import { useCallback, useEffect, useMemo, useState, type ReactNode } from 'react';
import {
  AlertCircle,
  Calculator,
  HelpCircle,
  Info,
  Printer,
  RefreshCw,
  RotateCcw,
  Save,
  TrendingDown,
} from 'lucide-react';
import { toast } from 'sonner';
import { api } from '@/api';
import { Button } from '@/components/ui/button';
import { Input } from '@/components/ui/input';
import { Label } from '@/components/ui/label';
import { Tooltip, TooltipContent, TooltipProvider, TooltipTrigger } from '@/components/ui/tooltip';
import {
  Select,
  SelectContent,
  SelectGroup,
  SelectItem,
  SelectLabel,
  SelectSeparator,
  SelectTrigger,
  SelectValue,
} from '@/components/ui/select';
import { cn, errMessage } from '@/lib/utils';
import { formatUSD, formatUSDWhole, asDollars } from '@/lib/money';
import PayoffChart from '@/components/snowball/PayoffChart';
import type { Bill } from '@/types';

interface ScheduleMonth {
  month: number;
  balance: number;
  interest: number;
}

// ─── Print isolation ──────────────────────────────────────────────────────────

const PRINT_STYLES = `
@media print {
  * { visibility: hidden !important; }
  #payoff-print-area,
  #payoff-print-area * { visibility: visible !important; }
  #payoff-print-area {
    position: absolute !important;
    top: 0 !important; left: 0 !important; right: 0 !important;
    width: 100% !important;
    padding: 24px !important;
    margin: 0 !important;
    background: #fff !important;
    color: #111 !important;
  }
  #payoff-print-area .no-print { display: none !important; }
  #payoff-print-area .print-only { display: block !important; }
}
`;

// ─── Helpers ──────────────────────────────────────────────────────────────────

function fmt(v: number | null | undefined): string {
  return formatUSD(asDollars(Number(v) || 0));
}

function fmtShort(v: number | null | undefined): string {
  return formatUSDWhole(asDollars(Number(v) || 0));
}

function buildPayoffSchedule(
  balance: number,
  annualRatePct: number,
  monthlyPayment: number,
  oneTimeExtra = 0,
): ScheduleMonth[] {
  if (!balance || balance <= 0 || !monthlyPayment || monthlyPayment <= 0) return [];
  const rate = (annualRatePct || 0) / 100 / 12;
  if (rate > 0 && monthlyPayment <= balance * rate) return [];
  let bal = balance;
  const months: ScheduleMonth[] = [];
  for (let i = 0; i < 600; i++) {
    const interest = Math.round(bal * rate * 100) / 100;
    const pmt = Math.min(bal + interest, i === 0 ? monthlyPayment + oneTimeExtra : monthlyPayment);
    const principal = Math.max(0, pmt - interest);
    bal = Math.round(Math.max(0, bal - principal) * 100) / 100;
    months.push({ month: i + 1, balance: bal, interest });
    if (bal < 0.01) break;
  }
  return months;
}

function payoffLabel(track: ScheduleMonth[], now = new Date()): string | null {
  if (!track.length) return null;
  const d = new Date(now.getFullYear(), now.getMonth() + track.length, 1);
  return d.toLocaleDateString(undefined, { month: 'short', year: 'numeric' });
}

function numMonths(track: ScheduleMonth[]): string | null {
  if (!track.length) return null;
  const y = Math.floor(track.length / 12);
  const m = track.length % 12;
  if (y === 0) return `${m} mo`;
  if (m === 0) return `${y} yr`;
  return `${y} yr ${m} mo`;
}

// ─── Sub-components ───────────────────────────────────────────────────────────

