import { useEffect, useState } from "react";
import { useTranslation } from "react-i18next";
import {
  ApiError,
  createTariffDraft,
  deleteTariffDraft,
  fetchTariff,
  fetchTariffDrafts,
  publishTariffVersion,
  simulateTariff,
  updateTariffDraft,
  type SimulateResult,
  type TariffDraft,
  type TariffState,
} from "./api.js";
import { TariffEditorForm, emptyForm, formFromActive, formFromVersion, toStructure, type FormState } from "./TariffEditorForm.js";
import { Modal } from "./ui/Modal.js";
import { formatClock, formatDateTime, formatMoney, formatDuration } from "./lib/format.js";
import type { FeeBreakdown } from "@parking/shared";
import type { TFunction } from "i18next";

// The TARIFF LAB — a sandbox for composing + pricing EXPERIMENTAL rate cards. Drafts
// live in their own mutable table (tariff_drafts), so experimenting never churns the
// immutable published versions or risks a half-baked card going live: the admin
// composes a draft in the modal (the same form the composer page uses), simulates
// hypothetical stays against it (entry + exit, nothing else), and only when satisfied
// PUBLISHES it through the normal immutable-version path. Pricing uses the SAME
// `priceSession` the booth uses (server-side), so the lab and the live booth can
// never diverge. No ledger writes. See wiki/concepts/tariff.md.

/** <input type="datetime-local"> wants "YYYY-MM-DDTHH:mm" in LOCAL time. */
function toLocalInput(iso: string): string {
  const d = new Date(iso);
  if (Number.isNaN(d.getTime())) return "";
  const pad = (n: number) => String(n).padStart(2, "0");
  return `${d.getFullYear()}-${pad(d.getMonth() + 1)}-${pad(d.getDate())}T${pad(d.getHours())}:${pad(d.getMinutes())}`;
}
/** A local datetime-local value → ISO-8601 (treats the value as local wall-clock). */
function fromLocalInput(v: string): string {
  const d = new Date(v);
  return Number.isNaN(d.getTime()) ? "" : d.toISOString();
}
function nowLocal(): string {
  return toLocalInput(new Date().toISOString());
}

/** What the simulation runs against: the live card, a historical published
 *  version, or one lab draft. */
type Selection = { kind: "active" } | { kind: "version"; id: string } | { kind: "draft"; id: string };

/** Modal state: a draft being composed (id null = not yet saved). */
interface DraftEdit {
  id: string | null;
  name: string;
  form: FormState;
}

export function TariffLab() {
  const { t } = useTranslation();
  const [state, setState] = useState<TariffState | null>(null);
  const [drafts, setDrafts] = useState<TariffDraft[]>([]);
  const [selected, setSelected] = useState<Selection>({ kind: "active" });
  const [err, setErr] = useState<string | null>(null);
  const [notice, setNotice] = useState<string | null>(null);

  // The hypothetical stay: entry + exit, nothing else.
  const [entered, setEntered] = useState<string>(() => {
    const d = new Date();
    d.setHours(d.getHours() - 3); // default: a 3h-ago entry
    return toLocalInput(d.toISOString());
  });
  const [exit, setExit] = useState<string>(nowLocal);

  const [result, setResult] = useState<SimulateResult | null>(null);
  const [busy, setBusy] = useState(false);

  // The draft-composer modal.
  const [edit, setEdit] = useState<DraftEdit | null>(null);
  const [saving, setSaving] = useState(false);
  const [editErr, setEditErr] = useState<string | null>(null);

  async function refresh() {
    const [s, d] = await Promise.all([fetchTariff(), fetchTariffDrafts()]);
    setState(s);
    setDrafts(d.drafts);
    return d.drafts;
  }
  useEffect(() => {
    refresh().catch((e) => setErr((e as Error).message));
  }, []);

  const selectedDraft = selected.kind === "draft" ? drafts.find((d) => d.id === selected.id) ?? null : null;
  const selectedVersion =
    selected.kind === "version" ? state?.versions.find((v) => v.id === selected.id) ?? null : null;

