using System;
using System.Linq;
using NewLife.Log;
using XCode;
using XCode.Configuration;

/*
 *  时间点抽取流程：
 *      验证时间start，越界则退出
 *          有步进且位于第一页时，重新计算最小时间 FindAll(UpdateTime >= start, UpdateTime.Min(), 0, 0)
 *          结束时间有效时，设定末端边界
 *      抽取一批数据 list = FindAll(UpdateTime >= start, UpdateTime.Asc() & ID.Asc(), null, Row, 1000)
 *      有数据list.Count > 0
 *          last = list.Last().UpdateTime
 *          满一批，后续还有数据 list.Count == 1000
 *              最大时间行数 lastCount = list.Count(e=>UpdateTime==last)
 *              Row += lastCount
 *              滑动时间点 start = last
 *          不满一批，后续没有数据
 *              Row = 0;
 *              滑动时间点 start = last + 1
 *      没有数据
 *          有步进
 *              Row = 0;
 *              滑动时间窗口 start = end
 *      返回这一批数据
 */

namespace XCode.Transform
{
    /// <summary>以时间为比较点的数据抽取器</summary>
    public class TimeExtracter : IExtracter
    {
        #region 属性
        /// <summary>名称</summary>
        public String Name { get; set; }

        /// <summary>设置</summary>
        public IExtractSetting Setting { get; set; }

        /// <summary>实体工厂</summary>
        public IEntityOperate Factory { get; set; }

        /// <summary>获取 或 设置 时间字段</summary>
        public String FieldName { get; set; }

        /// <summary>附加条件</summary>
        public String Where { get; set; }

        private FieldItem _Field;
        /// <summary>时间字段</summary>
        public FieldItem Field
        {
            get
            {
                if (_Field == null)
                {
                    _Field = Factory.Table.FindByName(FieldName);
                    if (_Field == null) throw new ArgumentNullException(nameof(Field));
                }
                return _Field;
            }
        }

        /// <summary>本批数据结束时间</summary>
        public DateTime BatchEnd { get; set; }
        #endregion

        #region 构造
        /// <summary>实例化时基抽取算法</summary>
        public TimeExtracter()
        {
            Name = GetType().Name.TrimEnd("Extracter", "Worker");
        }
        #endregion

        #region 方法
        /// <summary>初始化</summary>
        public virtual void Init()
        {
            // 自动找时间字段
            if (FieldName.IsNullOrEmpty())
            {
                var fi = Factory.Fields.FirstOrDefault(e => e.Type == typeof(DateTime) && e.Name.StartsWithIgnoreCase("UpdateTime", "Modify", "Modified"));
                if (fi != null) FieldName = fi.Name;
            }
        }
        #endregion

        #region 抽取数据
        /// <summary>抽取一批数据</summary>
        /// <returns></returns>
        public virtual IEntityList Fetch()
        {
            if (Field == null) throw new ArgumentNullException(nameof(FieldName), "未指定用于顺序抽取数据的时间字段！");

            var set = Setting;
            if (set == null) set = Setting = new ExtractSetting();
            if (!set.Enable) return null;

            // 验证时间段
            var start = set.Start;
            // 有步进且位于第一页时，重新计算最小时间
            if (set.Step > 0 && set.Row == 0) start = GetMinTime(start);
            var now = DateTime.Now;
            if (start >= now) return null;

            // 结束时间，必须是小于当前时间的有效值
            var end = set.Step <= 0 ? DateTime.MaxValue : start.AddSeconds(set.Step);
            //var end = DateTime.MaxValue;
            // 结束时间有效时，设定末端边界
            if (set.End > DateTime.MinValue && set.End < DateTime.MaxValue && set.End < end)
                end = set.End;

            // 区间无效
            if (start >= end) return null;
            BatchEnd = end;

            var size = set.BatchSize;
            if (size <= 0) size = 1000;

            // 分批获取数据，如果没有取到，则结束
            var list = FetchData(start, end, set.Row, size);
            // 取到数据，需要滑动窗口
            if (list.Count > 0)
            {
                var last = (DateTime)list.Last()[FieldName];
                // 满一批，后续还有数据
                if (list.Count >= size)
                {
                    // 最大时间行数
                    var maxCount = list.Count(e => (DateTime)e[FieldName] == last);
                    // 以最后时间为起点，跳过若干行。注意可能产生连续分页的情况
                    if (last == NextStart)
                        NextRow = set.Row + maxCount;
                    else
                        NextRow = maxCount;
                    NextStart = last;
                }
                else
                {
                    NextStart = last.AddSeconds(1);
                    NextRow = 0;
                }
            }
            else if (set.Step > 0)
            {
                NextStart = end;
                NextRow = 0;
            }

            return list;
        }

        /// <summary>分段分页抽取数据</summary>
        /// <param name="start"></param>
        /// <param name="end"></param>
        /// <param name="startRow"></param>
        /// <param name="maxRows"></param>
        /// <returns></returns>
        protected virtual IEntityList FetchData(DateTime start, DateTime end, Int32 startRow, Int32 maxRows)
        {
            var fi = Field;
            var exp = fi.Between(start, end);

            if (!Where.IsNullOrEmpty()) exp &= Where;

            // 先按时间升序，再按主键升序，避免同一秒存在多行数据时，数据顺序不统一
            var sort = fi.Asc();
            var uq = Factory.Unique;
            if (uq != null && uq.Name != fi.Name) sort &= uq.Asc();

            return Factory.FindAll(exp, sort, null, startRow, maxRows);
        }

        /// <summary>获取大于等于指定时间的最小修改时间</summary>
        /// <param name="start"></param>
        /// <returns></returns>
        protected virtual DateTime GetMinTime(DateTime start)
        {
            var fi = Field;
            var exp = new WhereExpression();
            if (start > DateTime.MinValue) exp &= fi >= start;

            if (!Where.IsNullOrEmpty()) exp &= Where;

            var list = Factory.FindAll(exp, null, fi.Min(), 0, 0);

            return list.Count > 0 ? (DateTime)list[0][FieldName] : DateTime.MaxValue;
        }

        private DateTime NextStart { get; set; }
        private Int32 NextRow { get; set; }

        /// <summary>当前批数据处理完成，移动到下一块</summary>
        public void SaveNext()
        {
            var set = Setting;
            set.Start = NextStart;
            set.Row = NextRow;
        }
        #endregion

        #region 日志
        /// <summary>日志</summary>
        public ILog Log { get; set; } = Logger.Null;

        /// <summary>写日志</summary>
        /// <param name="format"></param>
        /// <param name="args"></param>
        public void WriteLog(String format, params Object[] args)
        {
            Log?.Info(format, args);
        }
        #endregion
    }
}