import { getBookingsPage } from '@/api/doormile';
import { parseDoormileTimestamp } from '@/lib/doormileTimestamp';

/**
 * Reading bookings for the assistant.
 *
 * `GET /admin/bookings` caps `pagesize` at 100 server-side — NOT 1000, which is
 * what this comment claimed for a long time and what `express-console-api.md`
 * documented. A page is 100 rows, so MAX_PAGES x BULK_PAGESIZE is not the
 * reachable total: 12 pages is 1200 rows, not 12,000.
 *
 * It IS tenant-scoped, and it does accept `?status=` — but as an exact,
 * case-sensitive, single-value match against the stored capitalised enum
 * (`Pending_Pickup`). The status GROUPS this console renders as tabs each cover
 * several values in lowercase, so the server filter cannot express a tab and
 * the grouping still happens here. There is no date filter.
 *
 * The list is ordered `bookingid DESC`, so page 1 is the newest page and a
 * drain that stops early keeps the most recent bookings rather than the oldest.
 *
 * Every scan returns `{ rows, truncated, scanned, pagesFetched, total }` rather
 * than a bare array, and **`truncated` is not optional to handle**. A count
 * built on a capped scan is a floor, not a total — run it through `countPhrase`,
 * append `truncationNote` to the detail, and build the audit entry with
 * `scanCall`, which reports an error rather than a green tick beside a partial
 * number.
 */

const BULK_PAGESIZE = 1000;

/** 12k rows — generous, but bounded so one question cannot hammer the API. */
const MAX_PAGES = 12;

/**
 * Row order is not documented. When page 1 comes back newest-first the scan can
 * stop as soon as a page ends older than the window; otherwise it scans to the
 * budget. Detected per call rather than assumed, so a backend change degrades to
 * "scan everything" — slower, still correct — rather than to a wrong answer.
 */
const isDescendingByCreatedAt = (rows) => {
  if (rows.length < 2) return false;
  const first = parseDoormileTimestamp(rows[0].createdat);
  const last = parseDoormileTimestamp(rows[rows.length - 1].createdat);
  return first.isValid() && last.isValid() && first.valueOf() > last.valueOf();
};

const inRange = (booking, start, end) => {
  const at = parseDoormileTimestamp(booking.createdat);
  if (!at.isValid()) return false;
  const day = at.format('YYYY-MM-DD');
  return day >= start && day <= end;
};

/**
 * A short-lived page cache.
 *
 * A multi-part question runs several intents, and a comparison runs two ranges —
 * each would otherwise re-drain the same pages. Deliberately small and local:
 * this is not a caching layer to settle on.
 */
const PAGE_CACHE_TTL_MS = 20_000;
const pageCache = new Map();

const getPageCached = (page) => {
  const hit = pageCache.get(page);
  if (hit && Date.now() - hit.at < PAGE_CACHE_TTL_MS) return hit.promise;

  const promise = getBookingsPage(page, BULK_PAGESIZE).catch((err) => {
    /* Never cache a failure — the next question should retry, not inherit it. */
    pageCache.delete(page);
    throw err;
  });
  pageCache.set(page, { at: Date.now(), promise });
  return promise;
};

/**
 * Drain pages up to the budget and return every row, unfiltered.
 *
 * `makeStop` receives page 1's rows once and returns the per-page early-stop
 * predicate, so a range scan can bail as soon as it has read past its window
 * while an unfiltered drain simply reads to the budget.
 *
 * `fetchPage` is injectable because the page cache below is the wrong layer for
 * a caller that already has one. A TanStack-managed screen sets its own refetch
 * interval, and serving it from a 20s module-level cache would silently cap how
 * fresh that screen can ever be.
 */
const drainPages = async (makeStop, fetchPage = getPageCached) => {
  const firstPage = await fetchPage(1);
  const total = firstPage.total;
  const pageSize = Math.max(1, firstPage.rows?.length || 100);
  const pageCount = Math.max(1, Math.ceil(total / pageSize));
  const budget = Math.min(pageCount, MAX_PAGES);