  function select(sel: Selection) {
    setSelected(sel);
    setResult(null); // a stale price against another card would mislead
    setErr(null);
    setNotice(null);
  }

  async function run() {
    setErr(null);
    setBusy(true);
    try {
      const r = await simulateTariff({
        enteredAt: fromLocalInput(entered),
        asOf: fromLocalInput(exit),
        // A draft carries its own structure+currency; a historical version is
        // referenced by id; otherwise the ACTIVE version.
        ...(selectedDraft
          ? { structure: selectedDraft.structure, currency: selectedDraft.currency }
          : selectedVersion
            ? { tariffVersionId: selectedVersion.id }
            : {}),
      });
      setResult(r);
    } catch (e) {
      setErr((e as Error).message);
      setResult(null);
    } finally {
      setBusy(false);
    }
  }

  // --- draft actions ---
  function newDraft() {
    // Start from the live card when there is one — the admin usually experiments
    // with a variation of today's prices, not from a blank slate.
    const form = state?.active ? formFromActive(state) : emptyForm();
    setEditErr(null);
    setEdit({ id: null, name: "", form });
  }
  function editDraft(d: TariffDraft) {
    setEditErr(null);
    setEdit({ id: d.id, name: d.name, form: formFromVersion(d.currency, d.structure) });
  }

  async function saveDraft() {
    if (!edit) return;
    setSaving(true);
    setEditErr(null);
    try {
      const body = {
        name: edit.name.trim(),
        currency: edit.form.currency.trim().toUpperCase(),
        structure: toStructure(edit.form),
      };
      const saved = edit.id ? await updateTariffDraft(edit.id, body) : await createTariffDraft(body);
      await refresh();
      setEdit(null);
      select({ kind: "draft", id: saved.id });
    } catch (e) {
      const text =
        e instanceof ApiError && e.problems?.length ? `${e.message}: ${e.problems.join("; ")}` : (e as Error).message;
      setEditErr(text);
    } finally {
      setSaving(false);
    }
  }

  async function removeDraft(d: TariffDraft) {
    if (!confirm(t("lab.confirmDelete", { name: d.name }))) return;
    setErr(null);
    try {
      await deleteTariffDraft(d.id);
      await refresh();
      select({ kind: "active" });
    } catch (e) {
      setErr((e as Error).message);
    }
  }

  async function publishDraft(d: TariffDraft) {
    if (!confirm(t("lab.confirmPublish", { name: d.name }))) return;
    setErr(null);
    setNotice(null);
    try {
      // The draft's name rides along onto the immutable version.
      await publishTariffVersion({ currency: d.currency, structure: d.structure, name: d.name });
      await refresh();
      setNotice(t("tariff.publishedOk"));
    } catch (e) {
      const text =
        e instanceof ApiError && e.problems?.length ? `${e.message}: ${e.problems.join("; ")}` : (e as Error).message;
      setErr(text);
    }
  }

  const currency = result?.currency ?? selectedDraft?.currency ?? selectedVersion?.currency ?? state?.active?.currency ?? "ALL";

  return (
    <section className="px-4 py-6">
      <h2 className="mb-1 text-h4 font-semibold text-term-text">{t("lab.title")}</h2>
      <p className="hint mb-4">{t("lab.intro")}</p>

      <div className="flex flex-col gap-4 lg:flex-row">
        {/* Main: the hypothetical stay + result, priced against the selection. */}
        <div className="min-w-0 flex-1">
          {/* What we're pricing against + draft actions. */}
          <div className="mb-3 flex flex-wrap items-center gap-2">
            <span className="rounded bg-term-panel-2 px-2 py-1 text-[0.75rem] text-term-cyan">
              {selectedDraft
                ? selectedDraft.name
                : selectedVersion
                  ? selectedVersion.name ?? formatDateTime(selectedVersion.effectiveFrom, t)
                  : t("lab.activeTariff")}
            </span>
            {selectedDraft && (
              <>
                <button type="button" className="btn btn-sm" onClick={() => editDraft(selectedDraft)}>
                  {t("lab.edit")}
                </button>
                <button type="button" className="btn btn-sm" onClick={() => publishDraft(selectedDraft)}>
                  {t("lab.publish")}
                </button>
                <button type="button" className="btn btn-danger btn-sm" onClick={() => removeDraft(selectedDraft)}>
                  {t("lab.delete")}
                </button>
              </>
            )}
            {notice && <span className="text-[0.75rem] text-term-green">{notice}</span>}
          </div>

