interface API: add backup memory import/export functions (#930)

* Add backup memory import/export API to interface

* Add documentation for backup import/export functions

* Simplify API

Author: Konstantysz

desmume/src/frontend/interface/interface.cpp

@@ -287,6 +287,28 @@ EXPORTED char* desmume_savestate_slot_date(int index)
     return savestates[index].date;
 }
 
+EXPORTED BOOL desmume_backup_import_file(const char *filename, unsigned int force_size) {
+	if (!nds.backupDevice.isBackupDeviceAvailable()) {
+		return FALSE;
+	}
+	
+	bool success = nds.backupDevice.importData(filename, force_size);
+	
+	if (success) {
+		NDS_Reset();
+	}
+	
+	return success ? TRUE : FALSE;
+}
+
+EXPORTED BOOL desmume_backup_export_file(const char *filename) {
+	if (!nds.backupDevice.isBackupDeviceAvailable()) {
+		return FALSE;
+	}
+	
+	return nds.backupDevice.exportData(filename) ? TRUE : FALSE;
+}
+
 EXPORTED BOOL desmume_gpu_get_layer_main_enable_state(int layer_index)
 {
     return GPU->GetEngineMain()->GetLayerEnableState(layer_index);

desmume/src/frontend/interface/interface.h

@@ -106,6 +106,27 @@ EXPORTED void desmume_savestate_slot_save(int index);
 EXPORTED BOOL desmume_savestate_slot_exists(int index);
 EXPORTED char* desmume_savestate_slot_date(int index);
 
+// Battery save (backup memory) import/export
+
+/**
+ * Import battery save file with optional size override.
+ * Supports .sav (raw), .dsv (DeSmuME), .duc (Action Replay), .dss (DSOrganize).
+ * The emulator will automatically reset after successful import.
+ * 
+ * @param filename Path to battery save file
+ * @param force_size Backup size in bytes (0 = auto-detect, or explicit size like 524288 for 512KB)
+ * @return TRUE on success, FALSE on failure
+ */
+EXPORTED BOOL desmume_backup_import_file(const char *filename, unsigned int force_size);
+
+/**
+ * Export current battery save to .dsv file.
+ * 
+ * @param filename Destination path for .dsv file
+ * @return TRUE on success, FALSE on failure
+ */
+EXPORTED BOOL desmume_backup_export_file(const char *filename);
+
 EXPORTED BOOL desmume_gpu_get_layer_main_enable_state(int layer_index);
 EXPORTED BOOL desmume_gpu_get_layer_sub_enable_state(int layer_index);
 EXPORTED void desmume_gpu_set_layer_main_enable_state(int layer_index, BOOL the_state);