import uuid

from django.conf import settings
from django.db import models


class NotificationEventType(models.TextChoices):
    COURSE_ASSIGNED       = "course_assigned",       "Course Assigned"
    COURSE_DUE            = "course_due",             "Course Due Soon"
    ATTEMPT_LIMIT_REACHED = "attempt_limit_reached",  "Attempt Limit Reached"
    CERTIFICATE_ISSUED    = "certificate_issued",     "Certificate Issued"
    CERTIFICATE_EXPIRING  = "certificate_expiring",   "Certificate Expiring"


class DeliveryChannel(models.TextChoices):
    IN_APP = "in_app", "In-App"
    EMAIL  = "email",  "Email"


class DeliveryStatus(models.TextChoices):
    PENDING   = "pending",   "Pending"
    SENT      = "sent",      "Sent"
    FAILED    = "failed",    "Failed"
    DELIVERED = "delivered", "Delivered"


class Notification(models.Model):
    """
    In-app notification record.  One row per (recipient, event, object).
    idempotency_key prevents duplicate delivery for the same logical event.
    """
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    recipient = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.CASCADE,
        related_name="notifications",
    )
    event_type  = models.CharField(max_length=40, choices=NotificationEventType.choices, db_index=True)
    title       = models.CharField(max_length=255)
    body        = models.TextField(blank=True)
    object_type = models.CharField(max_length=64, blank=True)
    object_id   = models.CharField(max_length=128, blank=True)
    # Caller-supplied dedup key; format: "<event_type>:<object_type>:<object_id>:<recipient_id>"
    idempotency_key = models.CharField(max_length=255, unique=True, db_index=True)
    created_at  = models.DateTimeField(auto_now_add=True)
    read_at     = models.DateTimeField(null=True, blank=True)

    class Meta:
        db_table = "notifications_notification"
        ordering = ["-created_at"]

    def __str__(self):
        return f"{self.event_type} → {self.recipient_id}"

    @property
    def is_read(self):
        return self.read_at is not None


class NotificationDelivery(models.Model):
    """Audit record for each delivery attempt per channel."""
    id           = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    notification = models.ForeignKey(
        Notification, on_delete=models.CASCADE, related_name="deliveries"
    )
    channel      = models.CharField(max_length=20, choices=DeliveryChannel.choices)
    status       = models.CharField(
        max_length=20, choices=DeliveryStatus.choices, default=DeliveryStatus.PENDING
    )
    sent_at      = models.DateTimeField(null=True, blank=True)
    error_detail = models.TextField(blank=True)
    created_at   = models.DateTimeField(auto_now_add=True)

    class Meta:
        db_table = "notifications_delivery"
        ordering = ["-created_at"]

    def __str__(self):
        return f"{self.channel}/{self.status} for notification {self.notification_id}"