ScadaBridge/tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Shared/DataTablePagerTests.cs

using Bunit;
using Microsoft.AspNetCore.Components;
using ZB.MOM.WW.ScadaBridge.CentralUI.Components.Shared;

namespace ZB.MOM.WW.ScadaBridge.CentralUI.Tests.Shared;

/// <summary>
/// Regression tests for the <c>DataTable</c> pager, which looped
/// <c>for i = 1..totalPages</c> and emitted one numbered <c>&lt;li&gt;</c>
/// button per page; a few thousand records at page size 25 rendered hundreds
/// of buttons into the diff on every state change. The fix windows the pager
/// so only first / last / a small range around the current page render.
/// </summary>
public class DataTablePagerTests : BunitContext
{
    private IRenderedComponent<DataTable<int>> RenderTable(int itemCount, int pageSize = 25)
    {
        return Render<DataTable<int>>(parameters => parameters
            .Add(p => p.Items, Enumerable.Range(1, itemCount).ToList())
            .Add(p => p.PageSize, pageSize)
            .Add(p => p.ShowSearch, false)
            .Add(p => p.HeaderContent, (RenderFragment)(b => b.AddMarkupContent(0, "<th>N</th>")))
            .Add(p => p.RowContent, (RenderFragment<int>)(item => b => b.AddMarkupContent(0, $"<tr><td>{item}</td></tr>"))));
    }

    /// <summary>True empty results show no contradictory one-to-zero range.</summary>
    [Fact]
    public void EmptyTable_ShowsZeroItems()
    {
        var cut = RenderTable(0);
        Assert.Equal("0 items", cut.Find(".text-muted.small").TextContent.Trim());
    }

    /// <summary>Filtering to zero and clearing preserves the correct range and paging state.</summary>
    [Fact]
    public void FilterToEmpty_ThenClear_RestoresRealCount()
    {
        var cut = RenderTable(60);
        cut.Render(p => p.Add(c => c.ShowSearch, true).Add(c => c.SearchFilter, (item, search) => item.ToString().Contains(search)));
        cut.Find("input").Input("no-match");
        Assert.Equal("0 items", cut.Find(".text-muted.small").TextContent.Trim());
        cut.Find("button[aria-label='Clear search']").Click();
        Assert.Contains("1–25 of 60 items", cut.Find(".text-muted.small").TextContent);
    }

    /// <summary>The reusable table has one named keyboard-accessible overflow region.</summary>
    [Fact]
    public void Table_HasNamedKeyboardScrollRegion()
    {
        var cut = RenderTable(4);
        var region = cut.Find("[role=region]");
        Assert.Equal("Data table", region.GetAttribute("aria-label"));
        Assert.Equal("0", region.GetAttribute("tabindex"));
        Assert.Single(region.QuerySelectorAll("table"));
        cut.Render(p => p.Add(c => c.TableLabel, "Synthetic records"));
        Assert.Equal("Synthetic records", cut.Find("[role=region]").GetAttribute("aria-label"));
    }

    private static int NumberedPageButtons(IRenderedComponent<DataTable<int>> cut)
        => cut.FindAll("ul.pagination li.page-item button")
              .Count(b => int.TryParse(b.TextContent.Trim(), out _));

    /// <summary>Verifies that a pager with thousands of pages renders a window of buttons rather than every page.</summary>
    [Fact]
    public void Pager_WithThousandsOfPages_RendersWindowedNotEveryPage()
    {
        // 5000 items / 25 = 200 pages. The pre-fix pager rendered 200 numbered
        // buttons; the windowed pager renders at most a dozen.
        var cut = RenderTable(itemCount: 5000);

        var numbered = NumberedPageButtons(cut);

        Assert.True(numbered <= 12,
            $"Expected a windowed pager (<= 12 numbered buttons) but rendered {numbered}.");
    }

    /// <summary>Verifies that a pager over a small dataset still renders a button for every page.</summary>
    [Fact]
    public void Pager_SmallDataset_StillRendersEveryPage()
    {
        // 5 pages — small enough to render all numbered buttons (no windowing harm).
        var cut = RenderTable(itemCount: 125);

        var numbered = NumberedPageButtons(cut);

        Assert.Equal(5, numbered);
    }

    /// <summary>Verifies that the windowed pager always includes the first and last pages around the current page.</summary>
    [Fact]
    public void Pager_WindowedAroundCurrentPage_AlwaysIncludesFirstAndLast()
    {
        var cut = RenderTable(itemCount: 5000); // 200 pages

        var numbered = cut.FindAll("ul.pagination li.page-item button")
            .Select(b => b.TextContent.Trim())
            .Where(t => int.TryParse(t, out _))
            .ToList();

        // First and last page are always reachable from the windowed pager.
        Assert.Contains("1", numbered);
        Assert.Contains("200", numbered);
    }
}