E-invoicing that actually validates.

use pdfluent::{Sdk, invoice::{InvoiceBuilder, ZugferdProfile, ValidationLevel}};

let sdk = Sdk::init_with_license("license.json")?;

// Build the invoice data structure
let invoice = InvoiceBuilder::new()
    .profile(ZugferdProfile::En16931)
    .seller("Acme GmbH", "DE123456789")
    .buyer("BundesMinisterium", "DE987654321")
    .invoice_number("2024-001234")
    .issue_date("2024-03-15")
    .line_item("Consulting services", 10.0, 150.00, "H")  // 19% VAT
    .build()?;

// Validate against EN 16931 — 344 business rules
let validation = invoice.validate(ValidationLevel::En16931)?;
if !validation.is_valid() {
    for rule in validation.violations() {
        eprintln!("  {} — {}", rule.id(), rule.message());
    }
    return Err("Invoice failed EN 16931 validation".into());
}

// Embed XML into PDF/A-3b hybrid (ZUGFeRD)
let pdf  = sdk.open("invoice_template.pdf")?;
let hybrid = pdf.attach_zugferd_invoice(&invoice)?;
hybrid.save("invoice_2024-001234.pdf")?;