import { useEffect, useMemo, useState } from "react";
import { useTranslation } from "react-i18next";
import { useQuery } from "@tanstack/react-query";
import { fetchActiveSessions } from "./api.js";
import { qk } from "./lib/query.js";
import { formatCountdown, formatDuration, formatRelativeDateTime } from "./lib/format.js";
import { Panel } from "./ui/Panel.js";
import { FilterBar, SegGroup, type SegOption } from "./ui/FilterBar.js";

// Active Sessions panel. A session is "active" while still inside OR exited-but-
// within-grace (the barrier is UNCONFIRMED, so a paid/exited car is presumed
// possibly-present until grace runs out). Lets the operator find a stuck car —
// damaged ticket, dead scanner, or a phantom barrier re-close — without a scan:
// click a row → the pay/exit modal (pay an unpaid car, settle a subscriber's
// out-of-window charge, assist-open a prepaid subscriber, or review).
//
// OVERSTAY sessions (paid, grace expired, no signed exit) are no longer aged out — they
// stay listed with a distinct badge. A new period has begun (the car re-parked or is
// faulty/abandoned); occupancy lingers and the car owes a fresh top-up. The operator
// reconciles via the pay/exit modal — never a free barrier open.
// See wiki/concepts/booth-exit-flow.md.

type KindFilter = "transient" | "subscription";

export function ActiveSessions({ onPick }: { onPick: (identity: string) => void }) {
  const { t } = useTranslation();
  const { data, isLoading } = useQuery({
    queryKey: qk.activeSessions,
    queryFn: fetchActiveSessions,
    // Belt-and-braces refresh in case a grace window expires with no ledger event
    // to invalidate the cache (the WS only pushes on appends).
    refetchInterval: 15_000,
  });

  // A 1-second clock so the within-grace countdown badge ticks live (the query only
  // refetches every 15s; the badge needs per-second resolution).
  const [nowMs, setNowMs] = useState(() => Date.now());
  useEffect(() => {
    const id = setInterval(() => setNowMs(Date.now()), 1000);
    return () => clearInterval(id);
  }, []);

  // Filters: free-text search + transient-vs-subscriber. (No status filter — the status
  // column was dropped; an unpaid transient is normal and a subscriber is marked ★.)
  const [search, setSearch] = useState("");
  const [kind, setKind] = useState<KindFilter | "">("");

  const sessions = useMemo(() => data?.sessions ?? [], [data]);
  const filtered = useMemo(() => {
    const q = search.trim().toLowerCase();
    return sessions.filter((s) => {
      if (kind === "transient" && s.subscription) return false;
      if (kind === "subscription" && !s.subscription) return false;
      if (q) {
        // Include the enriched plate (`s.plate`, the displayed badge) so a plate search hits.
        const hay = `${s.identity} ${s.subscriptionHolder ?? ""} ${s.plate ?? ""}`.toLowerCase();
        if (!hay.includes(q)) return false;
      }
      return true;
    });
  }, [sessions, search, kind]);

  const kindOpts: SegOption<KindFilter>[] = [
    { value: "transient", label: t("booth.fKindTransient") },
    { value: "subscription", label: t("booth.fKindSubscription") },
  ];

  return (
    <Panel
      title={t("booth.activeSessions")}
      right={
        <span className="text-[0.625rem] uppercase tracking-wider text-term-muted">
          {filtered.length}
          {filtered.length !== sessions.length ? `/${sessions.length}` : ""} {t("booth.insideCount")}
        </span>
      }
      className="min-h-0 flex-1"
    >
      <div className="flex h-full flex-col">
        <FilterBar search={search} onSearch={setSearch} searchPlaceholder={t("booth.filterSearchSessions")}>
          <SegGroup value={kind} options={kindOpts} onChange={setKind} allLabel={t("booth.filterAll")} />
        </FilterBar>

