// Calculs hypothécaires illustratifs (Canada/Québec). Hypothèses éditables ; aucun taux n'est « réel » sauf indication datée et sourcée.
export interface MortgageInput {
  price: number;
  downPayment: number;        // $
  rateAnnualPct: number;      // taux affiché (composé semestriellement au Canada pour les prêts fixes)
  amortYears: number;         // 25 ou 30
  paymentsPerYear?: 12 | 26 | 52;
  municipalTaxAnnual?: number | null;
  schoolTaxAnnual?: number | null;
  insuranceMonthly?: number | null;
  condoFeesMonthly?: number | null;
  heatingMonthly?: number | null;
}
export interface MortgageResult {
  principal: number; cmhcPremium: number; cmhcRatePct: number; loan: number; payment: number; paymentMonthlyEq: number;
  totalInterest: number; totalPaid: number; monthlyAllIn: number; minDownPayment: number; downPaymentPct: number;
  warnings: string[]; schedule: { year: number; interest: number; principal: number; balance: number }[];
  stressTest: { qualifyingRatePct: number; payment: number };
}

/** Mise de fonds minimale au Canada : 5 % jusqu'à 500 k$, 10 % sur la tranche 500 k$–1,5 M$, 20 % au-delà de 1,5 M$ (règle en vigueur depuis le 15 déc. 2024). */
export function minDownPayment(price: number): number {
  if (price > 1_500_000) return price * 0.2;
  if (price <= 500_000) return price * 0.05;
  return 500_000 * 0.05 + (price - 500_000) * 0.10;
}

/** Prime SCHL/Sagen/Canada Guaranty selon le rapport prêt-valeur (barème standard). */
export function cmhcRatePct(ltv: number): number {
  if (ltv <= 0.65) return 0.6;
  if (ltv <= 0.75) return 1.7;
  if (ltv <= 0.80) return 2.4;
  if (ltv <= 0.85) return 2.8;
  if (ltv <= 0.90) return 3.1;
  if (ltv <= 0.95) return 4.0;
  return NaN;
}

/** Taux périodique équivalent à partir d'un taux nominal composé semestriellement (norme canadienne). */
export function periodicRate(rateAnnualPct: number, paymentsPerYear: number): number {
  const semi = rateAnnualPct / 100 / 2;
  return Math.pow(1 + semi, 2 / paymentsPerYear) - 1;
}

export function paymentFor(loan: number, rateAnnualPct: number, amortYears: number, paymentsPerYear = 12): number {
  const r = periodicRate(rateAnnualPct, paymentsPerYear); const n = amortYears * paymentsPerYear;
  if (r === 0) return loan / n;
  return (loan * r) / (1 - Math.pow(1 + r, -n));
}

export function computeMortgage(i: MortgageInput): MortgageResult {
  const ppy = i.paymentsPerYear ?? 12;
  const warnings: string[] = [];
  const minDp = minDownPayment(i.price);
  const dp = Math.min(Math.max(i.downPayment, 0), i.price);
  if (dp < minDp - 1) warnings.push(`Mise de fonds inférieure au minimum réglementaire (${Math.round(minDp).toLocaleString("fr-CA")} $).`);
  const principal = i.price - dp;
  const ltv = principal / i.price;
  let premiumRate = 0;
  if (ltv > 0.8) {
    premiumRate = cmhcRatePct(ltv);
    if (Number.isNaN(premiumRate)) { warnings.push("Rapport prêt-valeur > 95 % : non assurable."); premiumRate = 0; }
    if (i.price >= 1_500_000) warnings.push("Prix ≥ 1,5 M$ : assurance prêt hypothécaire non disponible, 20 % de mise de fonds requis.");
    if (i.amortYears > 25) warnings.push("Prêt assuré : amortissement de 30 ans réservé aux premiers acheteurs ou aux constructions neuves.");
  }
  const cmhcPremium = principal * premiumRate / 100;
  const loan = principal + cmhcPremium;
  const payment = paymentFor(loan, i.rateAnnualPct, i.amortYears, ppy);
  const paymentMonthlyEq = payment * ppy / 12;
  const totalPaid = payment * i.amortYears * ppy;
  const totalInterest = totalPaid - loan;
  const extras = (i.municipalTaxAnnual ?? 0) / 12 + (i.schoolTaxAnnual ?? 0) / 12 + (i.insuranceMonthly ?? 0) + (i.condoFeesMonthly ?? 0) + (i.heatingMonthly ?? 0);
  // Tableau d'amortissement annuel
  const r = periodicRate(i.rateAnnualPct, ppy);
  let bal = loan; const schedule: MortgageResult["schedule"] = [];
  for (let y = 1; y <= i.amortYears; y++) {
    let yi = 0, yp = 0;
    for (let k = 0; k < ppy; k++) { const int = bal * r; const pr = Math.min(payment - int, bal); yi += int; yp += pr; bal -= pr; if (bal <= 0.005) { bal = 0; break; } }
    schedule.push({ year: y, interest: yi, principal: yp, balance: Math.max(0, bal) });
    if (bal === 0) break;
  }
  const qualifyingRatePct = Math.max(i.rateAnnualPct + 2, 5.25);
  return {
    principal, cmhcPremium, cmhcRatePct: premiumRate, loan, payment, paymentMonthlyEq, totalInterest, totalPaid, monthlyAllIn: paymentMonthlyEq + extras,
    minDownPayment: minDp, downPaymentPct: dp / i.price, warnings, schedule, stressTest: { qualifyingRatePct, payment: paymentFor(loan, qualifyingRatePct, i.amortYears, ppy) * ppy / 12 },
  };
}

/** Droits de mutation (« taxe de bienvenue ») — barème provincial 2026 ; Montréal applique des tranches supérieures additionnelles (non modélisées ici). */
export function transferDuty(price: number, montreal = false): number {
  const brackets: [number, number][] = montreal
    ? [[61_500, 0.005], [307_800, 0.01], [552_300, 0.015], [1_104_700, 0.02], [2_136_500, 0.025], [3_113_000, 0.035], [Infinity, 0.04]]
    : [[61_500, 0.005], [307_800, 0.01], [Infinity, 0.015]];
  let duty = 0, prev = 0;
  for (const [cap, rate] of brackets) { if (price <= prev) break; duty += (Math.min(price, cap) - prev) * rate; prev = cap; }
  return duty;
}