gen5: fix dex skin footer, fix musical terminator

Closes #4603
Add some filename import length sanitization

PKHeX.Core/Saves/SAV5.cs

@@ -213,6 +213,13 @@ protected ushort WriteExtSection(ReadOnlySpan<byte> data, int offset, int size,
         ArgumentOutOfRangeException.ThrowIfNotEqual(data.Length, size);
         SetData(data, offset);
 
+        return RefreshExtSectionFooter(offset, size, count);
+    }
+
+    private ushort RefreshExtSectionFooter(int offset, int size, ushort count)
+    {
+        var data = Data.Slice(offset, size);
+
         // Update Tail Section
         ushort chk = Checksums.CRC16_CCITT(data);
         var tail = Data[(offset + size)..];
@@ -292,8 +299,9 @@ public void SetMusical(ReadOnlySpan<byte> data, ushort count = 1)
     public void SetPokeDexSkin(ReadOnlySpan<byte> data, ushort count = 1)
     {
         WriteExtSection(data, ExtPokeDexSkinOffset, PokeDexSkin5.SIZE, count);
+        IsAvailablePokedexSkin = true; // checksum might be changed via this, need to refresh footer to be safe
+        RefreshExtSectionFooter(ExtPokeDexSkinOffset, PokeDexSkin5.SIZE, count);
         PlayerData.UpdateExtData(ExtDataSectionNote5.PokedexSkin, count);
-        IsAvailablePokedexSkin = true;
     }
 
     private Span<byte> DexSkinFooter => Data.Slice(ExtPokeDexSkinOffset + PokeDexSkin5.SIZE - 4, 4);

PKHeX.Core/Saves/Substructures/Gen5/Musical5.cs

@@ -6,12 +6,12 @@ public sealed class Musical5(SAV5 SAV, Memory<byte> raw) : SaveBlock<SAV5>(SAV,
 {
     public const int MusicalNameMaxLength = 20;
 
-    private Span<byte> MusicalTrash => Data.Slice(0x208, MusicalNameMaxLength * 2);
+    private Span<byte> MusicalTrash => Data.Slice(0x208, MusicalNameMaxLength * 2 + 2); // require terminator, so +2 for 0xFFFF
 
     public string MusicalName
     {
         get => StringConverter5.GetString(MusicalTrash);
-        set => StringConverter5.SetString(MusicalTrash, value, MusicalNameMaxLength, 0, StringConverterOption.ClearZero);
+        set => StringConverter5.SetString(MusicalTrash, value, MusicalNameMaxLength, SAV.Language, StringConverterOption.ClearZero);
     }
 
     private const int PropOffset = 0x258;

PKHeX.WinForms/Subforms/Save Editors/Gen5/SAV_DLC5.cs

@@ -180,6 +180,38 @@ private static void ExportFile(string extension, string name, ReadOnlySpan<byte>
         File.WriteAllBytes(sfd.FileName, data);
     }
 
+    private static string GetImportedMusicalName(string path)
+    {
+        var name = Path.GetFileNameWithoutExtension(path).Trim();
+
+        var split = name.LastIndexOf(" - ", StringComparison.Ordinal);
+        if (split >= 0 && split + 3 < name.Length)
+            name = name[(split + 3)..].Trim();
+
+        var suffix = name.LastIndexOf(" (", StringComparison.Ordinal);
+        if (suffix > 0 && name[^1] == ')' && IsLikelyLanguageTag(name[(suffix + 2)..^1]))
+            name = name[..suffix].TrimEnd();
+
+        if (name.Length > Musical5.MusicalNameMaxLength)
+            name = name[..Musical5.MusicalNameMaxLength].TrimEnd();
+
+        return name;
+    }
+
+    private static bool IsLikelyLanguageTag(ReadOnlySpan<char> value)
+    {
+        if (value.Length is < 2 or > 5)
+            return false;
+
+        foreach (var c in value)
+        {
+            if ((uint)(c - 'A') > 'Z' - 'A')
+                return false;
+        }
+
+        return true;
+    }
+
     private void B_ImportPNGCGear_Click(object sender, EventArgs e)
     {
         using var ofd = new OpenFileDialog();
@@ -355,7 +387,7 @@ private void B_MusicalImport_Click(object sender, EventArgs e)
         var musical = new MusicalShow5(data);
         SAV.SetMusical(data);
         if (LastImportedFile is { } name)
-            SAV.Musical.MusicalName = musical.IsUninitialized ? "" : Path.GetFileNameWithoutExtension(name).Trim();
+            SAV.Musical.MusicalName = musical.IsUninitialized ? "" : GetImportedMusicalName(name);
     }
 
     private void B_MusicalExport_Click(object sender, EventArgs e)

Tests/PKHeX.Core.Tests/Saves/SAV5DLC.cs

@@ -0,0 +1,29 @@
+using FluentAssertions;
+using Xunit;
+using static System.Buffers.Binary.BinaryPrimitives;
+
+namespace PKHeX.Core.Tests.Saves;
+
+public class SAV5DLC
+{
+    [Fact]
+    public void SetPokeDexSkin_RecomputesChecksumAfterSettingAvailabilityFlag()
+    {
+        var sav = new SAV5B2W2();
+
+        // Create a random garbage PokeDex skin data with the last 4 bytes reserved for the availability flag and checksum
+        byte[] data = new byte[PokeDexSkin5.SIZE];
+        for (int i = 0; i < data.Length - sizeof(uint); i++)
+            data[i] = (byte)i;
+
+        sav.SetPokeDexSkin(data);
+
+        sav.IsAvailablePokedexSkin.Should().BeTrue();
+        ReadUInt32LittleEndian(sav.PokedexSkinData.Span[^sizeof(uint)..]).Should().Be(1u);
+
+        const int offset = 0x6D800;
+        var tail = sav.Data[(offset + PokeDexSkin5.SIZE)..];
+        ReadUInt16LittleEndian(tail).Should().Be(1);
+        ReadUInt16LittleEndian(tail[2..]).Should().Be(Checksums.CRC16_CCITT(sav.PokedexSkinData.Span));
+    }
+}