// What a patient reads for a coded answer from a terminology value set. The value sets answer in their own case and
// words ("unmarried", "Interlocutory", "asked but unknown"); a patient reads sentence case, and an answer whose word
// says little is explained. Presentation only: the stored system, code and display are never replaced by these
// labels, and an answer not mapped here keeps the words it was recorded with.
//
// Keyed by system and code, never by display, so the same word in another code system is left alone. Distinct
// answers stay distinct: unmarried is not never married, unknown is not asked-but-unknown, and an interlocutory
// decree is not a final divorce or a legal separation.

interface Concept {
    system?: string;
    code?: string;
    display?: string;
}

// The current and the older address of each code system; a stored coding may carry either.
const MARITAL_SYSTEMS = ['http://terminology.hl7.org/CodeSystem/v3-MaritalStatus', 'http://hl7.org/fhir/v3/MaritalStatus'];
const NULL_FLAVOR_SYSTEMS = ['http://terminology.hl7.org/CodeSystem/v3-NullFlavor', 'http://hl7.org/fhir/v3/NullFlavor'];

// HL7 v3 MaritalStatus (terminology.hl7.org 7.0.0).
const MARITAL: Record<string, string> = {
    A: 'Annulled',
    C: 'Common law',
    D: 'Divorced',
    I: 'Interim court decree (interlocutory)',
    L: 'Legally separated',
    M: 'Married',
    P: 'Polygamous',
    S: 'Never married',
    T: 'Domestic partner',
    U: 'Unmarried',
    W: 'Widowed',
};

// HL7 v3 NullFlavor (terminology.hl7.org 7.0.1). Only the codes whose meaning is verified are mapped.
const NULL_FLAVOR: Record<string, string> = {
    UNK: 'Unknown',
    ASKU: 'Asked, but not known',
};

export const codedAnswerLabel = (concept: Concept): string => {
    const code = concept.code ?? '';
    const mapped = MARITAL_SYSTEMS.includes(concept.system ?? '') ? MARITAL[code]
        : NULL_FLAVOR_SYSTEMS.includes(concept.system ?? '') ? NULL_FLAVOR[code]
        : undefined;
    return mapped ?? concept.display ?? code;
};