Fix th06.ksy so we no longer edit the generated Python file.

See #61. I found this pattern online to better represent stages with
offsets.

project/thscoreboard/replays/kaitai_parsers/th06.py

@@ -47,10 +47,43 @@ def _read(self):
             self.unknown_5 = self._io.read_u4le()
             self.stage_offsets = []
             for i in range(7):
-                self.stage_offsets.append(self._io.read_u4le())
+                self.stage_offsets.append(Th06.StagePointer(self._io, self, self._root))
 
 
 
+    class StagePointer(KaitaiStruct):
+        def __init__(self, _io, _parent=None, _root=None):
+            self._io = _io
+            self._parent = _parent
+            self._root = _root if _root else self
+            self._read()
+
+        def _read(self):
+            self.raw_offset = self._io.read_u4le()
+
+        @property
+        def offset(self):
+            """Offset relative to decrypted file."""
+            if hasattr(self, '_m_offset'):
+                return self._m_offset
+
+            self._m_offset = (self.raw_offset - 15)
+            return getattr(self, '_m_offset', None)
+
+        @property
+        def body(self):
+            if hasattr(self, '_m_body'):
+                return self._m_body
+
+            if self.raw_offset != 0:
+                _pos = self._io.pos()
+                self._io.seek(self.offset)
+                self._m_body = Th06.Stage(self._io, self, self._root)
+                self._io.seek(_pos)
+
+            return getattr(self, '_m_body', None)
+
+
     class Stage(KaitaiStruct):
         def __init__(self, _io, _parent=None, _root=None):
             self._io = _io
@@ -68,25 +101,4 @@ def _read(self):
             self.rank = self._io.read_u1()
 
 
-    @property
-    def stages(self):
-        if hasattr(self, '_m_stages'):
-            return self._m_stages
-
-        _pos = self._io.pos()
-        self._m_stages = []
-        for i in range(7):
-            _on = self.file_header.stage_offsets[i]
-            if _on == 0:
-                self._m_stages.append(Th06.Dummy(self._io, self, self._root))
-            else:
-                #   the th06 decryptor only returns the decrypted data instead of the full file
-                #   the game stores these stage offsets from the start of the file
-                #   thus we must adjust them to account for this difference when reading the stage data
-                self._io.seek(self.file_header.stage_offsets[i]-15)
-                self._m_stages.append(Th06.Stage(self._io, self, self._root))
-
-        self._io.seek(_pos)
-        return getattr(self, '_m_stages', None)
-
 

project/thscoreboard/replays/replay_parsing.py

@@ -126,9 +126,9 @@ def _Parse06(rep_raw):
     rep_stages = []
 
     enumerated_non_dummy_stages = [
-        (i, _stage)
-        for i, _stage in enumerate(replay.stages)
-        if replay.file_header.stage_offsets[i] != 0
+        (i, _pointer.body)
+        for i, _pointer in enumerate(replay.file_header.stage_offsets)
+        if _pointer.body
     ]
     # TH06 stores stage data values from the start of the stage but score from the end
     for (i, current_stage), (j, next_stage) in zip(

ref/threp-ksy/th06.ksy

@@ -5,16 +5,6 @@ meta:
 seq:
   - id: file_header
     type: file_header
-instances:
-  stages:
-    pos: file_header.stage_offsets[_index] - 15
-    type:
-      switch-on: file_header.stage_offsets[_index]
-      cases:
-        0: dummy
-        _: stage
-    repeat: expr
-    repeat-expr: 7
 types:
   dummy:
     doc: blank type
@@ -43,9 +33,25 @@ types:
       - id: unknown_5
         type: u4
       - id: stage_offsets
-        type: u4
+        type: stage_pointer
         repeat: expr
         repeat-expr: 7
+  stage_pointer:
+    seq:
+      - id: raw_offset
+        doc: Raw offset, relative to encrypted file
+        type: u4
+    instances:
+      offset:
+        doc: Offset relative to decrypted file
+        value: raw_offset - 15
+      # See https://github.com/kaitai-io/kaitai_struct/issues/14
+      # for an explanation of this pattern.
+      body:
+        pos: offset
+        type: stage
+        if: raw_offset != 0
+
   stage:
     seq:
       - id: score