import { useState } from 'react';
import { ChevronDown, History } from 'lucide-react';
import { Collapsible, CollapsibleContent, CollapsibleTrigger } from '@/components/ui/collapsible';
import { cn } from '@/lib/utils';
import { formatUSD, formatUSDWhole } from '@/lib/money';
import type { Dollars } from '@/lib/money';

interface SnowballPlanDebt {
  bill_id: number;
  name: string;
  starting_balance: Dollars;
  projected_payoff_date?: string | null;
  projected_total_interest?: Dollars | null;
}

interface SnowballPlanSnapshot {
  debts?: SnowballPlanDebt[];
  projected_months?: number;
  projected_payoff_date?: string | null;
  interest_saved?: Dollars;
  minimum_only_months?: number;
}

interface CurrentDebt {
  bill_id: number;
  current_balance?: Dollars | null;
}

export interface SnowballPlan {
  id: number;
  name: string;
  status: string;
  method: string;
  started_at?: string | null;
  completed_at?: string | null;
  paused_at?: string | null;
  extra_payment?: Dollars;
  notes?: string | null;
  plan_snapshot?: SnowballPlanSnapshot;
  current_debts?: CurrentDebt[];
}

function fmt(v: Dollars | null | undefined): string {
  return formatUSDWhole(v);
}

function fmtFull(v: Dollars | null | undefined): string {
  return formatUSD(v);
}

function dateRange(plan: SnowballPlan): string {
  const start = plan.started_at
    ? new Date(plan.started_at).toLocaleDateString(undefined, { month: 'short', year: 'numeric' })
    : '—';
  const endDate = plan.completed_at || plan.paused_at;
  const end = endDate
    ? new Date(endDate).toLocaleDateString(undefined, { month: 'short', year: 'numeric' })
    : plan.status === 'abandoned' ? 'abandoned' : 'present';
  return `${start} – ${end}`;
}

function StatusBadge({ status }: { status: string }) {
  const map = {
    active:    'bg-emerald-500/12 text-emerald-600 dark:text-emerald-400',
    paused:    'bg-amber-500/12   text-amber-600   dark:text-amber-400',
    completed: 'bg-indigo-500/12  text-indigo-600  dark:text-indigo-400',
    abandoned: 'bg-rose-500/12    text-rose-600    dark:text-rose-400',
  };
  const labels: Record<string, string> = { active: 'Active', paused: 'Paused', completed: 'Completed', abandoned: 'Abandoned' };
  return (
    <span className={cn('rounded-full px-2 py-0.5 text-[10px] font-bold uppercase tracking-wide', map[status as keyof typeof map] ?? map.abandoned)}>
      {labels[status] ?? status}
    </span>
  );
}

function MethodBadge({ method }: { method: string }) {
  const map: Record<string, string> = { snowball: 'Snowball', avalanche: 'Avalanche', custom: 'Custom' };
  return (
    <span className="rounded-full px-2 py-0.5 text-[10px] font-medium bg-muted/60 text-muted-foreground">
      {map[method] ?? method}
    </span>
  );
}

// ─── Expanded plan detail ─────────────────────────────────────────────────────

function PlanDetail({ plan }: { plan: SnowballPlan }) {
  const snapshot = plan.plan_snapshot ?? {};
  const debts    = snapshot.debts ?? [];

  return (
    <div className="px-4 pb-4 space-y-3">
      {/* Summary stats */}
      <div className="grid grid-cols-2 sm:grid-cols-4 gap-2 pt-1">
        {snapshot.projected_months && (
          <div className="rounded-lg bg-muted/30 px-3 py-2 text-center">
            <p className="text-[10px] text-muted-foreground uppercase tracking-wide">Projected payoff</p>
            <p className="text-xs font-mono font-semibold mt-0.5">{snapshot.projected_payoff_date ?? '—'}</p>
          </div>
        )}
        {(snapshot.interest_saved ?? 0) > 0 && (
          <div className="rounded-lg bg-emerald-500/8 border border-emerald-400/15 px-3 py-2 text-center">
            <p className="text-[10px] text-muted-foreground uppercase tracking-wide">Interest saved</p>
            <p className="text-xs font-mono font-semibold text-emerald-600 dark:text-emerald-400 mt-0.5">{fmt(snapshot.interest_saved)}</p>
          </div>
        )}
        {snapshot.minimum_only_months && (
          <div className="rounded-lg bg-muted/30 px-3 py-2 text-center">
            <p className="text-[10px] text-muted-foreground uppercase tracking-wide">Minimum-only months</p>
            <p className="text-xs font-mono font-semibold mt-0.5">{snapshot.minimum_only_months}</p>
          </div>
        )}
        {(plan.extra_payment ?? 0) > 0 && (
          <div className="rounded-lg bg-muted/30 px-3 py-2 text-center">
            <p className="text-[10px] text-muted-foreground uppercase tracking-wide">Extra/mo</p>
            <p className="text-xs font-mono font-semibold mt-0.5">{fmtFull(plan.extra_payment)}</p>
          </div>
        )}
      </div>

