From 8c393c8f9ef6454a453cb74626f196315aebfbeb Mon Sep 17 00:00:00 2001
From: Daniel Dybing <daniel.dybing@gmail.com>
Date: Sun, 11 Jan 2026 11:40:20 +0100
Subject: [PATCH] Fix language detection bit swap in T42 header parsing
 Correctly map C12 and C13 control bits to fix misidentification of
 Swedish/Finnish (010) and German (001). Also ensures Page model, Renderer,
 and UI properly propagate and display the detected language.

---
 src/teletext/io.py       | 18 +++++++++++++++---
 src/teletext/models.py   |  1 +
 src/teletext/renderer.py |  6 ++++++
 src/teletext/ui.py       | 17 +++++++++++++++--
 4 files changed, 37 insertions(+), 5 deletions(-)

diff --git a/src/teletext/io.py b/src/teletext/io.py
index f2f6d81..77046a2 100644
--- a/src/teletext/io.py
+++ b/src/teletext/io.py
@@ -43,10 +43,10 @@ def load_t42(file_path: str, progress_callback: Optional[Callable[[int, int], No
                 # or find the existing one if we want to support updates (but T42 usually is a stream capture).
                 # If it's an editor file, it's likely sequential.
                 
-                p_num, sub_code = parse_header(packet.data)
+                p_num, sub_code, language = parse_header(packet.data)
                 
                 # Create new page
-                new_page = Page(magazine=packet.magazine, page_number=p_num, sub_code=sub_code)
+                new_page = Page(magazine=packet.magazine, page_number=p_num, sub_code=sub_code, language=language)
                 new_page.packets.append(packet)
                 service.pages.append(new_page)
             else:
@@ -209,4 +209,16 @@ def parse_header(data: bytearray):
     
     sub_code = s1 | (s2 << 4) | (s3 << 8) | (s4 << 12)
     
-    return page_num, sub_code
+    # Control bits C12, C13, C14 are in Byte 8 (index 8)
+    # They determine the National Option (Language)
+    c_bits_2 = decode_hamming_8_4(data[8])
+    
+    # Fix for Language Detection:
+    # It seems C12 and C13 are swapped in the Hamming decoding or file format relative to expected values.
+    # C12 is bit 0, C13 is bit 1.
+    # We swap them so D1 maps to C13 (Swedish bit) and D2 maps to C12 (German bit).
+    # Original: language = c_bits_2 & 0b111
+    
+    language = ((c_bits_2 & 1) << 1) | ((c_bits_2 & 2) >> 1) | (c_bits_2 & 4)
+    
+    return page_num, sub_code, language
diff --git a/src/teletext/models.py b/src/teletext/models.py
index 90273e6..6fa2639 100644
--- a/src/teletext/models.py
+++ b/src/teletext/models.py
@@ -76,6 +76,7 @@ class Page:
     magazine: int
     page_number: int  # 00-99
     sub_code: int = 0 # Subpage code (0000 to 3F7F hex usually, simplest is 0-99 equivalent)
+    language: int = 0 # National Option (0-7)
     packets: List[Packet] = field(default_factory=list)
     
     @property
diff --git a/src/teletext/renderer.py b/src/teletext/renderer.py
index f2888d1..96b1dfd 100755
--- a/src/teletext/renderer.py
+++ b/src/teletext/renderer.py
@@ -139,6 +139,12 @@ class TeletextCanvas(QWidget):
     
     def set_page(self, page: Page):
         self.page = page
+        # Set language from page header
+        if page:
+            self.subset_idx = page.language
+        else:
+            self.subset_idx = 0
+            
         self.cursor_x = 0
         self.cursor_y = 0
         self.redraw()
diff --git a/src/teletext/ui.py b/src/teletext/ui.py
index 39efb94..904861e 100644
--- a/src/teletext/ui.py
+++ b/src/teletext/ui.py
@@ -127,10 +127,22 @@ class MainWindow(QMainWindow):
         
         self.status_label = QLabel("Ready")
         self.status_bar.addWidget(self.status_label)
+        
+        self.language_label = QLabel("Lang: English")
+        self.status_bar.addPermanentWidget(self.language_label)
+
+        self.language_names = ["English", "German", "Swedish/Finnish", "Italian", "French", "Portuguese/Spanish", "Turkish", "Romania"]
 
         # Menus
         self.create_menus()
 
+    def update_language_label(self):
+        idx = self.canvas.subset_idx
+        if 0 <= idx < len(self.language_names):
+            self.language_label.setText(f"Lang: {self.language_names[idx]}")
+        else:
+            self.language_label.setText(f"Lang: Unknown ({idx})")
+
     def set_modified(self, modified: bool):
         self.is_modified = modified
         title = "Teletext Editor"
@@ -222,8 +234,7 @@ class MainWindow(QMainWindow):
         view_menu = menu_bar.addMenu("View")
         
         lang_menu = view_menu.addMenu("Language")
-        langs = ["English", "German", "Swedish/Finnish", "Italian", "French", "Portuguese/Spanish", "Turkish", "Romania"]
-        for i, lang in enumerate(langs):
+        for i, lang in enumerate(self.language_names):
             action = QAction(lang, self)
             action.setData(i)
             action.triggered.connect(self.set_language)
@@ -236,6 +247,7 @@ class MainWindow(QMainWindow):
             self.canvas.subset_idx = idx
             self.canvas.redraw()
             self.canvas.update()
+            self.update_language_label()
 
     def prev_subpage(self):
         count = self.subpage_combo.count()
@@ -516,6 +528,7 @@ class MainWindow(QMainWindow):
         if isinstance(page, Page):
             self.current_page = page
             self.canvas.set_page(page)
+            self.update_language_label()
             self.canvas.setFocus()
 
     def insert_char(self, char_code):