/**
 * 日期工具函数
 */

/**
 * 格式化日期
 * @param {Date} date - 日期对象
 * @param {String} format - 格式字符串，默认 'YYYY-MM-DD'
 * @returns {String} 格式化后的日期字符串
 */
function formatDate(date, format = 'YYYY-MM-DD') {
  if (!date) return ''
  
  const d = new Date(date)
  const year = d.getFullYear()
  const month = String(d.getMonth() + 1).padStart(2, '0')
  const day = String(d.getDate()).padStart(2, '0')
  const hour = String(d.getHours()).padStart(2, '0')
  const minute = String(d.getMinutes()).padStart(2, '0')
  const second = String(d.getSeconds()).padStart(2, '0')
  
  return format
    .replace('YYYY', year)
    .replace('MM', month)
    .replace('DD', day)
    .replace('HH', hour)
    .replace('mm', minute)
    .replace('ss', second)
}

/**
 * 计算距离今天还有多少天
 * @param {Date} targetDate - 目标日期
 * @returns {Number} 天数差
 */
function getDaysUntil(targetDate) {
  const today = new Date()
  today.setHours(0, 0, 0, 0)
  
  const target = new Date(targetDate)
  target.setHours(0, 0, 0, 0)
  
  const diff = target.getTime() - today.getTime()
  return Math.ceil(diff / (1000 * 60 * 60 * 24))
}

/**
 * 判断是否是今天
 */
function isToday(date) {
  return getDaysUntil(date) === 0
}

/**
 * 判断是否已过期
 */
function isPast(date) {
  return getDaysUntil(date) < 0
}

/**
 * 判断是否即将到来
 */
function isUpcoming(date) {
  const days = getDaysUntil(date)
  return days > 0 && days <= 7
}

/**
 * 获取星期几
 */
function getWeekDay(date) {
  const weekdays = ['日', '一', '二', '三', '四', '五', '六']
  const d = new Date(date)
  return weekdays[d.getDay()]
}

/**
 * 判断是否在本月
 */
function isInThisMonth(date) {
  const today = new Date()
  const target = new Date(date)
  return today.getFullYear() === target.getFullYear() && 
         today.getMonth() === target.getMonth()
}

/**
 * 获取本月的开始日期和结束日期
 */
function getMonthRange(year, month) {
  const start = new Date(year, month - 1, 1)
  const end = new Date(year, month, 0)
  return { start, end }
}

/**
 * 获取日期对象（从YYYY-MM-DD字符串）
 */
function parseDate(dateString) {
  if (!dateString) return null
  const parts = dateString.split('-')
  return new Date(parseInt(parts[0]), parseInt(parts[1]) - 1, parseInt(parts[2]))
}

module.exports = {
  formatDate,
  getDaysUntil,
  isToday,
  isPast,
  isUpcoming,
  getWeekDay,
  isInThisMonth,
  getMonthRange,
  parseDate
}