Build a FHIR Patient (Java)

Instructions

A FHIR Patient resource is a JSON document. Before a server can store or return one, your code has to construct it and serialize it to canonical JSON — the same bytes every time, so downstream systems and tests can rely on it.

This kata is the offline, deterministic version of Batch-1 Day 5, Week 1, Assignment 3/4 (stand up a FHIR server and create Patient resources). Instead of posting to a live server, you build the resource in memory and emit its JSON.

Implement FhirPatient with a fluent builder:

• static Builder builder() — start building a patient.
• On Builder: id(String), active(boolean), family(String), addGiven(String), gender(String), birthDate(String), and build() returning a FhirPatient.
• String toJson() — return compact JSON (no whitespace) with keys in exactly this order, omitting optional keys when unset:

{"resourceType":"Patient"[,"id":"<id>"][,"active":<true|false>],"name":[{"use":"official","family":"<family>"[,"given":["<g1>","<g2>",...]]}],"gender":"<gender>","birthDate":"<birthDate>"}

Rules

• resourceType is always "Patient" and always first.
• id is included only when set.
• active is included only when it has been set explicitly (an unset active is omitted — it is not defaulted to false).
• given is an array, included only when at least one given name has been added, in the order they were added.
• family, gender, and birthDate are required.
• Validation at build() — throw IllegalArgumentException when:
  • family is null or empty,
  • gender is not one of male, female, other, unknown,
  • birthDate does not match ^\d{4}-\d{2}-\d{2}$.
• JSON escaping: escape backslash (\) and double-quote (") in the string values of id, family, and given.