add pdf code and pdf letterheads

requirements/base.txt

@@ -3,3 +3,5 @@ django-allauth>=0.23.0
 django-bootstrap3>=7.0.0
 django-environ>=0.4.0
 psycopg2>=2.6.1
+PyPDF2>=1.25.1
+django-wkhtmltopdf>=3.0.0

shop/pdf.py

@@ -0,0 +1,45 @@
+from wkhtmltopdf.views import PDFTemplateResponse
+from PyPDF2 import PdfFileWriter, PdfFileReader
+from django.test.client import RequestFactory
+from django.conf import settings
+import StringIO
+
+def generate_pdf_letter(template, formatdict):
+    ### produce text-only PDF from template
+    pdfgenerator = PDFTemplateResponse(
+        request=RequestFactory().get('/'), 
+        template=template, 
+        context=formatdict,
+        cmd_options={
+            'margin-top': 40,
+            'margin-bottom': 50,
+        },
+    )
+    textonlypdf = StringIO.StringIO()
+    textonlypdf.write(pdfgenerator.rendered_content)
+
+    ### create a blank pdf to work with
+    finalpdf = PdfFileWriter()
+
+    ### open the text-only pdf
+    pdfreader = PdfFileReader(textonlypdf)
+
+    ### get watermark from watermark file
+    watermark = PdfFileReader(open(settings.LETTERHEAD_PDF_PATH, 'rb'))
+
+    ### add the watermark to all pages
+    for pagenum in xrange(pdfreader.getNumPages()):
+        page = pdfreader.getPage(pagenum)
+        try:
+            page.mergePage(watermark.getPage(0))
+        except ValueError:
+            ### watermark pdf might be broken?
+            return False
+        ### add page to output
+        finalpdf.addPage(page)
+
+    ### return a file object with the data
+    returnfile = StringIO.StringIO()
+    finalpdf.write(returnfile)
+    return returnfile
+