import { auth } from "@/auth";
import { redirect } from "next/navigation";
import Link from "next/link";
import type { Metadata } from "next";
import { ChevronRight } from "lucide-react";
import { hasPermission } from "@/lib/permissions";
import { formatCurrency, formatCompactINR } from "@/lib/utils";
import {
  getReportDataset,
  costCentreRows,
  applyScope,
  parseScope,
  parseGranularity,
  resolveFy,
  fyLabel,
  FY_MONTHS,
  SCOPE_LABELS,
} 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: "Cost Centres — Reports" };

const sum = (a: number[]) => a.reduce((x, y) => x + y, 0);

export default async function CostCentresReport({
  searchParams,
}: {
  searchParams: Promise<{ fy?: string; gran?: string; scope?: 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 gran = parseGranularity(sp.gran);
  const scope = parseScope(sp.scope);
  const fy = resolveFy(ds, sp.fy);
  const yearly = gran === "yearly";

  const ranked = costCentreRows(ds, fy);
  const rankOf = (r: { total: number; fyTotals: number[] }) => (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 totalSpend = shown.reduce((s, r) => s + (yearly ? sum(r.fyTotals) : r.total), 0);
  const top = shown[0];

  // YoY across the shown cost centres (latest two FYs).
  const n = ds.fys.length;
  const curT = n >= 1 ? shown.reduce((s, r) => s + r.fyTotals[n - 1], 0) : 0;
  const prevT = n >= 2 ? shown.reduce((s, r) => s + r.fyTotals[n - 2], 0) : 0;
  const yoy = prevT ? ((curT - prevT) / prevT) * 100 : 0;

  // Comparison chart series.
  let chartData: Record<string, string | number>[];
  let series: Series[];
  const colored = (i: number) => SERIES_COLORS[i % SERIES_COLORS.length];
  if (yearly) {
    chartData = shown.map((r) => {
      const row: Record<string, string | number> = { name: r.name };
      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.name] = r.months[i]));
      return row;
    });
    series = shown.map((r, i) => ({ key: r.name, color: colored(i) }));
  }

  const periodLabel = yearly ? ds.fys.map(fyLabel).join(" · ") : fyLabel(fy);
  const exportHref = `/api/reports/spend?dim=cost-centre&fy=${fy}&gran=${gran}&scope=${scope}`;
  const detailHref = (id: string) => `/reports/cost-centres/${id}?fy=${fy}&gran=${gran}`;

  return (
    <div>
      <ReportBreadcrumb trail={[{ label: "Cost Centres" }]} />
      <ReportsToolbar fys={ds.fys} fy={fy} gran={gran} scope={scope} exportHref={exportHref} />

      <ReportTitle
        title="Cost Centres"
        subtitle="Approved spend compared across cost centres (vessels). Click a row to open its report."
      />

      {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(totalSpend)} sub={periodLabel} />
            <Kpi label="Cost centres" value={String(shown.length)} sub={`${SCOPE_LABELS[scope]} shown`} />
            <Kpi label="Highest spender" value={top?.name ?? "—"} sub={formatCompactINR(rankOf(top ?? { total: 0, fyTotals: [] }))} />
            <Kpi label="YoY change" value={`${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 cost centre — year over year" : "Monthly spend by cost centre"}
              </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">
            <table className="w-full text-sm">
              <thead className="border-b border-neutral-200 bg-neutral-50 text-left text-xs font-semibold uppercase tracking-wider text-neutral-400">
                <tr>
                  <th className="px-5 py-3">Cost Centre</th>
                  <th className="px-5 py-3">Trend</th>
                  <th className="px-5 py-3 text-right">Total Spend</th>
                  <th className="px-5 py-3 text-right">% of Shown</th>
                  <th className="px-5 py-3 text-right">POs</th>
                  <th className="px-5 py-3" />
                </tr>
              </thead>
              <tbody className="divide-y divide-neutral-100">
                {shown.map((r) => {
                  const value = rankOf(r);
                  const pct = grand ? (value / grand) * 100 : 0;
                  return (
                    <tr key={r.id} className="group hover:bg-primary-50/40">
                      <td className="px-5 py-3">
                        <Link href={detailHref(r.id)} className="block font-medium text-neutral-900 group-hover:text-primary-700">
                          {r.name}
                          <span className="ml-2 text-xs font-normal text-neutral-400">{r.code}</span>
                        </Link>
                      </td>
                      <td className="px-5 py-3">
                        <Sparkline values={yearly ? r.fyTotals : r.months} />
                      </td>
                      <td className="px-5 py-3 text-right font-medium tabular-nums">{formatCurrency(value)}</td>
                      <td className="px-5 py-3 text-right">
                        <div className="flex items-center justify-end gap-2">
                          <div className="h-1.5 w-16 overflow-hidden rounded-full bg-neutral-100">
                            <div className="h-full rounded-full bg-primary-600" style={{ width: `${Math.min(pct, 100)}%` }} />
                          </div>
                          <span className="w-10 text-right tabular-nums text-neutral-500">{pct.toFixed(0)}%</span>
                        </div>
                      </td>
                      <td className="px-5 py-3 text-right tabular-nums text-neutral-500">{r.poCount}</td>
                      <td className="px-5 py-3 text-right">
                        <Link href={detailHref(r.id)}>
                          <ChevronRight className="inline h-4 w-4 text-neutral-300 group-hover:text-primary-500" />
                        </Link>
                      </td>
                    </tr>
                  );
                })}
              </tbody>
            </table>
          </div>
        </>
      )}
    </div>
  );
}