// Focusable inline-help tooltip for a non-obvious figure (keyboard + SR accessible).
function Help({ text, label }: { text: string; label: string }) {
  return (
    <Tooltip>
      <TooltipTrigger asChild>
        <button
          type="button"
          aria-label={`${label}: help`}
          className="ml-1 inline-flex h-3.5 w-3.5 items-center justify-center rounded-full text-muted-foreground/70 transition-colors hover:text-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring no-print"
        >
          <HelpCircle className="h-3 w-3" />
        </button>
      </TooltipTrigger>
      <TooltipContent className="max-w-[240px] text-xs leading-relaxed">{text}</TooltipContent>
    </Tooltip>
  );
}

function StatCard({
  label,
  value,
  sub,
  color = 'amber',
  help,
}: {
  label: ReactNode;
  value: ReactNode;
  sub?: ReactNode;
  color?: string;
  help?: string;
}) {
  const colors: Record<string, string> = {
    amber: 'bg-amber-500/8 border-amber-400/20 text-amber-500 dark:text-amber-400',
    teal: 'bg-teal-500/8  border-teal-400/20  text-teal-500  dark:text-teal-400',
    slate: 'bg-muted/40    border-border/60     text-foreground',
  };
  return (
    <div className={cn('rounded-xl border p-4 text-center', colors[color])}>
      <p className="text-[11px] font-medium uppercase tracking-widest text-muted-foreground mb-1 inline-flex items-center justify-center">
        {label}
        {help && typeof label === 'string' && <Help text={help} label={label} />}
      </p>
      <p className={cn('text-2xl font-bold font-mono tabular-nums', colors[color])}>{value}</p>
      {sub && <p className="text-[11px] text-muted-foreground mt-0.5">{sub}</p>}
    </div>
  );
}

function InputRow({
  label,
  hint,
  children,
}: {
  label: ReactNode;
  hint?: ReactNode;
  children: ReactNode;
}) {
  return (
    <div className="space-y-1.5">
      <div className="flex items-baseline justify-between">
        <Label className="text-xs font-semibold uppercase tracking-wider text-muted-foreground">
          {label}
        </Label>
        {hint && <span className="text-[11px] text-muted-foreground">{hint}</span>}
      </div>
      {children}
    </div>
  );
}

function EmptyDebts() {
  return (
    <div className="flex flex-col items-center justify-center rounded-xl bg-muted/20 px-6 py-16 text-center">
      <TrendingDown className="h-10 w-10 text-muted-foreground/40 mb-4" />
      <p className="text-sm font-medium text-foreground">No bills with a balance found</p>
      <p className="text-xs text-muted-foreground mt-1">
        Add a current balance to your bills on the{' '}
        <a href="/snowball" className="underline text-primary hover:opacity-80">
          Snowball page
        </a>
        , or use the <strong>Custom</strong> option in the dropdown above.
      </p>
    </div>
  );
}

function NoSelection() {
  return (
    <div className="flex flex-col items-center justify-center rounded-xl bg-muted/20 px-6 py-16 text-center">
      <Calculator className="h-10 w-10 text-muted-foreground/40 mb-4" />
      <p className="text-sm font-medium text-foreground">Select a loan or debt to begin</p>
      <p className="text-xs text-muted-foreground mt-1">
        Choose from the dropdown above, or select <strong>Custom</strong> to simulate any loan.
      </p>
    </div>
  );
}

// ─── PayoffPage ───────────────────────────────────────────────────────────────

export default function PayoffPage() {
  const [bills, setBills] = useState<Bill[]>([]);
  const [loading, setLoading] = useState(true);
  const [loadError, setLoadError] = useState<string | null>(null);
  const [selectedId, setSelectedId] = useState<number | 'custom' | null>(null);

  // Custom mode inputs
  const [customName, setCustomName] = useState('');
  const [customBalance, setCustomBalance] = useState('');

  // Per-simulation inputs (reset when selection changes)
  const [simPayment, setSimPayment] = useState('');
  const [simRate, setSimRate] = useState('');
  const [oneTimeExtra, setOneTimeExtra] = useState('');
  const [applying, setApplying] = useState(false);

  const isCustom = selectedId === 'custom';

