Search a FHIR Bundle (Java)

Instructions

A FHIR Bundle is a container that carries a collection of resources — for example the results of a search on a server. This kata is the offline, deterministic version of Batch-1 Day 4, Assignment 1 (searching resources on an OpenMRS FHIR facade): instead of calling a live server, you are handed the Bundle in memory and must implement the search/filter utilities a client would use.

The resource model

A resource is modelled by the immutable helper class BundleSearch.Resource, which is already provided for you:

• Resource(String type, String id, Map<String,String> fields) — construct a resource, e.g. type "Patient", id "1", fields {name: "Smith"}.
• String type() — the resource type, e.g. "Patient".
• String id() — the logical id, e.g. "1".
• String field(String key) — the value of a field, or null if absent.

A Bundle is simply a List<Resource>.

Your task

Implement the four static search methods on BundleSearch:

• List<Resource> ofType(List<Resource> bundle, String type) — every entry whose type equals type, preserving the input order.
• Optional<Resource> byId(List<Resource> bundle, String type, String id) — the first entry matching both type and id, or Optional.empty() if none.
• List<Resource> where(List<Resource> bundle, String type, String field, String value) — every entry of type whose field(field) equals value, in input order.
• int count(List<Resource> bundle, String type) — how many entries have the given type.

Rules

• Preserve the bundle's input order in every returned list.
• Matching is exact string equality on type, id, and field values.
• No match returns an empty list, Optional.empty(), or 0 — never null and never an exception.