// THREAD-ID CONTRACT - must stay byte-identical to the server's
// aws/sam/services/api/src/utils/encounterRoomThread.ts. The server is authoritative; this
// module exists only to mirror it. A drifted id does not error: it routes a read to the WRONG ROSTER,
// which is a cross-thread disclosure rather than a routing nuisance.
//
// A visit's messages live in a thread whose roster is the people actually admitted to the room. The id is
// deterministic (`encounter#{encounterId}`) so the meeting can find its thread with no lookup, keyed by
// ENCOUNTER not session: a visit that drops and reconnects is one room and one thread.
//
// The prefix is deliberately the SAME string the video context uses (`encounter#{encounterId}`,
// videoContract.ts) - the identical dual use `collabteam#{teamId}` already has (collaborationTeamThread.ts).
// Deliberate, not coincidence: one id for one room.

export const ENCOUNTER_ROOM_THREAD_PREFIX = 'encounter#';

export const buildEncounterRoomThreadId = (encounterId: string): string =>
    `${ENCOUNTER_ROOM_THREAD_PREFIX}${encounterId}`;

/**
 * NOT a bare `startsWith`, and the extra condition is load-bearing.
 *
 * `encounter` is a VALID FHIR id (`[A-Za-z0-9\-\.]{1,64}`), and a direct thread id is
 * `patientId#organizationId#staffAccountId` (Communication/thread/post.ts, server side). So a direct
 * thread for a patient whose id is literally `encounter` serialises to `encounter#org#staff` - which a
 * prefix-only predicate would claim as a room thread, routing a two-party direct thread through the ROOM
 * roster. That is a cross-thread read, not a routing nuisance.
 *
 * A room thread id has EXACTLY ONE '#'; a direct thread has two. FHIR ids cannot contain '#', so the
 * suffix of a genuine room thread id never does either. This makes the kinds provably disjoint for every
 * possible patient id, rather than disjoint-in-practice-because-ids-happen-to-be-UUIDs.
 *
 * The sibling `collabteam#` / `collabaside#` predicates (collaborationTeamThread.ts) still use a bare
 * `startsWith` and carry the same latent hole. Not changed here - that is someone else's blast radius -
 * but worth closing.
 */
export const isEncounterRoomThreadId = (threadId: string | null | undefined): threadId is string => {
    if (typeof threadId !== 'string' || !threadId.startsWith(ENCOUNTER_ROOM_THREAD_PREFIX)) {
        return false;
    }

    const encounterId = threadId.slice(ENCOUNTER_ROOM_THREAD_PREFIX.length);

    return encounterId.length > 0 && !encounterId.includes('#');
};

/** Only meaningful for an id `isEncounterRoomThreadId` has already accepted. */
export const extractEncounterIdFromRoomThreadId = (threadId: string): string =>
    threadId.slice(ENCOUNTER_ROOM_THREAD_PREFIX.length);