Inboxintel/tests/InboxIntel.IntegrationTests/KeysetPaginationTests.cs

using FluentAssertions;
using InboxIntel.Application.Abstractions;
using InboxIntel.Application.DTOs;
using InboxIntel.Domain.Entities;
using InboxIntel.Infrastructure.Persistence;
using InboxIntel.Infrastructure.Search;
using Microsoft.EntityFrameworkCore;
using Xunit;

namespace InboxIntel.IntegrationTests;

/// <summary>
/// RECOMMENDATIONS #8: keyset (cursor) pagination for the browse path — the window after a
/// (SentAtUtc, Id) cursor returns the next rows with no duplicates/skips and no OFFSET scan.
/// </summary>
public class KeysetPaginationTests
{
    private sealed class FakeCurrentUser : ICurrentUser
    {
        public Guid UserId { get; set; }
        public bool IsAuthenticated => UserId != Guid.Empty;
    }

    [Fact]
    public async Task Cursor_window_continues_exactly_after_the_previous_page()
    {
        var user = Guid.NewGuid();
        var opts = new DbContextOptionsBuilder<AppDbContext>()
            .UseInMemoryDatabase(nameof(Cursor_window_continues_exactly_after_the_previous_page)).Options;

        var baseline = DateTimeOffset.UtcNow;
        using (var seed = new AppDbContext(opts, new FakeCurrentUser()))
        {
            var sender = new Sender { UserId = user, Address = "s@x.x" };
            seed.Senders.Add(sender);
            for (var i = 0; i < 5; i++)
                seed.Emails.Add(new Email { UserId = user, GmailMessageId = $"m{i}", Sender = sender, SentAtUtc = baseline.AddMinutes(-i) });
            await seed.SaveChangesAsync();
        }

        using var ctx = new AppDbContext(opts, new FakeCurrentUser { UserId = user });
        var svc = new SearchService(ctx);

        // First window via offset (page 1, size 2): m0, m1 (newest first).
        var page1 = await svc.SearchAsync(user, new SearchRequestDto(null, null, null, null, null, null, null, false, 1, 2));
        page1.Items.Select(i => i.GmailMessageId).Should().Equal("m0", "m1");

        // Next window via cursor from the last row of page 1.
        var last = page1.Items[^1];
        var page2 = await svc.SearchAsync(user, new SearchRequestDto(
            null, null, null, null, null, null, null, false, 1, 2,
            AfterSentAtUtc: last.SentAtUtc, AfterId: last.Id));

        page2.Items.Select(i => i.GmailMessageId).Should().Equal("m2", "m3"); // no dupes, no skips
        page2.TotalCount.Should().Be(-1, "cursor windows skip the COUNT — that's the perf win");
    }
}