// src/utils/auditEventQuery.ts
//
// - NARROWING THE ACCESS LOG AT THE SERVER, WHICH IS THE ONLY PLACE IT CAN WORK.
//
// THE DEFECT THIS EXISTS TO END. The page fetched EVERY page of the audit history before rendering
// anything - 45 sequential requests, ~20 seconds on a blank screen, 5000 rows in the DOM - and then
// showed the lot. Measured 2026-08-31: all 5000 rendered rows carried ONE date, today, because a single
// day of reads fills the window. Yesterday's entries were not filtered out; they were never asked for.
//
// SO A CLIENT-SIDE FILTER WOULD HAVE BEEN WORSE THAN NONE. It would give a working-looking date control
// over rows that all come from the same day, and reaching an older entry would still be impossible - a
// control that cannot fail visibly is the trap this card names. The narrowing has to be in the query.
//
// `date` IS THE SEARCH PARAMETER FOR `recorded`, and it is a standard AuditEvent parameter rather than
// anything we defined. Two bounds are sent as two `date` values, which is an AND in FHIR - `ge` on the
// start of the day and `le` on the end of it.
//
// NO `_sort`. Not because ordering does not matter but because nobody has measured that HealthLake
// accepts it on this resource, and a rejected parameter takes the whole screen down rather than
// degrading. The natural order is what the page has always rendered.

import { dayStartIn } from './reportDrillPeriod';
import { addCalendarDays } from './practiceTimezone';
/** One of the FHIR audit action codes, as the page's filter offers them. */
export type AuditActionCode = 'C' | 'R' | 'U' | 'D' | 'E';

export interface AuditEventQuery {
    /** Inclusive lower bound, as `YYYY-MM-DD`. */
    from?: string;
    /** Inclusive upper bound, as `YYYY-MM-DD`. */
    to?: string;
    /** The clock the days are counted on; without one the server reads them as UTC days. */
    zone?: string;
    action?: AuditActionCode;
    /** FHIR AuditEvent `patient` — forwarded as-is when present. */
    patient?: string;
    /** How many rows to ask for. The page asks for one screenful, not the whole history. */
    count: number;
    /** The opaque cursor from the previous page's `next` link, when following one. */
    page?: string;
}

const ISO_DAY = /^\d{4}-\d{2}-\d{2}$/;

/**
 * The query string for one page of the access log.
 *
 * A bound that is not a plain `YYYY-MM-DD` is DROPPED rather than sent. A half-typed date in a date
 * field is a normal intermediate state, and sending `2026-08-` would have the server reject the request
 * and blank the screen while somebody is still typing.
 */
export const auditEventSearchParams = (query: AuditEventQuery): string => {
    const params = new URLSearchParams();

    params.append('_count', String(query.count));

    if (query.from && ISO_DAY.test(query.from)) {
        params.append('date', query.zone ? 'ge' + dayStartIn(query.from, query.zone) : `ge${query.from}`);
    }

    if (query.to && ISO_DAY.test(query.to)) {
        // The whole of the closing day, not the instant it starts. `le2026-08-30` against a `recorded`
        // of `2026-08-30T14:22:11Z` is a comparison a reader would expect to include, and FHIR date
        // precision makes it so - but being explicit here is what stops the off-by-one-day report.
        params.append('date', query.zone ? 'lt' + dayStartIn(addCalendarDays(query.to, 1), query.zone) : `le${query.to}`);
    }

    if (query.action) {
        params.append('action', query.action);
    }

    if (query.patient) {
        params.append('patient', query.patient);
    }

    if (query.page) {
        params.set('page', query.page);
    }

    return params.toString();
};

/**
 * The cursor for the next page, or `undefined` when this is the last one.
 *
 * THE `next` URL POINTS AT THE DATASTORE, WHICH THE BROWSER CANNOT CALL. Only the opaque `page` token
 * inside it is ours to reuse, against our own gateway - the same reading `fetchAllBundlePages` does.
 * Do not "simplify" this to following the URL.
 */
export const nextAuditPage = (bundle: { link?: { relation?: string; url?: string }[] }): string | undefined => {
    const next = bundle.link?.find((link) => link.relation === 'next')?.url;
    const token = next?.match(/page=([^&]*)/)?.[1];
    return token ? decodeURIComponent(token) : undefined;
};