import { useEffect, useState } from "react";
import { Link, Navigate, useNavigate, useSearchParams } from "react-router-dom";
import { useAuth } from "../auth/AuthContext";
import { PageHeader } from "../components/layout/PageHeader";
import { Button, Card, Input } from "../components/ui";
import { useRepos } from "../data/DataContext";
import { useI18n } from "../i18n/I18nContext";
import { getPlanRights, planCtaLabel } from "../lib/planRights";
import { PLANS, type PlanId } from "../lib/usageMeter";

function isPlanId(v: string | null): v is PlanId {
  return v === "free" || v === "starter" || v === "pro";
}

/**
 * 結帳：訂單摘要 + 權益 + 一鍵完成（mock 付款與生效合一）。
 */
export function PlanCheckoutPage() {
  const repos = useRepos();
  const { member } = useAuth();
  const { t, formatPlanPrice } = useI18n();
  const navigate = useNavigate();
  const [params] = useSearchParams();
  const planParam = params.get("plan");

  const planId: PlanId | null = isPlanId(planParam) ? planParam : null;
  const plan = planId ? PLANS[planId] : null;
  const rights = planId ? getPlanRights(planId, t) : null;

  const [currentId, setCurrentId] = useState<PlanId>("free");
  const [cardName, setCardName] = useState(member?.display_name || "");
  const [cardLast4, setCardLast4] = useState("4242");
  const [busy, setBusy] = useState(false);
  const [error, setError] = useState("");

  useEffect(() => {
    void repos.usage.getPlanId().then(setCurrentId);
  }, [repos.usage]);

  const free = plan?.price_twd === 0;
  const already = planId != null && currentId === planId;

  if (!member) return <Navigate to="/login" replace />;
  if (!plan || !planId || !rights) {
    return (
      <>
        <PageHeader title={t("checkout.title")} />
        <Card>
          <p className="text-muted" style={{ margin: 0 }}>
            {t("checkout.pickFirst")}
          </p>
          <div style={{ marginTop: "0.75rem" }}>
            <Link to="/app/usage/plans">
              <Button type="button">{t("checkout.viewPlans")}</Button>
            </Link>
          </div>
        </Card>
      </>
    );
  }

  async function submit() {
    if (!planId || already) return;
    setError("");
    if (!free) {
      const digits = cardLast4.replace(/\D/g, "");
      if (digits.length < 4) {
        setError(t("checkout.cardLast4Required"));
        return;
      }
      if (!cardName.trim()) {
        setError(t("checkout.cardNameRequired"));
        return;
      }
    }
    setBusy(true);
    try {
      await repos.usage.purchasePlan(planId, {
        mock_ref: free ? "free" : `****${cardLast4.replace(/\D/g, "").slice(-4)}`,
      });
      navigate("/app/usage", {
        replace: true,
        state: { purchaseOk: planId },
      });
    } catch (e) {
      setError(e instanceof Error ? e.message : t("checkout.fail"));
    } finally {
      setBusy(false);
    }
  }

  const actionLabel = free
    ? t("checkout.confirmFree")
    : t("checkout.payAndAction", {
        action: planCtaLabel(currentId, planId, t),
        price: formatPlanPrice(plan.price_twd),
      });

  return (
    <>
      <PageHeader title={t("checkout.title")} />

      {error ? (
        <p className="hb-form-error" role="alert">
          {error}
        </p>
      ) : null}

      <div className="hb-checkout">
        <div className="hb-checkout__main hb-stack">
          <Card>
            <div className="hb-checkout__order">
              <div>
                <p className="hb-usage-checkout__label">{t("checkout.subscribe")}</p>
                <p className="hb-usage-checkout__name">{plan.name}</p>
                <p
                  className="text-muted"
                  style={{ margin: "0.35rem 0 0", fontSize: "var(--hb-text-sm)" }}
                >
                  {rights.headline}
                </p>
              </div>
              <div className="hb-checkout__price-block">
                <p className="hb-checkout__big-price">
                  {formatPlanPrice(plan.price_twd)}
                  <span className="hb-checkout__period">{t("checkout.perMonth")}</span>
                </p>
                <p className="text-muted" style={{ margin: 0, fontSize: "var(--hb-text-sm)" }}>
                  {t("checkout.monthlyCredits", { n: plan.monthly_credits })}
                </p>
              </div>
            </div>

            <div className="hb-usage-checkout__rights">
              <section className="hb-usage-checkout__block">
                <h3 className="hb-usage-checkout__h">{t("checkout.youGet")}</h3>
                <ul className="hb-usage-checkout__list">
                  {rights.rights.map((line) => (
                    <li key={line}>{line}</li>
                  ))}
                </ul>
              </section>
              <section className="hb-usage-checkout__block">
                <h3 className="hb-usage-checkout__h">{t("checkout.quota")}</h3>
                <ul className="hb-usage-checkout__list">
                  {rights.quota.map((line) => (
                    <li key={line}>{line}</li>
                  ))}
                </ul>
              </section>
              <section className="hb-usage-checkout__block">
                <h3 className="hb-usage-checkout__h">{t("checkout.notes")}</h3>
                <ul className="hb-usage-checkout__list hb-usage-checkout__list--notes">
                  {rights.notes.map((line) => (
                    <li key={line}>{line}</li>
                  ))}
                </ul>
              </section>
            </div>
          </Card>

          {!free && !already ? (
            <Card>
              <div className="hb-stack">
                <Input
                  label={t("checkout.cardholder")}
                  value={cardName}
                  onChange={(e) => setCardName(e.target.value)}
                  autoComplete="cc-name"
                  disabled={busy}
                />
                <Input
                  label={t("checkout.cardLast4")}
                  value={cardLast4}
                  onChange={(e) => setCardLast4(e.target.value.replace(/\D/g, "").slice(0, 4))}
                  inputMode="numeric"
                  maxLength={4}
                  placeholder="4242"
                  disabled={busy}
                />
              </div>
            </Card>
          ) : null}
        </div>

        <aside className="hb-checkout__aside">
          <Card>
            <p className="hb-usage-checkout__label">{t("checkout.amountDue")}</p>
            <p className="hb-checkout__big-price">
              {formatPlanPrice(plan.price_twd)}
              <span className="hb-checkout__period">{t("checkout.perMonth")}</span>
            </p>
            <p className="text-muted" style={{ margin: "0.25rem 0 1rem", fontSize: "var(--hb-text-sm)" }}>
              {t("checkout.billedMonthly", { name: plan.name })}
            </p>
            {already ? (
              <p className="hb-banner-ok" style={{ margin: "0 0 0.75rem" }}>
                {t("checkout.already")}
              </p>
            ) : null}
            <Button type="button" disabled={busy || already} onClick={() => void submit()}>
              {busy
                ? t("checkout.processing")
                : already
                  ? t("checkout.currentPlan")
                  : actionLabel}
            </Button>
            <div className="hb-checkout__links">
              <Link to="/app/usage/plans">{t("checkout.pickOther")}</Link>
              <Link to="/app/usage">{t("checkout.cancel")}</Link>
            </div>
          </Card>
        </aside>
      </div>
    </>
  );
}