import string

from django.utils.crypto import get_random_string

def generate_access_code():

    ''' Generates an access code for users' payments as well as their

    fulfilment code for check-in.

    The access code will 4 characters long, which allows for 1,500,625

    unique codes, which really should be enough for anyone. '''

    length = 4

    # all upper-case letters + digits 1-9 (no 0 vs O confusion)

    chars = string.uppercase + string.digits[1:]

    # 4 chars => 35 ** 4 = 1500625 (should be enough for anyone)

    return get_random_string(length=length, allowed_chars=chars)

def all_arguments_optional(ntcls):

    ''' Takes a namedtuple derivative and makes all of the arguments optional.

    '''

    ntcls.__new__.__defaults__ = (

        (None,) * len(ntcls._fields)

    )

    return ntcls

    PRODUCTS_FORM_PREFIX = "products"

    VOUCHERS_FORM_PREFIX = "vouchers"

    # Handle the voucher form *before* listing products.

    # Products can change as vouchers are entered.

    v = _handle_voucher(request, VOUCHERS_FORM_PREFIX)

    voucher_form, voucher_handled = v

    category_id = int(category_id)  # Routing is [0-9]+

    category = inventory.Category.objects.get(pk=category_id)

    products = ProductController.available_products(

        request.user,

        category=category,

    )

    if not products:

        messages.warning(

            request,

            "There are no products available from category: " + category.name,

        )

        return redirect("dashboard")

    p = _handle_products(request, category, products, PRODUCTS_FORM_PREFIX)

    products_form, discounts, products_handled = p

    if request.POST and not voucher_handled and not products_form.errors:

        # Only return to the dashboard if we didn't add a voucher code

        # and if there's no errors in the products form

        messages.success(

            request,

            "Your reservations have been updated.",

        )

        return redirect("dashboard")

    data = {

        "category": category,

        "discounts": discounts,

        "form": products_form,

        "voucher_form": voucher_form,

    }

    return render(request, "registrasion/product_category.html", data)

def _handle_products(request, category, products, prefix):

    ''' Handles a products list form in the given request. Returns the

    form instance, the discounts applicable to this form, and whether the

    contents were handled. '''

    current_cart = CartController.for_user(request.user)

    ProductsForm = forms.ProductsForm(category, products)

    # Create initial data for each of products in category

    items = commerce.ProductItem.objects.filter(

        product__in=products,

        cart=current_cart.cart,

    ).select_related("product")

    quantities = []

    seen = set()

    for item in items:

        quantities.append((item.product, item.quantity))

        seen.add(item.product)

    zeros = set(products) - seen

    for product in zeros:

        quantities.append((product, 0))

    products_form = ProductsForm(

        request.POST or None,

        product_quantities=quantities,

        prefix=prefix,

    )

    if request.method == "POST" and products_form.is_valid():

        if products_form.has_changed():

            _set_quantities_from_products_form(products_form, current_cart)

        # If category is required, the user must have at least one

        # in an active+valid cart

        if category.required:

            carts = commerce.Cart.objects.filter(user=request.user)

            items = commerce.ProductItem.objects.filter(

                product__category=category,

                cart=carts,

            )

            if len(items) == 0:

                products_form.add_error(

                    None,

                    "You must have at least one item from this category",

                )

    handled = False if products_form.errors else True

        request.user,

        [],

        products,

    )

    return products_form, discounts, handled

def _set_quantities_from_products_form(products_form, current_cart):

    quantities = list(products_form.product_quantities())

    pks = [i[0] for i in quantities]

    products = inventory.Product.objects.filter(

        id__in=pks,

    ).select_related("category")

    product_quantities = [

        (products.get(pk=i[0]), i[1]) for i in quantities

    ]

    field_names = dict(

        (i[0][0], i[1][2]) for i in zip(product_quantities, quantities)

    )

    try:

        current_cart.set_quantities(product_quantities)

    except CartValidationError as ve:

        for ve_field in ve.error_list:

            product, message = ve_field.message

            if product in field_names:

                field = field_names[product]

            elif isinstance(product, inventory.Product):

                continue

            else:

                field = None

            products_form.add_error(field, message)

def _handle_voucher(request, prefix):

    ''' Handles a voucher form in the given request. Returns the voucher

    form instance, and whether the voucher code was handled. '''

    voucher_form = forms.VoucherForm(request.POST or None, prefix=prefix)

    current_cart = CartController.for_user(request.user)

    if (voucher_form.is_valid() and

            voucher_form.cleaned_data["voucher"].strip()):

        voucher = voucher_form.cleaned_data["voucher"]

        voucher = inventory.Voucher.normalise_code(voucher)

        if len(current_cart.cart.vouchers.filter(code=voucher)) > 0:

            # This voucher has already been applied to this cart.

            # Do not apply code

            handled = False

        else:

            try:

                current_cart.apply_voucher(voucher)

            except Exception as e:

                voucher_form.add_error("voucher", e)

            handled = True

    else:

        handled = False

    return (voucher_form, handled)

@login_required

def checkout(request):

    ''' Runs the checkout process for the current cart.

    If the query string contains ``fix_errors=true``, Registrasion will attempt

    to fix errors preventing the system from checking out, including by

    cancelling expired discounts and vouchers, and removing any unavailable

    products.

    Returns:

        render or redirect:

            If the invoice is generated successfully, or there's already a

            valid invoice for the current cart, redirect to ``invoice``.

            If there are errors when generating the invoice, render

            ``registrasion/checkout_errors.html`` with the following data::

                {

                    "error_list", [str, ...]  # The errors to display.

                }

    '''

    current_cart = CartController.for_user(request.user)

    if "fix_errors" in request.GET and request.GET["fix_errors"] == "true":

        current_cart.fix_simple_errors()

    try:

        current_invoice = InvoiceController.for_cart(current_cart.cart)