          <div className="card card-body grid grid-cols-[max-content_1fr] items-center gap-x-4 gap-y-2">
            <label className="label">{t("lab.entered")}</label>
            <input type="datetime-local" className="input w-64" value={entered} onChange={(e) => setEntered(e.target.value)} />

            <label className="label">{t("lab.exit")}</label>
            <span className="flex items-center gap-2">
              <input type="datetime-local" className="input w-64" value={exit} onChange={(e) => setExit(e.target.value)} />
              <button type="button" className="btn btn-sm" onClick={() => setExit(nowLocal())}>
                {t("lab.now")}
              </button>
            </span>
          </div>

          <div className="mt-4 flex items-center gap-3">
            <button type="button" className="btn btn-primary btn-lg" onClick={run} disabled={busy}>
              {busy ? t("lab.pricing") : t("lab.price")}
            </button>
            {err && <span className="text-[0.75rem] text-term-red">{err}</span>}
          </div>

          {result && (
            <div className="mt-6 grid gap-4 md:grid-cols-2">
              {/* Outcome */}
              <div className="card card-body">
                <h3 className="mb-2 text-h6 font-semibold uppercase tracking-wider text-term-text">{t("lab.outcome")}</h3>
                <dl className="grid grid-cols-[max-content_1fr] gap-x-4 gap-y-1 text-[0.8125rem]">
                  <dt className="text-term-muted">{t("lab.amountDue")}</dt>
                  <dd className="text-2xl font-bold text-term-cyan">{formatMoney(result.pricing.amountMinor, currency)}</dd>
                  <dt className="text-term-muted">{t("lab.billedPeriod")}</dt>
                  <dd className="text-term-text">
                    {formatDuration(result.pricing.periodStart, fromLocalInput(exit))}
                    {result.pricing.overstay && (
                      <span className="ml-2 rounded bg-term-red/15 px-1.5 py-0.5 text-[0.625rem] uppercase text-term-red">
                        {t("lab.overstay")}
                      </span>
                    )}
                    {result.pricing.withinGrace && (
                      <span className="ml-2 rounded bg-term-green/15 px-1.5 py-0.5 text-[0.625rem] uppercase text-term-green">
                        {t("lab.settled")}
                      </span>
                    )}
                  </dd>
                  <dt className="text-term-muted">{t("lab.periodStart")}</dt>
                  <dd className="text-term-text">{formatDateTime(result.pricing.periodStart, t)}</dd>
                  {result.pricing.graceExpiresAt && (
                    <>
                      <dt className="text-term-muted">{t("lab.graceExpires")}</dt>
                      <dd className="text-term-text">{formatDateTime(result.pricing.graceExpiresAt, t)}</dd>
                    </>
                  )}
                </dl>
                {/* HOW the sum is produced — line items from the SAME engine walk
                    (their sum is the amount by construction). */}
                {result.breakdown && (
                  <BreakdownTable b={result.breakdown} periodStart={result.pricing.periodStart} currency={currency} t={t} />
                )}
              </div>

              {/* Duration curve from entry — see where the cap flattens / windows shift. */}
              <div className="card card-body">
                <h3 className="mb-2 text-h6 font-semibold uppercase tracking-wider text-term-text">{t("lab.curve")}</h3>
                <p className="hint mb-2">{t("lab.curveHint")}</p>
                <table className="w-full text-[0.75rem] tabular-nums">
                  <tbody>
                    {result.curve.map((c) => (
                      <tr key={c.minutes} className="border-b border-term-border/40">
                        <td className="py-0.5 text-term-muted">{labelMin(c.minutes)}</td>
                        <td className="py-0.5 text-right text-term-text">{formatMoney(c.amountMinor, currency)}</td>
                      </tr>
                    ))}
                  </tbody>
                </table>
              </div>
            </div>
          )}
        </div>

