feat: async PDF cache i API media putanje za putne naloge

Uvodi background request tok za generiranje PDF-a s 24h cache-om i cleanup taskom preko Celery beat-a. Dodaje notification metadata download_url za ponovno preuzimanje bez regeneracije, API image endpointe za putne naloge i račune, te frontend integraciju za async download i produkcijski prikaz slika.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

backend/modules/fleet/tasks.py

@@ -3,6 +3,7 @@ from celery import shared_task
 from django.core.mail import send_mail
 from django.conf import settings
 from django.utils import timezone
+from django.core.files.base import ContentFile
 import logging
 from io import BytesIO
 import base64
@@ -10,7 +11,7 @@ from PIL import Image, UnidentifiedImageError
 from reportlab.lib.pagesizes import A4
 from reportlab.lib.utils import ImageReader
 from reportlab.pdfgen import canvas
-from .models import VehicleNotification
+from .models import VehicleNotification, GeneratedWorkOrderPdf
 from .pdf_layout import register_unicode_fonts, draw_standard_header_footer
 
 logger = logging.getLogger(__name__)
@@ -205,4 +206,106 @@ def build_work_order_invoices_pdf_task(work_order_id):
     return {
         "filename": filename,
         "pdf_base64": pdf_b64,
-    }
+    }
+
+
+@shared_task
+def cleanup_expired_generated_pdfs_task():
+    now = timezone.now()
+    expired = GeneratedWorkOrderPdf.objects.filter(
+        is_active=True,
+        expires_at__isnull=False,
+        expires_at__lte=now,
+    )
+    deleted = 0
+    for item in expired:
+        if item.file:
+            item.file.delete(save=False)
+        item.is_active = False
+        item.status = 'failed'
+        item.error_message = 'PDF cache istekao.'
+        item.save(update_fields=['is_active', 'status', 'error_message', 'updated_at'])
+        deleted += 1
+    return {"deleted": deleted}
+
+
+@shared_task
+def build_work_order_pdf_cached_task(generated_pdf_id):
+    from .views import _build_work_order_pdf, _build_work_order_service_records_pdf
+    from .services import NotificationService
+
+    generated = (
+        GeneratedWorkOrderPdf.objects
+        .select_related('work_order', 'work_order__vehicle', 'requested_by')
+        .filter(pk=generated_pdf_id, is_active=True)
+        .first()
+    )
+    if generated is None:
+        return {"error": "Generated PDF zapis nije pronađen."}
+
+    work_order = generated.work_order
+
+    try:
+        if generated.pdf_type == 'invoices':
+            payload = build_work_order_invoices_pdf_task(str(work_order.pk))
+            if not isinstance(payload, dict) or payload.get('error'):
+                raise ValueError(payload.get('error') if isinstance(payload, dict) else 'Neuspješno generiranje PDF računa.')
+            pdf_b64 = payload.get('pdf_base64')
+            if not pdf_b64:
+                raise ValueError('PDF sadržaj nije dostupan.')
+            pdf_bytes = base64.b64decode(pdf_b64)
+        elif generated.pdf_type == 'service_records':
+            pdf_bytes = _build_work_order_service_records_pdf(work_order)
+        else:
+            pdf_bytes = _build_work_order_pdf(work_order)
+
+        filename = generated.filename or f"{work_order.pk}.{generated.pdf_type}.pdf"
+        generated.file.save(filename, ContentFile(pdf_bytes), save=False)
+        generated.status = 'ready'
+        generated.error_message = ''
+        generated.save(update_fields=['file', 'status', 'error_message', 'updated_at'])
+
+        if generated.requested_by:
+            NotificationService.create_notification(
+                recipient=generated.requested_by,
+                title="PDF spreman",
+                message=f"PDF dokument je uspješno generiran za WO-{work_order.pk}.",
+                level="success",
+                send_email=False,
+                metadata={
+                    "entity_type": "work_order_pdf",
+                    "work_order_id": str(work_order.pk),
+                    "vehicle_id": str(work_order.vehicle_id),
+                    "section": "work-orders",
+                    "pdf_type": generated.pdf_type,
+                    "stage": "completed",
+                    "generated_pdf_id": str(generated.pk),
+                    "download_url": f"/api/fleet/work-orders/{work_order.pk}/generated-pdfs/{generated.pk}/download/",
+                    "filename": generated.filename or filename,
+                    "expires_at": generated.expires_at.isoformat() if generated.expires_at else None,
+                },
+            )
+        return {"status": "ready", "generated_pdf_id": str(generated.pk)}
+    except Exception as exc:
+        generated.status = 'failed'
+        generated.error_message = str(exc)
+        generated.save(update_fields=['status', 'error_message', 'updated_at'])
+        if generated.requested_by:
+            NotificationService.create_notification(
+                recipient=generated.requested_by,
+                title="Greška kod PDF-a",
+                message=f"Generiranje PDF dokumenta nije uspjelo za WO-{work_order.pk}.",
+                level="warning",
+                send_email=False,
+                metadata={
+                    "entity_type": "work_order_pdf",
+                    "work_order_id": str(work_order.pk),
+                    "vehicle_id": str(work_order.vehicle_id),
+                    "section": "work-orders",
+                    "pdf_type": generated.pdf_type,
+                    "stage": "failed",
+                    "generated_pdf_id": str(generated.pk),
+                },
+            )
+        logger.exception("Greška kod build_work_order_pdf_cached_task: %s", exc)
+        return {"status": "failed", "error": str(exc)}