"""Invoice PDF generation using Jinja2 + WeasyPrint."""
import logging
import os
from datetime import datetime, timezone
from pathlib import Path

logger = logging.getLogger(__name__)

# PDF output directory (mounted as a Docker volume in production)
PDF_DIR = Path(os.getenv("PDF_DIR", "/app/data/invoices"))


def generate_invoice_pdf(invoice_id: str, db_session) -> str:
    """
    Render the invoice HTML template and convert to PDF via WeasyPrint.

    Args:
        invoice_id: UUID of the Invoice to generate
        db_session: synchronous SQLAlchemy session (used from Celery tasks)

    Returns:
        Absolute path to the generated PDF file.
    """
    from app.models.billing import Invoice, InvoiceLineItem
    from app.models.school import School
    from jinja2 import Environment, FileSystemLoader
    from weasyprint import HTML

    # Load invoice + line items + school
    inv = db_session.get(Invoice, invoice_id)
    if not inv:
        raise ValueError(f"Invoice {invoice_id} not found")

    school = db_session.get(School, inv.school_id)
    line_items = db_session.query(InvoiceLineItem).filter_by(invoice_id=invoice_id).all()

    # Format dates
    def _fmt(d) -> str:
        if not d:
            return ""
        if hasattr(d, "strftime"):
            return d.strftime("%B %d, %Y")
        return str(d)

    context = {
        "invoice": inv,
        "school": school,
        "line_items": line_items,
        "issued_date": _fmt(inv.created_at),
        "period_start": _fmt(inv.billing_period_start),
        "period_end": _fmt(inv.billing_period_end),
        "due_date": _fmt(inv.due_date),
        "paid_date": _fmt(inv.paid_at),
        "generated_date": datetime.now(timezone.utc).strftime("%Y-%m-%d %H:%M UTC"),
    }

    # Render Jinja2 template
    template_dir = Path(__file__).parent.parent / "templates"
    env = Environment(loader=FileSystemLoader(str(template_dir)), autoescape=True)
    template = env.get_template("invoice.html")
    html_content = template.render(**context)

    # Generate PDF
    PDF_DIR.mkdir(parents=True, exist_ok=True)
    output_path = PDF_DIR / f"{invoice_id}.pdf"

    HTML(string=html_content).write_pdf(str(output_path))
    logger.info("Generated PDF: %s", output_path)

    return str(output_path)