[FIX] snailmail: overwrite margins in letters

In order to pass the validation of the snailmail provider, the margins
are required to have nothing but white pixels. To avoid letters being
stuck until their layout is fixed, we fill the margins with white.

closes odoo/odoo#107111

X-original-commit: 9022cba0
Signed-off-by: Florian Daloze (fda) <fda@odoo.com>
Signed-off-by: Louis Baudoux (lba) <lba@odoo.com>
Signed-off-by: Solan Delvenne (sode) <sode@odoo.com>

addons/snailmail/models/snailmail_letter.py

@@ -4,7 +4,7 @@ import re
 import base64
 import io
 
-from PyPDF2 import PdfFileReader, PdfFileMerger
+from PyPDF2 import PdfFileReader, PdfFileMerger, PdfFileWriter
 from reportlab.platypus import Frame, Paragraph, KeepInFrame
 from reportlab.lib.units import mm
 from reportlab.lib.pagesizes import A4
@@ -149,6 +149,7 @@ class SnailmailLetter(models.Model):
             if (paperformat.format == 'custom' and paperformat.page_width != 210 and paperformat.page_height != 297) or paperformat.format != 'A4':
                 raise UserError(_("Please use an A4 Paper format."))
             pdf_bin, unused_filetype = report.with_context(snailmail_layout=not self.cover, lang='en_US')._render_qweb_pdf(self.res_id)
+            pdf_bin = self._overwrite_margins(pdf_bin)
             if self.cover:
                 pdf_bin = self._append_cover_page(pdf_bin)
             attachment = self.env['ir.attachment'].create({
@@ -462,3 +463,49 @@ class SnailmailLetter(models.Model):
         out_buff = io.BytesIO()
         merger.write(out_buff)
         return out_buff.getvalue()
+
+    def _overwrite_margins(self, invoice_bin: bytes):
+        """
+        Fill the margins with white for validation purposes.
+        """
+        pdf_buf = io.BytesIO()
+        canvas = Canvas(pdf_buf, pagesize=A4)
+        canvas.setFillColorRGB(255, 255, 255)
+        page_width = A4[0]
+        page_height = A4[1]
+
+        # Horizontal Margin
+        hmargin_width = page_width
+        hmargin_height = 5 * mm
+
+        # Vertical Margin
+        vmargin_width = 5 * mm
+        vmargin_height = page_height
+
+        # Bottom left square
+        sq_width = 15 * mm
+
+        # Draw the horizontal margins
+        canvas.rect(0, 0, hmargin_width, hmargin_height, stroke=0, fill=1)
+        canvas.rect(0, page_height, hmargin_width, -hmargin_height, stroke=0, fill=1)
+
+        # Draw the vertical margins
+        canvas.rect(0, 0, vmargin_width, vmargin_height, stroke=0, fill=1)
+        canvas.rect(page_width, 0, -vmargin_width, vmargin_height, stroke=0, fill=1)
+
+        # Draw the bottom left white square
+        canvas.rect(0, 0, sq_width, sq_width, stroke=0, fill=1)
+        canvas.save()
+        pdf_buf.seek(0)
+
+        new_pdf = PdfFileReader(pdf_buf)
+        curr_pdf = PdfFileReader(io.BytesIO(invoice_bin))
+        out = PdfFileWriter()
+        for page in curr_pdf.pages:
+            page.mergePage(new_pdf.getPage(0))
+            out.addPage(page)
+        out_stream = io.BytesIO()
+        out.write(out_stream)
+        out_bin = out_stream.getvalue()
+        out_stream.close()
+        return out_bin