From af695a70b318a39a530120faf522d11bd4fe7a22 Mon Sep 17 00:00:00 2001
From: scientificworld <scientificworld@users.noreply.github.com>
Date: Thu, 5 Feb 2026 00:10:10 +0800
Subject: [PATCH] feat: support NEKOPACK old version

---
 ArcFormats/Nekopack/ArcDAT.cs | 130 ++++++++++++++++++++++++++++++++++
 1 file changed, 130 insertions(+)
 create mode 100644 ArcFormats/Nekopack/ArcDAT.cs

diff --git a/ArcFormats/Nekopack/ArcDAT.cs b/ArcFormats/Nekopack/ArcDAT.cs
new file mode 100644
index 00000000..25fe6ee1
--- /dev/null
+++ b/ArcFormats/Nekopack/ArcDAT.cs
@@ -0,0 +1,130 @@
+//! \file       ArcDAT.cs
+//! \date       2026-02-04
+//! \brief      Nekopack archive format implementation.
+//
+// Copyright (C) 2016 by morkt
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to
+// deal in the Software without restriction, including without limitation the
+// rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+// sell copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+// IN THE SOFTWARE.
+//
+
+using System.Collections.Generic;
+using System.ComponentModel.Composition;
+using System.IO;
+using GameRes.Utility;
+
+namespace GameRes.Formats.Neko
+{
+    internal class NekoItaEntry : Entry
+    {
+        public byte ExtraKey;
+    }
+
+    [Export(typeof(ArchiveFormat))]
+    public class DatOpener : ArchiveFormat
+    {
+        public override string         Tag { get { return "DAT/NEKOPACK"; } }
+        public override string Description { get { return "NekoPack resource archive"; } }
+        public override uint     Signature { get { return 0x4f4b454e; } } // "NEKO"
+        public override bool  IsHierarchic { get { return true; } }
+        public override bool      CanWrite { get { return false; } }
+
+        public DatOpener ()
+        {
+            Extensions = new string[] { "dat" };
+        }
+
+        public override ArcFile TryOpen (ArcView file)
+        {
+            if (!file.View.AsciiEqual (4, "PACK"))
+                return null;
+
+            int count = file.View.ReadInt32 (0x10);
+            if (!IsSaneCount (count))
+                return null;
+
+            var table = new uint[0x270];
+            int pos = 0;
+            InitTable (table, 0x9999);
+
+            var dir = new List<Entry> (count);
+            uint index_offset = 0x14;
+            for (int i = 0; i < count; ++i)
+            {
+                byte extra = file.View.ReadByte (index_offset);
+                uint name_length = file.View.ReadByte (index_offset + 1);
+                var name_buffer = file.View.ReadBytes (index_offset + 2, name_length);
+                pos = Decrypt (name_buffer, 0, (int)name_length, table, pos);
+                var name = Binary.GetCString (name_buffer, 0, (int)name_length);
+                var entry = Create<NekoItaEntry> (name);
+                index_offset += name_length + 2;
+                entry.Offset = file.View.ReadUInt32 (index_offset);
+                entry.Size = file.View.ReadUInt32 (index_offset + 4);
+                if (!entry.CheckPlacement (file.MaxOffset))
+                    return null;
+                if (entry.Name.HasExtension (".img"))
+                    entry.Type = "";
+                entry.ExtraKey = extra;
+                dir.Add (entry);
+                index_offset += 8;
+            }
+            return new ArcFile (file, this, dir);
+        }
+
+        public override Stream OpenEntry (ArcFile arc, Entry entry)
+        {
+            var nent = (NekoItaEntry)entry;
+            var input = arc.File.View.ReadBytes (nent.Offset, nent.Size);
+            if (nent.ExtraKey != 0)
+            {
+                var table = new uint[0x270];
+                InitTable (table, (uint)(0x9999 + nent.ExtraKey));
+                Decrypt (input, 0, (int)nent.Size, table, 0);
+            }
+            return new BinMemoryStream (input);
+        }
+
+        void InitTable (uint[] table, uint key)
+        {
+            for (int i = 0; i < table.Length; i++)
+            {
+                key *= 0x10dcd;
+                table[i] = key;
+            }
+        }
+
+        int Decrypt (byte[] data, int pos, int length, uint[] table, int table_pos)
+        {
+            for (int i = pos; i < pos + length; i++)
+            {
+                if (table_pos == table.Length)
+                {
+                    InitTable (table, table[table.Length - 1]);
+                    table_pos = 0;
+                }
+                uint key = table[table_pos++];
+                key ^= key >> 11;
+                key ^= (key << 7) & 0x31518a63;
+                key ^= (key << 15) & 0x17f1ca43;
+                key ^= key >> 18;
+                data[i] ^= (byte)key;
+            }
+            return table_pos;
+        }
+    }
+}