Boliglånskalkulator

    const result = `<span class="result-highlight">$${fmt(payment)}/mo</span>
      <div class="result-grid"><div class="result-grid-item"><div class="label">Total Paid</div><div class="value">$${fmt(total)}</div></div><div class="result-grid-item"><div class="label">Total Interest</div><div class="value">$${fmt(interest)}</div></div></div>
      <div style="display:flex;gap:1rem;flex-wrap:wrap;margin:1.5rem 0">
        <canvas id="mortPieChart" style="max-height:220px;flex:1;min-width:200px"></canvas>
        <canvas id="mortLineChart" style="max-height:220px;flex:2;min-width:280px"></canvas>
      </div>
      <div class="result-breakdown"><div class="result-breakdown-item"><span class="result-breakdown-label">Principal</span><div class="result-breakdown-bar"><div class="result-breakdown-fill" style="width:${pPct}%;background:var(--blue)">${pPct}%</div></div></div><div class="result-breakdown-item"><span class="result-breakdown-label">Interest</span><div class="result-breakdown-bar"><div class="result-breakdown-fill" style="width:${iPct}%;background:#f59e0b">${iPct}%</div></div></div></div>
      ${tbl}`;

    const el = document.getElementById('result');
    el.innerHTML = result;
    el.style.display = 'block';
    el.scrollIntoView({ behavior: 'smooth', block: 'nearest' });

    // Charts: pie + amortization line
    _loadChartJs(() => {
      // Pie chart: principal vs interest
      const pieCtx = document.getElementById('mortPieChart');
      if (pieCtx) {
        if (window._mortPieChart) { try { window._mortPieChart.destroy(); } catch(e){} }
        window._mortPieChart = new Chart(pieCtx, {
          type: 'doughnut',
          data: {
            labels: ['Principal', 'Total Interest'],
            datasets: [{
              data: [+loan.toFixed(2), +interest.toFixed(2)],
              backgroundColor: ['#2563eb', '#f59e0b'],
              borderWidth: 0,
              hoverOffset: 6
            }]
          },
          options: {
            responsive: true,
            cutout: '55%',
            plugins: {
              legend: { position: 'bottom', labels: { font: { size: 11 } } },
              title: { display: true, text: 'Cost Breakdown', font: { size: 13 } },
              tooltip: { callbacks: { label: (ctx) => ` $${fmt(ctx.raw)}` } }
            }
          }
        });
      }

      // Line chart: remaining balance over time
      const lineCtx = document.getElementById('mortLineChart');
      if (lineCtx) {
        if (window._mortLineChart) { try { window._mortLineChart.destroy(); } catch(e){} }
        const balData = [], principalPaid = [], interestPaid = [];
        let b = loan, cumP = 0, cumI = 0;
        const step = Math.max(1, Math.floor(years / 20));
        const lineLabels = [];
        for (let yr = 0; yr <= years; yr++) {
          if (yr === 0 || yr % step === 0 || yr === years) {
            lineLabels.push(`Yr ${yr}`);
            balData.push(+Math.max(b, 0).toFixed(2));
            principalPaid.push(+cumP.toFixed(2));
            interestPaid.push(+cumI.toFixed(2));
          }
          if (yr < years) {
            for (let m = 0; m < 12; m++) {
              const mi = b * r;
              cumI += mi;
              cumP += payment - mi;
              b -= payment - mi;
            }
          }
        }
        window._mortLineChart = new Chart(lineCtx, {
          type: 'line',
          data: {
            labels: lineLabels,
            datasets: [{
              label: 'Remaining Balance',
              data: balData,
              borderColor: '#2563eb',
              backgroundColor: '#2563eb22',
              fill: true,
              tension: 0.3,
              pointRadius: 2
            }, {
              label: 'Interest Paid',
              data: interestPaid,
              borderColor: '#f59e0b',
              backgroundColor: 'transparent',
              tension: 0.3,
              pointRadius: 2
            }]
          },
          options: {
            responsive: true,
            interaction: { mode: 'index', intersect: false },
            plugins: {
              legend: { position: 'bottom', labels: { font: { size: 10 } } },
              title: { display: true, text: 'Amortization Over Time', font: { size: 13 } },
              tooltip: { callbacks: { label: (ctx) => ` ${ctx.dataset.label}: $${fmt(ctx.raw)}` } }
            },
            scales: {
              x: { ticks: { maxTicksLimit: 6 } },
              y: { ticks: { callback: v => `$${v >= 1000 ? (v/1000).toFixed(0)+'k' : v}` } }
            }
          }
        });
      }
    });
  } catch(e) {
    document.getElementById('result').innerHTML = 'Please fill in all fields correctly.';
    document.getElementById('result').style.display = 'block';
  }
});

function _loadChartJs(cb) {
  if (window.Chart) return cb();
  const s = document.createElement('script');
  s.src = 'https://cdn.jsdelivr.net/npm/chart.js@4/dist/chart.umd.min.js';
  s.onload = cb;
  document.head.appendChild(s);
}

// Enter key triggers calc
document.getElementById('calcForm').addEventListener('keydown', (e) => {
  if (e.key === 'Enter') { e.preventDefault(); document.getElementById('calcBtn').click(); }
});
// Live calculation on input change
function _dbCalc(fn, ms) { let t; return (...a) => { clearTimeout(t); t = setTimeout(() => fn(...a), ms); }; }
document.querySelectorAll('#calcForm input, #calcForm select').forEach(el => {
  el.addEventListener('input', _dbCalc(() => document.getElementById('calcBtn').click(), 150));
});