/**
 * 到期预警计算工具
 *
 * 各业务模块的预警阈值不同：
 *   车辆年检/保险、房屋租赁合同、设备校准、报表有效期 → 30 天
 *   宽带与通信下次缴费 → 15 天
 *   销售台账合同原件约定回传日期 → 提前 N 天（由项目管理配置决定）
 * 统一用 warnDays 传入，避免各页面各写一套日期差逻辑。
 */

const MS_PER_DAY = 24 * 60 * 60 * 1000;

/**
 * 解析后端返回的日期，兼容时间戳 / Date / 'YYYY-MM-DD' / 'YYYY/MM/DD' / 'YYYY-MM-DD HH:mm:ss'
 */
export function parseDate(value) {
  if (value === undefined || value === null || value === "") return null;
  if (value instanceof Date) {
    return Number.isNaN(value.getTime()) ? null : new Date(value.getTime());
  }
  if (typeof value === "number") {
    const d = new Date(value);
    return Number.isNaN(d.getTime()) ? null : d;
  }
  const matched = String(value)
    .trim()
    .replace(/\//g, "-")
    .replace("T", " ")
    .match(/^(\d{4})-(\d{1,2})-(\d{1,2})/);
  if (!matched) return null;
  const date = new Date(
    Number(matched[1]),
    Number(matched[2]) - 1,
    Number(matched[3])
  );
  return Number.isNaN(date.getTime()) ? null : date;
}

/**
 * 距离到期日的剩余天数
 * 正数=还有 N 天，0=今天到期，负数=已逾期 N 天，无法解析返回 null
 */
export function remainDays(dateStr) {
  const target = parseDate(dateStr);
  if (!target) return null;
  const today = new Date();
  today.setHours(0, 0, 0, 0);
  target.setHours(0, 0, 0, 0);
  return Math.round((target.getTime() - today.getTime()) / MS_PER_DAY);
}

/**
 * 预警级别：overdue 已逾期 / warning 即将到期 / normal 正常 / none 无日期
 */
export function warnLevel(dateStr, warnDays = 30) {
  const days = remainDays(dateStr);
  if (days === null) return "none";
  if (days < 0) return "overdue";
  if (days <= warnDays) return "warning";
  return "normal";
}

export function warnColor(level) {
  const colors = {
    overdue: "#f56c6c",
    warning: "#ff9900",
    normal: "#19be6b",
    none: "#909399",
  };
  return colors[level] || colors.none;
}

export function warnText(level, days) {
  if (level === "overdue") return `已逾期${Math.abs(days)}天`;
  if (level === "warning") return days === 0 ? "今天到期" : `即将到期(${days}天)`;
  if (level === "normal") return "正常";
  return "";
}

/**
 * 一次拿到渲染预警标记所需的全部信息
 * @returns {{days: number|null, level: string, color: string, text: string}}
 */
export function getWarnInfo(dateStr, warnDays = 30) {
  const days = remainDays(dateStr);
  const level = warnLevel(dateStr, warnDays);
  return {
    days,
    level,
    color: warnColor(level),
    text: warnText(level, days),
  };
}

/**
 * 是否已逾期或即将到期（用于列表筛选、高亮）
 */
export function isExpiringSoon(dateStr, warnDays = 30) {
  const level = warnLevel(dateStr, warnDays);
  return level === "overdue" || level === "warning";
}

/**
 * 按天/月推算日期，用于"下次缴费日期 = 安装日期 + 缴费周期月"这类自动计算
 * @returns {string} 'YYYY-MM-DD'，无法计算返回 ''
 */
export function addMonths(dateStr, months) {
  const base = parseDate(dateStr);
  if (!base || !Number.isFinite(Number(months))) return "";
  const day = base.getDate();
  base.setDate(1);
  base.setMonth(base.getMonth() + Number(months));
  // 处理 1/31 + 1 月这类溢出，回退到当月最后一天
  const lastDay = new Date(base.getFullYear(), base.getMonth() + 1, 0).getDate();
  base.setDate(Math.min(day, lastDay));
  const pad = n => String(n).padStart(2, "0");
  return `${base.getFullYear()}-${pad(base.getMonth() + 1)}-${pad(base.getDate())}`;
}

/**
 * 生成 [start, end] 之间的月份列表（含首尾），用于房屋租赁的月度费用子表
 * @returns {string[]} ['2026-01', '2026-02', ...]
 */
export function monthRange(startStr, endStr) {
  const start = parseDate(startStr);
  const end = parseDate(endStr);
  if (!start || !end || end < start) return [];
  const months = [];
  const cursor = new Date(start.getFullYear(), start.getMonth(), 1);
  const last = new Date(end.getFullYear(), end.getMonth(), 1);
  while (cursor <= last && months.length < 600) {
    const pad = n => String(n).padStart(2, "0");
    months.push(`${cursor.getFullYear()}-${pad(cursor.getMonth() + 1)}`);
    cursor.setMonth(cursor.getMonth() + 1);
  }
  return months;
}