from django.db import models
from functools import reduce
from django.contrib.auth import get_user_model
from django.core.validators import MinValueValidator
from django.utils.translation import gettext_lazy as _
from django.utils import timezone
from math import ceil
from datetime import timedelta
from calendar import monthrange
import uncloud_pay.stripe

from decimal import Decimal
import uuid

# Define DecimalField properties, used to represent amounts of money.
AMOUNT_MAX_DIGITS=10
AMOUNT_DECIMALS=2

# See https://docs.djangoproject.com/en/dev/ref/models/fields/#field-choices-enum-types
class RecurringPeriod(models.TextChoices):
    ONE_TIME   = 'ONCE', _('Onetime')
    PER_YEAR   = 'YEAR', _('Per Year')
    PER_MONTH  = 'MONTH', _('Per Month')
    PER_MINUTE = 'MINUTE', _('Per Minute')
    PER_DAY    = 'DAY', _('Per Day')
    PER_HOUR   = 'HOUR', _('Per Hour')
    PER_SECOND = 'SECOND', _('Per Second')

###
# Payments and Payment Methods.

class Payment(models.Model):
    uuid = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)

    owner = models.ForeignKey(get_user_model(),
            on_delete=models.CASCADE)

    amount = models.DecimalField(
            default=0.0,
            max_digits=AMOUNT_MAX_DIGITS,
            decimal_places=AMOUNT_DECIMALS,
            validators=[MinValueValidator(0)])

    source = models.CharField(max_length=256,
                              choices = (
                                  ('wire', 'Wire Transfer'),
                                  ('stripe', 'Stripe'),
                                  ('voucher', 'Voucher'),
                                  ('referral', 'Referral'),
                                  ('unknown', 'Unknown')
                              ),
                              default='unknown')
    timestamp = models.DateTimeField(editable=False, auto_now_add=True)

class PaymentMethod(models.Model):
    uuid = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    owner = models.ForeignKey(get_user_model(),
            on_delete=models.CASCADE,
            editable=False)
    source = models.CharField(max_length=256,
            choices = (
                ('stripe', 'Stripe'),
                ('unknown', 'Unknown'),
                ),
            default='stripe')
    description = models.TextField()
    primary = models.BooleanField(default=True)

    # Only used for "Stripe" source
    stripe_card_id = models.CharField(max_length=32, blank=True, null=True)

    @property
    def stripe_card_last4(self):
        if self.source == 'stripe':
            card_request = uncloud_pay.stripe.get_card(
                    StripeCustomer.objects.get(owner=self.owner).stripe_id,
                    self.stripe_card_id)
            if card_request['error'] == None:
                return card_request['response_object']['last4']
            else:
                return None
        else:
            return None


    def charge(self, amount):
        if amount > 0: # Make sure we don't charge negative amount by errors...
            if self.source == 'stripe':
                stripe_customer = StripeCustomer.objects.get(owner=self.owner).stripe_id
                charge_request = uncloud_pay.stripe.charge_customer(amount, stripe_customer, self.stripe_card_id)
                if charge_request['error'] == None:
                    payment = Payment(owner=self.owner, source=self.source, amount=amount)
                    payment.save() # TODO: Check return status

                    return payment
                else:
                    raise Exception('Stripe error: {}'.format(charge_request['error']))
            else:
                raise Exception('This payment method is unsupported/cannot be charged.')
        else:
            raise Exception('Cannot charge negative amount.')

    class Meta:
        unique_together = [['owner', 'primary']]

class StripeCustomer(models.Model):
    owner = models.OneToOneField( get_user_model(),
            primary_key=True,
            on_delete=models.CASCADE)
    stripe_id = models.CharField(max_length=32)

###
# Bills & Payments.

class Bill(models.Model):
    uuid = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    owner = models.ForeignKey(get_user_model(),
            on_delete=models.CASCADE)

    creation_date = models.DateTimeField(auto_now_add=True)
    starting_date = models.DateTimeField()
    ending_date = models.DateTimeField()
    due_date = models.DateField()

    valid = models.BooleanField(default=True)

    @property
    def records(self):
        bill_records = []
        orders = Order.objects.filter(bill=self)
        for order in orders:
            for order_record in order.records:
                bill_record = BillRecord(self, order_record)
                bill_records.append(bill_record)

        return bill_records

    @property
    def total(self):
        return reduce(lambda acc, record: acc + record.amount, self.records, 0)

    @property
    def final(self):
        # A bill is final when its ending date is passed.
        return self.ending_date < timezone.now()

class BillRecord():
    """
    Entry of a bill, dynamically generated from order records.
    """

    def __init__(self, bill, order_record):
        self.bill = bill
        self.order = order_record.order
        self.recurring_price = order_record.recurring_price
        self.recurring_period = order_record.recurring_period
        self.description = order_record.description

        if self.order.starting_date > self.bill.starting_date:
            self.one_time_price = order_record.one_time_price
        else:
            self.one_time_price = 0

