FHIR Reference (Java)

Instructions

In FHIR, resources point at each other with references. A relative literal reference looks like:

Patient/123
Observation/abc-1/_history/4

• ResourceType/id — points at the current version of a resource.
• ResourceType/id/_history/versionId — points at a specific version.

This kata is the offline, deterministic version of Batch-1 Day 4, Assignment 1 (searching an OpenMRS FHIR facade): before you can follow a reference to another resource, you must be able to parse and build one.

Implement FhirReference with:

• static FhirReference parse(String reference) — parse a relative reference.
• String type() — the resource type, e.g. "Patient".
• String id() — the logical id, e.g. "123".
• Optional<String> version() — the _history version id if present, else empty.
• boolean isVersioned() — true when a version id is present.
• String format() — reconstruct the canonical reference string.

Rules

• A valid reference has a non-empty resource type and a non-empty id.
• The type must start with an uppercase letter (FHIR resource types are PascalCase).
• A versioned reference has exactly the segments Type/id/_history/vid, and vid must be non-empty.
• Anything else (null, empty, "Patient", "Patient/", "/123", "Patient/123/foo/4", "Patient/123/_history/") must throw IllegalArgumentException.
• format() must round-trip: FhirReference.parse(s).format().equals(s) for every valid s.