PDF stamping of approved invoices (#3698)

- [x] Add approved by staff to the approved invoice pdfs
- [x] Add inovice approver and date

Closes: https://github.com/HyphaApp/hypha/issues/3539

hypha/apply/projects/templates/application_projects/pdf_invoce_approved_page.html

+{% load invoice_tools i18n %}
+
+
+<h1>{% trans "Invoice Status" %}</h1>
+
+<ul>
+    {% for activity in activities %}
+        {% extract_status activity request.user as activity_status %}
+        <li><strong> {{ activity_status }} ({{ activity.user.email }})</strong> on {{ activity.timestamp }}</li>
+    {% endfor %}
+</ul>
+
+<p style="border-top: 1px solid #ccc; margin-top: 1.5em; padding-top: 0.5em; color: #656d76;">
+    <small>
+        {% trans "Generated" %}: {{ generated_at|date:"c" }} &middot; {{ request.scheme }}://{{ request.get_host }}{{ invoice.get_absolute_url}}
+    </small>
+</p>

hypha/apply/projects/views/payment.py

@@ -6,6 +6,7 @@ from django.contrib.auth.models import Group
 from django.core.exceptions import PermissionDenied
 from django.db import transaction
 from django.shortcuts import get_object_or_404, redirect
+from django.template.loader import render_to_string
 from django.utils import timezone
 from django.utils.decorators import method_decorator
 from django.utils.safestring import mark_safe
@@ -35,6 +36,7 @@ from hypha.apply.todo.views import (
 )
 from hypha.apply.users.decorators import staff_or_finance_required
 from hypha.apply.users.groups import STAFF_GROUP_NAME
+from hypha.apply.utils.pdfs import html_to_pdf, merge_pdf
 from hypha.apply.utils.storage import PrivateMediaView
 from hypha.apply.utils.views import (
     DelegateableListView,
@@ -121,6 +123,7 @@ class ChangeInvoiceStatusView(DelegatedViewMixin, InvoiceAccessMixin, UpdateView
             and self.request.user.is_finance_level_1
             and self.object.status == APPROVED_BY_FINANCE
         ):
+            self.object.save()
             messenger(
                 MESSAGES.APPROVE_INVOICE,
                 request=self.request,
@@ -416,12 +419,35 @@ class InvoicePrivateMedia(UserPassesTestMixin, PrivateMediaView):
         return super().dispatch(*args, **kwargs)
 
     def get_media(self, *args, **kwargs):
-        file_pk = kwargs.get("file_pk")
-        if not file_pk:
-            return self.invoice.document
+        # check if the request is for a supporting document
+        if file_pk := kwargs.get("file_pk"):
+            document = get_object_or_404(self.invoice.supporting_documents, pk=file_pk)
+            return document.document
 
-        document = get_object_or_404(self.invoice.supporting_documents, pk=file_pk)
-        return document.document
+        # if not, then it's for invoice document
+        if (
+            self.invoice.status == APPROVED_BY_STAFF
+            and self.invoice.document.file.name.endswith(".pdf")
+        ):
+            if activities := Activity.actions.filter(
+                related_content_type__model="invoice",
+                related_object_id=self.invoice.id,
+                message__icontains="Approved by",
+            ).visible_to(self.request.user):
+                approval_pdf_page = html_to_pdf(
+                    render_to_string(
+                        "application_projects/pdf_invoce_approved_page.html",
+                        context={
+                            "invoice": self.invoice,
+                            "generated_at": timezone.now(),
+                            "activities": activities,
+                        },
+                        request=self.request,
+                    )
+                )
+                return merge_pdf(self.invoice.document.file, approval_pdf_page)
+
+        return self.invoice.document
 
     def test_func(self):
         if self.request.user.is_apply_staff:

hypha/apply/utils/pdfs.py

-import io
 import os
+from io import BytesIO
 from itertools import cycle
 
 from bs4 import BeautifulSoup, NavigableString
+from django.core.files import File
+from pypdf import PdfReader, PdfWriter
 from reportlab.lib import pagesizes
 from reportlab.lib.colors import Color, white
 from reportlab.lib.styles import ParagraphStyle as PS
@@ -23,6 +25,7 @@ from reportlab.platypus import (
     Table,
     TableStyle,
 )
+from xhtml2pdf import pisa
 
 STYLES = {
     "Question": PS(
@@ -164,7 +167,7 @@ class ReportDocTemplate(BaseDocTemplate):
 
 def make_pdf(title, sections, pagesize):
     prepare_fonts()
-    buffer = io.BytesIO()
+    buffer = BytesIO()
     page_width, page_height = getattr(pagesizes, pagesize)
 
     doc = ReportDocTemplate(
@@ -460,3 +463,39 @@ def draw_project_content(content):
         paragraphs.extend(flowables)
 
     return paragraphs
+
+
+def html_to_pdf(html_body: str) -> BytesIO:
+    """Convert HTML to PDF.
+
+    Args:
+        html_body: The body of the html as string
+
+    Returns:
+        BytesIO: PDF file
+    """
+    packet = BytesIO()
+    source_html = f"<html><body>{html_body}</body></html>"
+    pisa.CreatePDF(source_html, dest=packet, raise_exception=True, encoding="utf-8")
+    packet.seek(0)
+    return packet
+
+
+def merge_pdf(origin_pdf: BytesIO, input_pdf: BytesIO) -> File:
+    """Given two PDFs, merge them together.
+
+    Args:
+        origin_pdf: a file-like object containing a PDF
+        input_pdf: a file-like object containing a PDF
+
+    Returns:
+        Return a File object containing the merged PDF and with the same name as the
+        original PDF.
+    """
+    merger = PdfWriter(clone_from=BytesIO(origin_pdf.read()))
+    merger.append(PdfReader(input_pdf))
+
+    output_pdf = BytesIO()
+    merger.write(output_pdf)
+    output_pdf.seek(0)
+    return File(output_pdf, name=origin_pdf.name)