fix: reduce memory usage for monthly ZIP archive flow

Replace generated archive download response with FileResponse streaming so ZIP files are not fully loaded into process memory.

Move monthly archive task output to a temporary file and upload that file to storage, and write invoice attachments into ZIP archives in chunks.

Add Celery memory guard settings, a memory-aware base task hook, and periodic /tmp cleanup for prefixed archive files older than one day.

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

backend/modules/fleet/tasks.py

@@ -5,6 +5,7 @@ from django.core.mail import EmailMessage
 from django.conf import settings
 from django.utils import timezone
 from django.core.files.base import ContentFile
+from django.core.files import File
 import logging
 from io import BytesIO
 from io import StringIO
@@ -13,6 +14,9 @@ import base64
 import re
 import csv
 import mimetypes
+import os
+import tempfile
+import zipfile
 from decimal import Decimal, InvalidOperation
 from smtplib import SMTPSenderRefused
 from datetime import timedelta
@@ -838,10 +842,9 @@ def process_work_order_invoice_ocr(invoice_id):
 @shared_task
 def build_monthly_archive_cached_task(generated_archive_id):
     from .models import GeneratedFleetArchive
-    from .services import NotificationService
     from .views import (
-        _build_monthly_service_tasks_archive_content,
-        _build_monthly_work_orders_archive_content,
+        _write_monthly_service_tasks_archive_entries,
+        _write_monthly_work_orders_archive_entries,
         _notify_monthly_archive_request,
     )
 
@@ -854,25 +857,39 @@ def build_monthly_archive_cached_task(generated_archive_id):
     if generated is None:
         return {"status": "failed", "error": "Generated archive record not found"}
 
+    tmp_dir = str(getattr(settings, 'APP_TMP_CLEANUP_DIR', '/tmp'))
+    with tempfile.NamedTemporaryFile(
+        mode='w+b',
+        delete=False,
+        dir=tmp_dir if os.path.isdir(tmp_dir) else None,
+        prefix='erp-fleet-archive-',
+        suffix='.zip',
+    ) as temp_zip:
+        temp_zip_path = temp_zip.name
     try:
-        if generated.archive_type == 'service_tasks':
-            archive_content = _build_monthly_service_tasks_archive_content(
-                user=generated.requested_by,
-                year=generated.year,
-                month=generated.month,
-            )
-        else:
-            archive_content = _build_monthly_work_orders_archive_content(
-                user=generated.requested_by,
-                year=generated.year,
-                month=generated.month,
-            )
-
-        if not archive_content:
+        with zipfile.ZipFile(temp_zip_path, mode='w', compression=zipfile.ZIP_DEFLATED) as archive:
+            if generated.archive_type == 'service_tasks':
+                entries_written = _write_monthly_service_tasks_archive_entries(
+                    archive,
+                    user=generated.requested_by,
+                    year=generated.year,
+                    month=generated.month,
+                )
+            else:
+                entries_written = _write_monthly_work_orders_archive_entries(
+                    archive,
+                    user=generated.requested_by,
+                    year=generated.year,
+                    month=generated.month,
+                )
+        if entries_written == 0:
             raise ValueError('ZIP arhiva je prazna.')
 
+        if os.path.getsize(temp_zip_path) <= 0:
+            raise ValueError('ZIP arhiva je prazna.')
         filename = generated.filename or f"{generated.archive_type}-{generated.year}-{generated.month}.zip"
-        generated.file.save(filename, ContentFile(archive_content), save=False)
+        with open(temp_zip_path, 'rb') as temp_file:
+            generated.file.save(filename, File(temp_file), save=False)
         generated.status = 'ready'
         generated.error_message = ''
         generated.save(update_fields=['file', 'status', 'error_message', 'updated_at'])
@@ -902,6 +919,12 @@ def build_monthly_archive_cached_task(generated_archive_id):
             )
         logger.exception("Greška kod build_monthly_archive_cached_task: %s", exc)
         return {"status": "failed", "error": str(exc)}
+    finally:
+        try:
+            if os.path.exists(temp_zip_path):
+                os.remove(temp_zip_path)
+        except OSError:
+            logger.warning("Ne mogu obrisati privremenu ZIP datoteku: %s", temp_zip_path)
 
 
 @shared_task
@@ -944,6 +967,46 @@ def cleanup_expired_generated_pdfs_task():
     return {"deleted": deleted}
 
 
+@shared_task
+def cleanup_tmp_files_task():
+    tmp_dir = str(getattr(settings, 'APP_TMP_CLEANUP_DIR', '/tmp'))
+    max_age_hours = int(getattr(settings, 'APP_TMP_CLEANUP_MAX_AGE_HOURS', 24))
+    prefixes = tuple(getattr(settings, 'APP_TMP_CLEANUP_PREFIXES', ['erp-fleet-archive-']))
+
+    if max_age_hours <= 0:
+        raise ValueError('APP_TMP_CLEANUP_MAX_AGE_HOURS mora biti > 0.')
+    if not prefixes:
+        raise ValueError('APP_TMP_CLEANUP_PREFIXES ne smije biti prazan.')
+    if not os.path.isdir(tmp_dir):
+        return {'deleted': 0, 'tmp_dir': tmp_dir, 'reason': 'tmp-dir-not-found'}
+
+    now = timezone.now().timestamp()
+    cutoff = now - (max_age_hours * 3600)
+    deleted = 0
+
+    for name in os.listdir(tmp_dir):
+        if not any(name.startswith(prefix) for prefix in prefixes):
+            continue
+        full_path = os.path.join(tmp_dir, name)
+        try:
+            stat_info = os.stat(full_path)
+        except FileNotFoundError:
+            continue
+        if stat_info.st_mtime > cutoff:
+            continue
+        if os.path.isdir(full_path):
+            try:
+                os.rmdir(full_path)
+            except OSError:
+                logger.warning("Preskačem %s: direktorij nije prazan ili je nedostupan.", full_path)
+                continue
+        else:
+            os.remove(full_path)
+        deleted += 1
+
+    return {'deleted': deleted, 'tmp_dir': tmp_dir, 'max_age_hours': max_age_hours}
+
+
 @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