Add line 16 subtotal calculation

Added:
- Line 16: Subtotal of lines 08, 09, 9B (for user reference)
- calculateLine16() method that sums VAT amounts from lines 08, 09, 9B
- Line 16 definition in CA-3 line definitions
- Line 16 will appear automatically in the view page
- This provides a subtotal for the user before line 17 (manual entry)

core/class/declarationtva.class.php

@@ -281,6 +281,9 @@ class DeclarationTVA
         // Debug totals
         error_log("DeclarationTVA: Total VAT collected: $total_vat_collected, Total VAT deductible: $total_vat_deductible");
         
+        // Calculate line 16: Subtotal of lines 08, 09, 9B (for user reference)
+        $this->calculateLine16($declaration_id);
+        
         // Calculate D-section result lines (25, 26, 28, 29)
         $this->calculateDSectionLines($declaration_id, $total_vat_collected, $total_vat_deductible);
 
@@ -295,6 +298,40 @@ class DeclarationTVA
         return true;
     }
 
+    /**
+     * Calculate line 16: Subtotal of lines 08, 09, 9B (for user reference)
+     *
+     * @param int $declaration_id Declaration ID
+     * @return bool Success
+     */
+    private function calculateLine16($declaration_id)
+    {
+        // Get the amounts from lines 08, 09, 9B
+        $sql = "SELECT ca3_line, vat_amount FROM " . MAIN_DB_PREFIX . "declarationtva_ca3_lines 
+                WHERE declaration_id = " . (int)$declaration_id . " 
+                AND ca3_line IN ('08', '09', '9B')";
+        
+        $result = $this->db->query($sql);
+        $line_16_total = 0;
+        $account_labels = array();
+        
+        if ($result) {
+            while ($obj = $this->db->fetch_object($result)) {
+                $line_16_total += $obj->vat_amount;
+                $account_labels[] = "Line " . $obj->ca3_line . ": " . number_format($obj->vat_amount, 2);
+            }
+        }
+        
+        // Create line 16 record
+        $this->createCA3Line($declaration_id, '16', 'Subtotal: ' . implode(', ', $account_labels), array(
+            'base_amount' => 0,
+            'vat_amount' => $line_16_total,
+            'total_amount' => $line_16_total
+        ));
+        
+        return true;
+    }
+
     /**
      * Calculate D-section result lines (25, 26, 28, 29)
      *

core/class/declarationtva_config.class.php

@@ -291,6 +291,13 @@ class DeclarationTVA_Config
                 'description' => 'Base HT and VAT amounts due at reduced rates (5,5% and 2,1%)',
                 'pcg_accounts' => 'Base: 7xxxx (Sales); VAT: 44573x (5,5%) / 44574x (2,1%)'
             ),
+            '16' => array(
+                'label' => 'Sous-total TVA due (08 + 09 + 9B)',
+                'type' => 'calculated',
+                'section' => 'B',
+                'description' => 'Subtotal of VAT due (calculated from lines 08, 09, 9B)',
+                'pcg_accounts' => 'Calculated automatically'
+            ),
             '17' => array(
                 'label' => 'TVA due au titre des acquisitions intracommunautaires (autoliquidation)',
                 'type' => 'vat',