      {/* Per-debt snapshot table */}
      {debts.length > 0 && (
        <div className="space-y-1.5">
        <p className="text-[10px] font-bold uppercase tracking-[0.1em] text-muted-foreground/50">Debt snapshot at start of plan</p>
        <div className="rounded-lg border border-border/50 overflow-hidden">
          <table className="w-full text-xs">
            <thead>
              <tr className="bg-muted/30 border-b border-border/50">
                <th className="text-left px-3 py-2 font-semibold text-muted-foreground uppercase tracking-wide text-[10px]">Debt</th>
                <th className="text-right px-3 py-2 font-semibold text-muted-foreground uppercase tracking-wide text-[10px]">Starting balance</th>
                <th className="text-right px-3 py-2 font-semibold text-muted-foreground uppercase tracking-wide text-[10px] hidden sm:table-cell">Projected payoff</th>
                <th className="text-right px-3 py-2 font-semibold text-muted-foreground uppercase tracking-wide text-[10px] hidden sm:table-cell">Projected interest</th>
                <th className="text-right px-3 py-2 font-semibold text-muted-foreground uppercase tracking-wide text-[10px]">Current balance</th>
              </tr>
            </thead>
            <tbody className="divide-y divide-border/30">
              {debts.map(d => {
                const current = plan.current_debts?.find(c => c.bill_id === d.bill_id);
                const curBal  = current?.current_balance;
                const isPaidOff = curBal !== null && curBal !== undefined && curBal <= 0;
                return (
                  <tr key={d.bill_id} className="hover:bg-muted/10 transition-colors">
                    <td className="px-3 py-2 font-medium">{d.name}</td>
                    <td className="px-3 py-2 text-right font-mono tabular-nums">{fmtFull(d.starting_balance)}</td>
                    <td className="px-3 py-2 text-right font-mono hidden sm:table-cell">{d.projected_payoff_date ?? '—'}</td>
                    <td className="px-3 py-2 text-right font-mono text-rose-500 hidden sm:table-cell">
                      {d.projected_total_interest != null ? fmtFull(d.projected_total_interest) : '—'}
                    </td>
                    <td className="px-3 py-2 text-right font-mono tabular-nums">
                      {isPaidOff ? (
                        <span className="text-emerald-600 dark:text-emerald-400 font-semibold">Paid off ✓</span>
                      ) : curBal != null ? (
                        fmtFull(curBal)
                      ) : (
                        <span className="text-muted-foreground italic">removed</span>
                      )}
                    </td>
                  </tr>
                );
              })}
            </tbody>
          </table>
        </div>
        </div>
      )}

      {plan.notes && (
        <p className="text-xs text-muted-foreground italic">{plan.notes}</p>
      )}
    </div>
  );
}

// ─── Single plan row ──────────────────────────────────────────────────────────

function PlanRow({ plan }: { plan: SnowballPlan }) {
  const [expanded, setExpanded] = useState(false);
  const snapshot  = plan.plan_snapshot ?? {};
  const debtCount = (snapshot.debts ?? []).length;

  return (
    <Collapsible open={expanded} onOpenChange={setExpanded}>
      <CollapsibleTrigger asChild>
        <button type="button" className="w-full text-left hover:bg-muted/20 transition-colors px-4 py-3 flex items-center gap-3">
          <StatusBadge status={plan.status} />
          <div className="flex-1 min-w-0">
            <div className="flex items-center gap-2 flex-wrap">
              <span className="text-sm font-medium">{plan.name}</span>
              <MethodBadge method={plan.method} />
            </div>
            <p className="text-[11px] text-muted-foreground mt-0.5">
              {dateRange(plan)}
              {debtCount > 0 && ` · ${debtCount} debt${debtCount !== 1 ? 's' : ''}`}
              {(snapshot.interest_saved ?? 0) > 0 && ` · ${fmt(snapshot.interest_saved)} interest saved`}
            </p>
          </div>
          <ChevronDown className={cn('h-4 w-4 text-muted-foreground transition-transform shrink-0', expanded && 'rotate-180')} />
        </button>
      </CollapsibleTrigger>
      <CollapsibleContent>
        <div className="border-t border-border/30">
          <PlanDetail plan={plan} />
        </div>
      </CollapsibleContent>
    </Collapsible>
  );
}

// ─── PlanHistoryPanel ─────────────────────────────────────────────────────────

export default function PlanHistoryPanel({ plans = [] }: { plans?: SnowballPlan[] }) {
  const [open, setOpen] = useState(false);

  const historical = plans.filter(p => !['active', 'paused'].includes(p.status));
  if (historical.length === 0) return null;

  return (
    <div className="mt-6">
      <Collapsible open={open} onOpenChange={setOpen}>
        <div className="rounded-xl border border-border/60 overflow-hidden">
          <CollapsibleTrigger asChild>
            <button type="button" className="w-full text-left px-4 py-3 flex items-center gap-3 bg-muted/10 hover:bg-muted/20 transition-colors">
              <History className="h-4 w-4 text-muted-foreground shrink-0" />
              <span className="text-xs font-bold uppercase tracking-widest text-muted-foreground flex-1">
                Plan History · {historical.length} plan{historical.length !== 1 ? 's' : ''}
              </span>
              <ChevronDown className={cn('h-4 w-4 text-muted-foreground transition-transform', open && 'rotate-180')} />
            </button>
          </CollapsibleTrigger>
          <CollapsibleContent>
            <div className="divide-y divide-border/40">
              {historical.map(plan => (
                <PlanRow key={plan.id} plan={plan} />
              ))}
            </div>
          </CollapsibleContent>
        </div>
      </Collapsible>
    </div>
  );
}