# -*- coding: utf-8 -*-
from __future__ import unicode_literals

from six import with_metaclass
from decimal import Decimal
from django.core.exceptions import ImproperlyConfigured, PermissionDenied
from django.db import models, transaction
from django.db.models.aggregates import Sum
from django.utils.encoding import python_2_unicode_compatible
from django.utils.module_loading import import_string
from django.utils.functional import cached_property
from django.utils.translation import ugettext_lazy as _, pgettext_lazy, get_language_from_request
from django.utils.six.moves.urllib.parse import urljoin
from jsonfield.fields import JSONField
from ipware.ip import get_ip
from django_fsm import FSMField, transition
from cms.models import Page
from shop import settings as shop_settings
from shop.models.cart import CartItemModel
from shop.money.fields import MoneyField, MoneyMaker
from .product import BaseProduct
from . import deferred


class OrderManager(models.Manager):
    @transaction.atomic
    def create_from_cart(self, cart, request):
        """
        This creates a new Order object with all its OrderItems using the current Cart object
        with its Cart Items. Whenever on Order Item is created from a Cart Item, that item is
        removed from the Cart.
        """
        cart.update(request)
        order = self.model(customer=cart.customer, currency=cart.total.currency,
            _subtotal=Decimal(0), _total=Decimal(0), stored_request=self.stored_request(request))
        order.get_or_assign_number()
        order.save()
        order.customer.get_or_assign_number()
        for cart_item in cart.items.all():
            cart_item.update(request)
            order_item = OrderItemModel(order=order)
            try:
                order_item.populate_from_cart_item(cart_item, request)
                order_item.save()
                cart_item.delete()
            except CartItemModel.DoesNotExist:
                pass
        order.populate_from_cart(cart, request)
        order.save()
        return order

    def stored_request(self, request):
        """
        Extract useful information about the request to be used for emulating a Django request
        during offline rendering.
        """
        return {
            'language': get_language_from_request(request),
            'absolute_base_uri': request.build_absolute_uri('/'),
            'remote_ip': get_ip(request),
            'user_agent': request.META.get('HTTP_USER_AGENT'),
        }

    def filter_from_request(self, request):
        """
        Return a queryset containing the orders for the customer associated with the given
        request object.
        """
        if request.customer.is_visitor():
            msg = _("Only signed in customers can view their orders")
            raise PermissionDenied(msg)
        return self.get_queryset().filter(customer=request.customer).order_by('-updated_at',)

    def get_summary_url(self):
        """
        Returns the URL of the page with the list view for all orders related to the current customer
        """
        if not hasattr(self, '_summary_url'):
            try:
                page = Page.objects.public().get(reverse_id='shop-order')
            except Page.DoesNotExist:
                page = Page.objects.public().filter(application_urls='OrderApp').first()
            finally:
                self._summary_url = page and page.get_absolute_url() or 'cms-page-with--reverse_id=shop-order--does-not-exist/'
        return self._summary_url

    def get_latest_url(self):
        """
        Returns the URL of the page with the detail view for the latest order related to the
        current customer. This normally is the thank-you view.
        """
        try:
            return Page.objects.public().get(reverse_id='shop-order-last').get_absolute_url()
        except Page.DoesNotExist:
            pass  # TODO: could be retrieved by last order
        return 'cms-page-with--reverse_id=shop-order-last--does-not-exist/'


class WorkflowMixinMetaclass(deferred.ForeignKeyBuilder):
    """
    Add configured Workflow mixin classes to `OrderModel` and `OrderPayment` to customize
    all kinds of state transitions in a pluggable manner.
    """
    def __new__(cls, name, bases, attrs):
        if 'BaseOrder' in (b.__name__ for b in bases):
            bases = tuple(import_string(mc) for mc in shop_settings.ORDER_WORKFLOWS) + bases
            # merge the dicts of TRANSITION_TARGETS
            attrs.update(_transition_targets={}, _auto_transitions={})
            for b in reversed(bases):
                TRANSITION_TARGETS = getattr(b, 'TRANSITION_TARGETS', {})
                delattr(b, 'TRANSITION_TARGETS')
                if set(TRANSITION_TARGETS.keys()).intersection(attrs['_transition_targets']):
                    msg = "Mixin class {} already contains a transition named '{}'"
                    raise ImproperlyConfigured(msg.format(b.__name__, ', '.join(TRANSITION_TARGETS.keys())))
                attrs['_transition_targets'].update(TRANSITION_TARGETS)
                attrs['_auto_transitions'].update(cls.add_to_auto_transitions(b))
        Model = super(WorkflowMixinMetaclass, cls).__new__(cls, name, bases, attrs)
        return Model

