// ─── CHURCH ACOUSTIC GEOMETRY ENGINE ─────────────────────────────────────────
// Pure functions — no React dependencies. All dimensions in mm unless noted.
// Coordinate origin = centre floor datum (lowest point of the dish).
//
// KEY RULES:
//   • Ceiling is FLAT at hall.ceilFlat above the centre datum (main seating zone).
//   • Floor rises linearly from 0 mm at row1Radius outward to hall.dishRise at row8Back.
//     The communion table zone (r < row1Radius) is flat at 0 mm.
//   • Corner zone ceiling is structurally lower; absolute height =
//       hall.cornerCeilClearance + floorHeightAtRadius(r)
//   • Speaker height (absolute) = ceilAbsoluteAt(spk.radius) − spk.dropRod
//   • Ear height (absolute)     = hall.earHeight + floorHeightAtRadius(row.radius)

// ─── FLOOR ────────────────────────────────────────────────────────────────────

/**
 * Floor height above centre datum at radius r.
 * Flat at 0 mm inside row1Radius (communion table zone).
 * Linear rise from 0 mm at row1Radius to dishRise at row8Back, extrapolated beyond.
 */
export function floorHeightAtRadius(r, hall) {
  if (r <= hall.row1Radius) return 0;
  const span = hall.row8Back - hall.row1Radius;   // 6201 mm for confirmed hall
  return Math.round(((r - hall.row1Radius) / span) * hall.dishRise);
}

// ─── CEILING ──────────────────────────────────────────────────────────────────

/**
 * Boundary radius where the ceiling transitions from the flat main zone
 * to the structurally lower corner zone.
 */
function cornerZoneStartR(hall) {
  // Corner row 1 front is cornerFrontOffset mm inside the building half-width
  return hall.hallWidth / 2 - hall.cornerFrontOffset;  // ≈ 9837 mm
}

/**
 * Absolute ceiling height above centre datum at radius r.
 *   Main zone  → hall.ceilFlat  (constant — it's a flat ceiling)
 *   Corner zone → hall.cornerCeilClearance + floorHeightAtRadius(r)
 *                 (the soffit drops structurally at the perimeter)
 */
export function ceilAbsoluteAt(r, hall) {
  if (r >= cornerZoneStartR(hall)) {
    return hall.cornerCeilClearance + floorHeightAtRadius(r, hall);
  }
  return hall.ceilFlat;
}

/**
 * Floor-to-ceiling clearance at radius r (what a listener experiences as room height).
 * Decreases toward the perimeter because the floor rises while the ceiling stays flat.
 */
export function floorToCeilingAt(r, hall) {
  return ceilAbsoluteAt(r, hall) - floorHeightAtRadius(r, hall);
}

// ─── ROW GEOMETRY ─────────────────────────────────────────────────────────────

/**
 * Build per-row geometry for all main rows and corner rows.
 * Each entry: { row, radius, frontEdge, floorRise, ceilHeight, earAFF, earToCell, isCorner }
 *   radius    — mid-bench ear position (radial)
 *   ceilHeight — absolute ceiling above centre datum at that radius
 *   earAFF    — absolute ear height above centre datum
 *   earToCell — ear-to-ceiling clearance (critical for flutter and ARTA window)
 */
export function computeHallGeometry(hall) {
  const { rows, row1Radius, rowPitch, earHeight, hasCornerRows, cornerRows, cornerFrontOffset, hallWidth } = hall;
  const halfW   = hallWidth / 2;
  const rowData = [];

  // Main circular rows 1–N
  for (let r = 1; r <= rows; r++) {
    const frontEdge = row1Radius + (r - 1) * rowPitch;
    const radius    = frontEdge + Math.round(rowPitch / 2);  // mid-bench
    const floorRise = floorHeightAtRadius(radius, hall);
    const ceilH     = ceilAbsoluteAt(radius, hall);
    const earAFF    = earHeight + floorRise;
    const earToCell = ceilH - earAFF;
    rowData.push({ row: r, radius, frontEdge, floorRise, ceilHeight: ceilH, earAFF, earToCell, isCorner: false });
  }

  // Corner rows (face inward from building perimeter)
  // Front of corner row 1 is cornerFrontOffset mm inside the half-width wall
  if (hasCornerRows) {
    const cRow1Front = halfW - cornerFrontOffset;
    for (let cr = 1; cr <= cornerRows; cr++) {
      const frontEdge = cRow1Front + (cr - 1) * rowPitch;
      const radius    = frontEdge + Math.round(rowPitch / 2);
      const floorRise = floorHeightAtRadius(radius, hall);
      const ceilH     = ceilAbsoluteAt(radius, hall);
      const earAFF    = earHeight + floorRise;
      const earToCell = ceilH - earAFF;
      rowData.push({ row: `C${cr}`, radius, frontEdge, floorRise, ceilHeight: ceilH, earAFF, earToCell, isCorner: true, cornerRow: cr });
    }
  }
  return rowData;
}

// ─── COVERAGE ─────────────────────────────────────────────────────────────────

const RINGS = ['centre', 'inner', 'outer', 'corner'];

