using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;

namespace Infrastructure.Application
{
    public class PagedList<T> : IPagedList, IValidatableObject
    {
        public PagedList()
        {
            PageNumber = 1;
            PageSize = this.DefaultPageSize;
        }

        [ScaffoldColumn(false)]
        public int DefaultPageSize { get; set; } = 20;

        [ScaffoldColumn(false)]
        public int PageNumber { get; set; }

        [ScaffoldColumn(false)]
        public int PageSize { get; set; }

        [ScaffoldColumn(false)]
        public int TotalRow { get; set; }

        public int[] GetPageSizes()
        {
            return new int[] { 20, 50, 100 };
        }

        public int PageCount()
        {
            return (int)Math.Ceiling(this.TotalRow / (double)this.PageSize);
        }

        public bool HasPrev()
        {
            return PageNumber > 1;
        }

        public bool HasNext()
        {
            return PageNumber < PageCount();
        }

        public IEnumerable<int> GetPageIndexs()
        {
            var pageCount = PageCount();
            var maxLinks = 10;
            var left = maxLinks / 2;
            var start = PageNumber - left;
            start = start > 1 ? start : 1;
            var end = PageNumber + (maxLinks - left - 1);
            end = end > pageCount ? pageCount : end;
            if (start == 1 && end < pageCount)
            {
                while (end - start + 1 < maxLinks && end < pageCount)
                {
                    end++;
                }
            }
            if (end == pageCount && start > 1)
            {
                while (end - start + 1 < maxLinks && start > 1)
                {
                    start--;
                }
            }
            var list = new List<int>();
            for (int i = start; i <= end; i++)
            {
                list.Add(i);
            }
            return list;
        }

        public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
        {
            if (PageNumber < 1)
            {
                yield return new ValidationResult("当前页索引必须大于等于1");
            }
            if (PageSize > 1000)
            {
                yield return new ValidationResult("分页数量超出系统限制");
            }
        }

        [ScaffoldColumn(false)]
        public List<T> List { get; } = new List<T>();
    }
}