  const collected = [...(firstPage.rows || [])];
  const shouldStop = makeStop ? makeStop(firstPage.rows) : () => false;

  let stoppedEarly = shouldStop(firstPage.rows) || collected.length >= total;
  let lastPageFetched = 1;

  for (let page = 2; page <= budget && !stoppedEarly; page += 1) {
    const next = await fetchPage(page);
    lastPageFetched = page;
    if (!next.rows?.length) {
      stoppedEarly = true;
      break;
    }
    collected.push(...next.rows);
    if (collected.length >= total) {
      break;
    }
    stoppedEarly = shouldStop(next.rows);
  }

  return {
    rows: collected,
    /* Truncated only if the budget ran out with pages still unread AND the scan
       did not stop early because it had already passed the window. */
    truncated: !stoppedEarly && pageCount > budget,
    scanned: collected.length,
    pagesFetched: lastPageFetched,
    total,
  };
};

export const fetchBookingsInRange = async (start, end) => {
  const scan = await drainPages((firstRows) => {
    const descending = isDescendingByCreatedAt(firstRows);
    /* Newest-first and this page already ends before the window opens → every
       later page is older still, so there is nothing left to find. */
    return (rows) => {
      if (!descending || !rows.length) return false;
      const oldest = parseDoormileTimestamp(rows[rows.length - 1].createdat);
      return oldest.isValid() && oldest.format('YYYY-MM-DD') < start;
    };
  });

  /* `scanned` deliberately stays the pre-filter count — it describes how much of
     the account was read, which is what `truncated` has to be judged against. */
  return { ...scan, rows: scan.rows.filter((booking) => inRange(booking, start, end)) };
};

/**
 * Every booking the account has, up to the page budget, with **no date filter**.
 *
 * For screens that show the whole list rather than a window. Deliberately not
 * `fetchBookingsInRange` with sentinel bounds: that path still runs `inRange`,
 * which drops any row whose `createdat` will not parse. Dropping a row from a
 * date-scoped answer is defensible; dropping it from "every order" is not — the
 * row exists and the operator has to be able to see it.
 */
export const drainBookings = ({ cached = true } = {}) =>
  drainPages(undefined, cached ? getPageCached : (page) => getBookingsPage(page, BULK_PAGESIZE));

export const fetchBookingsForDay = (day) => fetchBookingsInRange(day, day);

/**
 * A full scan with no date window — for a per-order lookup, which has to look
 * everywhere rather than inside a range. The sentinel bounds keep one code path:
 * they can never trigger the early stop, so this always drains to the page
 * budget and reports `truncated` honestly if the id could be further back.
 */
export const scanBookings = () => fetchBookingsInRange('0000-01-01', '9999-12-31');

/** A count over a truncated scan is a floor — say so. */
export const countPhrase = (scan, n) => `${scan.truncated ? 'At least ' : ''}${n}`;

export const truncationNote = (scan) =>
  scan.truncated
    ? `\n\nScanned the most recent ${scan.scanned.toLocaleString('en-IN')} of ${scan.total.toLocaleString(
        'en-IN'
      )} bookings — this is a floor, not a complete count.`
    : '';

/**
 * The audit entry for a scan. Reports the real page count, and flags itself as
 * an error when truncated so the sources strip cannot show a green "complete"
 * beside a partial number.
 */
export const scanCall = (scan, note) => ({
  name: 'getBookingsPage',
  target: `/admin/bookings (${scan.pagesFetched} page${scan.pagesFetched === 1 ? '' : 's'} × ${BULK_PAGESIZE})`,
  status: scan.truncated ? 'error' : 'complete',
  errorMessage: scan.truncated ? `Scan capped at ${MAX_PAGES} pages; ${scan.total} bookings exist` : undefined,
  stats: note,
});

/** A plain audit entry for a non-scan call. */
export const call = (name, target, stats) => ({ name, target, status: 'complete', stats });