Implement professional PDF-based label printing for boxes and locations

- Replace ZPL/image-based printing with ReportLab PDF generation
- Box labels: 8cm x 5cm landscape with 'BOX Nr:' header and CODE128 barcode
- Location labels: 8cm x 5cm landscape with 'Location nr:' header and CODE128 barcode
- Add /generate_box_label_pdf endpoint using same approach as print_module
- Update FG scan quick box creation to use PDF printing with default printer
- Switch from CDN QZ Tray to local patched version for pairing-key auth
- Improve error handling and logging throughout printing workflow
- Fix import issues (add mm unit to warehouse.py)
- Optimize barcode size and spacing for better readability

py_app/app/routes.py

@@ -3710,6 +3710,133 @@ def generate_labels_pdf(order_id, paper_saving_mode='true'):
         return jsonify({'error': str(e)}), 500
 
 
+@bp.route('/generate_box_label_pdf', methods=['POST'])
+def generate_box_label_pdf():
+    """Generate a PDF box label with barcode for printing via QZ Tray"""
+    
+    if 'role' not in session:
+        return jsonify({'error': 'Access denied. Please log in.'}), 403
+    
+    try:
+        from io import BytesIO
+        from reportlab.lib.pagesizes import letter
+        from reportlab.pdfgen import canvas
+        from reportlab.lib import colors
+        from reportlab.lib.units import mm
+        from reportlab.graphics.barcode import code128
+        from flask import make_response
+        
+        # Get box number from request
+        box_number = request.form.get('box_number', 'Unknown')
+        
+        print(f"DEBUG: Generating box label PDF for box: {box_number}")
+        
+        # Create PDF buffer
+        pdf_buffer = BytesIO()
+        
+        # Create canvas with 8cm x 5cm size in landscape orientation
+        page_width = 80 * mm   # 8 cm
+        page_height = 50 * mm  # 5 cm
+        c = canvas.Canvas(pdf_buffer, pagesize=(page_width, page_height))
+        
+        # Optimize for label printer
+        c.setPageCompression(1)
+        c.setCreator("Trasabilitate Box Label System")
+        c.setTitle("Box Label - Optimized for Label Printers")
+        
+        # Define margins and usable area
+        margin = 2 * mm
+        usable_width = page_width - (2 * margin)
+        usable_height = page_height - (2 * margin)
+        
+        # Calculate vertical layout
+        # Top section: "BOX Nr: XXXXXXXX" text
+        # Bottom section: Barcode
+        text_height = 12 * mm  # Space for text at top (reduced from 15mm)
+        barcode_height = usable_height - text_height - (1 * mm)  # Rest for barcode with minimal spacing (reduced from 3mm)
+        
+        # === TOP SECTION: BOX Nr Label ===
+        # Position from top of usable area
+        text_y = page_height - margin - text_height
+        
+        # Draw "BOX Nr:" label
+        c.setFont("Helvetica-Bold", 14)
+        label_text = "BOX Nr:"
+        label_width = c.stringWidth(label_text, "Helvetica-Bold", 14)
+        
+        # Draw box number
+        c.setFont("Helvetica-Bold", 18)
+        number_text = box_number
+        number_width = c.stringWidth(number_text, "Helvetica-Bold", 18)
+        
+        # Calculate total width and center everything
+        total_text_width = label_width + 3*mm + number_width  # 3mm spacing between label and number
+        start_x = margin + (usable_width - total_text_width) / 2
+        
+        # Draw label text
+        c.setFont("Helvetica-Bold", 14)
+        c.drawString(start_x, text_y + 5*mm, label_text)
+        
+        # Draw box number
+        c.setFont("Helvetica-Bold", 18)
+        c.drawString(start_x + label_width + 3*mm, text_y + 5*mm, number_text)
+        
+        # === BOTTOM SECTION: Barcode ===
+        barcode_y = margin
+        
+        try:
+            # Create barcode for box number
+            barcode = code128.Code128(
+                box_number, 
+                barWidth=0.4*mm,  # Thicker bars for better scanning
+                barHeight=barcode_height,
+                humanReadable=True,
+                fontSize=10
+            )
+            
+            # Calculate scaling to fit width
+            scale_factor = usable_width / barcode.width
+            
+            # Center the barcode horizontally
+            barcode_x = margin + (usable_width - (barcode.width * scale_factor)) / 2
+            
+            # Draw the barcode
+            c.saveState()
+            c.translate(barcode_x, barcode_y)
+            c.scale(scale_factor, 1)
+            barcode.drawOn(c, 0, 0)
+            c.restoreState()
+            
+            print(f"DEBUG: Barcode generated successfully with scale factor: {scale_factor}")
+            
+        except Exception as e:
+            print(f"DEBUG: Error generating barcode: {e}")
+            # Fallback: draw text if barcode fails
+            c.setFont("Helvetica-Bold", 12)
+            text_width = c.stringWidth(box_number, "Helvetica-Bold", 12)
+            c.drawString((page_width - text_width) / 2, barcode_y + barcode_height/2, box_number)
+        
+        c.save()
+        
+        # Get PDF data
+        pdf_buffer.seek(0)
+        pdf_data = pdf_buffer.getvalue()
+        
+        # Create response
+        response = make_response(pdf_data)
+        response.headers['Content-Type'] = 'application/pdf'
+        response.headers['Content-Disposition'] = f'inline; filename="box_label_{box_number}.pdf"'
+        
+        print(f"DEBUG: Box label PDF generated successfully")
+        return response
+        
+    except Exception as e:
+        print(f"DEBUG: Error generating box label PDF: {e}")
+        import traceback
+        traceback.print_exc()
+        return jsonify({'error': str(e)}), 500
+
+
 @bp.route('/generate_label_pdf', methods=['POST'])
 def generate_label_pdf():
     """Generate a single label PDF for thermal printing via QZ Tray"""