        <div className="min-h-0 flex-1 overflow-y-auto pr-1">
          {filtered.length === 0 ? (
            <div className="text-term-muted">
              {isLoading
                ? t("common.loading")
                : sessions.length === 0
                  ? t("booth.noActiveSessions")
                  : t("booth.noMatch")}
            </div>
          ) : (
            // A real table — aligned columns (who · plate · entry · elapsed). No status
            // column: an unpaid transient is the normal case, and a subscriber is already
            // marked with ★ + holder name. Overstay (a top-up is owed) keeps a row tint so
            // that fraud-relevant signal isn't lost. The whole row is clickable (→ pay/exit
            // modal).
            <table className="w-full text-[0.75rem] tabular-nums">
              <thead className="sticky top-0 bg-term-panel-2 text-[0.6875rem] uppercase tracking-wider text-term-muted">
                <tr>
                  <th className="px-2 py-1.5 text-left font-semibold">{t("booth.colWho")}</th>
                  <th className="px-2 py-1.5 text-left font-semibold">{t("booth.colPlate")}</th>
                  <th className="whitespace-nowrap px-2 py-1.5 text-left font-semibold">{t("booth.colEntry")}</th>
                  <th className="whitespace-nowrap px-2 py-1.5 text-left font-semibold">{t("booth.colElapsed")}</th>
                </tr>
              </thead>
              <tbody>
                {filtered.map((s) => {
                  // EXITED-WITHIN-GRACE: a paid transient whose exit is recorded but the
                  // barrier didn't confirm — it lingers here until grace runs out. Mark it
                  // so the operator can tell it apart from a still-inside car (clicking it
                  // opens the modal's manual barrier re-open, not a pay flow).
                  const closedInGrace = !s.open && s.withinGrace && !s.subscription;
                  // Live grace-remaining for the badge (M:SS). Null once it lapses — the
                  // next refetch (≤15s) reclassifies the row (overstay / gone); until then
                  // we show a generic label so the badge doesn't flicker empty.
                  const graceLeft = closedInGrace ? formatCountdown(s.graceExpiresAt, nowMs) : null;
                  return (
                    <tr
                      key={s.identity}
                      onClick={() => onPick(s.identity)}
                      className={`cursor-pointer border-t border-term-border/50 hover:bg-term-panel-2 ${
                        s.overstay ? "bg-term-red/5" : closedInGrace ? "bg-term-amber/5 text-term-muted" : ""
                      }`}
                      title={closedInGrace ? t("booth.openReopenBarrier") : t("booth.openPayExit")}
                    >
                      <td className="px-2 py-1.5 text-term-text">
                        {s.subscription ? (
                          <span className="text-term-cyan">★ {s.subscriptionHolder ?? t("subs.unnamed")}</span>
                        ) : (
                          <span className="inline-flex items-center gap-1.5">
                            {s.identity}
                            {closedInGrace && (
                              <span
                                className="rounded border border-term-amber/60 px-1 text-[0.5625rem] uppercase tracking-wider tabular-nums text-term-amber"
                                title={t("booth.exitedGraceTitle")}
                              >
                                {graceLeft ? t("booth.exitedGraceLeft", { time: graceLeft }) : t("booth.exitedGrace")}
                              </span>
                            )}
                          </span>
                        )}
                      </td>
                      <td className="px-2 py-1.5">
                        {s.plate && (
                          <span
                            className="rounded border border-term-border px-1 font-semibold tracking-wide text-term-amber"
                            title={t("booth.plateTitle")}
                          >
                            {s.plate}
                          </span>
                        )}
                      </td>
                      <td className="whitespace-nowrap px-2 py-1.5 text-term-muted">
                        {formatRelativeDateTime(s.enteredAt, t)}
                      </td>
                      <td className="whitespace-nowrap px-2 py-1.5 text-term-muted">
                        {/* Freeze the elapsed at the recorded exit for a closed-in-grace row. */}
                        {formatDuration(s.enteredAt, (closedInGrace ? s.exitedAt : null) ?? new Date().toISOString())}
                      </td>
                    </tr>
                  );
                })}
              </tbody>
            </table>
          )}
        </div>
      </div>
    </Panel>
  );
}