    @property
    def recurring_count(self):
        # Compute billing delta.
        billed_until = self.bill.ending_date
        if self.order.ending_date != None and self.order.ending_date < self.order.ending_date:
            billed_until = self.order.ending_date

        billed_from = self.bill.starting_date
        if self.order.starting_date > self.bill.starting_date:
            billed_from = self.order.starting_date

        if billed_from > billed_until:
            # TODO: think about and check edges cases. This should not be
            # possible.
            raise Exception('Impossible billing delta!')

        billed_delta = billed_until - billed_from

        # TODO: refactor this thing?
        # TODO: weekly
        # TODO: yearly
        if self.recurring_period == RecurringPeriod.PER_MONTH:
            days = ceil(billed_delta / timedelta(days=1))

            # XXX: we assume monthly bills for now.
            if (self.bill.starting_date.year != self.bill.starting_date.year or
                self.bill.starting_date.month != self.bill.ending_date.month):
                    raise Exception('Bill {} covers more than one month. Cannot bill PER_MONTH.'.
                        format(self.bill.uuid))

            # XXX: minumal length of monthly order is to be enforced somewhere else.
            (_, days_in_month) = monthrange(
                    self.bill.starting_date.year,
                    self.bill.starting_date.month)
            return Decimal(days / days_in_month)
        elif self.recurring_period == RecurringPeriod.PER_DAY:
            days = ceil(billed_delta / timedelta(days=1))
            return Decimal(days)
        elif self.recurring_period == RecurringPeriod.PER_HOUR:
            hours = ceil(billed_delta / timedelta(hours=1))
            return Decimal(hours)
        elif self.recurring_period == RecurringPeriod.PER_SECOND:
            seconds = ceil(billed_delta / timedelta(seconds=1))
            return Decimal(seconds)
        elif self.recurring_period == RecurringPeriod.ONE_TIME:
            return Decimal(0)
        else:
            raise Exception('Unsupported recurring period: {}.'.
                    format(record.recurring_period))

    @property
    def amount(self):
        return self.recurring_price * self.recurring_count + self.one_time_price

###
# Orders.

# Order are assumed IMMUTABLE and used as SOURCE OF TRUST for generating
# bills. Do **NOT** mutate then!
class Order(models.Model):
    uuid = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    owner = models.ForeignKey(get_user_model(),
                              on_delete=models.CASCADE,
                              editable=False)

    # TODO: enforce ending_date - starting_date to be larger than recurring_period.
    creation_date = models.DateTimeField(auto_now_add=True)
    starting_date = models.DateTimeField(auto_now_add=True)
    ending_date = models.DateTimeField(blank=True,
                                       null=True)

    bill = models.ManyToManyField(Bill,
                                  editable=False,
                                  blank=True)

    recurring_period = models.CharField(max_length=32,
                              choices = RecurringPeriod.choices,
                              default = RecurringPeriod.PER_MONTH)

    @property
    def records(self):
        return OrderRecord.objects.filter(order=self)

    @property
    def one_time_price(self):
        return reduce(lambda acc, record: acc + record.one_time_price, self.records, 0)

    @property
    def recurring_price(self):
        return reduce(lambda acc, record: acc + record.recurring_price, self.records, 0)

    def add_record(self, one_time_price, recurring_price, description):
        OrderRecord.objects.create(order=self,
                one_time_price=one_time_price,
                recurring_price=recurring_price,
                description=description)

class OrderRecord(models.Model):
    """
    Order records store billing informations for products: the actual product
    might be mutated and/or moved to another order but we do not want to loose
    the details of old orders.

    Used as source of trust to dynamically generate bill entries.
    """

    order = models.ForeignKey(Order, on_delete=models.CASCADE)
    one_time_price = models.DecimalField(default=0.0,
            max_digits=AMOUNT_MAX_DIGITS,
            decimal_places=AMOUNT_DECIMALS,
            validators=[MinValueValidator(0)])
    recurring_price = models.DecimalField(default=0.0,
            max_digits=AMOUNT_MAX_DIGITS,
            decimal_places=AMOUNT_DECIMALS,
            validators=[MinValueValidator(0)])

    description = models.TextField()

    @property
    def recurring_period(self):
        return self.order.recurring_period

    @property
    def starting_date(self):
        return self.order.starting_date

    @property
    def ending_date(self):
        return self.order.ending_date


###
# Products

# Abstract (= no database representation) class used as parent for products
# (e.g.  uncloud_vm.models.VMProduct).
class Product(models.Model):
    uuid = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    owner = models.ForeignKey(get_user_model(),
                              on_delete=models.CASCADE,
                              editable=False)

    description = ""

    status = models.CharField(max_length=256,
                              choices = (
                                  ('pending', 'Pending'),
                                  ('being_created', 'Being created'),
                                  ('active', 'Active'),
                                  ('deleted', 'Deleted')
                              ),
                              default='pending'
    )

    order = models.ForeignKey(Order,
                              on_delete=models.CASCADE,
                              editable=False,
                              null=True)

    @property
    def recurring_price(self, recurring_period=RecurringPeriod.PER_MONTH):
        pass # To be implemented in child.

    @property
    def one_time_price(self):
        return 0

    @property
    def recurring_period(self):
        return self.order.recurring_period

    @staticmethod
    def allowed_recurring_periods():
        return RecurringPeriod.choices

    class Meta:
        abstract = True