using System;
using System.Globalization;
using System.Runtime.InteropServices;

namespace Masuit.Tools.DateTimeExt
{
    /// <summary>
    /// 日期时间帮助类
    /// </summary>
    public static class DateTimeHelper
    {
        /// <summary>
        /// 获取某一年有多少周
        /// </summary>
        /// <param name="_"></param>
        /// <param name="year">年份</param>
        /// <returns>该年周数</returns>
        public static int GetWeekAmount(this DateTime _, int year)
        {
            var end = new DateTime(year, 12, 31); //该年最后一天
            var gc = new GregorianCalendar();
            return gc.GetWeekOfYear(end, CalendarWeekRule.FirstDay, DayOfWeek.Monday); //该年星期数
        }

        /// <summary>
        /// 返回年度第几个星期   默认星期日是第一天
        /// </summary>
        /// <param name="date">时间</param>
        /// <returns>第几周</returns>
        public static int WeekOfYear(this DateTime date)
        {
            var gc = new GregorianCalendar();
            return gc.GetWeekOfYear(date, CalendarWeekRule.FirstDay, DayOfWeek.Sunday);
        }

        /// <summary>
        /// 返回年度第几个星期
        /// </summary>
        /// <param name="date">时间</param>
        /// <param name="week">一周的开始日期</param>
        /// <returns>第几周</returns>
        public static int WeekOfYear(this DateTime date, DayOfWeek week)
        {
            var gc = new GregorianCalendar();
            return gc.GetWeekOfYear(date, CalendarWeekRule.FirstDay, week);
        }

        /// <summary>
        /// 得到一年中的某周的起始日和截止日
        /// 年 nYear
        /// 周数 nNumWeek
        /// 周始 out dtWeekStart
        /// 周终 out dtWeekeEnd
        /// </summary>
        /// <param name="_"></param>
        /// <param name="nYear">年份</param>
        /// <param name="nNumWeek">第几周</param>
        /// <param name="dtWeekStart">开始日期</param>
        /// <param name="dtWeekeEnd">结束日期</param>
        public static void GetWeekTime(this DateTime _, int nYear, int nNumWeek, out DateTime dtWeekStart, out DateTime dtWeekeEnd)
        {
            var dt = new DateTime(nYear, 1, 1);
            dt += new TimeSpan((nNumWeek - 1) * 7, 0, 0, 0);
            dtWeekStart = dt.AddDays(-(int)dt.DayOfWeek + (int)DayOfWeek.Monday);
            dtWeekeEnd = dt.AddDays((int)DayOfWeek.Saturday - (int)dt.DayOfWeek + 1);
        }

        /// <summary>
        /// 得到一年中的某周的起始日和截止日    周一到周五  工作日
        /// </summary>
        /// <param name="_"></param>
        /// <param name="nYear">年份</param>
        /// <param name="nNumWeek">第几周</param>
        /// <param name="dtWeekStart">开始日期</param>
        /// <param name="dtWeekeEnd">结束日期</param>
        public static void GetWeekWorkTime(this DateTime _, int nYear, int nNumWeek, out DateTime dtWeekStart, out DateTime dtWeekeEnd)
        {
            var dt = new DateTime(nYear, 1, 1);
            dt += new TimeSpan((nNumWeek - 1) * 7, 0, 0, 0);
            dtWeekStart = dt.AddDays(-(int)dt.DayOfWeek + (int)DayOfWeek.Monday);
            dtWeekeEnd = dt.AddDays((int)DayOfWeek.Saturday - (int)dt.DayOfWeek + 1).AddDays(-2);
        }

        #region P/Invoke 设置本地时间

        [DllImport("kernel32.dll")]
        private static extern bool SetLocalTime(ref SystemTime time);

        [StructLayout(LayoutKind.Sequential)]
        private struct SystemTime
        {
            public short year;
            public short month;
            public short dayOfWeek;
            public short day;
            public short hour;
            public short minute;
            public short second;
            public short milliseconds;
        }

        /// <summary>
        /// 设置本地计算机时间
        /// </summary>
        /// <param name="dt">DateTime对象</param>
        public static void SetLocalTime(this DateTime dt)
        {
            SystemTime st;

            st.year = (short)dt.Year;
            st.month = (short)dt.Month;
            st.dayOfWeek = (short)dt.DayOfWeek;
            st.day = (short)dt.Day;
            st.hour = (short)dt.Hour;
            st.minute = (short)dt.Minute;
            st.second = (short)dt.Second;
            st.milliseconds = (short)dt.Millisecond;

            SetLocalTime(ref st);
        }

        #endregion
    }
}