/**
 * AdmissionsSection — primary detail pages.
 *
 * Not shared with the secondary page: the two versions were only 14% similar
 * (this one carries the year/trend toggle and the offer-rate chart; the
 * secondary one is a much simpler panel). See SecondaryAdmissionsSection.
 *
 * Server component. The year/trend toggle is delegated to the small
 * AdmissionsViewToggle client island, which receives both views as
 * server-rendered children. When there is only one year of offer data no
 * toggle renders at all, so such pages ship zero admissions JavaScript.
 *
 * The two views are stacked in one grid cell so switching never shifts layout,
 * which means the card is sized by the TALLER of them. Keep any view added
 * here close to the tile grid in height: a cut-off-distance view carrying a
 * chart, a table and a map was tried, measured 1402px against the tiles' 316px,
 * and left the default view as four tiles adrift in blank card. It now lives in
 * DistanceSection.
 */

import type { ReactNode } from 'react';
import type { SchoolAdmissions, SchoolAdmissionDistance } from '@/lib/types';
import { formatAcademicYear, formatPercentage } from '@/lib/utils';
import { summariseAdmissions } from '@/lib/compareLogic';
import { Section, sectionStyles as styles } from './sectionShared';
import { AdmissionsViewToggle, type AdmissionsView } from './AdmissionsViewToggle';
import { AdmissionsTrendChart } from './charts';
import { describeCutoff, CUTOFF_NOTE, CUTOFF_MEASUREMENT_NOTE } from './lastDistanceOffered';


export function AdmissionsSection({
  admissions,
  admissionsHistory,
  admissionDistance,
  isAllThrough,
}: {
  /* Nullable: the two data sources are independent. A minority of schools have
     a published cut-off distance but no EES admissions row (3% of the schools
     that render, sampled against staging), and for those this section exists
     to carry the distance alone. */
  admissions: SchoolAdmissions | null;
  admissionsHistory: SchoolAdmissions[];
  admissionDistance: SchoolAdmissionDistance | null;
  isAllThrough: boolean;
}) {
  const cutoff = describeCutoff(admissionDistance);

  // Trend toggle only appears with ≥2 years carrying an offer rate.
  const admissionsOfferYears = admissionsHistory.filter((h) => h.first_preference_offer_pct != null).length;
  const showAdmissionsTrend = admissions != null && admissionsOfferYears >= 2;
  // Banded interpretation of the first-choice offer rate ("More than half of
  // first choices missed out" etc.) — the same banding the compare screen
  // uses, so a low offer rate reads as how severe it actually is.
  const admissionsSummary = admissions ? summariseAdmissions(admissions) : null;

  const title = (
    <>Admissions{!showAdmissionsTrend && admissions && ` (${formatAcademicYear(admissions.year)})`}</>
  );

  {/* All-through admissions data covers a single entry point (usually the
      Year 7 secondary intake), not reception — say so, or a parent could
      read these as the whole-school figures. */}
  const subtitle: ReactNode = isAllThrough && admissions?.school_phase ? (
    <p className={styles.sectionSubtitle}>
      These figures are for {admissions.school_phase.toLowerCase()} entry
      {/secondary/i.test(admissions.school_phase) ? ' (Year 7)' : /primary/i.test(admissions.school_phase) ? ' (Reception)' : ''}.
    </p>
  ) : null;

  {/* Spans both columns rather than taking a half-width cell. This is the
      figure parents come to the page for, and at tile width the two-line
      "0.31 miles / September 2025" pairing wraps badly. */}
  {/* The {' '} between the figure and its metric support is not decoration.
      The two are flex children, so the gap is drawn by CSS and the text layer
      had nothing between them: textContent read "0.88 miles1.4 km", which is
      what a screen reader announces and what any text matcher sees. Whitespace
      text nodes are not rendered as flex items, so this changes the reading
      without changing the layout. */}
  const distanceTile = cutoff && (
    <div className={`${styles.admissionsTile} ${styles.admissionsTileDistance}`}>
      <dd className={styles.admissionsTileNum}>
        {cutoff.primary}{' '}
        <span className={styles.admissionsTileSub}>{cutoff.secondary}</span>
      </dd>
      <dt className={styles.admissionsTileLabel}>
        Last distance offered · {cutoff.entryYear}
      </dt>
    </div>
  );

  const distanceNote = cutoff && (
    <p className={styles.admissionsDistanceNote}>
      {CUTOFF_NOTE} {CUTOFF_MEASUREMENT_NOTE}
      {cutoff.routeNote && <> {cutoff.routeNote}</>}
    </p>
  );

