https://github.com/IBM/FHIR/pull/2181/files with my recommended javadoc updates.

[lmsurpre]

was just reading at https://www.hl7.org/fhir/operation-codesystem-subsumes.html

The “A” Coding that is to be tested. The code system does not have to match the specified subsumption code system, but the relationships between the code systems must be well established

we don’t support subsumption testing across codesystems, right? is that a limitation of the current interface?

I discussed this with @JohnTimm and he wanted to keep just the single-system variant for now (since this is all we support at the moment). If/when we get a FHIRTermServiceProvider implementation that can test for subsumption across systems, we'll need to update the interface to support that.