  // isInitial=true drives the full-page loading/error state (first load + retry).
  // A background refresh (after a save/undo) is "silent": it updates the data
  // without flashing the skeleton or replacing the page on a transient failure.
  const loadData = useCallback((isInitial = false) => {
    if (isInitial) {
      setLoading(true);
      setLoadError(null);
    }
    // Use api.bills() so ALL active bills with a balance appear (not just debt categories)
    (api.bills() as Promise<Bill[]>)
      .then((allBills) => {
        const withBalance = (allBills || [])
          .filter((b) => (b.current_balance ?? 0) > 0 && !b.is_subscription)
          .sort((a, b) => a.name.localeCompare(b.name));
        setBills(withBalance);
        // Only auto-pick a bill on the initial load — never yank the user's
        // current selection on a background refresh (functional update reads the
        // live value, avoiding the stale-closure snap-back).
        if (withBalance.length > 0) {
          setSelectedId((prev) => (prev == null ? withBalance[0]!.id : prev));
        }
      })
      .catch((err) => {
        if (isInitial) setLoadError(errMessage(err, 'Failed to load data'));
        else toast.error(errMessage(err, "Couldn't refresh the debt list"));
      })
      .finally(() => {
        if (isInitial) setLoading(false);
      });
  }, []);

  useEffect(() => {
    loadData(true);
  }, [loadData]);

  const bill = useMemo(
    () => (isCustom ? null : (bills.find((b) => b.id === selectedId) ?? null)),
    [bills, selectedId, isCustom],
  );

  // Reset sim inputs whenever selection changes
  useEffect(() => {
    if (isCustom) {
      setSimPayment('');
      setSimRate('0');
      setOneTimeExtra('');
      return;
    }
    if (!bill) return;
    setSimPayment(String(Math.max(bill.minimum_payment ?? 0, bill.expected_amount ?? 0)));
    setSimRate(String(bill.interest_rate ?? 0));
    setOneTimeExtra('');
  }, [selectedId]); // eslint-disable-line react-hooks/exhaustive-deps

  // Derived numeric values
  const simPaymentN = Math.max(0, Number(simPayment) || 0);
  const simRateN = Math.max(0, Number(simRate) || 0);
  const oneTimeExtraN = Math.max(0, Number(oneTimeExtra) || 0);
  const minPayment = bill?.minimum_payment ?? 0;
  const activeBalance = isCustom ? parseFloat(customBalance) || 0 : (bill?.current_balance ?? 0);
  const activeName = isCustom ? customName.trim() || 'Custom Loan' : (bill?.name ?? '');

  // The "vs minimum" baseline only makes sense when the bill actually has a
  // minimum payment on record; without one we show absolute payoff figures.
  const hasMinimum = !isCustom && minPayment > 0;
  const { minTrack, simTrack } = useMemo(() => {
    if (!activeBalance) return { minTrack: [] as ScheduleMonth[], simTrack: [] as ScheduleMonth[] };
    return {
      minTrack: hasMinimum ? buildPayoffSchedule(activeBalance, simRateN, minPayment) : [],
      simTrack: buildPayoffSchedule(activeBalance, simRateN, simPaymentN, oneTimeExtraN),
    };
  }, [activeBalance, hasMinimum, minPayment, simRateN, simPaymentN, oneTimeExtraN]);

  const minInterest = useMemo(() => minTrack.reduce((s, m) => s + m.interest, 0), [minTrack]);
  const simInterest = useMemo(() => simTrack.reduce((s, m) => s + m.interest, 0), [simTrack]);
  const hasBaseline = minTrack.length > 0; // a real, amortizing minimum to compare against
  const interestSavings = Math.max(0, minInterest - simInterest);
  const timeSavings = Math.max(0, minTrack.length - simTrack.length);
  const simTotalPaid = simInterest + activeBalance;

  const simPayoffLabel = payoffLabel(simTrack);
  const minPayoffLabel = payoffLabel(minTrack);
  const simDuration = numMonths(simTrack);

