"use client";

import { useEffect, useState, useSyncExternalStore } from "react";

import { Button } from "@/components/ui";
import { haptic } from "@/lib/haptics";
import { localeHeader, useI18n } from "@/lib/i18n";
import { authHeaders, saveSettings, settingsStore } from "@/lib/settings";

const GOALS = [10, 20, 30, 50];

type PushStatus = { enabled: boolean; publicKey?: string };

function urlBase64ToUint8Array(base64: string): Uint8Array {
  const padding = "=".repeat((4 - (base64.length % 4)) % 4);
  const normalized = (base64 + padding).replace(/-/g, "+").replace(/_/g, "/");
  const raw = atob(normalized);
  const bytes = new Uint8Array(raw.length);
  for (let index = 0; index < raw.length; index++) bytes[index] = raw.charCodeAt(index);
  return bytes;
}

/**
 * Settings → Learning: the daily goal, plus push reminders — but only when
 * the server has VAPID keys configured. Without them the reminder block is
 * hidden completely, exactly as if the feature did not exist.
 */
export function LearningSection() {
  const { t } = useI18n();
  const dailyGoal = useSyncExternalStore(
    settingsStore.subscribe,
    () => settingsStore.getSnapshot().dailyGoal,
    () => 20,
  );
  const [status, setStatus] = useState<PushStatus | null>(null);
  const [subscribed, setSubscribed] = useState(false);
  const [endpoint, setEndpoint] = useState<string | null>(null);
  const [busy, setBusy] = useState(false);
  const [notice, setNotice] = useState<string | null>(null);

  const pushSupported =
    typeof window !== "undefined" &&
    "serviceWorker" in navigator &&
    "PushManager" in window &&
    "Notification" in window;

  useEffect(() => {
    if (!pushSupported) return;
    let cancelled = false;
    void (async () => {
      try {
        const response = await fetch("/api/push", {
          headers: { ...authHeaders(), ...localeHeader() },
          cache: "no-store",
        });
        const body = (await response.json()) as PushStatus;
        if (cancelled) return;
        setStatus(body);
        if (body.enabled) {
          const registration = await navigator.serviceWorker.ready.catch(() => null);
          const subscription = await registration?.pushManager.getSubscription();
          if (!cancelled && subscription) {
            setSubscribed(true);
            setEndpoint(subscription.endpoint);
          }
        }
      } catch {
        if (!cancelled) setStatus({ enabled: false });
      }
    })();
    return () => {
      cancelled = true;
    };
  }, [pushSupported]);

  const enable = async () => {
    if (!status?.publicKey) return;
    setBusy(true);
    setNotice(null);
    try {
      const permission = await Notification.requestPermission();
      if (permission !== "granted") {
        setNotice(t("settings.reminderDenied"));
        return;
      }
      const registration = await navigator.serviceWorker.ready;
      const subscription = await registration.pushManager.subscribe({
        userVisibleOnly: true,
        applicationServerKey: urlBase64ToUint8Array(status.publicKey) as unknown as BufferSource,
      });
      const response = await fetch("/api/push", {
        method: "POST",
        headers: { "Content-Type": "application/json", ...authHeaders(), ...localeHeader() },
        body: JSON.stringify(subscription.toJSON()),
      });
      if (!response.ok) throw new Error("subscribe failed");
      setSubscribed(true);
      setEndpoint(subscription.endpoint);
      setNotice(t("settings.reminderOn"));
      haptic("toggle");
    } catch {
      setNotice(t("settings.reminderError"));
    } finally {
      setBusy(false);
    }
  };

  const disable = async () => {
    setBusy(true);
    setNotice(null);
    try {
      const registration = await navigator.serviceWorker.ready.catch(() => null);
      const subscription = await registration?.pushManager.getSubscription();
      if (subscription) {
        await fetch(`/api/push?endpoint=${encodeURIComponent(subscription.endpoint)}`, {
          method: "DELETE",
          headers: { ...authHeaders(), ...localeHeader() },
        });
        await subscription.unsubscribe();
      }
      setSubscribed(false);
      setEndpoint(null);
      setNotice(t("settings.reminderOff"));
    } catch {
      setNotice(t("settings.reminderError"));
    } finally {
      setBusy(false);
    }
  };

  const test = async () => {
    if (!endpoint) return;
    setBusy(true);
    setNotice(null);
    try {
      const response = await fetch("/api/push/test", {
        method: "POST",
        headers: { "Content-Type": "application/json", ...authHeaders(), ...localeHeader() },
        body: JSON.stringify({ endpoint }),
      });
      if (!response.ok) throw new Error("test failed");
      setNotice(t("settings.reminderOn"));
    } catch {
      setNotice(t("settings.reminderError"));
    } finally {
      setBusy(false);
    }
  };

  const iosNeedsInstall =
    typeof navigator !== "undefined" &&
    /iPhone|iPad|iPod/.test(navigator.userAgent) &&
    !(navigator as Navigator & { standalone?: boolean }).standalone;

  return (
    <section className="mb-4 space-y-3 rounded-2xl border border-[var(--hairline)] bg-[var(--surface-sunken)] p-3">
      <h3 className="text-sm font-semibold text-frost-950 dark:text-frost-50">{t("settings.learning")}</h3>

      <div className="space-y-1.5">
        <p className="text-[12px] font-semibold text-[var(--text)]">{t("settings.dailyGoal")}</p>
        <p className="text-[11px] leading-snug text-[var(--text-subtle)]">{t("settings.dailyGoalNote")}</p>
        <div className="segmented" role="group" aria-label={t("settings.dailyGoal")}>
          {GOALS.map((goal) => (
            <button
              key={goal}
              type="button"
              aria-pressed={dailyGoal === goal}
              onClick={() => {
                haptic("toggle");
                saveSettings({ dailyGoal: goal });
              }}
            >
              <span className="seg-label">{goal}</span>
            </button>
          ))}
        </div>
      </div>

      {pushSupported && status?.enabled ? (
        <div className="space-y-2 border-t border-[var(--hairline-soft)] pt-2.5">
          <p className="text-[12px] font-semibold text-[var(--text)]">{t("settings.reminders")}</p>
          <p className="text-[11px] leading-snug text-[var(--text-subtle)]">{t("settings.remindersNote")}</p>
          {iosNeedsInstall ? (
            <p className="text-[11px] font-medium leading-snug text-amber-700 dark:text-amber-300">
              {t("settings.remindersIos")}
            </p>
          ) : null}
          <div className="flex flex-wrap gap-2">
            {subscribed ? (
              <>
                <Button size="sm" variant="secondary" loading={busy} onClick={() => void test()}>
                  {t("settings.reminderTest")}
                </Button>
                <Button size="sm" variant="ghost" loading={busy} onClick={() => void disable()}>
                  {t("settings.reminderDisable")}
                </Button>
              </>
            ) : (
              <Button size="sm" loading={busy} onClick={() => void enable()}>
                {t("settings.reminderEnable")}
              </Button>
            )}
          </div>
          {notice ? <p className="text-[12px] font-medium text-[var(--text-muted)]">{notice}</p> : null}
        </div>
      ) : null}
    </section>
  );
}