        {/* Sidebar: lab drafts + the full published history; click any to price
            against it. */}
        <aside className="w-full shrink-0 lg:w-72">
          <div className="mb-2 flex items-center justify-between">
            <h3 className="text-h6 font-semibold uppercase tracking-wider text-term-text">{t("lab.drafts")}</h3>
            <button type="button" className="btn btn-sm" onClick={newDraft}>
              {t("lab.newDraft")}
            </button>
          </div>
          <ul className="flex flex-col gap-1">
            {drafts.map((d) => (
              <li key={d.id}>
                <button
                  type="button"
                  onClick={() => select({ kind: "draft", id: d.id })}
                  className={`w-full rounded-term border px-3 py-2 text-left text-[0.8125rem] ${
                    selected.kind === "draft" && selected.id === d.id
                      ? "border-term-amber bg-term-amber/10 text-term-text"
                      : "border-term-border text-term-muted hover:text-term-text"
                  }`}
                >
                  <span className="block font-semibold">{d.name}</span>
                  <span className="block text-[0.6875rem] text-term-muted">
                    {d.currency} · {formatDateTime(d.updatedAt, t)}
                  </span>
                </button>
              </li>
            ))}
            {drafts.length === 0 && <li className="hint px-1 py-2">{t("lab.noDrafts")}</li>}
          </ul>

          {/* Published versions: the active card first, then the immutable history
              (older versions still price past sessions — see wiki/concepts/tariff.md). */}
          <h3 className="mb-2 mt-5 text-h6 font-semibold uppercase tracking-wider text-term-text">
            {t("lab.published")}
          </h3>
          <ul className="flex flex-col gap-1">
            <li>
              <button
                type="button"
                onClick={() => select({ kind: "active" })}
                className={`w-full rounded-term border px-3 py-2 text-left text-[0.8125rem] ${
                  selected.kind === "active"
                    ? "border-term-amber bg-term-amber/10 text-term-text"
                    : "border-term-border text-term-muted hover:text-term-text"
                }`}
              >
                <span className="block font-semibold">
                  {t("lab.activeTariff")}
                  {state?.active?.name ? ` — ${state.active.name}` : ""}
                </span>
                <span className="block text-[0.6875rem] text-term-muted">
                  {state?.active ? formatDateTime(state.active.effectiveFrom, t) : t("tariff.noRateCard")}
                </span>
              </button>
            </li>
            {state?.versions
              .filter((v) => v.id !== state.active?.id)
              .map((v) => (
                <li key={v.id}>
                  <button
                    type="button"
                    onClick={() => select({ kind: "version", id: v.id })}
                    className={`w-full rounded-term border px-3 py-2 text-left text-[0.8125rem] ${
                      selected.kind === "version" && selected.id === v.id
                        ? "border-term-amber bg-term-amber/10 text-term-text"
                        : "border-term-border text-term-muted hover:text-term-text"
                    }`}
                  >
                    <span className="block font-semibold">
                      {v.name ?? formatDateTime(v.effectiveFrom, t)}
                    </span>
                    <span className="block text-[0.6875rem] text-term-muted">
                      {v.name ? `${formatDateTime(v.effectiveFrom, t)} · ` : ""}
                      {v.currency}
                    </span>
                  </button>
                </li>
              ))}
          </ul>
        </aside>
      </div>