  // No APR on record → the schedule is running interest-free (distinct from a
  // genuine 0%). `interest_rate == null` means the field was never set.
  const aprMissing = !isCustom && !!bill && bill.interest_rate == null;
  const simCapped = simTrack.length >= 600; // hit the 600-month cap → won't realistically pay off
  const paymentBelowMin =
    !isCustom && simPaymentN > 0 && simPaymentN < minPayment && minPayment > 0;
  const paymentTooLow =
    activeBalance > 0 && simPaymentN > 0 && (simTrack.length === 0 || simCapped);
  const customNeedsBalance = isCustom && !customBalance;

  const defaultSimPayment = bill
    ? String(Math.max(bill.minimum_payment ?? 0, bill.expected_amount ?? 0))
    : '';
  const defaultRate = bill ? String(bill.interest_rate ?? 0) : '';
  const isDirty =
    !isCustom &&
    (simPayment !== defaultSimPayment || simRate !== defaultRate || oneTimeExtra !== '');

  const handleReset = () => {
    if (!bill) return;
    setSimPayment(defaultSimPayment);
    setSimRate(defaultRate);
    setOneTimeExtra('');
  };

  const handlePrint = () => window.print();

  // Persist the tuned APR back to the bill (the one durable fact worth keeping —
  // it makes every future estimate interest-aware). Deliberately does NOT touch
  // expected_amount / the budget. Rate differs from what's stored ⇒ offer it.
  const rateChanged = !isCustom && !!bill && simRateN !== (bill.interest_rate ?? 0);

  const handleSaveApr = async () => {
    if (!bill || applying) return;
    const prevRate = bill.interest_rate ?? null;
    setApplying(true);
    try {
      await api.updateBill(bill.id, { interest_rate: simRateN });
      toast.success(
        `Saved ${simRateN}% APR to "${bill.name}" — payoff estimates now include interest`,
        {
          action: {
            label: 'Undo',
            onClick: async () => {
              try {
                await api.updateBill(bill.id, { interest_rate: prevRate });
                toast.success('Interest rate reverted');
                loadData();
              } catch (err) {
                toast.error(errMessage(err, "Couldn't revert the interest rate"));
              }
            },
          },
        },
      );
      loadData();
    } catch (err) {
      toast.error(errMessage(err, "Couldn't save the interest rate"));
    } finally {
      setApplying(false);
    }
  };

  const handleSelectChange = (val: string) => {
    setSelectedId(val === 'custom' ? 'custom' : Number(val));
  };

  // ── Render ──────────────────────────────────────────────────────────────────

  if (loading) {
    return (
      <div className="space-y-6 animate-pulse">
        <div className="h-8 w-64 rounded-lg bg-muted/50" />
        <div className="h-4 w-96 rounded bg-muted/50" />
        <div className="grid grid-cols-1 lg:grid-cols-[360px_1fr] gap-6">
          <div className="space-y-4">
            {[1, 2, 3, 4].map((i) => (
              <div key={i} className="h-16 rounded-xl bg-muted/40" />
            ))}
          </div>
          <div className="h-96 rounded-xl bg-muted/40" />
        </div>
      </div>
    );
  }

  if (loadError) {
    return (
      <div className="flex flex-col items-center justify-center py-24 text-center rounded-xl border border-destructive/20 bg-destructive/5">
        <AlertCircle className="h-10 w-10 text-destructive mb-3" />
        <p className="text-sm font-medium">Failed to load data</p>
        <p className="mt-1 text-xs text-muted-foreground">{loadError}</p>
        <Button
          size="sm"
          variant="outline"
          onClick={() => loadData(true)}
          className="mt-4 gap-1.5 text-xs"
        >
          <RefreshCw className="h-3 w-3" /> Try again
        </Button>
      </div>
    );
  }

