feat(content): add physical blob aliases to pak writer

tests/AcDream.Content.Tests/PakAliasTests.cs

@@ -0,0 +1,148 @@
+using AcDream.Content.Pak;
+
+namespace AcDream.Content.Tests;
+
+public sealed class PakAliasTests : IDisposable
+{
+    private readonly string _path =
+        Path.Combine(Path.GetTempPath(), $"acdream-pak-alias-{Guid.NewGuid():N}.pak");
+
+    public void Dispose()
+    {
+        try
+        {
+            if (File.Exists(_path))
+                File.Delete(_path);
+        }
+        catch
+        {
+            // Best-effort test cleanup.
+        }
+    }
+
+    [Fact]
+    public void Alias_HasIndependentKeyAndSharedPhysicalReceipt()
+    {
+        var primaryKey = PakKey.Compose(PakAssetType.EnvCellMesh, 0xA9B4_0100);
+        var aliasKey = PakKey.Compose(PakAssetType.EnvCellMesh, 0xA9B4_0101);
+        var expected = MakeData(0x2_1234_5678);
+
+        using (var writer = NewWriter())
+        {
+            writer.AddBlob(primaryKey, expected);
+            writer.AddAlias(aliasKey, primaryKey);
+            writer.Finish();
+        }
+
+        using var reader = new PakReader(_path);
+        Assert.True(reader.TryReadObjectMeshData(primaryKey, out var primary));
+        Assert.True(reader.TryReadObjectMeshData(aliasKey, out var alias));
+        Assert.NotNull(primary);
+        Assert.NotNull(alias);
+        Assert.Equal(expected.ObjectId, primary.ObjectId);
+        Assert.Equal(expected.ObjectId, alias.ObjectId);
+
+        var primaryReceipt = reader.GetTocEntryForTest(primaryKey);
+        var aliasReceipt = reader.GetTocEntryForTest(aliasKey);
+        Assert.Equal(primaryReceipt.Offset, aliasReceipt.Offset);
+        Assert.Equal(primaryReceipt.Length, aliasReceipt.Length);
+        Assert.Equal(primaryReceipt.Crc32, aliasReceipt.Crc32);
+        Assert.Equal(2u, reader.Header.TocCount);
+    }
+
+    [Fact]
+    public void Alias_CorruptSharedPayload_MakesBothKeysMissing()
+    {
+        var primaryKey = PakKey.Compose(PakAssetType.EnvCellMesh, 1);
+        var aliasKey = PakKey.Compose(PakAssetType.EnvCellMesh, 2);
+
+        using (var writer = NewWriter())
+        {
+            writer.AddBlob(primaryKey, MakeData(0x2_1234_5678));
+            writer.AddAlias(aliasKey, primaryKey);
+            writer.Finish();
+        }
+
+        long offset;
+        using (var reader = new PakReader(_path))
+            offset = reader.GetBlobOffsetForTest(primaryKey);
+
+        using (var stream = new FileStream(_path, FileMode.Open, FileAccess.ReadWrite))
+        {
+            stream.Position = offset;
+            int value = stream.ReadByte();
+            stream.Position = offset;
+            stream.WriteByte((byte)(value ^ 0xFF));
+        }
+
+        using var corruptReader = new PakReader(_path);
+        Assert.False(corruptReader.TryReadObjectMeshData(primaryKey, out _));
+        Assert.False(corruptReader.TryReadObjectMeshData(aliasKey, out _));
+    }
+
+    [Fact]
+    public void Alias_RejectsMissingSourceWithoutReservingAliasKey()
+    {
+        var sourceKey = PakKey.Compose(PakAssetType.EnvCellMesh, 1);
+        var aliasKey = PakKey.Compose(PakAssetType.EnvCellMesh, 2);
+
+        using var writer = NewWriter();
+        Assert.Throws<KeyNotFoundException>(() => writer.AddAlias(aliasKey, sourceKey));
+
+        writer.AddBlob(aliasKey, MakeData(2));
+        writer.Finish();
+    }
+
+    [Fact]
+    public void Alias_RejectsSelfAndDuplicateKeys()
+    {
+        var primaryKey = PakKey.Compose(PakAssetType.EnvCellMesh, 1);
+        var aliasKey = PakKey.Compose(PakAssetType.EnvCellMesh, 2);
+
+        using var writer = NewWriter();
+        writer.AddBlob(primaryKey, MakeData(1));
+        Assert.Throws<ArgumentException>(() => writer.AddAlias(primaryKey, primaryKey));
+        writer.AddAlias(aliasKey, primaryKey);
+        Assert.Throws<ArgumentException>(() => writer.AddAlias(aliasKey, primaryKey));
+        Assert.Throws<ArgumentException>(() => writer.AddBlob(aliasKey, MakeData(2)));
+        writer.Finish();
+    }
+
+    [Fact]
+    public void Alias_RejectsMutationAfterFinish()
+    {
+        var primaryKey = PakKey.Compose(PakAssetType.EnvCellMesh, 1);
+        var aliasKey = PakKey.Compose(PakAssetType.EnvCellMesh, 2);
+
+        using var writer = NewWriter();
+        writer.AddBlob(primaryKey, MakeData(1));
+        writer.Finish();
+
+        Assert.Throws<InvalidOperationException>(() => writer.AddAlias(aliasKey, primaryKey));
+    }
+
+    private PakWriter NewWriter() =>
+        new(
+            _path,
+            new PakHeader
+            {
+                PortalIteration = 1,
+                CellIteration = 2,
+                HighResIteration = 3,
+                LanguageIteration = 4,
+                BakeToolVersion = 1,
+            });
+
+    private static ObjectMeshData MakeData(ulong objectId) =>
+        new()
+        {
+            ObjectId = objectId,
+            Vertices =
+            [
+                new(
+                    new System.Numerics.Vector3(1, 2, 3),
+                    System.Numerics.Vector3.UnitZ,
+                    new System.Numerics.Vector2(0.25f, 0.75f)),
+            ],
+        };
+}