Fix 503: make xhtml2pdf import lazy to prevent app crash

If xhtml2pdf fails to install on Flatlogic's server (missing C
libraries), the top-level import crashed the entire WSGI app.
Now it imports lazily inside render_to_pdf() so the app starts
even without xhtml2pdf — only PDF generation degrades gracefully.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

core/utils.py

@@ -1,10 +1,17 @@
 # === PDF GENERATION ===
 # Converts a Django HTML template into a PDF file using xhtml2pdf.
 # Used for payslip and receipt PDF attachments sent via email.
+#
+# IMPORTANT: xhtml2pdf is imported LAZILY (inside the function, not at the
+# top of the file). This is intentional — if xhtml2pdf fails to install on
+# the server (missing C libraries), the rest of the app still works.
+# Only PDF generation will fail gracefully.
 
+import logging
 from io import BytesIO
 from django.template.loader import get_template
-from xhtml2pdf import pisa
+
+logger = logging.getLogger(__name__)
 
 
 def render_to_pdf(template_src, context_dict=None):
@@ -21,6 +28,17 @@ def render_to_pdf(template_src, context_dict=None):
     if context_dict is None:
         context_dict = {}
 
+    # --- Lazy import: only load xhtml2pdf when actually generating a PDF ---
+    # This prevents the entire app from crashing if xhtml2pdf isn't installed.
+    try:
+        from xhtml2pdf import pisa
+    except ImportError:
+        logger.error(
+            "xhtml2pdf is not installed — cannot generate PDF. "
+            "Install it with: pip install xhtml2pdf"
+        )
+        return None
+
     # Load and render the HTML template
     template = get_template(template_src)
     html = template.render(context_dict)

core/views.py

@@ -22,7 +22,9 @@ from django.conf import settings
 
 from .models import Worker, Project, WorkLog, Team, PayrollRecord, Loan, PayrollAdjustment
 from .forms import AttendanceLogForm, PayrollAdjustmentForm
-from .utils import render_to_pdf
+# NOTE: render_to_pdf is NOT imported here at the top level.
+# It's imported lazily inside process_payment() to avoid crashing the
+# entire app if xhtml2pdf is not installed on the server.
 
 
 # === PAYROLL CONSTANTS ===
@@ -812,6 +814,10 @@ def process_payment(request, worker_id):
     # EMAIL PAYSLIP (outside the transaction — if email fails, payment is
     # still saved. We don't want a network error to roll back a real payment.)
     # =========================================================================
+
+    # Lazy import — avoids crashing the app if xhtml2pdf isn't installed
+    from .utils import render_to_pdf
+
     subject = f"Payslip for {worker.name} - {payroll_record.date}"
 
     # Context for both the HTML email body and the PDF attachment
@@ -827,7 +833,7 @@ def process_payment(request, worker_id):
     html_message = render_to_string('core/email/payslip_email.html', email_context)
     plain_message = strip_tags(html_message)
 
-    # 2. Render PDF attachment
+    # 2. Render PDF attachment (returns None if xhtml2pdf is not installed)
     pdf_content = render_to_pdf('core/pdf/payslip_pdf.html', email_context)
 
     # 3. Send email with PDF attached