Feature: Enhanced Editing, Hex Inspector, Color Shortcuts

- Enhanced Editing: Auto-create packets, Enter key support.
- Cursor: Fixed visibility (composition mode), click-to-move, immediate redraw.
- Hex Inspector: Added Hex Value display and input panel.
- Shortcuts: Added Color Insert buttons.
- Fixes: Resolved Hamming encoding for save, fixed duplicate spaces bug, fixed IndentationError.

src/teletext/io.py

@@ -62,24 +62,74 @@ def load_t42(file_path: str) -> TeletextService:
 
     return service
 
+
+def encode_hamming_8_4(value):
+    # Value is 4 bits (0-15)
+    d1 = (value >> 0) & 1
+    d2 = (value >> 1) & 1
+    d3 = (value >> 2) & 1
+    d4 = (value >> 3) & 1
+    
+    # Parity bits (Odd parity default? Or standard Hamming?)
+    # Teletext spec: 
+    # P1 = 1 + D1 + D2 + D4 (mod 2) -> Inverse of even parity check?
+    # Actually, simpler to look up or calculate. 
+    # Let's match typical implementation:
+    # P1 (b0) covers 1,3,7 (D1, D2, D4)
+    # P2 (b2) covers 1,5,7 (D1, D3, D4)
+    # P3 (b4) covers 3,5,7 (D2, D3, D4)
+    # P4 (b6) covers all.
+    # Teletext uses ODD parity for the hamming bits usually?
+    # "Hamming 8/4 with odd parity"
+    
+    p1 = 1 ^ d1 ^ d2 ^ d4
+    p2 = 1 ^ d1 ^ d3 ^ d4
+    p3 = 1 ^ d2 ^ d3 ^ d4
+    
+    res = (p1 << 0) | (d1 << 1) | \
+          (p2 << 2) | (d2 << 3) | \
+          (p3 << 4) | (d3 << 5) | \
+          (d4 << 7)
+          
+    # P4 (bit 6) makes total bits odd
+    # Count set bits so far
+    set_bits = bin(res).count('1')
+    p4 = 1 if (set_bits % 2 == 0) else 0
+    
+    res |= (p4 << 6)
+    
+    return res
+
 def save_t42(file_path: str, service: TeletextService):
     with open(file_path, 'wb') as f:
-        # User requirement: "without rearranging the order of the packets"
-        # Implies we should iterate the original list.
-        # However, if we edit data, we modify the Packet objects in place.
-        # If we Add/Delete packets, we need to handle that.
-        
         for packet in service.all_packets:
-            # Reconstruct the 42 bytes from the packet fields
-            # The packet.data (bytearray) should be mutable and edited by the UI.
-            # packet.original_data (first 2 bytes) + packet.data
+            # Reconstruct header bytes from packet.magazine and packet.row
+            # Byte 1: M1 M2 M3 R1
+            # Byte 2: R2 R3 R4 R5
             
-            # Note: If we changed Magazine or Row, we'd need to re-encode the first 2 bytes.
-            # For now, assume we primarily edit content (bytes 2-41).
+            mag = packet.magazine
+            if mag == 8: mag = 0 # 0 encoded as 8
             
-            header = packet.original_data[:2] # Keep original address for now
-            # TODO: regenerating header if Mag/Row changed
+            # Bits:
+            # B1 data: M1(0) M2(1) M3(2) R1(3)
+            m1 = (mag >> 0) & 1
+            m2 = (mag >> 1) & 1
+            m3 = (mag >> 2) & 1
+            r1 = (packet.row >> 0) & 1
             
+            b1_val = m1 | (m2 << 1) | (m3 << 2) | (r1 << 3)
+            b1_enc = encode_hamming_8_4(b1_val)
+            
+            # B2 data: R2(0) R3(1) R4(2) R5(3)
+            r2 = (packet.row >> 1) & 1
+            r3 = (packet.row >> 2) & 1
+            r4 = (packet.row >> 3) & 1
+            r5 = (packet.row >> 4) & 1
+            
+            b2_val = r2 | (r3 << 1) | (r4 << 2) | (r5 << 3)
+            b2_enc = encode_hamming_8_4(b2_val)
+            
+            header = bytes([b1_enc, b2_enc])
             f.write(header + packet.data)
 
 def decode_hamming_8_4(byte_val):