diff --git a/back/app/contract/print/pdf_generator.py b/back/app/contract/print/pdf_generator.py new file mode 100644 index 00000000..733b5076 --- /dev/null +++ b/back/app/contract/print/pdf_generator.py @@ -0,0 +1,152 @@ +from weasyprint import HTML, CSS + + +class PdfGenerator: + """ + Generate a PDF out of a rendered template, with the possibility to integrate nicely + a header and a footer if provided. + + Notes: + ------ + - When Weasyprint renders an html into a PDF, it goes though several intermediate steps. + Here, in this class, we deal mostly with a box representation: 1 `Document` have 1 `Page` + or more, each `Page` 1 `Box` or more. Each box can contain other box. Hence the recursive + method `get_element` for example. + For more, see: + https://weasyprint.readthedocs.io/en/stable/hacking.html#dive-into-the-source + https://weasyprint.readthedocs.io/en/stable/hacking.html#formatting-structure + - Warning: the logic of this class relies heavily on the internal Weasyprint API. This + snippet was written at the time of the release 47, it might break in the future. + - This generator draws its inspiration and, also a bit of its implementation, from this + discussion in the library github issues: https://github.com/Kozea/WeasyPrint/issues/92 + """ + OVERLAY_LAYOUT = '@page {size: A4 portrait; margin: 0;}' + + def __init__(self, main_html, header_html=None, footer_html=None, + base_url=None, side_margin=2, extra_vertical_margin=30): + """ + Parameters + ---------- + main_html: str + An HTML file (most of the time a template rendered into a string) which represents + the core of the PDF to generate. + header_html: str + An optional header html. + footer_html: str + An optional footer html. + base_url: str + An absolute url to the page which serves as a reference to Weasyprint to fetch assets, + required to get our media. + side_margin: int, interpreted in cm, by default 2cm + The margin to apply on the core of the rendered PDF (i.e. main_html). + extra_vertical_margin: int, interpreted in pixel, by default 30 pixels + An extra margin to apply between the main content and header and the footer. + The goal is to avoid having the content of `main_html` touching the header or the + footer. + """ + self.main_html = main_html + self.header_html = header_html + self.footer_html = footer_html + self.base_url = base_url + self.side_margin = side_margin + self.extra_vertical_margin = extra_vertical_margin + + def _compute_overlay_element(self, element: str): + """ + Parameters + ---------- + element: str + Either 'header' or 'footer' + + Returns + ------- + element_body: BlockBox + A Weasyprint pre-rendered representation of an html element + element_height: float + The height of this element, which will be then translated in a html height + """ + html = HTML( + string=getattr(self, f'{element}_html'), + base_url=self.base_url, + ) + element_doc = html.render(stylesheets=[CSS(string=self.OVERLAY_LAYOUT)]) + element_page = element_doc.pages[0] + element_body = PdfGenerator.get_element(element_page._page_box.all_children(), 'body') + element_body = element_body.copy_with_children(element_body.all_children()) + element_html = PdfGenerator.get_element(element_page._page_box.all_children(), element) + + if element == 'header': + element_height = element_html.height + if element == 'footer': + element_height = element_page.height - element_html.position_y + + return element_body, element_height + + def _apply_overlay_on_main(self, main_doc, header_body=None, footer_body=None): + """ + Insert the header and the footer in the main document. + + Parameters + ---------- + main_doc: Document + The top level representation for a PDF page in Weasyprint. + header_body: BlockBox + A representation for an html element in Weasyprint. + footer_body: BlockBox + A representation for an html element in Weasyprint. + """ + for page in main_doc.pages: + page_body = PdfGenerator.get_element(page._page_box.all_children(), 'body') + + if header_body: + page_body.children += header_body.all_children() + if footer_body: + page_body.children += footer_body.all_children() + + def render_pdf(self): + """ + Returns + ------- + pdf: a bytes sequence + The rendered PDF. + """ + if self.header_html: + header_body, header_height = self._compute_overlay_element('header') + else: + header_body, header_height = None, 0 + if self.footer_html: + footer_body, footer_height = self._compute_overlay_element('footer') + else: + footer_body, footer_height = None, 0 + + margins = '{header_size}px {side_margin} {footer_size}px {side_margin}'.format( + header_size=header_height + self.extra_vertical_margin, + footer_size=footer_height + self.extra_vertical_margin, + side_margin=f'{self.side_margin}cm', + ) + content_print_layout = '@page {size: A4 portrait; margin: %s;}' % margins + + html = HTML( + string=self.main_html, + base_url=self.base_url, + ) + main_doc = html.render(stylesheets=[CSS(string=content_print_layout)]) + + if self.header_html or self.footer_html: + self._apply_overlay_on_main(main_doc, header_body, footer_body) + pdf = main_doc.write_pdf() + + return pdf + + @staticmethod + def get_element(boxes, element): + """ + Given a set of boxes representing the elements of a PDF page in a DOM-like way, find the + box which is named `element`. + + Look at the notes of the class for more details on Weasyprint insides. + """ + for box in boxes: + if box.element_tag == element: + return box + return PdfGenerator.get_element(box.all_children(), element) \ No newline at end of file diff --git a/back/app/contract/print/templates/styles.css b/back/app/contract/print/templates/styles.css index 876ba814..2e838af2 100644 --- a/back/app/contract/print/templates/styles.css +++ b/back/app/contract/print/templates/styles.css @@ -93,7 +93,6 @@ h2 { text-align: right; } - .content h2 { page-break-before: always; }