import { loadUiPrefs } from "./i18n/prefs";
import { translate } from "./i18n/messages";
import type { AppLocale } from "./i18n/types";

/** Unix nanoseconds (UTC), matching product contract. */
export function nowUnixNano(): number {
  return Date.now() * 1_000_000;
}

function currentLocale(): AppLocale {
  return loadUiPrefs().locale;
}

function t(key: string, params?: Record<string, string | number>): string {
  return translate(currentLocale(), key, params);
}

/** 後端可能回 ns／ms／sec；統一成 unix nanoseconds（顯示用，毫秒精度即可） */
export function normalizeUnixNano(raw: number | string | null | undefined): number | null {
  if (raw === null || raw === undefined || raw === "") return null;
  let n: number;
  if (typeof raw === "string") {
    const trimmed = raw.trim();
    if (!trimmed) return null;
    // 大整數字串：用 BigInt 收到毫秒再還原 ns，避免 Number 精準度問題
    try {
      const bi = BigInt(trimmed);
      if (bi <= 0n) return null;
      // sec ~1e9, ms ~1e12, ns ~1e18
      if (bi < 1_000_000_000_000n) return Number(bi) * 1_000_000_000; // sec
      if (bi < 1_000_000_000_000_000n) return Number(bi) * 1_000_000; // ms
      return Number(bi / 1_000_000n) * 1_000_000; // ns → ms 精度
    } catch {
      n = Number(trimmed);
    }
  } else {
    n = raw;
  }
  if (!Number.isFinite(n) || n <= 0) return null;
  if (n < 1e12) return Math.round(n * 1e9); // seconds
  if (n < 1e15) return Math.round(n * 1e6); // milliseconds
  return n; // nanoseconds
}

export function formatLocalDateTime(nano: number | null | undefined): string {
  const n = normalizeUnixNano(nano ?? null);
  if (!n) return "—";
  const ms = Math.floor(n / 1_000_000);
  const locale = currentLocale() === "en" ? "en-US" : "zh-TW";
  return new Date(ms).toLocaleString(locale, {
    year: "numeric",
    month: "2-digit",
    day: "2-digit",
    hour: "2-digit",
    minute: "2-digit",
  });
}

export type SessionExpiryKind = "unknown" | "ok" | "soon" | "expired";

/** soon = 48h 內到期 */
export function sessionExpiryKind(
  expiresAt: number | null | undefined,
  now = nowUnixNano(),
): SessionExpiryKind {
  const exp = normalizeUnixNano(expiresAt ?? null);
  if (exp == null || exp <= 0) return "unknown";
  if (exp <= now) return "expired";
  const soonNs = 48 * 60 * 60 * 1_000_000_000;
  if (exp - now <= soonNs) return "soon";
  return "ok";
}

export function formatRelativeFromNow(
  nano: number | null | undefined,
  now = nowUnixNano(),
): string {
  const n = normalizeUnixNano(nano ?? null);
  if (n == null || n <= 0) return "—";
  const diffMs = Math.floor((n - now) / 1_000_000);
  const abs = Math.abs(diffMs);
  const min = Math.round(abs / 60_000);
  const hour = Math.round(abs / 3_600_000);
  const day = Math.round(abs / 86_400_000);
  let span: string;
  if (min < 60) span = t("time.min", { n: Math.max(1, min) });
  else if (hour < 48) span = t("time.hour", { n: hour });
  else span = t("time.day", { n: day });
  if (diffMs < 0) return t("time.expired", { span });
  return t("time.remaining", { span });
}

/** 過去時間：通知列表用（剛剛／N 分前） */
export function formatTimeAgo(nano: number | null | undefined, now = nowUnixNano()): string {
  // 這裡是唯一漏掉正規化的時間格式化函式：後端若回秒或毫秒，未換算的數值會遠小於 now，
  // 算出來就變成「56 年前」。
  const n = normalizeUnixNano(nano ?? null);
  if (n == null || n <= 0) return "—";
  const diffMs = Math.floor((now - n) / 1_000_000);
  if (diffMs < 45_000) return t("time.justNow");
  const min = Math.floor(diffMs / 60_000);
  if (min < 60) return t("time.minAgo", { n: min });
  const hour = Math.floor(diffMs / 3_600_000);
  if (hour < 48) return t("time.hourAgo", { n: hour });
  const day = Math.floor(diffMs / 86_400_000);
  if (day < 14) return t("time.dayAgo", { n: day });
  return formatLocalDateTime(nano);
}

export function formatSessionExpiry(expiresAt: number | null | undefined): {
  kind: SessionExpiryKind;
  absolute: string;
  relative: string;
  label: string;
} {
  const exp = normalizeUnixNano(expiresAt ?? null);
  const kind = sessionExpiryKind(exp);
  const absolute = formatLocalDateTime(exp);
  const relative = formatRelativeFromNow(exp);
  const label =
    kind === "unknown"
      ? t("time.sessionUnknown")
      : kind === "expired"
        ? t("time.sessionExpired", { absolute })
        : kind === "soon"
          ? t("time.sessionSoon", { relative, absolute })
          : t("time.sessionOk", { relative, absolute });
  return { kind, absolute, relative, label };
}

export function fromDatetimeLocalValue(value: string): number {
  if (!value) return nowUnixNano();
  const ms = new Date(value).getTime();
  if (Number.isNaN(ms)) return nowUnixNano();
  return ms * 1_000_000;
}

export function toDatetimeLocalValue(nano: number | null | undefined): string {
  if (!nano) return "";
  const d = new Date(Math.floor(nano / 1_000_000));
  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())}`;
}