def paid_invoices_by_date(request, form):
    ''' Shows the number of paid invoices containing given products or
    categories per day. '''

    products = form.cleaned_data["product"]
    categories = form.cleaned_data["category"]

    invoices = commerce.Invoice.objects.filter(
        (
            Q(lineitem__product__in=products) |
            Q(lineitem__product__category__in=categories)
        ),
        status=commerce.Invoice.STATUS_PAID,
    )

    # Invoices with payments will be paid at the time of their latest payment
    payments = commerce.PaymentBase.objects.all()
    payments = payments.filter(
        invoice__in=invoices,
    )
    payments = payments.order_by("invoice")
    invoice_max_time = payments.values("invoice").annotate(
        max_time=Max("time")
    )

    # Zero-value invoices will have no payments, so they're paid at issue time
    zero_value_invoices = invoices.filter(value=0)

    times = itertools.chain(
        (line["max_time"] for line in invoice_max_time),
        (invoice.issue_time for invoice in zero_value_invoices),
    )

    by_date = collections.defaultdict(int)
    for time in times:
        date = datetime.datetime(
            year=time.year, month=time.month, day=time.day
        )
        by_date[date] += 1

    data = [(date_, count) for date_, count in sorted(by_date.items())]
    data = [(date_.strftime("%Y-%m-%d"), count) for date_, count in data]

    return ListReport(
        "Paid Invoices By Date",
        ["date", "count"],
        data,
    )
Shows the number of paid invoices containing given products or
    categories per day.