Boot: Move StateFlags from Boot_WiiWAD to Boot

It's not specific to WADs. The BS2 emulation boot code will also need
to update the state file.

Move the struct to Boot and add a helper function that will handle
reading + computing the checksum + writing the state file.

Source/Core/Core/Boot/Boot.cpp

@@ -5,7 +5,10 @@
 #include "Core/Boot/Boot.h"
 
 #include <algorithm>
+#include <array>
+#include <cstring>
 #include <memory>
+#include <numeric>
 #include <optional>
 #include <string>
 #include <unordered_set>
@@ -25,6 +28,7 @@
 
 #include "Core/Boot/DolReader.h"
 #include "Core/Boot/ElfReader.h"
+#include "Core/CommonTitles.h"
 #include "Core/ConfigManager.h"
 #include "Core/FifoPlayer/FifoPlayer.h"
 #include "Core/HLE/HLE.h"
@@ -418,3 +422,38 @@ BootExecutableReader::BootExecutableReader(const std::vector<u8>& bytes) : m_byt
 }
 
 BootExecutableReader::~BootExecutableReader() = default;
+
+void StateFlags::UpdateChecksum()
+{
+  constexpr size_t length_in_bytes = sizeof(StateFlags) - 4;
+  constexpr size_t num_elements = length_in_bytes / sizeof(u32);
+  std::array<u32, num_elements> flag_data;
+  std::memcpy(flag_data.data(), &flags, length_in_bytes);
+  checksum = std::accumulate(flag_data.cbegin(), flag_data.cend(), 0U);
+}
+
+void UpdateStateFlags(std::function<void(StateFlags*)> update_function)
+{
+  const std::string file_path =
+      Common::GetTitleDataPath(Titles::SYSTEM_MENU, Common::FROM_SESSION_ROOT) + WII_STATE;
+
+  File::IOFile file;
+  StateFlags state;
+  if (File::Exists(file_path))
+  {
+    file.Open(file_path, "r+b");
+    file.ReadBytes(&state, sizeof(state));
+  }
+  else
+  {
+    File::CreateFullPath(file_path);
+    file.Open(file_path, "a+b");
+    memset(&state, 0, sizeof(state));
+  }
+
+  update_function(&state);
+  state.UpdateChecksum();
+
+  file.Seek(0, SEEK_SET);
+  file.WriteBytes(&state, sizeof(state));
+}

Source/Core/Core/Boot/Boot.h

@@ -5,6 +5,7 @@
 #pragma once
 
 #include <cstdlib>
+#include <functional>
 #include <memory>
 #include <optional>
 #include <string>
@@ -128,3 +129,18 @@ public:
 protected:
   std::vector<u8> m_bytes;
 };
+
+struct StateFlags
+{
+  void UpdateChecksum();
+  u32 checksum;
+  u8 flags;
+  u8 type;
+  u8 discstate;
+  u8 returnto;
+  u32 unknown[6];
+};
+
+// Reads the state file from the NAND, then calls the passed update function to update the struct,
+// and finally writes the updated state file to the NAND.
+void UpdateStateFlags(std::function<void(StateFlags*)> update_function);

Source/Core/Core/Boot/Boot_WiiWAD.cpp

@@ -2,15 +2,12 @@
 // Licensed under GPLv2+
 // Refer to the license.txt file included.
 
-#include <array>
 #include <cstddef>
 #include <memory>
-#include <numeric>
 #include <string>
 
 #include "Common/CommonPaths.h"
 #include "Common/CommonTypes.h"
-#include "Common/File.h"
 #include "Common/FileUtil.h"
 #include "Common/MsgHandler.h"
 #include "Common/NandPaths.h"
@@ -24,55 +21,11 @@
 
 #include "DiscIO/NANDContentLoader.h"
 
-struct StateFlags
-{
-  u32 checksum;
-  u8 flags;
-  u8 type;
-  u8 discstate;
-  u8 returnto;
-  u32 unknown[6];
-};
-
-static u32 StateChecksum(const StateFlags& flags)
-{
-  constexpr size_t length_in_bytes = sizeof(StateFlags) - 4;
-  constexpr size_t num_elements = length_in_bytes / sizeof(u32);
-  std::array<u32, num_elements> flag_data;
-
-  std::memcpy(flag_data.data(), &flags.flags, length_in_bytes);
-
-  return std::accumulate(flag_data.cbegin(), flag_data.cend(), 0U);
-}
-
 bool CBoot::Boot_WiiWAD(const std::string& _pFilename)
 {
-  std::string state_filename(
-      Common::GetTitleDataPath(Titles::SYSTEM_MENU, Common::FROM_SESSION_ROOT) + WII_STATE);
-
-  if (File::Exists(state_filename))
-  {
-    File::IOFile state_file(state_filename, "r+b");
-    StateFlags state;
-    state_file.ReadBytes(&state, sizeof(StateFlags));
-
-    state.type = 0x03;  // TYPE_RETURN
-    state.checksum = StateChecksum(state);
-
-    state_file.Seek(0, SEEK_SET);
-    state_file.WriteBytes(&state, sizeof(StateFlags));
-  }
-  else
-  {
-    File::CreateFullPath(state_filename);
-    File::IOFile state_file(state_filename, "a+b");
-    StateFlags state;
-    memset(&state, 0, sizeof(StateFlags));
-    state.type = 0x03;       // TYPE_RETURN
-    state.discstate = 0x01;  // DISCSTATE_WII
-    state.checksum = StateChecksum(state);
-    state_file.WriteBytes(&state, sizeof(StateFlags));
-  }
+  UpdateStateFlags([](StateFlags* state) {
+    state->type = 0x03;  // TYPE_RETURN
+  });
 
   const DiscIO::NANDContentLoader& ContentLoader =
       DiscIO::NANDContentManager::Access().GetNANDLoader(_pFilename);