Fixed double-sided printing

ref #14

src/PdfCreator.ts

@@ -129,10 +129,11 @@ export class PdfCreator {
             const pdfs = await Promise.all(pdf_promises);
             return await this.mergePdfs(pdfs);
         }
+        const cards_swapped = this.swapArrayPairs(cards);
         await i18next.changeLanguage(locale);
         const template_source = fs.readFileSync(`${this.templateDir}/runner_card.html`, 'utf8');
         const template = Handlebars.compile(template_source);
-        const result = template({ cards, eventname: "LfK! 2069" })
+        const result = template({ cards, cards_swapped, eventname: "LfK! 2069" })
         const pdf = await this.renderPdf(result, { format: "A4", landscape: false });
         return pdf
     }
@@ -220,4 +221,22 @@ export class PdfCreator {
         runner.group = group;
         return runner;
     }
+
+    /**
+     * Swaps pairs (0/1, 2/3, ...) of elements in an array recursively.
+     * If the last element has no partner it inserts an empty element at the end and swaps the two
+     * This is needed to generate pdfs with front- and backside that get printet on one paper.
+     * @param array The array which's pairs shall get switched.
+     * @returns Array with swapped pairs,
+     */
+    private swapArrayPairs(array): Array<any> {
+        if (array.length == 1) {
+            return [null, array[0]];
+        }
+        if (array.length == 0) {
+            return null;
+        }
+
+        return [array[1], array[0]].concat(this.swapArrayPairs(array.slice(2)));
+    }
 }