  // Capped (hit the 600-month wall) counts as "won't pay off" — don't present a
  // bogus payoff date / results for it.
  const showResults =
    !simCapped &&
    ((isCustom && activeBalance > 0 && simTrack.length > 0) ||
      (!isCustom && !!bill && simTrack.length > 0));

  return (
    <TooltipProvider delayDuration={200}>
      <style>{PRINT_STYLES}</style>

      <div id="payoff-print-area">
        {/* ── Print-only summary header (hidden on screen) ── */}
        <div className="print-only" style={{ display: 'none' }}>
          <h2 style={{ fontSize: '18px', fontWeight: 700, marginBottom: '4px' }}>
            Payoff Simulator — {activeName || '—'}
          </h2>
          {activeBalance > 0 && (
            <p style={{ fontSize: '12px', color: '#555', marginBottom: '12px' }}>
              Balance: {fmt(activeBalance)}
              {simRateN > 0 && ` · Rate: ${simRateN}%`}
              {simPaymentN > 0 && ` · Payment: ${fmt(simPaymentN)}/mo`}
              {oneTimeExtraN > 0 && ` · One-time extra: ${fmt(oneTimeExtraN)}`}
            </p>
          )}
        </div>

        {/* ── Page header ── */}
        <div className="mb-6 flex items-start justify-between gap-4 no-print">
          <div>
            <h1 className="text-2xl font-bold tracking-tight">Payoff Simulator</h1>
            <p className="text-sm text-muted-foreground mt-0.5">
              A what-if calculator for one debt — see how a bigger monthly payment and your APR
              change the payoff date and total interest. (For a whole-plan strategy across debts,
              use the Snowball page.)
            </p>
          </div>
          <div className="flex items-center gap-2 shrink-0 mt-1">
            {isDirty && (
              <Button size="sm" variant="ghost" onClick={handleReset} className="gap-1.5 text-xs">
                <RotateCcw className="h-3 w-3" /> Reset
              </Button>
            )}
            <Button
              size="sm"
              variant="outline"
              onClick={handlePrint}
              className="gap-1.5 text-xs"
              title="Print-friendly view"
            >
              <Printer className="h-3.5 w-3.5" /> Print
            </Button>
          </div>
        </div>

        {/* ── Bill/debt selector ── */}
        <div className="mb-6 no-print">
          <Select
            value={selectedId != null ? String(selectedId) : ''}
            onValueChange={handleSelectChange}
          >
            <SelectTrigger className="w-80">
              <SelectValue placeholder="Select a loan or debt…" />
            </SelectTrigger>
            <SelectContent>
              {bills.length > 0 && (
                <SelectGroup>
                  <SelectLabel>Your Bills</SelectLabel>
                  {bills.map((b) => (
                    <SelectItem key={b.id} value={String(b.id)}>
                      <span className="font-medium">{b.name}</span>
                      <span className="ml-2 text-muted-foreground font-mono text-xs">
                        {fmt(b.current_balance)}
                      </span>
                    </SelectItem>
                  ))}
                </SelectGroup>
              )}
              {bills.length > 0 && <SelectSeparator />}
              <SelectGroup>
                <SelectLabel>Manual Entry</SelectLabel>
                <SelectItem value="custom">Custom — not in Bill Tracker</SelectItem>
              </SelectGroup>
            </SelectContent>
          </Select>

          {bills.length === 0 && !isCustom && (
            <p className="mt-3 text-xs text-muted-foreground">
              No bills with a current balance found.{' '}
              <button
                type="button"
                className="underline text-primary hover:opacity-80"
                onClick={() => setSelectedId('custom')}
              >
                Use Custom instead
              </button>
            </p>
          )}
        </div>

        {/* ── Empty / no-selection states ── */}
        {!isCustom && !bill && bills.length === 0 && <EmptyDebts />}
        {!isCustom && !bill && bills.length > 0 && <NoSelection />}