    @staticmethod
    def add_to_auto_transitions(base):
        result = {}
        for name, method in base.__dict__.items():
            if callable(method) and hasattr(method, '_django_fsm'):
                for name, transition in method._django_fsm.transitions.items():
                    if transition.custom.get('auto'):
                        result.update({name: method})
        return result


@python_2_unicode_compatible
class BaseOrder(with_metaclass(WorkflowMixinMetaclass, models.Model)):
    """
    An Order is the "in process" counterpart of the shopping cart, which freezes the state of the
    cart on the moment of purchase. It also holds stuff like the shipping and billing addresses,
    and keeps all the additional entities, as determined by the cart modifiers.
    """
    TRANSITION_TARGETS = {
        'new': _("New order without content"),
        'created': _("Order freshly created"),
        'payment_confirmed': _("Payment confirmed"),
    }
    decimalfield_kwargs = {
        'max_digits': 30,
        'decimal_places': 2,
    }
    decimal_exp = Decimal('.' + '0' * decimalfield_kwargs['decimal_places'])

    customer = deferred.ForeignKey('BaseCustomer', verbose_name=_("Customer"), related_name='orders')
    status = FSMField(default='new', protected=True, verbose_name=_("Status"))
    currency = models.CharField(max_length=7, editable=False,
        help_text=_("Currency in which this order was concluded"))
    _subtotal = models.DecimalField(_("Subtotal"), **decimalfield_kwargs)
    _total = models.DecimalField(_("Total"), **decimalfield_kwargs)
    created_at = models.DateTimeField(_("Created at"), auto_now_add=True)
    updated_at = models.DateTimeField(_("Updated at"), auto_now=True)
    extra = JSONField(verbose_name=_("Extra fields"), default={},
        help_text=_("Arbitrary information for this order object on the moment of purchase."))
    stored_request = JSONField(default={},
        help_text=_("Parts of the Request objects on the moment of purchase."))

    objects = OrderManager()

    class Meta:
        abstract = True

    def __str__(self):
        return self.get_number()

    def __repr__(self):
        return "<{}(pk={})>".format(self.__class__.__name__, self.pk)

    def get_or_assign_number(self):
        """
        Hook to get or to assign the order number. It shall be invoked, every time an Order
        object is created. If you prefer to use an order number which differs from the primary
        key, then override this method.
        """
        return self.get_number()

    def get_number(self):
        """
        Hook to get the order number.
        """
        return str(self.id)

    @cached_property
    def subtotal(self):
        """
        The summed up amount for all ordered items excluding extra order lines.
        """
        return MoneyMaker(self.currency)(self._subtotal)

    @cached_property
    def total(self):
        """
        The final total to charge for this order.
        """
        return MoneyMaker(self.currency)(self._total)

    @classmethod
    def round_amount(cls, amount):
        if amount.is_finite():
            return Decimal(amount).quantize(cls.decimal_exp)

    def get_absolute_url(self):
        """
        Returns the URL for the detail view of this order
        """
        return urljoin(OrderModel.objects.get_summary_url(), str(self.id))

    @transition(field=status, source='new', target='created')
    def populate_from_cart(self, cart, request):
        """
        Populate the order object with the fields from the given cart. Override this method,
        in case a customized cart has some fields which have to be transfered to the cart.
        """
        self._subtotal = Decimal(cart.subtotal)
        self._total = Decimal(cart.total)
        self.extra = dict(cart.extra)
        self.extra.update(rows=[(modifier, extra_row.data) for modifier, extra_row in cart.extra_rows.items()])

    def save(self, **kwargs):
        """
        Before saving the Order object to the database, round the total to the given decimal_places
        """
        auto_transition = self._auto_transitions.get(self.status)
        if callable(auto_transition):
            auto_transition(self)
        self._subtotal = BaseOrder.round_amount(self._subtotal)
        self._total = BaseOrder.round_amount(self._total)
        super(BaseOrder, self).save(**kwargs)

    @cached_property
    def amount_paid(self):
        """
        The amount paid is the sum of related orderpayments
        """
        amount = self.orderpayment_set.aggregate(amount=Sum('amount'))['amount']
        if amount is None:
            amount = MoneyMaker(self.currency)()
        return amount

    @property
    def outstanding_amount(self):
        """
        Return the outstanding amount paid for this order
        """
        return self.total - self.amount_paid

    def is_fully_paid(self):
        return self.amount_paid >= self.total

    @transition(field='status', source='*', target='payment_confirmed', conditions=[is_fully_paid])
    def acknowledge_payment(self, by=None):
        """
        Change status to `payment_confirmed`. This status code is known globally and can be used
        by all external plugins to check, if an Order object has been fully paid.
        """

