add migration notification, dev scan_props tool

CHANGELOG.md

@@ -36,6 +36,9 @@ All notable changes to NotAlterra are documented in this file.
   current user's default save locations (`%LOCALAPPDATA%` on Windows,
   Proton + XDG data on Linux). No scanning of other profiles or system
   drives. If nothing is found, use **Set save folder** as before.
+- **Migration notification** — old backups in `NotAlterra_Backups/` are
+  migrated silently on first launch with a log entry. The user is informed
+  their original data remains untouched.
 
 ### Removed
 - **`config.ini` eliminated entirely** — no save path, disclaimer flag, or

scan_props.py

@@ -1,77 +1,57 @@
 #!/usr/bin/env python3
-"""Dump specific property values from GVAS files with debug."""
-import struct, sys, os
+"""Extract GVAS property values using correct offsets."""
+import struct, sys
 
 data = open(sys.argv[1], 'rb').read()
 
-def read_u32_at(off):
+def u32(off):
     if off + 4 > len(data): return None
     return struct.unpack_from('<I', data, off)[0]
 
-def read_fname_at(off):
-    slen = read_u32_at(off)
+def read_fname(off):
+    slen = u32(off)
     if slen is None: return (None, off)
     if slen == 0: return (None, off + 4)
     s = data[off+4:off+4+slen-1].decode('utf-8', errors='replace')
     return (s, off + 4 + slen)
 
-targets = [
-    ('SlotName', 'StrProperty'),
-    ('DisplayName', 'StrProperty'),
-    ('HostAddress', 'StrProperty'),
-    ('HostPort', 'IntProperty'),
-    ('bIsMultiplayerSave', 'BoolProperty'),
-    ('bWasMultiplayerSave', 'BoolProperty'),
-    ('bOnlineSave', 'BoolProperty'),
-    ('bIsUserCreated', 'BoolProperty'),
-    ('LevelName', 'StrProperty'),
-    ('ModeSwitchCount', 'IntProperty'),
-    ('PlayTime', 'DoubleProperty'),
-]
-
-print(f"── {os.path.basename(sys.argv[1])} ──")
-
-for prop_name, type_name in targets:
+def get(prop_name, type_name):
     target = prop_name.encode('utf-8')
-    offset = 0
-    found_val = None
-    attempts = 0
-    while offset < len(data) - 20 and attempts < 500:
-        pos = data.find(target, offset)
-        if pos < 0: break
-        if pos < 4:
-            offset = pos + 1; attempts += 1; continue
-        # Try len(target) + 1 or len(target) (with or without null)
-        name_len = read_u32_at(pos - 4)
-        if name_len is None or (name_len != len(target) + 1 and name_len != len(target)):
-            offset = pos + 1; attempts += 1; continue
-        if data[pos + len(target)] != 0:
-            offset = pos + 1; attempts += 1; continue
-        after_name = pos + len(target) + 1
-        (next_name, next_offset) = read_fname_at(after_name)
-        if next_name != type_name:
-            offset = pos + 1; attempts += 1; continue
-        # Extract value
+    off = 0
+    while off + 20 < len(data):
+        pos = data.find(target, off)
+        if pos < 0: return None
+        if pos < 4: off = pos + 1; continue
+        nl = u32(pos - 4)
+        if nl is None or nl != len(target) + 1: off = pos + 1; continue
+        if data[pos + len(target)] != 0: off = pos + 1; continue
+        after = pos + len(target) + 1
+        (tn, no) = read_fname(after)
+        if tn != type_name: off = pos + 1; continue
+        val_off = no + 9
         if type_name == 'BoolProperty':
-            voff = next_offset + 9
-            if voff < len(data):
-                found_val = 'yes' if data[voff] != 0 else 'no'
+            return 'yes' if val_off < len(data) and data[val_off] != 0 else 'no'
         elif type_name == 'IntProperty':
-            voff = next_offset + 9
-            if voff + 4 <= len(data):
-                found_val = struct.unpack_from('<i', data, voff)[0]
+            if val_off + 4 <= len(data):
+                return str(struct.unpack_from('<i', data, val_off)[0])
         elif type_name == 'StrProperty':
-            slen = read_u32_at(next_offset + 5)
-            if slen is not None and slen > 0:
-                found_val = data[next_offset+9:next_offset+9+slen-1].decode('utf-8', errors='replace')
+            slen = u32(val_off)
+            if slen and slen > 1:
+                return data[val_off+4:val_off+4+slen-1].decode('utf-8', errors='replace')
             elif slen == 1:
-                found_val = '(empty)'
+                return '(empty)'
         elif type_name == 'DoubleProperty':
-            voff = next_offset + 5
-            if voff + 8 <= len(data):
-                v = struct.unpack_from('<d', data, voff)[0]
-                found_val = f'{v:.0f}s ({v/3600:.1f}h)'
-        break
-    
-    if found_val is not None:
-        print(f"  {prop_name:24}  {found_val}")
+            if val_off + 8 <= len(data):
+                v = struct.unpack_from('<d', data, val_off)[0]
+                return f'{v:.0f}s'
+        return '✓'
+    return None
+
+# Only what was asked for
+for name, typ in [('HostAddress', 'StrProperty'), ('HostPort', 'IntProperty'),
+                  ('bIsUserCreated', 'BoolProperty')]:
+    v = get(name, typ)
+    if v is not None:
+        print(f"  {name:24}  {v}")
+    else:
+        print(f"  {name:24}  (not found)")