100 lines
3.2 KiB
C#
100 lines
3.2 KiB
C#
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using System;
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namespace Swan
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{
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/// <summary>
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/// A utility class to compute paging or batching offsets.
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/// </summary>
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public class Paginator
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{
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/// <summary>
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/// Initializes a new instance of the <see cref="Paginator" /> class.
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/// </summary>
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/// <param name="totalCount">The total count of items to page over.</param>
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/// <param name="pageSize">The desired size of individual pages.</param>
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public Paginator(int totalCount, int pageSize)
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{
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TotalCount = totalCount;
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PageSize = pageSize;
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PageCount = ComputePageCount();
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}
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/// <summary>
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/// Gets the desired number of items per page.
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/// </summary>
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public int PageSize { get; }
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/// <summary>
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/// Gets the total number of items to page over.
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/// </summary>
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public int TotalCount { get; }
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/// <summary>
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/// Gets the computed number of pages.
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/// </summary>
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public int PageCount { get; }
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/// <summary>
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/// Gets the start item index of the given page.
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/// </summary>
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/// <param name="pageIndex">Zero-based index of the page.</param>
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/// <returns>The start item index.</returns>
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public int GetFirstItemIndex(int pageIndex)
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{
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pageIndex = FixPageIndex(pageIndex);
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return pageIndex * PageSize;
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}
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/// <summary>
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/// Gets the end item index of the given page.
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/// </summary>
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/// <param name="pageIndex">Zero-based index of the page.</param>
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/// <returns>The end item index.</returns>
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public int GetLastItemIndex(int pageIndex)
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{
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var startIndex = GetFirstItemIndex(pageIndex);
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return Math.Min(startIndex + PageSize - 1, TotalCount - 1);
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}
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/// <summary>
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/// Gets the item count of the given page index.
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/// </summary>
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/// <param name="pageIndex">Zero-based index of the page.</param>
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/// <returns>The number of items that the page contains.</returns>
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public int GetItemCount(int pageIndex)
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{
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pageIndex = FixPageIndex(pageIndex);
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return (pageIndex >= PageCount - 1)
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? GetLastItemIndex(pageIndex) - GetFirstItemIndex(pageIndex) + 1
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: PageSize;
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}
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/// <summary>
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/// Fixes the index of the page by applying bound logic.
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/// </summary>
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/// <param name="pageIndex">Index of the page.</param>
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/// <returns>A limit-bound index.</returns>
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private int FixPageIndex(int pageIndex)
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{
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if (pageIndex < 0) return 0;
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return pageIndex >= PageCount ? PageCount - 1 : pageIndex;
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}
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/// <summary>
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/// Computes the number of pages for the paginator.
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/// </summary>
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/// <returns>The page count.</returns>
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private int ComputePageCount()
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{
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// include this if when you always want at least 1 page
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if (TotalCount == 0)
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return 0;
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return TotalCount % PageSize != 0
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? (TotalCount / PageSize) + 1
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: TotalCount / PageSize;
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}
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}
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}
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