import type { Communication } from 'fhir/r4';

// The server's version number, or null for a copy it has not confirmed (an optimistic line).
const versionOf = (message: Communication): number | null => {
    const version = Number(message.meta?.versionId);
    return Number.isInteger(version) && version > 0 ? version : null;
};

/**
 * Which copy of one message to show. The incoming copy wins, unless the held copy is a newer confirmed version: the
 * thread search trails a write, so a re-read can answer with the edition before a read receipt it already delivered.
 */
export const newerEdition = (held: Communication | undefined, incoming: Communication): Communication => {
    if (!held) return incoming;
    const heldVersion = versionOf(held);
    const incomingVersion = versionOf(incoming);
    return heldVersion !== null && incomingVersion !== null && heldVersion > incomingVersion ? held : incoming;
};