import forms
import views

from collections import namedtuple

from django.contrib.auth.decorators import user_passes_test
from django.core.urlresolvers import reverse
from django.db import models
from django.db.models import F, Q
from django.db.models import Sum
from django.db.models import Case, When, Value
from django.http import Http404
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, headings, data):
        self._headings = headings
        self._data = data

    @property
    def title(self):
        ''' Returns the title for this report. '''
        return self._title

    @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


''' A list of report views objects that can be used to load a list of
reports. '''
_all_report_views = []


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

    Arguments:
        form_type: A form class that can make this report display things.

    '''

    def _report(view):

        @wraps(view)
        @user_passes_test(views._staff_only)
        def inner_view(request, *a, **k):

            form = form_type(request.GET)
            if form.is_valid() and form.has_changed():
                report = view(request, form, *a, **k)
            else:
                report = None

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

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

        # Add this report to the list of reports -- makes this reversable.
        _all_report_views.append(inner_view)

        # Return the callable
        return inner_view
    return _report


@user_passes_test(views._staff_only)
def reports_list(request):
    ''' Lists all of the reports currently available. '''

    reports = []

    for report in _all_report_views:
        reports.append({
            "name" : report.__name__,
            "url" : reverse(report),
            "description" : report.__doc__,
        })

    reports.sort(key=lambda report: report["name"])

    ctx = {
        "reports" : reports,
    }

    print reports

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


# Report functions


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

    data = None
    headings = None

    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("Paid items", headings, data)


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

    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")

    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(
        "product__category__order",
        "product__order",
    ).values(
        "product",
        "product__category__name",
        "product__name",
    ).annotate(
        total_paid=Sum(Case(
            When(
                cart__status=commerce.Cart.STATUS_PAID,
                then=F("quantity"),
            ),
            default=Value(0),
        )),
        total_refunded=Sum(Case(
            When(
                cart__status=commerce.Cart.STATUS_RELEASED,
                then=F("quantity"),
            ),
            default=Value(0),
        )),
        total_unreserved=Sum(Case(
            When(
                (
                    Q(cart__status=commerce.Cart.STATUS_ACTIVE) &
                    Q(is_reserved=False)
                ),
                then=F("quantity"),
            ),
            default=Value(0),
        )),
        total_reserved=Sum(Case(
            When(
                (
                    Q(cart__status=commerce.Cart.STATUS_ACTIVE) &
                    Q(is_reserved=True)
                ),
                then=F("quantity"),
            ),
            default=Value(0),
        )),
    )

    headings = [
        "Product", "Paid", "Reserved", "Unreserved", "Refunded",
    ]
    data = []

    for item in items:
        data.append([
            "%s - %s" % (
                item["product__category__name"], item["product__name"]
            ),
            item["total_paid"],
            item["total_reserved"],
            item["total_unreserved"],
            item["total_refunded"],
        ])

    return Report("Inventory", headings, data)