DiscIO: Move the Korean GC mess out of VolumeGC

Source/Core/Core/TitleDatabase.cpp

@@ -97,12 +97,14 @@ static bool IsWiiTitle(const std::string& game_id)
 
 static bool IsJapaneseGCTitle(const std::string& game_id)
 {
-  return IsGCTitle(game_id) && DiscIO::CountrySwitch(game_id[3]) == DiscIO::Country::Japan;
+  return IsGCTitle(game_id) && DiscIO::CountrySwitch(game_id[3], DiscIO::Platform::GameCubeDisc) ==
+                                   DiscIO::Country::Japan;
 }
 
 static bool IsNonJapaneseGCTitle(const std::string& game_id)
 {
-  return IsGCTitle(game_id) && DiscIO::CountrySwitch(game_id[3]) != DiscIO::Country::Japan;
+  return IsGCTitle(game_id) && DiscIO::CountrySwitch(game_id[3], DiscIO::Platform::GameCubeDisc) !=
+                                   DiscIO::Country::Japan;
 }
 
 // Note that this function will not overwrite entries that already are in the maps

Source/Core/DiscIO/Enums.cpp

@@ -145,7 +145,7 @@ Country TypicalCountryForRegion(Region region)
   }
 }
 
-Region RegionSwitch(u8 country_code, Platform platform)
+Region RegionSwitch(u8 country_code, Platform platform, Region expected_region)
 {
   switch (country_code)
   {
@@ -153,8 +153,10 @@ Region RegionSwitch(u8 country_code, Platform platform)
   case 'W':
     return Region::NTSC_J;
 
-  case 'B':
   case 'E':
+    return expected_region == Region::NTSC_J ? Region::NTSC_J : Region::NTSC_U;
+
+  case 'B':
   case 'N':
   case 'Z':
     return Region::NTSC_U;
@@ -183,7 +185,7 @@ Region RegionSwitch(u8 country_code, Platform platform)
   }
 }
 
-Country CountrySwitch(u8 country_code)
+Country CountrySwitch(u8 country_code, Platform platform, Region region)
 {
   switch (country_code)
   {
@@ -222,6 +224,8 @@ Country CountrySwitch(u8 country_code)
 
   // NTSC
   case 'E':
+    return region == Region::NTSC_J ? Country::Korea : Country::USA;
+
   case 'N':  // Japanese import to USA and other NTSC regions
   case 'Z':  // Prince of Persia - The Forgotten Sands (Wii)
   case 'B':  // Ufouria: The Saga (Virtual Console)
@@ -236,7 +240,7 @@ Country CountrySwitch(u8 country_code)
     return Country::Korea;
 
   case 'W':
-    return Country::Taiwan;
+    return platform == Platform::GameCubeDisc ? Country::Korea : Country::Taiwan;
 
   default:
     if (country_code > 'A')  // Silently ignore IOS wads

Source/Core/DiscIO/Enums.h

@@ -77,8 +77,8 @@ bool IsNTSC(Region region);
 
 Country TypicalCountryForRegion(Region region);
 // Avoid using this function if you can. Country codes aren't always reliable region indicators.
-Region RegionSwitch(u8 country_code, Platform platform);
+Region RegionSwitch(u8 country_code, Platform platform, Region expected_region = Region::Unknown);
-Country CountrySwitch(u8 country_code);
+Country CountrySwitch(u8 country_code, Platform platform, Region region = Region::Unknown);
 
 Region GetSysMenuRegion(u16 title_version);
 std::string GetSysMenuVersionString(u16 title_version);

Source/Core/DiscIO/VolumeGC.cpp

@@ -87,18 +87,10 @@ Country VolumeGC::GetCountry(const Partition& partition) const
   const u8 country = ReadSwapped<u8>(3, partition).value_or(0);
   const Region region = GetRegion();
 
-  // Korean GC releases use NTSC-J.
+  if (RegionSwitch(country, Platform::GameCubeDisc, region) != region)
-  // E is normally used for America, but it's also used for English-language Korean GC releases.
-  // K is used by games that are in the Korean language.
-  // W means Taiwan for Wii games, but on the GC, it's used for English-language Korean releases.
-  // (There doesn't seem to be any pattern to which of E and W is used for Korean GC releases.)
-  if (region == Region::NTSC_J && (country == 'E' || country == 'K' || country == 'W'))
-    return Country::Korea;
-
-  if (RegionSwitch(country, Platform::GameCubeDisc) != region)
     return TypicalCountryForRegion(region);
 
-  return CountrySwitch(country);
+  return CountrySwitch(country, Platform::GameCubeDisc, region);
 }
 
 std::string VolumeGC::GetMakerID(const Partition& partition) const

Source/Core/DiscIO/VolumeWad.cpp

@@ -88,7 +88,7 @@ Country VolumeWAD::GetCountry(const Partition& partition) const
   if (country_code == 2)  // SYSMENU
     return TypicalCountryForRegion(GetSysMenuRegion(m_tmd.GetTitleVersion()));
 
-  return CountrySwitch(country_code);
+  return CountrySwitch(country_code, Platform::WiiWAD);
 }
 
 const IOS::ES::TMDReader& VolumeWAD::GetTMD(const Partition& partition) const

Source/Core/DiscIO/VolumeWii.cpp

@@ -293,10 +293,10 @@ Country VolumeWii::GetCountry(const Partition& partition) const
   const u8 country_byte = ReadSwapped<u8>(3, partition).value_or(0);
   const Region region = GetRegion();
 
-  if (RegionSwitch(country_byte, Platform::WiiDisc) != region)
+  if (RegionSwitch(country_byte, Platform::WiiDisc, region) != region)
     return TypicalCountryForRegion(region);
 
-  return CountrySwitch(country_byte);
+  return CountrySwitch(country_byte, Platform::WiiDisc, region);
 }
 
 std::string VolumeWii::GetMakerID(const Partition& partition) const