implemented live price update in document view

Signed-off-by: Stephan Richter <s.richter@srsoftware.de>

frontend/src/routes/document/PositionList.svelte

@@ -14,6 +14,23 @@
     } = $props();
 
     let editable = $derived(document.state == 1);
+    let sums = $derived.by(calcSums);
+
+    function calcSums(){
+        let data  = {}
+        let net   = 0;
+        let gross = 0;
+        for (let pos of Object.values(document.positions)){
+            let net_price = pos.unit_price * pos.amount;
+            let tax       = +pos.tax;
+            data[tax]     = net_price + (data[tax] ? data[tax] : 0);
+            net          += net_price;
+        }
+        for (let [tax, price] of Object.entries(data)) gross += price * (+tax+100)/100;
+        data['net']   = net/100;
+        data['gross'] = (gross/100).toFixed(2);
+        return data;
+    }
 
     async function updatePositions(resp){
         let json           = await resp.json();
@@ -73,9 +90,9 @@
         <tr class="sums">
             <td colspan="2"></td>
             <td>{t('net_sum')}</td>
-            <td>{document.net_sum/100}&nbsp;{document.currency}</td>
+            <td>{sums['net']}&nbsp;{document.currency}</td>
             <td colspan="2">{t('gross_sum')}</td>
-            <td>{document.gross_sum/100}&nbsp;{document.currency}</td>
+            <td>{sums['gross']}&nbsp;{document.currency}</td>
             <td></td>
         </tr>
     </tbody>