using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace CallCenter.Utility.Time
{
    public class DateTools
    {
        /// <summary>  
        /// 得到本周第一天(以星期天为第一天)  
        /// </summary>  
        /// <param name="datetime"></param>  
        /// <returns></returns>  
        public static DateTime GetWeekFirstDaySun(DateTime datetime)
        {
            //星期天为第一天  
            int weeknow = Convert.ToInt32(datetime.DayOfWeek);
            int daydiff = (-1) * weeknow;

            //本周第一天  
            string FirstDay = datetime.AddDays(daydiff).ToString("yyyy-MM-dd");
            return Convert.ToDateTime(FirstDay);
        }

        /// <summary>  
        /// 得到本周第一天(以星期一为第一天)  
        /// </summary>  
        /// <param name="datetime"></param>  
        /// <returns></returns>  
        public static DateTime GetWeekFirstDayMon(DateTime datetime)
        {
            //星期一为第一天  
            int weeknow = Convert.ToInt32(datetime.DayOfWeek);

            //因为是以星期一为第一天，所以要判断weeknow等于0时，要向前推6天。  
            weeknow = (weeknow == 0 ? (7 - 1) : (weeknow - 1));
            int daydiff = (-1) * weeknow;

            //本周第一天  
            string FirstDay = datetime.AddDays(daydiff).ToString("yyyy-MM-dd");
            return Convert.ToDateTime(FirstDay);
        }

        /// <summary>  
        /// 得到本周最后一天(以星期六为最后一天)  
        /// </summary>  
        /// <param name="datetime"></param>  
        /// <returns></returns>  
        public static DateTime GetWeekLastDaySat(DateTime datetime)
        {
            //星期六为最后一天  
            int weeknow = Convert.ToInt32(datetime.DayOfWeek);
            int daydiff = (7 - weeknow) - 1;

            //本周最后一天  
            string LastDay = datetime.AddDays(daydiff).ToString("yyyy-MM-dd");
            return Convert.ToDateTime(LastDay);
        }

        /// <summary>  
        /// 得到本周最后一天(以星期天为最后一天)  
        /// </summary>  
        /// <param name="datetime"></param>  
        /// <returns></returns>  
        public static DateTime GetWeekLastDaySun(DateTime datetime)
        {
            //星期天为最后一天  
            int weeknow = Convert.ToInt32(datetime.DayOfWeek);
            weeknow = (weeknow == 0 ? 7 : weeknow);
            int daydiff = (7 - weeknow);

            //本周最后一天  
            string LastDay = datetime.AddDays(daydiff).ToString("yyyy-MM-dd");
            return Convert.ToDateTime(LastDay);
        }

        /// <summary>
        /// 取得某月的第一天
        /// </summary>
        /// <param name="datetime">要取得月份第一天的时间</param>
        /// <returns></returns>
        public static DateTime FirstDayOfMonth(DateTime datetime)
        {
            return datetime.AddDays(1 - datetime.Day);
        }
        /// <summary>
            /// 取得某月的最后一天
            /// </summary>
            /// <param name="datetime">要取得月份最后一天的时间</param>
            /// <returns></returns>
        public static DateTime LastDayOfMonth(DateTime datetime)
        {
            return datetime.AddDays(1 - datetime.Day).AddMonths(1).AddDays(-1);
        }

        /// <summary>
        /// 取得上个月第一天
        /// </summary>
        /// <param name="datetime">要取得上个月第一天的当前时间</param>
        /// <returns></returns>
        public static DateTime FirstDayOfPreviousMonth(DateTime datetime)
        {
            return datetime.AddDays(1 - datetime.Day).AddMonths(-1);
        }

        
        /// <summary>
        /// 取得上个月的最后一天
        /// </summary>
        /// <param name="datetime">要取得上个月最后一天的当前时间</param>
        /// <returns></returns>
        public static DateTime LastDayOfPrdviousMonth(DateTime datetime)
        {
            return datetime.AddDays(1 - datetime.Day).AddDays(-1);
        }

    }
}