        {/* ── Main content ── */}
        {(isCustom || bill) && (
          <div className="grid grid-cols-1 lg:grid-cols-[340px_1fr] gap-6 items-start">
            {/* ── Left panel ── */}
            <div className="table-surface p-5 space-y-5">
              {/* Custom mode: Name + Balance inputs */}
              {isCustom && (
                <>
                  <InputRow label="Loan / Debt Name" hint="Optional">
                    <Input
                      value={customName}
                      onChange={(e) => setCustomName(e.target.value)}
                      placeholder="e.g. Car Loan, Mortgage…"
                      className="no-print"
                    />
                    <p className="print-only hidden text-sm font-semibold">
                      {customName || 'Custom Loan'}
                    </p>
                  </InputRow>

                  <InputRow label="Current Balance" hint="Required">
                    <div className="flex items-center gap-2 no-print">
                      <span className="text-sm text-muted-foreground shrink-0">$</span>
                      <Input
                        type="number"
                        min="0"
                        step="100"
                        value={customBalance}
                        onChange={(e) => setCustomBalance(e.target.value)}
                        className="font-mono"
                        placeholder="0.00"
                        autoFocus
                      />
                    </div>
                    <p className="print-only hidden font-mono text-sm font-semibold">
                      {fmt(activeBalance)}
                    </p>
                    {customNeedsBalance && (
                      <p className="text-[11px] text-amber-500 mt-1 flex items-center gap-1 no-print">
                        <AlertCircle className="h-3 w-3 shrink-0" />
                        Balance is required to run the simulation
                      </p>
                    )}
                  </InputRow>
                </>
              )}

              {/* Bill mode: Required minimum display */}
              {!isCustom && (
                <div className="rounded-lg bg-muted/30 px-4 py-3 flex items-center justify-between">
                  <span className="text-xs font-semibold uppercase tracking-wider text-muted-foreground inline-flex items-center">
                    Required Minimum
                    <Help
                      label="Required Minimum"
                      text="The smallest payment your lender requires each month."
                    />
                  </span>
                  <span className="font-mono text-lg font-bold tabular-nums">
                    {minPayment > 0 ? (
                      fmt(minPayment)
                    ) : (
                      <span className="text-muted-foreground text-sm">Not set</span>
                    )}
                  </span>
                </div>
              )}

              {!isCustom && minPayment <= 0 && (
                <p className="text-xs text-amber-600 dark:text-amber-400 flex items-center gap-1.5 no-print">
                  <AlertCircle className="h-3.5 w-3.5 shrink-0" />
                  No minimum payment on this bill — edit the bill's Debt Details to add one and
                  unlock the savings-vs-minimum comparison.
                </p>
              )}

              {/* Interest rate */}
              <InputRow
                label={
                  <span className="inline-flex items-center">
                    Interest Rate
                    <Help
                      label="Interest Rate"
                      text="Your annual rate (APR). Save it to the bill so every future estimate includes interest — otherwise payoff is calculated interest-free."
                    />
                  </span>
                }
                hint="Override to test scenarios"
              >
                <div className="flex items-center gap-2">
                  <Input
                    type="number"
                    min="0"
                    max="99"
                    step="0.01"
                    value={simRate}
                    onChange={(e) => setSimRate(e.target.value)}
                    className="font-mono no-print"
                    placeholder="0.00"
                  />
                  <span className="text-sm text-muted-foreground shrink-0">%</span>
                  <span className="print-only hidden font-mono text-sm">{simRateN}%</span>
                </div>
                {aprMissing && simRateN <= 0 && (
                  <p className="text-[11px] text-amber-600 dark:text-amber-400 flex items-start gap-1 mt-1.5 no-print">
                    <Info className="h-3 w-3 shrink-0 mt-0.5" />
                    No interest rate on this bill — this estimate assumes 0% (interest-free). Enter
                    your APR, then Save it.
                  </p>
                )}
                {rateChanged && (
                  <button
                    type="button"
                    onClick={handleSaveApr}
                    disabled={applying}
                    className="mt-1.5 inline-flex items-center gap-1 text-[11px] text-primary hover:underline disabled:opacity-50 no-print"
                  >
                    <Save className="h-3 w-3 shrink-0" />
                    {applying ? 'Saving…' : `Save ${simRateN}% APR to this bill`}
                    <Help
                      label="Save APR"
                      text="Saves this rate to the bill. Doesn't change the bill's amount or your budget."
                    />
                  </button>
                )}
              </InputRow>

