cfg: fix config save atomicity (#760)

## Link to GitHub Issue or related Pull Request, if one exists
n/a

## Description of change
Fully flush `tmp` file and then use `MoveFileExW` instead of `CopyFileW`
which guarantees atomic operation on NTFS.

## Testing

src/spice2x/cfg/config.cpp

@@ -1331,17 +1331,32 @@ bool Config::firstFillConfigFile() {
 }
 
 void Config::saveConfigFile() {
-    // create a .tmp file and write to it...
+    // write the new config to a .tmp file first...
     const auto xml_result = this->configFile.SaveFile(this->configLocationTemp.c_str(), false);
     if (xml_result != tinyxml2::XMLError::XML_SUCCESS) {
         log_info("cfg", "failed to write file: {}", this->configLocationTemp);
         return;
     }
-    // copy the .tmp file to the main file...
-    if (CopyFileW(this->configLocationTemp.c_str(), this->configLocation.c_str(), false) == 0) {
-        log_warning("cfg", "CopyFileA failed: 0x{:08x}", GetLastError());
+
+    // ...flush the .tmp file to disk so a crash/power loss can't leave it half-written...
+    HANDLE tmp_handle = CreateFileW(
+        this->configLocationTemp.c_str(),
+        GENERIC_WRITE, FILE_SHARE_READ, nullptr,
+        OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr);
+    if (tmp_handle != INVALID_HANDLE_VALUE) {
+        FlushFileBuffers(tmp_handle);
+        CloseHandle(tmp_handle);
+    }
+
+    // ...then atomically replace the real config with the .tmp file.
+    // Unlike CopyFile (which truncates and rewrites the destination in place),
+    // an NTFS rename is atomic: the existing config is never left half-overwritten,
+    // so an interrupted save can't corrupt it. MoveFileEx also removes the .tmp on success.
+    if (MoveFileExW(
+            this->configLocationTemp.c_str(),
+            this->configLocation.c_str(),
+            MOVEFILE_REPLACE_EXISTING | MOVEFILE_WRITE_THROUGH) == 0) {
+        log_warning("cfg", "MoveFileExW failed: 0x{:08x}", GetLastError());
         return;
     }
-    // delete the .tmp file (not critical if this fails)
-    DeleteFileW(this->configLocationTemp.c_str());
 }

src/spice2x/cfg/controller_presets.cpp

@@ -359,13 +359,12 @@ namespace overlay::windows {
             return false;
         }
 
-        std::error_code ec;
-        std::filesystem::rename(path_tmp, path, ec);
-        if (ec) {
-            log_warning("templates", "failed to rename templates file: {}", ec.message());
+        if (MoveFileExW(path_tmp.c_str(), path.c_str(), MOVEFILE_REPLACE_EXISTING | MOVEFILE_WRITE_THROUGH) == 0) {
+            log_warning("templates", "failed to rename templates file: 0x{:08x}", GetLastError());
             return false;
         }
 
+        log_info("templates", "templates file saved successfully");
         return true;
     }
 
@@ -397,8 +396,7 @@ namespace overlay::windows {
             auto path_tmp = path;
             path_tmp.replace_extension(L"tmp");
             if (doc.SaveFile(path_tmp.c_str()) == tinyxml2::XML_SUCCESS) {
-                std::error_code ec;
-                std::filesystem::rename(path_tmp, path, ec);
+                MoveFileExW(path_tmp.c_str(), path.c_str(), MOVEFILE_REPLACE_EXISTING | MOVEFILE_WRITE_THROUGH);
             }
         }
 
@@ -434,8 +432,7 @@ namespace overlay::windows {
             auto path_tmp = path;
             path_tmp.replace_extension(L"tmp");
             if (doc.SaveFile(path_tmp.c_str()) == tinyxml2::XML_SUCCESS) {
-                std::error_code ec;
-                std::filesystem::rename(path_tmp, path, ec);
+                MoveFileExW(path_tmp.c_str(), path.c_str(), MOVEFILE_REPLACE_EXISTING | MOVEFILE_WRITE_THROUGH);
             }
         }
 

src/spice2x/overlay/windows/card_manager.cpp

@@ -536,7 +536,7 @@ namespace overlay::windows {
     }
 
     void CardManager::config_save() {
-        log_info("cardmanager", "saving config");
+        log_misc("cardmanager", "saving config...");
 
         // create document
         Document doc;

src/spice2x/util/fileutils.cpp

@@ -298,5 +298,19 @@ bool fileutils::write_config_file(const std::string_view &module, const std::fil
 
     // save file
     log_info(module, "saving config file: {}", censored_display);
-    return fileutils::text_write(path, text);
+
+    // write to a .tmp file first, then atomically replace the real config — this way
+    // a crash or disk-full mid-write can't corrupt the existing config file.
+    auto path_tmp = path;
+    path_tmp += L".tmp";
+    if (!fileutils::text_write(path_tmp, text)) {
+        log_warning(module, "failed to write temp config file: {}", censored_display);
+        return false;
+    }
+    if (MoveFileExW(path_tmp.c_str(), path.c_str(), MOVEFILE_REPLACE_EXISTING | MOVEFILE_WRITE_THROUGH) == 0) {
+        log_warning(module, "MoveFileExW failed: 0x{:08x}", GetLastError());
+        return false;
+    }
+
+    return true;
 }