Build a FHIR Patient (.NET)

Instructions

A FHIR Patient resource is a small JSON document. Before a server can store or exchange one, your code has to build it and serialize it correctly — the key order and the presence/absence of optional fields all matter to strict consumers.

This kata is the offline, deterministic version of Batch-1 Day 5, Week 1, Assignment 3 (the .NET Spark FHIR server): instead of standing up a server, you build a Patient in memory with a fluent builder and emit compact FHIR JSON.

Implement FhirPatient with a fluent builder:

var json = FhirPatient.Builder()
    .Id("123")
    .Family("Smith")
    .AddGiven("John")
    .AddGiven("Q")
    .Gender("male")
    .BirthDate("1980-05-15")
    .Build()
    .ToJson();

• static Builder Builder() — start a new builder.
• Builder.Id(string) — set the logical id (optional).
• Builder.Active(bool) — set the active flag (optional).
• Builder.Family(string) — set the family (last) name (required).
• Builder.AddGiven(string) — append a given (first/middle) name (optional, repeatable).
• Builder.Gender(string) — set the administrative gender (required).
• Builder.BirthDate(string) — set the birth date (required).
• Builder.Build() — validate and return an immutable FhirPatient.
• FhirPatient.ToJson() — emit compact FHIR JSON.

JSON shape

ToJson() returns compact JSON (no whitespace) with keys in exactly this order, omitting optional keys when they were never set:

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

• resourceType is always "Patient".
• id appears only if it was set.
• active appears only if it was explicitly set (as a JSON boolean, not a string).
• name is always an array with one object; use is always "official".
• given appears only if at least one given name was added.
• family, gender, and birthDate are always present.

Rules

• Build() throws ArgumentException 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}$.
• String values must be JSON-escaped: a backslash becomes \\ and a double quote becomes \".