              {/* Monthly payment */}
              <InputRow label="Monthly Payment">
                <div className="no-print">
                  <Input
                    type="number"
                    min="0"
                    step="1"
                    value={simPayment}
                    onChange={(e) => setSimPayment(e.target.value)}
                    className="font-mono"
                    placeholder="0.00"
                  />
                  {paymentBelowMin && (
                    <p className="text-[11px] text-amber-600 dark:text-amber-400 flex items-center gap-1 mt-1">
                      <AlertCircle className="h-3 w-3 shrink-0" />
                      Below minimum payment of {fmt(minPayment)}
                    </p>
                  )}
                  {paymentTooLow && !paymentBelowMin && (
                    <p className="text-[11px] text-destructive flex items-start gap-1 mt-1">
                      <AlertCircle className="h-3 w-3 shrink-0 mt-0.5" />
                      {simCapped && simRateN <= 0
                        ? 'This debt won’t pay off in a reasonable time at this payment.'
                        : 'Payment too low to overcome the interest — the balance never shrinks.'}
                    </p>
                  )}
                </div>
                <p className="print-only hidden font-mono text-sm font-semibold">
                  {fmt(simPaymentN)}/mo
                </p>
              </InputRow>

              {/* One-time extra */}
              <InputRow label="One-time Extra This Month" hint="Optional lump sum">
                <div className="flex items-center gap-1 no-print">
                  <Input
                    type="number"
                    min="0"
                    step="100"
                    value={oneTimeExtra}
                    onChange={(e) => setOneTimeExtra(e.target.value)}
                    className="font-mono"
                    placeholder="0.00"
                  />
                  <div className="flex flex-col gap-0.5">
                    <button
                      type="button"
                      className="rounded px-1.5 py-0.5 text-xs text-muted-foreground hover:bg-muted transition-colors"
                      onClick={() => setOneTimeExtra(String(Math.max(0, oneTimeExtraN + 100)))}
                    >
                      ▲
                    </button>
                    <button
                      type="button"
                      className="rounded px-1.5 py-0.5 text-xs text-muted-foreground hover:bg-muted transition-colors"
                      onClick={() => setOneTimeExtra(String(Math.max(0, oneTimeExtraN - 100)))}
                    >
                      ▼
                    </button>
                  </div>
                </div>
                {oneTimeExtraN > 0 && (
                  <p className="print-only hidden text-sm">{fmt(oneTimeExtraN)}</p>
                )}
              </InputRow>

              {/* Divider */}
              <div className="border-t border-border/50" />

              {/* Payoff date summary */}
              <div className="space-y-2">
                {simPayoffLabel ? (
                  <div className="flex items-baseline justify-between">
                    <span className="text-xs text-muted-foreground uppercase tracking-wider font-semibold">
                      Payoff
                    </span>
                    <div className="text-right">
                      <span className="text-xl font-bold font-mono text-amber-500 dark:text-amber-400">
                        {simPayoffLabel}
                      </span>
                      {simDuration && (
                        <p className="text-[11px] text-muted-foreground">{simDuration}</p>
                      )}
                    </div>
                  </div>
                ) : (
                  <p className="text-xs text-muted-foreground text-center">
                    {customNeedsBalance
                      ? 'Enter a balance to see payoff date'
                      : 'Enter a payment to see payoff date'}
                  </p>
                )}