    @classmethod
    def get_transition_name(cls, target):
        """Return the human readable name for a given transition target"""
        return cls._transition_targets.get(target, target)

    def status_name(self):
        """Return the human readable name for the current transition state"""
        return self._transition_targets.get(self.status, self.status)
    status_name.short_description = pgettext_lazy('order_models', "State")

OrderModel = deferred.MaterializedModel(BaseOrder)


class OrderPayment(with_metaclass(deferred.ForeignKeyBuilder, models.Model)):
    """
    A model to hold received payments for a given order.
    """
    order = deferred.ForeignKey(BaseOrder, verbose_name=_("Order"))
    amount = MoneyField(_("Amount paid"),
        help_text=_("How much was paid with this particular transfer."))
    transaction_id = models.CharField(_("Transaction ID"), max_length=255,
        help_text=_("The transaction processor's reference"))
    created_at = models.DateTimeField(_("Received at"), auto_now_add=True)
    payment_method = models.CharField(_("Payment method"), max_length=50,
        help_text=_("The payment backend used to process the purchase"))

    class Meta:
        verbose_name = pgettext_lazy('order_models', "Order payment")
        verbose_name_plural = pgettext_lazy('order_models', "Order payments")


@python_2_unicode_compatible
class BaseOrderItem(with_metaclass(deferred.ForeignKeyBuilder, models.Model)):
    """
    An item for an order.
    """
    order = deferred.ForeignKey(BaseOrder, related_name='items', verbose_name=_("Order"))
    product_name = models.CharField(_("Product name"), max_length=255, null=True, blank=True,
        help_text=_("Product name at the moment of purchase."))
    product_code = models.CharField(_("Product code"), max_length=255, null=True, blank=True,
        help_text=_("Product code at the moment of purchase."))
    product = deferred.ForeignKey(BaseProduct, null=True, blank=True, on_delete=models.SET_NULL,
        verbose_name=_("Product"))
    _unit_price = models.DecimalField(_("Unit price"), null=True,  # may be NaN
        help_text=_("Products unit price at the moment of purchase."), **BaseOrder.decimalfield_kwargs)
    _line_total = models.DecimalField(_("Line Total"), null=True,  # may be NaN
        help_text=_("Line total on the invoice at the moment of purchase."), **BaseOrder.decimalfield_kwargs)
    extra = JSONField(verbose_name=_("Extra fields"), default={},
        help_text=_("Arbitrary information for this order item"))

    class Meta:
        abstract = True
        verbose_name = _("Order item")
        verbose_name_plural = _("Order items")

    def __str__(self):
        return self.product_name

    @classmethod
    def perform_model_checks(cls):
        try:
            cart_field = [f for f in CartItemModel._meta.fields if f.attname == 'quantity'][0]
            order_field = [f for f in cls._meta.fields if f.attname == 'quantity'][0]
            if order_field.get_internal_type() != cart_field.get_internal_type():
                msg = "Field `{}.quantity` must be of one same type `{}.quantity`."
                raise ImproperlyConfigured(msg.format(cls.__name__, CartItemModel.__name__))
        except IndexError:
            msg = "Class `{}` must implement a field named `quantity`."
            raise ImproperlyConfigured(msg.format(cls.__name__))

    @property
    def unit_price(self):
        return MoneyMaker(self.order.currency)(self._unit_price)

    @property
    def line_total(self):
        return MoneyMaker(self.order.currency)(self._line_total)

    def populate_from_cart_item(self, cart_item, request):
        """
        From a given cart item, populate the current order item.
        If the operation was successful, the given item shall be removed from the cart.
        If a CartItem.DoesNotExist exception is raised, discard the order item.
        """
        if cart_item.quantity == 0:
            raise CartItemModel.DoesNotExist("Cart Item is on the Wish List")
        self.product = cart_item.product
        # for historical integrity, store the product's name and price at the moment of purchase
        self.product_name = cart_item.product.product_name
        self._unit_price = Decimal(cart_item.product.get_price(request))
        self._line_total = Decimal(cart_item.line_total)
        self.quantity = cart_item.quantity
        self.extra = dict(cart_item.extra)
        extra_rows = [(modifier, extra_row.data) for modifier, extra_row in cart_item.extra_rows.items()]
        self.extra.update(rows=extra_rows)

    def save(self, *args, **kwargs):
        """
        Before saving the OrderItem object to the database, round the amounts to the given decimal places
        """
        self._unit_price = BaseOrder.round_amount(self._unit_price)
        self._line_total = BaseOrder.round_amount(self._line_total)
        super(BaseOrderItem, self).save(*args, **kwargs)

OrderItemModel = deferred.MaterializedModel(BaseOrderItem)
