infrasynth-backend-kit/infrasynth/billing/invoice_generator.py

import io
import logging

from celery import shared_task

logger = logging.getLogger(__name__)


@shared_task(
    name="infrasynth.billing.generate_invoice_pdf",
    bind=True,
    max_retries=3,
    default_retry_delay=60,
)
def generate_invoice_pdf(self, invoice_id, tenant_id=None):
    """Generates a PDF for an invoice and stores it via the files service."""
    from infrasynth.tenancy.context import tenant_context
    from infrasynth.tenancy.models import Tenant

    from .models import Invoice

    tenant = Tenant.objects.filter(pk=tenant_id).first() if tenant_id else None
    with tenant_context(tenant):
        try:
            invoice = Invoice.all_objects.select_related("subscription", "subscription__plan", "gateway").get(
                pk=invoice_id
            )
        except Invoice.DoesNotExist:
            logger.warning("Invoice %s not found", invoice_id)
            return None

        try:
            pdf_bytes = _build_invoice_pdf(invoice)
        except Exception as exc:  # noqa: BLE001
            logger.exception("PDF generation failed for invoice %s", invoice_id)
            raise self.retry(exc=exc) from exc

        from django.core.files.base import ContentFile

        from infrasynth.files.services import FileService

        filename = f"invoice_{invoice.invoice_number}.pdf"
        content = ContentFile(pdf_bytes, name=filename)
        content.content_type = "application/pdf"
        stored = FileService().upload(
            content,
            filename=filename,
            metadata={"invoice_id": invoice.id, "invoice_number": invoice.invoice_number},
        )

        invoice.pdf_file = stored
        invoice.save(update_fields=["pdf_file"])
        return invoice.id


def _build_invoice_pdf(invoice) -> bytes:
    from reportlab.lib import colors
    from reportlab.lib.pagesizes import letter
    from reportlab.lib.styles import ParagraphStyle, getSampleStyleSheet
    from reportlab.lib.units import inch
    from reportlab.platypus import (
        Paragraph,
        SimpleDocTemplate,
        Spacer,
        Table,
        TableStyle,
    )

    styles = getSampleStyleSheet()
    title_style = ParagraphStyle("InvoiceTitle", parent=styles["Title"], textColor=colors.HexColor("#1a3a5c"))
    body_style = ParagraphStyle("InvoiceBody", parent=styles["BodyText"], fontSize=10, leading=14)

    buffer = io.BytesIO()
    doc = SimpleDocTemplate(
        buffer,
        pagesize=letter,
        rightMargin=0.75 * inch,
        leftMargin=0.75 * inch,
        topMargin=0.75 * inch,
        bottomMargin=0.75 * inch,
    )

    story = [
        Paragraph("Factura", title_style),
        Paragraph(
            f"<b>N&ordm;:</b> {invoice.invoice_number}<br/>"
            f"<b>Vencimiento:</b> {invoice.due_date.date() if invoice.due_date else '-'}",
            body_style,
        ),
        Spacer(1, 12),
        Paragraph("<b>Cliente</b>", body_style),
        Paragraph(
            f"{getattr(invoice.tenant, 'name', '')}",
            body_style,
        ),
        Spacer(1, 12),
    ]

    table_data = [["Descripci&oacute;n", "Cantidad", "Monto"]]
    for item in invoice.line_items:
        table_data.append(
            [
                item.get("description", ""),
                str(item.get("quantity", 1)),
                f"{item.get('amount', 0)} {invoice.currency}",
            ]
        )

    items_table = Table(table_data, colWidths=[3.5 * inch, 1 * inch, 1.5 * inch])
    items_table.setStyle(
        TableStyle(
            [
                ("BACKGROUND", (0, 0), (-1, 0), colors.HexColor("#1a3a5c")),
                ("TEXTCOLOR", (0, 0), (-1, 0), colors.white),
                ("GRID", (0, 0), (-1, -1), 0.5, colors.grey),
                ("FONTSIZE", (0, 0), (-1, -1), 9),
                ("ALIGN", (1, 0), (-1, -1), "RIGHT"),
            ]
        )
    )
    story.append(items_table)
    story.append(Spacer(1, 12))

    totals = [
        f"Subtotal: {invoice.amount} {invoice.currency}",
    ]
    if invoice.tax_name:
        totals.append(f"{invoice.tax_name}: {invoice.tax_amount} {invoice.currency}")
    total = invoice.amount + invoice.tax_amount
    totals.append(f"<b>Total: {total} {invoice.currency}</b>")

    totals_style = ParagraphStyle(
        "InvoiceTotals",
        parent=body_style,
        alignment=2,
        spaceAfter=4,
    )
    for line in totals:
        story.append(Paragraph(line, totals_style))

    doc.build(story)
    return buffer.getvalue()