From 8fdd96209cda51bfbf9358b016ea29b2238f2043 Mon Sep 17 00:00:00 2001
From: Kurt <kaphotics@gmail.com>
Date: Sat, 5 Mar 2022 17:14:25 -0800
Subject: [PATCH] Deduplicate some logic

No need to length check in the SwishCrypto hash check, as the methods pre-check length as well.
Extract checksum footer check for Gen5 saves
---
 .../Saves/Encryption/SwishCrypto/SCBlock.cs   |  4 ++++
 .../Encryption/SwishCrypto/SwishCrypto.cs     | 18 -----------------
 PKHeX.Core/Saves/Util/SaveUtil.cs             | 20 +++++++++++--------
 3 files changed, 16 insertions(+), 26 deletions(-)

diff --git a/PKHeX.Core/Saves/Encryption/SwishCrypto/SCBlock.cs b/PKHeX.Core/Saves/Encryption/SwishCrypto/SCBlock.cs
index fcce448f8..1f9d8b25e 100644
--- a/PKHeX.Core/Saves/Encryption/SwishCrypto/SCBlock.cs
+++ b/PKHeX.Core/Saves/Encryption/SwishCrypto/SCBlock.cs
@@ -203,6 +203,10 @@ public static SCBlock ReadFromOffset(ReadOnlySpan<byte> data, ref int offset)
             }
         }
 
+        /// <summary>
+        /// Merges the properties from <see cref="other"/> into this object.
+        /// </summary>
+        /// <param name="other">Block to copy all values from.</param>
         public void CopyFrom(SCBlock other)
         {
             if (Type.IsBoolean())
diff --git a/PKHeX.Core/Saves/Encryption/SwishCrypto/SwishCrypto.cs b/PKHeX.Core/Saves/Encryption/SwishCrypto/SwishCrypto.cs
index 7ebeedaf5..fd0e19676 100644
--- a/PKHeX.Core/Saves/Encryption/SwishCrypto/SwishCrypto.cs
+++ b/PKHeX.Core/Saves/Encryption/SwishCrypto/SwishCrypto.cs
@@ -82,24 +82,6 @@ private static byte[] ComputeHash(byte[] data)
         /// <returns>True if hash matches</returns>
         public static bool GetIsHashValid(byte[] data)
         {
-            if (!SaveUtil.SizesSWSH.Contains(data.Length))
-                return false;
-
-            var hash = ComputeHash(data);
-            var span = data.AsSpan()[^hash.Length..];
-            return span.SequenceEqual(hash);
-        }
-
-        /// <summary>
-        /// Checks if the file is a rough example of a save file.
-        /// </summary>
-        /// <param name="data">Encrypted save data</param>
-        /// <returns>True if hash matches</returns>
-        public static bool GetIsHashValidLA(byte[] data)
-        {
-            if (data.Length is not (SaveUtil.SIZE_G8LA or SaveUtil.SIZE_G8LA_1))
-                return false;
-
             var hash = ComputeHash(data);
             var span = data.AsSpan()[^hash.Length..];
             return span.SequenceEqual(hash);
diff --git a/PKHeX.Core/Saves/Util/SaveUtil.cs b/PKHeX.Core/Saves/Util/SaveUtil.cs
index e26edd9b4..602b52564 100644
--- a/PKHeX.Core/Saves/Util/SaveUtil.cs
+++ b/PKHeX.Core/Saves/Util/SaveUtil.cs
@@ -428,16 +428,20 @@ private static GameVersion GetIsG5SAV(ReadOnlySpan<byte> data)
             if (data.Length != SIZE_G5RAW)
                 return Invalid;
 
-            // check the checksum block validity; nobody would normally modify this region
-            ushort chk1 = ReadUInt16LittleEndian(data[(SIZE_G5BW - 0x100 + 0x8C + 0xE)..]);
-            ushort actual1 = Checksums.CRC16_CCITT(data.Slice(SIZE_G5BW - 0x100, 0x8C));
-            if (chk1 == actual1)
+            // check the checksum footer block validity; nobody would normally modify this region
+            if (IsValidFooter(data, SIZE_G5BW, 0x8C))
                 return BW;
-            ushort chk2 = ReadUInt16LittleEndian(data[(SIZE_G5B2W2 - 0x100 + 0x94 + 0xE)..]);
-            ushort actual2 = Checksums.CRC16_CCITT(data.Slice(SIZE_G5B2W2 - 0x100, 0x94));
-            if (chk2 == actual2)
+            if (IsValidFooter(data, SIZE_G5B2W2, 0x94))
                 return B2W2;
             return Invalid;
+
+            static bool IsValidFooter(ReadOnlySpan<byte> data, int mainSize, int infoLength)
+            {
+                var footer = data.Slice(mainSize - 0x100, infoLength + 0x10);
+                ushort stored = ReadUInt16LittleEndian(footer[^2..]);
+                ushort actual = Checksums.CRC16_CCITT(footer[..infoLength]);
+                return stored == actual;
+            }
         }
 
         /// <summary>Checks to see if the data belongs to a Gen6 save</summary>
@@ -514,7 +518,7 @@ private static GameVersion GetIsG8SAV_LA(byte[] data)
             if (data.Length is not (SIZE_G8LA or SIZE_G8LA_1))
                 return Invalid;
 
-            return SwishCrypto.GetIsHashValidLA(data) ? PLA : Invalid;
+            return SwishCrypto.GetIsHashValid(data) ? PLA : Invalid;
         }
 
         private static bool GetIsBank7(ReadOnlySpan<byte> data) => data.Length == SIZE_G7BANK && data[0] != 0;