feat: drop created-at card sort and add card display ordering

YKanBan.Tests/Models/CardOrderingTests.cs

@@ -0,0 +1,46 @@
+using YKanBan.Models;
+using YKanBan.Storage.AppData;
+
+namespace YKanBan.Tests.Models;
+
+/// <summary>
+/// Tests for the in-column card display order: each sort option plus the id
+/// ascending tie-breaker.
+/// </summary>
+[TestClass]
+public class CardOrderingTests
+{
+    private static CardModel Card(long id, string title = "", long updatedAt = 0) =>
+        new(id, 1, title, string.Empty, 0, updatedAt, []);
+
+    private static long[] Ids(IEnumerable<CardModel> cards, CardSortOption option) =>
+        CardOrdering.Sort(cards, option).Select(card => card.Id).ToArray();
+
+    [TestMethod]
+    public void IdSortsAscending()
+    {
+        CollectionAssert.AreEqual(new[] { 1L, 2L, 3L }, Ids([Card(3), Card(1), Card(2)], CardSortOption.Id));
+    }
+
+    [TestMethod]
+    public void UpdatedAtSortsMostRecentFirstThenById()
+    {
+        CardModel[] cards = [Card(1, updatedAt: 10), Card(2, updatedAt: 30), Card(3, updatedAt: 10), Card(4, updatedAt: 20)];
+        CollectionAssert.AreEqual(new[] { 2L, 4L, 1L, 3L }, Ids(cards, CardSortOption.UpdatedAt));
+    }
+
+    [TestMethod]
+    public void TitleSortsByCodePointWithEmptyFirstThenById()
+    {
+        CardModel[] cards = [Card(1, "b"), Card(2, "B"), Card(3, ""), Card(4, "a"), Card(5, "b")];
+        CollectionAssert.AreEqual(new[] { 3L, 2L, 4L, 1L, 5L }, Ids(cards, CardSortOption.Title));
+    }
+
+    [TestMethod]
+    public void TitleSortsSupplementaryCharactersAfterBmpPrivateUse()
+    {
+        // U+1F600 is a surrogate pair in UTF-16, so ordinal comparison would put it before U+E000.
+        CardModel[] cards = [Card(1, "\U0001F600"), Card(2, "")];
+        CollectionAssert.AreEqual(new[] { 2L, 1L }, Ids(cards, CardSortOption.Title));
+    }
+}

YKanBan.Tests/Storage/AppData/AppConfigStoreTests.cs

@@ -145,7 +145,7 @@ public class AppConfigStoreTests
         {
             Language = "zh-Hans",
             Theme = ThemeOption.Light,
-            Sort = new SortSettings { Card = CardSortOption.CreatedAt },
+            Sort = new SortSettings { Card = CardSortOption.Title },
             ColumnWidth = new ColumnWidthSettings { Preset = ColumnWidthPreset.Wide },
             Confirmations = new ConfirmationSettings { DiscardEdit = false },
         };

YKanBan/Models/CardOrdering.cs

@@ -0,0 +1,70 @@
+using System.Text;
+using YKanBan.Storage.AppData;
+
+namespace YKanBan.Models;
+
+/// <summary>
+/// Computes the in-column card display order for a <see cref="CardSortOption"/>.
+/// Columns are not affected: they always stay in id order. Every option falls
+/// back to id ascending as the final tie-breaker, so the order is total.
+/// </summary>
+public static class CardOrdering
+{
+    /// <summary>
+    /// Orders cards for display.
+    /// </summary>
+    /// <param name="cards">The cards to order, typically those of one column.</param>
+    /// <param name="option">The selected sort option.</param>
+    /// <returns>The cards in display order.</returns>
+    public static IReadOnlyList<CardModel> Sort(IEnumerable<CardModel> cards, CardSortOption option)
+    {
+        IOrderedEnumerable<CardModel> ordered = option switch
+        {
+            CardSortOption.Id => cards.OrderBy(card => card.Id),
+
+            // Most recently modified first.
+            CardSortOption.UpdatedAt => cards.OrderByDescending(card => card.UpdatedAt).ThenBy(card => card.Id),
+
+            // Code point order, matching SQLite's BINARY collation; the empty title sorts first.
+            CardSortOption.Title => cards.OrderBy(card => card.Title, CodePointComparer.Instance).ThenBy(card => card.Id),
+
+            _ => throw new ArgumentOutOfRangeException(nameof(option), option, "Unknown card sort option."),
+        };
+        return ordered.ToList();
+    }
+
+    /// <summary>
+    /// Compares strings by Unicode code points. Unlike ordinal UTF-16 comparison
+    /// it orders supplementary characters after U+E000–U+FFFF, as BINARY does on UTF-8.
+    /// </summary>
+    private sealed class CodePointComparer : IComparer<string>
+    {
+        public static readonly CodePointComparer Instance = new();
+
+        public int Compare(string? x, string? y)
+        {
+            if (x is null || y is null)
+            {
+                return x is null ? (y is null ? 0 : -1) : 1;
+            }
+
+            StringRuneEnumerator left = x.EnumerateRunes();
+            StringRuneEnumerator right = y.EnumerateRunes();
+            while (true)
+            {
+                bool hasLeft = left.MoveNext();
+                bool hasRight = right.MoveNext();
+                if (!hasLeft || !hasRight)
+                {
+                    return hasLeft.CompareTo(hasRight);
+                }
+
+                int result = left.Current.Value.CompareTo(right.Current.Value);
+                if (result != 0)
+                {
+                    return result;
+                }
+            }
+        }
+    }
+}

YKanBan/Storage/AppData/AppConfig.cs

@@ -13,10 +13,6 @@ public enum CardSortOption
     [EnumMember(Value = "id")]
     Id,
 
-    /// <summary>Creation time, oldest first.</summary>
-    [EnumMember(Value = "created-at")]
-    CreatedAt,
-
     /// <summary>Last modification time, most recently modified first.</summary>
     [EnumMember(Value = "updated-at")]
     UpdatedAt,