      {/* The draft composer — the SAME form the /setup/tariff page uses, in a modal. */}
      <Modal
        open={edit != null}
        onClose={() => setEdit(null)}
        title={edit?.id ? t("lab.editDraftTitle") : t("lab.newDraftTitle")}
        width="max-w-3xl"
      >
        {edit && (
          <div>
            <div className="mb-4 flex items-center gap-2">
              <label className="label">{t("lab.draftName")}</label>
              <input
                className="input w-72"
                value={edit.name}
                onChange={(e) => setEdit((d) => (d ? { ...d, name: e.target.value } : d))}
                placeholder={t("lab.draftNamePh")}
              />
            </div>
            <TariffEditorForm
              form={edit.form}
              onChange={(update) => setEdit((d) => (d ? { ...d, form: update(d.form) } : d))}
            />
            <div className="mt-6 flex items-center gap-3">
              <button type="button" className="btn btn-primary" onClick={saveDraft} disabled={saving || !edit.name.trim()}>
                {saving ? t("lab.savingDraft") : t("lab.saveDraft")}
              </button>
              {editErr && <span className="text-[0.75rem] text-term-red">{editErr}</span>}
            </div>
          </div>
        )}
      </Modal>
    </section>
  );
}

function labelMin(min: number): string {
  if (min < 60) return `${min}m`;
  if (min < 1440) return `${min / 60}h`;
  return `${min / 1440}d`;
}

/** The fee's line items — every row states its time window / rule and its amount, so
 *  the operator can retrace the exact sum (caps show as negative adjustments). */
function BreakdownTable({
  b,
  periodStart,
  currency,
  t,
}: {
  b: FeeBreakdown;
  periodStart: string;
  currency: string;
  t: TFunction;
}) {
  const startMs = Date.parse(periodStart);
  const multiDay = b.billedMinutes > 1440;
  const at = (min: number) => {
    const iso = new Date(startMs + min * 60_000).toISOString();
    return multiDay ? formatDateTime(iso, t) : formatClock(iso);
  };
  const money = (m: number) => formatMoney(m, currency);
  const hours = (min: number) => (min % 60 === 0 ? `${min / 60}` : (min / 60).toFixed(1));

  return (
    <div className="mt-3 border-t border-term-border pt-2">
      <div className="mb-1 text-[0.6875rem] uppercase tracking-wider text-term-muted">{t("lab.bd.title")}</div>
      {b.billedMinutes > 0 && (
        <p className="hint mb-1.5">
          {t("lab.bd.rounding", { raw: b.rawMinutes, billed: b.billedMinutes, inc: b.incrementMin })}
        </p>
      )}
      <table className="w-full text-[0.75rem] tabular-nums">
        <tbody>
          {b.items.map((it, i) => {
            let label: string;
            let amount: number;
            let cls = "text-term-text";
            switch (it.kind) {
              case "grace":
                label = t("lab.bd.grace", { min: it.minutes });
                amount = 0;
                cls = "text-term-green";
                break;
              case "band":
                label = `${at(it.fromMin)}–${at(it.toMin)} · ${it.increments} × ${money(it.unitMinor)}${it.card ? ` · ${it.card}` : ""}`;
                amount = it.amountMinor;
                break;
              case "package":
                label = `${at(it.fromMin)} · ${it.card} — ${t("lab.bd.package")}`;
                amount = it.amountMinor;
                break;
              case "step":
                label = it.repeated
                  ? t("lab.bd.stepRepeated", { day: it.day })
                  : t("lab.bd.step", { day: it.day, hours: hours(it.uptoMin) });
                amount = it.amountMinor;
                break;
              case "cap":
                label = t("lab.bd.cap", { day: it.day, cap: money(it.capMinor) });
                amount = it.amountMinor;
                cls = "text-term-red";
                break;
            }
            return (
              <tr key={i} className="border-b border-term-border/40">
                <td className="py-0.5 pr-2 text-term-muted">{label}</td>
                <td className={`whitespace-nowrap py-0.5 text-right ${cls}`}>{money(amount)}</td>
              </tr>
            );
          })}
          <tr>
            <td className="py-1 pr-2 font-semibold text-term-text">{t("lab.bd.total")}</td>
            <td className="whitespace-nowrap py-1 text-right font-semibold text-term-cyan">{money(b.totalMinor)}</td>
          </tr>
        </tbody>
      </table>
    </div>
  );
}