feat(BillingService): add file path resolution for PDF templates

- Implemented a new method to resolve existing file paths for PDF templates, enhancing file handling robustness.
- Updated PDF storage path handling to ensure correct resolution of paths before file operations, improving error handling and reliability.
- Refactored related logic to utilize the new path resolution method across various template operations.

backend/services/billingService.js

@@ -30,6 +30,30 @@ const toMonthDate = (value, endOfMonth = false) => {
 };
 
 class BillingService {
+  _resolveExistingFilePath(storedPath) {
+    const rawPath = String(storedPath || '').trim();
+    if (!rawPath) return null;
+
+    const candidates = [];
+    if (path.isAbsolute(rawPath)) {
+      candidates.push(rawPath);
+    } else {
+      const normalizedRawPath = rawPath.replace(/^\.?[\\/]/, '');
+      candidates.push(path.resolve(rawPath));
+      candidates.push(path.resolve(process.cwd(), rawPath));
+      candidates.push(path.resolve(process.cwd(), normalizedRawPath));
+      candidates.push(path.resolve(process.cwd(), 'backend', normalizedRawPath));
+      candidates.push(path.resolve(process.cwd(), '..', normalizedRawPath));
+    }
+
+    for (const candidate of candidates) {
+      if (candidate && fs.existsSync(candidate)) {
+        return candidate;
+      }
+    }
+    return null;
+  }
+
   _normalizeIban(raw, withoutCountry = false) {
     const cleaned = String(raw || '').replace(/[^a-zA-Z0-9]/g, '').toUpperCase();
     if (!cleaned) return '';
@@ -347,7 +371,7 @@ class BillingService {
       clubId,
       name,
       description: payload?.description ? String(payload.description).trim() : null,
-      pdfStoragePath: file.path,
+      pdfStoragePath: path.resolve(file.path),
       pdfFilename: file.originalname,
       pdfMimeType: file.mimetype || 'application/pdf',
       isActive: true,
@@ -386,9 +410,10 @@ class BillingService {
       throw error;
     }
 
-    if (template.pdfStoragePath && fs.existsSync(template.pdfStoragePath)) {
+    const storedTemplatePath = this._resolveExistingFilePath(template.pdfStoragePath);
+    if (storedTemplatePath) {
       try {
-        fs.unlinkSync(template.pdfStoragePath);
+        fs.unlinkSync(storedTemplatePath);
       } catch (error) {
         // Ignore file cleanup errors, DB deletion already succeeded.
       }
@@ -568,7 +593,8 @@ class BillingService {
       return { status: 404, response: { success: false, error: 'Abrechnungslauf nicht gefunden' } };
     }
     await checkAccess(userToken, run.clubId);
-    if (!run.template?.pdfStoragePath || !fs.existsSync(run.template.pdfStoragePath)) {
+    const resolvedTemplatePath = this._resolveExistingFilePath(run.template?.pdfStoragePath);
+    if (!resolvedTemplatePath) {
       return { status: 404, response: { success: false, error: 'Vorlagen-PDF nicht gefunden' } };
     }
     const computed = await this._collectTrainingSessions(run.clubId, run.periodStart, run.periodEnd);
@@ -583,7 +609,7 @@ class BillingService {
     const generatedPath = path.resolve('uploads/billing-generated', generatedFilename);
 
     await this._renderBillingPdfFromTemplate(
-      run.template.pdfStoragePath,
+      resolvedTemplatePath,
       generatedPath,
       run,
       sessionsWithLabel,
@@ -656,13 +682,14 @@ class BillingService {
     const template = await BillingTemplate.findByPk(templateId);
     if (!template) return { status: 404, response: { success: false, error: 'Vorlage nicht gefunden' } };
     await checkAccess(userToken, template.clubId);
-    if (!template.pdfStoragePath || !fs.existsSync(template.pdfStoragePath)) {
+    const resolvedTemplatePath = this._resolveExistingFilePath(template.pdfStoragePath);
+    if (!resolvedTemplatePath) {
       return { status: 404, response: { success: false, error: 'Datei nicht gefunden' } };
     }
     return {
       status: 200,
       file: {
-        path: path.resolve(template.pdfStoragePath),
+        path: resolvedTemplatePath,
         name: template.pdfFilename,
         mimeType: template.pdfMimeType || 'application/pdf'
       }