import forms

from django.db import models
from django.db.models import Q
from django.db.models import Sum
from django.db.models import Case, When, Value
from django.shortcuts import render
from functools import wraps

from models import commerce
from models import inventory


'''

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, title, form, headings, data):
        self._title = title
        self._form = form
        self._headings = headings
        self._data = data

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

    @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 = {
            "title": report.title,
            "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. '''

    title = "Paid items"

    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"]

        line_items = commerce.LineItem.objects.filter(
            Q(product__in=products) | Q(product__category__in=categories),
            invoice__status=commerce.Invoice.STATUS_PAID,
        ).select_related("invoice")

        line_items = line_items.order_by(
            # sqlite requires an order_by for .values() to work
            "-price", "description",
        ).values(
            "price", "description",
        ).annotate(
            total_quantity=Sum("quantity"),
        )

        print line_items

        headings = ["Description", "Quantity", "Price", "Total"]

        data = []
        total_income = 0
        for line in line_items:
            cost = line["total_quantity"] * line["price"]
            data.append([
                line["description"], line["total_quantity"],
                line["price"], cost,
            ])
            total_income += cost

        data.append([
            "(TOTAL)", "--", "--", total_income,
        ])

    return Report(title, form, headings, data)


@report
def inventory(request):
    ''' Summarises the inventory status of the given items, grouping by
    invoice status. '''

    title = "Inventory"

    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"]

        items = commerce.ProductItem.objects.filter(
            Q(product__in=products) | Q(product__category__in=categories),
        ).select_related("cart", "product")

        # TODO annotate with whether the item is reserved or not.

        items = items.annotate(is_reserved=Case(
            When(cart__in=commerce.Cart.reserved_carts(), then=Value(1)),
            default=Value(0),
            output_field=models.BooleanField(),
        ))

        items = items.order_by(
            "cart__status",
            "product__category__order",
            "product__order",
        ).values(
            "product",
            "product__category__name",
            "product__name",
            "cart__status",
            "is_reserved",
        ).annotate(
            total_quantity=Sum("quantity"),
        )

        headings = ["Product", "Status", "Quantity"]
        data = []

        def status(reserved, status):
            r = "Reserved" if reserved else "Unreserved"
            s = "".join(
                "%s" % i[1]
                for i in commerce.Cart.STATUS_TYPES if i[0]==status
            )
            return "%s - %s" % (r, s)

        for item in items:
            print commerce.Cart.STATUS_TYPES
            data.append([
                "%s - %s" % (
                    item["product__category__name"], item["product__name"]
                ),
                status(item["is_reserved"], item["cart__status"]),
                item["total_quantity"],
            ])

    return Report(title, form, headings, data)