/**
 * For every row × speaker ring combination, compute:
 *   slantM      — 3-D slant distance speaker→ear (metres)
 *   delay       — propagation delay (ms)
 *   haasExcess  — ms beyond the nearest speaker to this row (Haas reference)
 *   offAxisDeg  — angle from directly below the speaker (0° = on-axis)
 *   splAtEar    — estimated SPL at ear using inverse-square + sensitivity + power
 *   inCoverage  — whether offAxisDeg ≤ 55° (MS6 rated coverage angle)
 *   haasStatus  — 'primary' | 'ok' | 'warn' | 'danger'
 */
export function computeCoverage(hall, speakers, rowData) {
  const c = hall.speedOfSound;
  const results = [];

  for (const row of rowData) {
    // 1. Find minimum delay to this row (Haas reference = nearest speaker)
    let minDelay = Infinity;
    for (const ring of RINGS) {
      const spk = speakers[ring];
      if (!spk?.enabled) continue;
      const spkH     = ceilAbsoluteAt(spk.radius, hall) - spk.dropRod;
      const vertDiff = spkH - row.earAFF;
      const horiz    = Math.abs(row.radius - spk.radius);
      const delay    = Math.sqrt(vertDiff ** 2 + horiz ** 2) / 1000 / c * 1000;
      if (delay < minDelay) minDelay = delay;
    }

    // 2. Per-ring metrics
    const rowResults = {
      row: row.row, radius: row.radius,
      earAFF: row.earAFF, ceilHeight: row.ceilHeight, earToCell: row.earToCell,
      speakers: {},
    };

    for (const ring of RINGS) {
      const spk = speakers[ring];
      if (!spk?.enabled) { rowResults.speakers[ring] = null; continue; }

      const spkH      = ceilAbsoluteAt(spk.radius, hall) - spk.dropRod;
      const vertDiff  = spkH - row.earAFF;
      const horiz     = Math.abs(row.radius - spk.radius);
      const slant     = Math.sqrt(vertDiff ** 2 + horiz ** 2);
      const slantM    = slant / 1000;
      const delay     = slantM / c * 1000;
      const haasExcess = Math.max(0, delay - minDelay);

      // 0° = directly below speaker; increases toward horizontal
      const offAxisDeg = Math.round(Math.atan2(horiz, Math.max(vertDiff, 1)) * 180 / Math.PI);

      // SPL = sensitivity + 20·log10(1/d) + 10·log10(W)
      const splAtEar = spk.sensitivity
        + 20 * Math.log10(1 / Math.max(slantM, 0.1))
        + 10 * Math.log10(Math.max(spk.power, 0.01));

      const inCoverage = offAxisDeg <= 55;

      let haasStatus = 'primary';
      if      (haasExcess > 30) haasStatus = 'danger';
      else if (haasExcess > 10) haasStatus = 'warn';
      else if (haasExcess >  0) haasStatus = 'ok';

      rowResults.speakers[ring] = {
        slantM, delay, haasExcess, offAxisDeg,
        splAtEar: Math.round(splAtEar * 10) / 10,
        inCoverage, haasStatus, spkH, vertDiff,
      };
    }
    results.push(rowResults);
  }
  return results;
}

// ─── FLUTTER ECHO ─────────────────────────────────────────────────────────────

/**
 * Flutter frequency = c / (2 × clearance).
 * Clearance = ceiling absolute height − ear absolute height.
 * As the floor rises toward the perimeter, ear moves closer to the flat ceiling
 * → higher flutter frequencies → harmonics land in speech band.
 *
 * Returns fundamentals at three positions plus harmonic series and tile diffraction.
 * (Dudley Wilkin: "standing waves from the flat floor in the centre of the dish and the ceiling")
 */
export function computeFlutter(hall) {
  const hz = (clearMm) => Math.round((hall.speedOfSound * 1000) / (2 * Math.max(clearMm, 50)));

  // Centre zone: floor = 0, ear at earHeight above centre datum
  const centreClearMm = hall.ceilFlat - hall.earHeight;

  // Row 8 mid-bench: floor extrapolated slightly beyond row8Back
  const row8MidR     = hall.row8Back - Math.round(hall.rowPitch / 2);
  const row8FloorRise = floorHeightAtRadius(row8MidR, hall);
  const row8ClearMm  = hall.ceilFlat - (hall.earHeight + row8FloorRise);

  // Last corner row mid
  const halfW        = hall.hallWidth / 2;
  const cRow1Front   = halfW - hall.cornerFrontOffset;
  const cLastMidR    = cRow1Front + (hall.cornerRows - 0.5) * hall.rowPitch;
  const cFloorRise   = floorHeightAtRadius(cLastMidR, hall);
  const cCeilAbs     = ceilAbsoluteAt(cLastMidR, hall);
  const cornerClearMm = cCeilAbs - (hall.earHeight + cFloorRise);

  const fundamentalCentre = hz(centreClearMm);
  // Harmonics 1–5 at centre (reference position cited by Dudley Wilkin)
  const harmonics = [1, 2, 3, 4, 5].map(n => Math.round(fundamentalCentre * n));

  // Tile diffraction grating: wavelength = tileGrid → f = c/λ
  const tileDiffraction = Math.round((hall.speedOfSound * 1000) / hall.tileGrid);

  return {
    fundamentalCentre,
    fundamentalRow8: hz(row8ClearMm),
    fundamentalCorner: hz(cornerClearMm),
    harmonics,
    tileDiffraction,
    centreClearMm,
    row8ClearMm,
    cornerClearMm,
  };
}

// ─── HAAS DISPLAY HELPERS ─────────────────────────────────────────────────────

export const haasColor = (s) => ({
  primary: '#34d399',
  ok:      '#4f9eff',
  warn:    '#f0b429',
  danger:  '#f87171',
}[s] ?? '#475569');

export const haasLabel = (s) => ({
  primary: 'Primary',
  ok:      'OK <10ms',
  warn:    'Warn 10–30ms',
  danger:  'Echo >30ms',
}[s] ?? '—');