  /*
   * Which row template the tile grid needs.
   *
   * The grid reserves two equal rows so the year view matches the height of the
   * trend chart beside it. With a cut-off and no EES admissions there are no
   * metric tiles to fill them, and the reserved rows render as a bare block of
   * the grid's own gap colour under the distance tile.
   */
  const hasMetricTiles = admissions != null && (
    admissions.places_offered != null
    || admissions.first_preference_applications != null
    || admissions.first_preference_offer_pct != null
    || admissions.total_applications != null
  );
  const tilesClass = [
    styles.admissionsTiles,
    cutoff && hasMetricTiles ? styles.admissionsTilesWithDistance : '',
    cutoff && !hasMetricTiles ? styles.admissionsTilesDistanceOnly : '',
  ].filter(Boolean).join(' ');

  const yearView = (
    <>
      <dl className={tilesClass}>
        {admissions?.places_offered != null && (
          <div className={styles.admissionsTile}>
            <dd className={styles.admissionsTileNum}>{admissions.places_offered}</dd>
            <dt className={styles.admissionsTileLabel}>Places offered</dt>
          </div>
        )}
        {admissions?.first_preference_applications != null && (
          <div className={styles.admissionsTile}>
            <dd className={styles.admissionsTileNum}>{admissions.first_preference_applications}</dd>
            <dt className={styles.admissionsTileLabel}>Wanted it first</dt>
          </div>
        )}
        {admissions?.first_preference_offer_pct != null && (
          <div className={`${styles.admissionsTile} ${styles.admissionsTileAccent}`}>
            <dd className={styles.admissionsTileNum}>
              {admissions.first_preference_offers != null && admissions.first_preference_applications != null ? (
                <>
                  {admissions.first_preference_offers}
                  <span className={styles.admissionsTileSub}>
                    of {admissions.first_preference_applications} · {formatPercentage(admissions.first_preference_offer_pct)}
                  </span>
                </>
              ) : (
                formatPercentage(admissions.first_preference_offer_pct)
              )}
            </dd>
            <dt className={styles.admissionsTileLabel}>Got their first choice</dt>
          </div>
        )}
        {admissions?.total_applications != null && (
          <div className={styles.admissionsTile}>
            <dd className={styles.admissionsTileNum}>{admissions.total_applications.toLocaleString()}</dd>
            <dt className={styles.admissionsTileLabel}>Applied in total</dt>
          </div>
        )}
        {distanceTile}
      </dl>
      {admissionsSummary?.chip && (
        <p className={styles.admissionsTrendSummary}>{admissionsSummary.chip.text}</p>
      )}
      {distanceNote}
    </>
  );

  {/* Guarded rather than asserted: showAdmissionsTrend already requires
      admissions, and tying the two together in one expression keeps that
      invariant checked by the compiler instead of assumed. */}
  const trendView = admissions && (
    <>
      <div className={styles.admissionsChartCap}>First-choice offer rate</div>
      <AdmissionsTrendChart history={admissionsHistory} />
      <p className={styles.admissionsTrendSummary}>
        This year ({formatAcademicYear(admissions.year)}),{' '}
        {admissions.first_preference_applications != null && (
          <><strong>{admissions.first_preference_applications}</strong> families put it first for </>
        )}
        {admissions.places_offered != null && <><strong>{admissions.places_offered}</strong> places</>}
        {admissions.total_applications != null && ` — ${admissions.total_applications.toLocaleString()} applications in total`}.
      </p>
    </>
  );

  const views: AdmissionsView[] = [
    { id: 'year', label: 'This year', content: yearView, className: styles.admissionsViewYear },
  ];
  if (showAdmissionsTrend) {
    views.push({
      id: 'trend',
      label: `${admissionsHistory.length}-year trend`,
      content: trendView,
      className: styles.admissionsViewTrend,
    });
  }

  return (
    <Section id="admissions">
      {views.length > 1 ? (
        <AdmissionsViewToggle title={title} subtitle={subtitle} views={views} />
      ) : (
        /* One view — render statically, with no client component at all. */
        <>
          <div className={styles.admissionsHeader}>
            <h2 className={styles.sectionTitle}>{title}</h2>
          </div>
          {subtitle}
          <div className={styles.admissionsViewport}>
            <div className={styles.admissionsViewYear}>{yearView}</div>
          </div>
        </>
      )}
    </Section>
  );
}