/* ============================================================
   utils.js — Shared helpers (date, area, price, tenure)
   ============================================================ */

/** Parse URA contractDate "MMYY" → comparable number YYYYMM */
function parseTxDate(mmyy){
  if(!mmyy || mmyy.length < 4) return 0;
  const mm = parseInt(mmyy.slice(0,2), 10);
  const yy = parseInt(mmyy.slice(2,4), 10);
  return (2000 + yy) * 100 + mm;
}

/** Parse 4-digit year from contractDate "MMYY" */
function parseTxYear(mmyy){
  if(!mmyy || mmyy.length < 4) return 0;
  return 2000 + parseInt(mmyy.slice(2,4), 10);
}

/** Format "MMYY" → "Jan 2025" */
function formatTxDate(mmyy){
  if(!mmyy || mmyy.length < 4) return '—';
  const months = ['Jan','Feb','Mar','Apr','May','Jun',
                  'Jul','Aug','Sep','Oct','Nov','Dec'];
  const mm = parseInt(mmyy.slice(0,2), 10) - 1;
  const yy = parseInt(mmyy.slice(2,4), 10);
  return `${months[mm] || '?'} ${2000 + yy}`;
}

/** URA area is in sqm — convert to sqft */
function sqmToSqft(sqm){ return Math.round(parseFloat(sqm || 0) * 10.7639); }
function sqftToSqm(sqft){ return (parseFloat(sqft) * 0.092903).toFixed(1); }

/** Format price: 4200000 → "S$4.20M" */
function fmtPrice(p){
  const n = parseFloat(p);
  if(!n) return '—';
  if(n >= 1e6) return `S$${(n/1e6).toFixed(2)}M`;
  return `S$${Math.round(n/1000)}K`;
}

/** Format PSF: price / area_sqft */
function fmtPsf(price, areaSqft){
  if(!price || !areaSqft) return '—';
  return `S$${Math.round(parseFloat(price)/areaSqft).toLocaleString()} psf`;
}

/** Shorten property type label (maps URA raw values to display labels) */
function shortType(t){
  switch(t){
    // Landed
    case 'Terrace':               return 'Terrace';
    case 'Semi-detached':         return 'Semi-D';
    case 'Detached':              return 'Detached';
    case 'Strata Terrace':        return 'Strata Terrace';
    case 'Strata Semi-detached':  return 'Strata Semi-D';
    case 'Strata Detached':       return 'Strata Detached';
    // Non-landed
    case 'Apartment':             return 'Apt';
    case 'Condominium':           return 'Condo';
    case 'Executive Condominium': return 'EC';
    default:                      return t || '';
  }
}

/** Shorten tenure to badge text.
 *  Raw format: "NNN yrs lease commencing from YYYY" | "Freehold" | "999 years leasehold"
 *  Renders as: "NNNyr (YYYY)" — caller should set title= to the full raw string. */
function shortTenure(t){
  if(!t) return '—';
  if(/freehold/i.test(t)) return 'Freehold';
  const durMatch = t.match(/^(\d+)\s*yr/i);
  const yrMatch  = t.match(/(\d{4})/);
  const dur = durMatch ? durMatch[1] : '';
  const yr  = yrMatch  ? yrMatch[1]  : '';
  if(dur) return yr ? `${dur}yr (${yr})` : `${dur}yr`;
  return t;
}

/**
 * Infer unit type from floor area (sqft).
 * URA transaction data has no bedroom field — area is the standard proxy.
 * Returns short label e.g. "Studio", "1BR", "2BR"...
 */
function inferUnitType(areaSqft){
  if(!areaSqft || areaSqft <= 0) return '—';
  if(areaSqft <  430) return 'Studio';
  if(areaSqft <  700) return '1BR';
  if(areaSqft <  980) return '2BR';
  if(areaSqft < 1350) return '3BR';
  if(areaSqft < 2000) return '4BR';
  if(areaSqft < 3000) return '5BR';
  return 'PH';  // Penthouse / large unit
}

/** CSS class for tenure badge */
function tenureTagClass(t){
  if(!t) return 'tag-99';
  if(/freehold/i.test(t)) return 'tag-fh';
  if(/999/.test(t))       return 'tag-999';
  return 'tag-99';
}

/**
 * Convert SVY21 (Singapore local grid) to WGS84 lat/lng.
 * URA transaction data stores coordinates in SVY21: x = Easting, y = Northing.
 * Accuracy: ±5 m — sufficient for map markers.
 *
 * SVY21 parameters (SLA):
 *   Origin  1°22'02.9154"N, 103°49'31.9752"E
 *   False E 28001.642 m  |  False N 38744.572 m
 */
function svy21ToLatLng(northing, easting){
  const oLat = 1.3674876666667;   // origin latitude  (degrees)
  const oLon = 103.82554916667;   // origin longitude (degrees)
  const FN   = 38744.572;         // false northing   (metres)
  const FE   = 28001.642;         // false easting    (metres)
  // metres-per-degree at Singapore's latitude
  const mPerDegLat = 110540;
  const lat = oLat + (northing - FN) / mPerDegLat;
  const mPerDegLon = 111320 * Math.cos(lat * Math.PI / 180);
  const lng = oLon + (easting  - FE) / mPerDegLon;
  return [lat, lng];
}