import datetime
from decimal import Decimal
from typing import Optional

from django.db import models
from django.db.models import CASCADE

from zerver.models import Realm


class Customer(models.Model):
    """
    This model primarily serves to connect a Realm with
    the corresponding Stripe customer object for payment purposes
    and the active plan, if any.
    """

    realm: Realm = models.OneToOneField(Realm, on_delete=CASCADE)
    stripe_customer_id: str = models.CharField(max_length=255, null=True, unique=True)
    sponsorship_pending: bool = models.BooleanField(default=False)
    # A percentage, like 85.
    default_discount: Optional[Decimal] = models.DecimalField(
        decimal_places=4, max_digits=7, null=True
    )

    def __str__(self) -> str:
        return f"<Customer {self.realm} {self.stripe_customer_id}>"


def get_customer_by_realm(realm: Realm) -> Optional[Customer]:
    return Customer.objects.filter(realm=realm).first()


class CustomerPlan(models.Model):
    """
    This is for storing most of the fiddly details
    of the customer's plan.
    """

    # A customer can only have one ACTIVE plan, but old, inactive plans
    # are preserved to allow auditing - so there can be multiple
    # CustomerPlan objects pointing to one Customer.
    customer: Customer = models.ForeignKey(Customer, on_delete=CASCADE)

    automanage_licenses: bool = models.BooleanField(default=False)
    charge_automatically: bool = models.BooleanField(default=False)

    # Some non-profit organizations on manual license management pay only for their paid employees.
    # We don't prevent these organizations from adding more users than the number of licenses they purchased.
    exempt_from_from_license_number_check: bool = models.BooleanField(default=False)

    # Both of these are in cents. Exactly one of price_per_license or
    # fixed_price should be set. fixed_price is only for manual deals, and
    # can't be set via the self-serve billing system.
    price_per_license: Optional[int] = models.IntegerField(null=True)
    fixed_price: Optional[int] = models.IntegerField(null=True)

    # Discount that was applied. For display purposes only.
    discount: Optional[Decimal] = models.DecimalField(decimal_places=4, max_digits=6, null=True)

    billing_cycle_anchor: datetime.datetime = models.DateTimeField()
    ANNUAL = 1
    MONTHLY = 2
    billing_schedule: int = models.SmallIntegerField()

    next_invoice_date: Optional[datetime.datetime] = models.DateTimeField(db_index=True, null=True)
    invoiced_through: Optional["LicenseLedger"] = models.ForeignKey(
        "LicenseLedger", null=True, on_delete=CASCADE, related_name="+"
    )
    DONE = 1
    STARTED = 2
    INITIAL_INVOICE_TO_BE_SENT = 3
    invoicing_status: int = models.SmallIntegerField(default=DONE)

    STANDARD = 1
    PLUS = 2  # not available through self-serve signup
    ENTERPRISE = 10
    tier: int = models.SmallIntegerField()

    ACTIVE = 1
    DOWNGRADE_AT_END_OF_CYCLE = 2
    FREE_TRIAL = 3
    SWITCH_TO_ANNUAL_AT_END_OF_CYCLE = 4
    # "Live" plans should have a value < LIVE_STATUS_THRESHOLD.
    # There should be at most one live plan per customer.
    LIVE_STATUS_THRESHOLD = 10
    ENDED = 11
    NEVER_STARTED = 12
    status: int = models.SmallIntegerField(default=ACTIVE)

    # TODO maybe override setattr to ensure billing_cycle_anchor, etc are immutable

    @property
    def name(self) -> str:
        return {
            CustomerPlan.STANDARD: "Zulip Standard",
            CustomerPlan.PLUS: "Zulip Plus",
            CustomerPlan.ENTERPRISE: "Zulip Enterprise",
        }[self.tier]

    def get_plan_status_as_text(self) -> str:
        return {
            self.ACTIVE: "Active",
            self.DOWNGRADE_AT_END_OF_CYCLE: "Scheduled for downgrade at end of cycle",
            self.FREE_TRIAL: "Free trial",
            self.ENDED: "Ended",
            self.NEVER_STARTED: "Never started",
        }[self.status]

    def licenses(self) -> int:
        return LicenseLedger.objects.filter(plan=self).order_by("id").last().licenses

    def licenses_at_next_renewal(self) -> Optional[int]:
        if self.status == CustomerPlan.DOWNGRADE_AT_END_OF_CYCLE:
            return None
        return (
            LicenseLedger.objects.filter(plan=self).order_by("id").last().licenses_at_next_renewal
        )


def get_current_plan_by_customer(customer: Customer) -> Optional[CustomerPlan]:
    return CustomerPlan.objects.filter(
        customer=customer, status__lt=CustomerPlan.LIVE_STATUS_THRESHOLD
    ).first()


def get_current_plan_by_realm(realm: Realm) -> Optional[CustomerPlan]:
    customer = get_customer_by_realm(realm)
    if customer is None:
        return None
    return get_current_plan_by_customer(customer)


class LicenseLedger(models.Model):
    """
    This table's purpose is to store the current, and historical,
    count of "seats" purchased by the organization.

    Because we want to keep historical data, when the purchased
    seat count changes, a new LicenseLedger object is created,
    instead of updating the old one. This lets us preserve
    the entire history of how the seat count changes, which is
    important for analytics as well as auditing and debugging
    in case of issues.
    """

    plan: CustomerPlan = models.ForeignKey(CustomerPlan, on_delete=CASCADE)
    # Also True for the initial upgrade.
    is_renewal: bool = models.BooleanField(default=False)
    event_time: datetime.datetime = models.DateTimeField()
    licenses: int = models.IntegerField()
    # None means the plan does not automatically renew.
    # This cannot be None if plan.automanage_licenses.
    licenses_at_next_renewal: Optional[int] = models.IntegerField(null=True)