                {!isCustom &&
                  minPayoffLabel &&
                  simPayoffLabel &&
                  minPayoffLabel !== simPayoffLabel && (
                    <div className="flex items-baseline justify-between">
                      <span className="text-[11px] text-muted-foreground">Minimum only</span>
                      <span className="text-[11px] text-muted-foreground font-mono line-through">
                        {minPayoffLabel}
                      </span>
                    </div>
                  )}
              </div>
            </div>

            {/* ── Right panel ── */}
            <div className="space-y-4">
              {/* Chart */}
              {showResults ? (
                <>
                  <PayoffChart
                    minTrack={minTrack}
                    simTrack={simTrack}
                    startBalance={activeBalance}
                  />
                  <p className="text-[11px] text-muted-foreground text-center -mt-2 no-print">
                    Projected balance over time
                    {hasBaseline ? ' — dashed grey is paying only the minimum' : ''}.
                  </p>
                </>
              ) : (
                <div className="flex items-center justify-center rounded-xl bg-muted/20 h-[300px] text-center text-sm text-muted-foreground px-6">
                  {customNeedsBalance
                    ? 'Enter a balance and payment to see the chart'
                    : simPaymentN <= 0
                      ? 'Enter a monthly payment to see the chart'
                      : simCapped
                        ? 'This payment won’t pay the debt off — raise it to see a payoff curve.'
                        : 'Payment too low to pay off this debt'}
                </div>
              )}

              {/* Stats row */}
              {showResults && (
                <>
                  <div className="grid gap-3 grid-cols-2">
                    {hasBaseline ? (
                      <>
                        <StatCard
                          label="Interest Savings"
                          help="Interest you avoid at this payment vs paying only the minimum."
                          value={fmtShort(interestSavings)}
                          sub="vs minimum only"
                          color={interestSavings > 0 ? 'teal' : 'slate'}
                        />
                        <StatCard
                          label="Time Savings"
                          help="How many months sooner you're debt-free vs paying only the minimum."
                          value={timeSavings > 0 ? `${timeSavings} mo` : '—'}
                          sub={timeSavings > 0 ? 'months sooner' : 'same timeline'}
                          color={timeSavings > 0 ? 'amber' : 'slate'}
                        />
                      </>
                    ) : (
                      <>
                        <StatCard
                          label="Time to Payoff"
                          value={numMonths(simTrack) ?? '—'}
                          sub={simPayoffLabel ? `by ${simPayoffLabel}` : 'to pay off'}
                          color="amber"
                        />
                        <StatCard
                          label="Total Interest"
                          help="Total interest over the life of the debt at this payment and APR."
                          value={fmtShort(simInterest)}
                          sub="at this payment"
                          color={simInterest > 0 ? 'teal' : 'slate'}
                        />
                      </>
                    )}
                  </div>

                  {/* Breakdown */}
                  <div className="table-surface divide-y divide-border/50">
                    <div className="px-5 py-3 flex items-center justify-between">
                      <span className="text-sm text-muted-foreground">Balance today</span>
                      <span className="font-mono text-sm font-semibold">{fmt(activeBalance)}</span>
                    </div>
                    <div className="px-5 py-3 flex items-center justify-between">
                      <span className="text-sm text-muted-foreground">Total interest</span>
                      <span className="font-mono text-sm font-semibold text-rose-500">
                        {fmt(simInterest)}
                      </span>
                    </div>
                    <div className="px-5 py-3 flex items-center justify-between">
                      <span className="text-sm font-medium">Total paid</span>
                      <span className="font-mono text-sm font-bold">{fmt(simTotalPaid)}</span>
                    </div>
                  </div>
                </>
              )}
            </div>
          </div>
        )}
      </div>
      {/* /payoff-print-area */}
    </TooltipProvider>
  );
}