import { auth } from "@/auth";
import { redirect } from "next/navigation";
import Link from "next/link";
import type { Metadata } from "next";
import { ChevronRight, BarChart3 } from "lucide-react";
import { hasPermission } from "@/lib/permissions";
import { formatCurrency, formatCompactINR } from "@/lib/utils";
import {
  getReportDataset,
  buildAccountIndex,
  accountLevelRows,
  applyScope,
  parseScope,
  parseGranularity,
  resolveFy,
  fyLabel,
  FY_MONTHS,
  SCOPE_LABELS,
  type NodeSpend,
} from "@/lib/reports";
import { ReportsToolbar } from "@/components/reports/reports-toolbar";
import { ComparisonChart, Sparkline, SERIES_COLORS, type Series } from "@/components/reports/charts";
import { Kpi, KpiStrip } from "@/components/reports/kpi";
import { ReportBreadcrumb, ReportTitle } from "@/components/reports/report-header";

export const metadata: Metadata = { title: "Accounting Codes — Reports" };

const sum = (a: number[]) => a.reduce((x, y) => x + y, 0);
const tierBadgeCls: Record<string, string> = {
  Heading: "bg-primary-50 text-primary-700",
  "Sub-heading": "bg-violet-50 text-violet-700",
  Leaf: "bg-neutral-100 text-neutral-600",
};

export default async function AccountingCodesReport({
  searchParams,
}: {
  searchParams: Promise<{ fy?: string; gran?: string; scope?: string; parent?: string }>;
}) {
  const session = await auth();
  if (!session?.user) return null;
  if (!hasPermission(session.user.role, "view_analytics")) redirect("/dashboard");

  const sp = await searchParams;
  const ds = await getReportDataset();
  const idx = buildAccountIndex(ds.accounts);
  const gran = parseGranularity(sp.gran);
  const scope = parseScope(sp.scope);
  const fy = resolveFy(ds, sp.fy);
  const yearly = gran === "yearly";

  const parent = sp.parent && idx.byId.has(sp.parent) ? sp.parent : null;
  const parentNode = parent ? idx.byId.get(parent)! : null;

  const ranked = accountLevelRows(ds, idx, parent, fy);
  const rankOf = (r: NodeSpend) => (yearly ? sum(r.fyTotals) : r.total);
  ranked.sort((a, b) => rankOf(b) - rankOf(a));
  const shown = applyScope(ranked, scope);
  const grand = shown.reduce((s, r) => s + rankOf(r), 0);
  const childTier = shown[0]?.node.tier ?? "Heading";
  const top = shown[0];

  const nf = ds.fys.length;
  const curT = nf >= 1 ? shown.reduce((s, r) => s + r.fyTotals[nf - 1], 0) : 0;
  const prevT = nf >= 2 ? shown.reduce((s, r) => s + r.fyTotals[nf - 2], 0) : 0;
  const yoy = prevT ? ((curT - prevT) / prevT) * 100 : 0;

  const colored = (i: number) => SERIES_COLORS[i % SERIES_COLORS.length];
  let chartData: Record<string, string | number>[];
  let series: Series[];
  if (yearly) {
    chartData = shown.map((r) => {
      const row: Record<string, string | number> = { name: r.node.code };
      ds.fys.forEach((y, i) => (row[fyLabel(y)] = r.fyTotals[i]));
      return row;
    });
    series = ds.fys.map((y, i) => ({ key: fyLabel(y), color: colored(i) }));
  } else {
    chartData = FY_MONTHS.map((m, i) => {
      const row: Record<string, string | number> = { month: m };
      shown.forEach((r) => (row[r.node.code] = r.months[i]));
      return row;
    });
    series = shown.map((r, i) => ({ key: r.node.code, color: colored(i) }));
  }

  const periodLabel = yearly ? ds.fys.map(fyLabel).join(" · ") : fyLabel(fy);
  const linkWith = (parentId: string | null) => {
    const p = new URLSearchParams({ fy: String(fy), gran, scope });
    if (parentId) p.set("parent", parentId);
    return `/reports/accounting-codes?${p.toString()}`;
  };
  const detailHref = (id: string) => `/reports/accounting-codes/${id}?fy=${fy}&gran=${gran}`;
  const rowHref = (r: NodeSpend) => (idx.isLeaf(r.node.id) ? detailHref(r.node.id) : linkWith(r.node.id));
  const exportHref = `/api/reports/spend?dim=accounting-code&fy=${fy}&gran=${gran}&scope=${scope}${parent ? `&parent=${parent}` : ""}`;

