/** 中国星期名称 */
const WEEKDAY_CN = ["周日", "周一", "周二", "周三", "周四", "周五", "周六"] as const;

/** 中国时区 */
const TZ = "Asia/Shanghai";

/**
 * 获取中国时区下的日期数字（月、日、星期）
 * 无论服务器/客户端在何地，均返回中国公历
 */
function getChinaDateParts(): { year: number; month: number; day: number; weekday: number } {
  const now = new Date();
  const formatter = new Intl.DateTimeFormat("en-CA", {
    timeZone: TZ,
    year: "numeric",
    month: "numeric",
    day: "numeric",
    weekday: "short",
  });
  const parts = formatter.formatToParts(now);
  const get = (type: string) => parseInt(parts.find((p) => p.type === type)?.value ?? "0", 10);
  const weekdayStr = parts.find((p) => p.type === "weekday")?.value ?? "Sun";
  const weekdayMap: Record<string, number> = { Sun: 0, Mon: 1, Tue: 2, Wed: 3, Thu: 4, Fri: 5, Sat: 6 };
  return {
    year: get("year"),
    month: get("month"),
    day: get("day"),
    weekday: weekdayMap[weekdayStr] ?? 0,
  };
}

/**
 * 获取当前中国公历时间字符串，用于上传
 * 格式：YYYY-MM-DD HH:mm:ss（中国时区）
 */
export function getNowChinaStr(): string {
  const formatter = new Intl.DateTimeFormat("en-CA", {
    timeZone: TZ,
    year: "numeric",
    month: "2-digit",
    day: "2-digit",
    hour: "2-digit",
    minute: "2-digit",
    second: "2-digit",
    hour12: false,
  });
  const parts = formatter.formatToParts(new Date());
  const pad = (s: string) => s.padStart(2, "0");
  const get = (type: string) => parts.find((p) => p.type === type)?.value ?? "0";
  return `${get("year")}-${pad(get("month"))}-${pad(get("day"))} ${pad(get("hour"))}:${pad(get("minute"))}:${pad(get("second"))}`;
}

/**
 * 格式化为中文日期：M月D日 周X
 */
function formatDateCN(month: number, day: number, weekday: number): string {
  return `${month}月${day}日 ${WEEKDAY_CN[weekday]}`;
}

/**
 * 获取下一个周六、周日的日期（中国公历）
 * 使用 +08:00 显式构造，避免服务器/客户端时区影响
 */
export function getNextWeekendDates(): { saturday: string; sunday: string } {
  const { year, month, day, weekday } = getChinaDateParts();
  const pad = (n: number) => String(n).padStart(2, "0");
  const todayStr = `${year}-${pad(month)}-${pad(day)}T12:00:00+08:00`;
  const today = new Date(todayStr);

  const daysToSat = weekday === 0 ? 6 : weekday === 6 ? 0 : 6 - weekday;
  const saturday = new Date(today);
  saturday.setUTCDate(saturday.getUTCDate() + daysToSat);
  const sunday = new Date(saturday);
  sunday.setUTCDate(sunday.getUTCDate() + 1);

  return {
    saturday: formatDateCN(saturday.getUTCMonth() + 1, saturday.getUTCDate(), 6),
    sunday: formatDateCN(sunday.getUTCMonth() + 1, sunday.getUTCDate(), 0),
  };
}

/**
 * 获取中国公历本周一 00:00 至周日 23:59:59 的 UTC 时间范围
 * 用于 PocketBase created 过滤。PocketBase 要求 Y-m-d H:i:s.uZ 格式（空格非 T）
 */
export function getThisWeekRangeISO(): { start: string; end: string } {
  const { year, month, day, weekday } = getChinaDateParts();
  const pad = (n: number) => String(n).padStart(2, "0");
  const todayStr = `${year}-${pad(month)}-${pad(day)}T12:00:00+08:00`;
  const today = new Date(todayStr);
  const daysToMonday = weekday === 0 ? 6 : weekday - 1;
  const monday = new Date(today);
  monday.setUTCDate(monday.getUTCDate() - daysToMonday);
  const sunday = new Date(monday);
  sunday.setUTCDate(sunday.getUTCDate() + 6);
  const mondayStr = `${monday.getUTCFullYear()}-${pad(monday.getUTCMonth() + 1)}-${pad(monday.getUTCDate())}T00:00:00+08:00`;
  const sundayStr = `${sunday.getUTCFullYear()}-${pad(sunday.getUTCMonth() + 1)}-${pad(sunday.getUTCDate())}T23:59:59.999+08:00`;
  const startDate = new Date(mondayStr);
  const endDate = new Date(sundayStr);
  const fmt = (d: Date, ms: string) => {
    const y = d.getUTCFullYear();
    const m = pad(d.getUTCMonth() + 1);
    const day = pad(d.getUTCDate());
    const h = pad(d.getUTCHours());
    const min = pad(d.getUTCMinutes());
    const s = pad(d.getUTCSeconds());
    return `${y}-${m}-${day} ${h}:${min}:${s}.${ms}Z`;
  };
  return {
    start: fmt(startDate, "000"),
    end: fmt(endDate, "999"),
  };
}

/**
 * 获取中国公历本周一、周日的日期字符串（YYYY-MM-DD），用于 submitted_at_cn 过滤
 */
export function getThisWeekRangeChinaStr(): { start: string; end: string } {
  const { year, month, day, weekday } = getChinaDateParts();
  const pad = (n: number) => String(n).padStart(2, "0");
  const todayStr = `${year}-${pad(month)}-${pad(day)}T12:00:00+08:00`;
  const today = new Date(todayStr);
  const daysToMonday = weekday === 0 ? 6 : weekday - 1;
  const monday = new Date(today);
  monday.setUTCDate(monday.getUTCDate() - daysToMonday);
  const sunday = new Date(monday);
  sunday.setUTCDate(sunday.getUTCDate() + 6);
  return {
    start: `${monday.getUTCFullYear()}-${pad(monday.getUTCMonth() + 1)}-${pad(monday.getUTCDate())} 00:00:00`,
    end: `${sunday.getUTCFullYear()}-${pad(sunday.getUTCMonth() + 1)}-${pad(sunday.getUTCDate())} 23:59:59`,
  };
}