import forms

from django.db.models import Q
from django.shortcuts import render
from functools import wraps

from models import commerce


'''

All reports must be viewable by staff only (permissions?)

Reports can have:

A form
 * Reports are all *gettable* - you can save a URL and get back to the same
 report
 * Fetching a report *cannot* break the underlying data.
A table
 * Headings
 * Data lines
 * Formats are pluggable

'''


class Report(object):

    def __init__(self, form, headings, data):
        self._form = form
        self._headings = headings
        self._data = data

    @property
    def form(self):
        ''' Returns the form. '''
        return self._form

    @property
    def headings(self):
        ''' Returns the headings for the table. '''
        return self._headings

    @property
    def data(self):
        ''' Returns the data rows for the table. '''
        return self._data


def report(view):
    ''' Decorator that converts a report view function into something that
    displays a Report.

    '''

    @wraps(view)
    def inner_view(request, *a, **k):
        report = view(request, *a, **k)

        ctx = {
            "form": report.form,
            "report": report,
        }

        return render(request, "registrasion/report.html", ctx)

    return inner_view


@report
def items_sold(request):
    ''' Summarises the items sold and discounts granted for a given set of
    products, or products from categories. '''

    form = forms.ProductAndCategoryForm(request.GET)

    data = None
    headings = None

    if form.is_valid() and form.has_changed():
        products = form.cleaned_data["product"]
        categories = form.cleaned_data["category"]

        # TODO augment the form to allow us to filter by invoice status.
        line_items = commerce.LineItem.objects.filter(
            Q(product=products) | Q(product__category=categories),
            invoice__status=commerce.Invoice.STATUS_PAID,
        ).select_related("invoice")

        headings = ["invoice_id", "description", "quantity", "price"]

        data = []
        for line in line_items:
            data.append([line.invoice.id, line.description, line.quantity, line.price])

    return Report(form, headings, data)