  // Breadcrumb: Reports / Accounting Codes / …ancestors… / current parent.
  const trail = [{ label: "Accounting Codes", href: parent ? linkWith(null) : undefined }];
  if (parentNode) {
    const path = idx.pathTo(parentNode.id);
    path.forEach((a, i) =>
      trail.push({ label: `${a.code} · ${a.name}`, href: i < path.length - 1 ? linkWith(a.id) : undefined })
    );
  }

  return (
    <div>
      <ReportBreadcrumb trail={trail} />
      <ReportsToolbar fys={ds.fys} fy={fy} gran={gran} scope={scope} exportHref={exportHref} />

      {parentNode && (
        <Link
          href={parentNode.parentId ? linkWith(parentNode.parentId) : linkWith(null)}
          className="mb-4 inline-flex items-center gap-1.5 text-sm font-medium text-primary-600 hover:text-primary-700"
        >
          ← Back to {parentNode.parentId ? idx.byId.get(parentNode.parentId)!.name : "Accounting Codes"}
        </Link>
      )}

      <ReportTitle
        title={parentNode ? `${parentNode.code} · ${parentNode.name}` : "Accounting Codes"}
        subtitle={
          parentNode
            ? `Comparing the ${childTier.toLowerCase()}s of ${parentNode.name}. Click a row to ${childTier === "Leaf" ? "open its report" : "drill deeper"}.`
            : "Comparing top-level headings. Click a heading to drill into its sub-headings."
        }
      />

      {grand === 0 ? (
        <div className="rounded-lg border border-dashed border-neutral-300 bg-white p-10 text-center text-sm text-neutral-500">
          No approved spend recorded for {periodLabel} yet.
        </div>
      ) : (
        <>
          <KpiStrip>
            <Kpi label="Total spend" value={formatCompactINR(shown.reduce((s, r) => s + (yearly ? sum(r.fyTotals) : r.total), 0))} sub={periodLabel} />
            <Kpi label={`${childTier}s`} value={String(shown.length)} sub={`${SCOPE_LABELS[scope]} shown`} />
            <Kpi label="Highest spender" value={top ? top.node.code : "—"} sub={top ? formatCompactINR(rankOf(top)) : ""} />
            <Kpi label="YoY change" value={`${yoy >= 0 ? "+" : ""}${yoy.toFixed(1)}%`} sub="vs prior FY" delta={yoy} />
          </KpiStrip>

          <div className="mb-6 rounded-lg border border-neutral-200 bg-white p-5">
            <div className="mb-4 flex items-center justify-between">
              <p className="text-sm font-semibold text-neutral-900">
                {yearly ? `Spend by ${childTier.toLowerCase()} — year over year` : `Monthly spend by ${childTier.toLowerCase()}`}
              </p>
              <span className="text-xs text-neutral-400">{periodLabel}</span>
            </div>
            <ComparisonChart kind={yearly ? "bars" : "lines"} data={chartData} xKey={yearly ? "name" : "month"} series={series} />
          </div>

          <div className="overflow-hidden rounded-lg border border-neutral-200 bg-white">
            {shown.map((r) => {
              const value = rankOf(r);
              const pct = grand ? (value / grand) * 100 : 0;
              const leaf = idx.isLeaf(r.node.id);
              return (
                <Link
                  key={r.node.id}
                  href={rowHref(r)}
                  className="group flex items-center gap-3 border-b border-neutral-100 px-5 py-3 last:border-0 hover:bg-primary-50/40"
                >
                  <span className="w-14 shrink-0 font-mono text-xs text-neutral-500">{r.node.code}</span>
                  <span className="flex-1 truncate text-sm font-medium text-neutral-900 group-hover:text-primary-700">{r.node.name}</span>
                  <span className={`rounded-full px-2 py-0.5 text-xs font-medium ${tierBadgeCls[r.node.tier]}`}>{r.node.tier}</span>
                  <Sparkline values={yearly ? r.fyTotals : r.months} width={80} height={24} />
                  <span className="w-28 text-right font-medium tabular-nums text-sm">{formatCurrency(value)}</span>
                  <div className="hidden w-12 text-right tabular-nums text-xs text-neutral-500 md:block">{pct.toFixed(0)}%</div>
                  {leaf ? (
                    <BarChart3 className="h-4 w-4 shrink-0 text-neutral-300 group-hover:text-primary-500" />
                  ) : (
                    <ChevronRight className="h-4 w-4 shrink-0 text-neutral-300 group-hover:text-primary-500" />
                  )}
                </Link>
              );
            })}
          </div>
        </>
      )}
    </div>
  );
}