import uuid

from django.contrib.auth import get_user_model
from django.db import models, IntegrityError

from courses.models import Course, Page

User = get_user_model()

# Gap threshold (seconds) below which two consecutive events are merged.
RECONNECT_TOLERANCE_SECONDS = 30

# Anti-idle cap: a merged dwell window longer than this is capped before counting.
MAX_VALID_EVENT_SECONDS = 120


class AuditEventClass(models.TextChoices):
    AUTH        = "auth",        "Authentication"
    PROGRESS    = "progress",    "Progression"
    ASSESSMENT  = "assessment",  "Assessment"
    TRAINER     = "trainer",     "Trainer Decision"
    CERTIFICATE = "certificate", "Certificate"
    ACCESS      = "access",      "Access Control"


_CLASS_PREFIX_MAP = {c.value: c.value for c in AuditEventClass}


class AuditEvent(models.Model):
    """Append-only compliance audit record. Never update or delete rows directly."""

    id            = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    occurred_at   = models.DateTimeField(db_index=True)
    recorded_at   = models.DateTimeField(auto_now_add=True)

    event_class   = models.CharField(max_length=32, choices=AuditEventClass.choices, db_index=True)
    event_type    = models.CharField(max_length=64, db_index=True)

    actor_id      = models.UUIDField(null=True, blank=True, db_index=True)
    actor_type    = models.CharField(max_length=32, default="user")
    actor_ip      = models.GenericIPAddressField(null=True, blank=True)

    object_type   = models.CharField(max_length=64, null=True, blank=True)
    object_id     = models.CharField(max_length=128, null=True, blank=True, db_index=True)

    metadata      = models.JSONField(default=dict)

    retention_class = models.CharField(max_length=32, db_index=True)

    class Meta:
        db_table = "tracking_audit_event"
        indexes = [
            models.Index(fields=["event_class", "occurred_at"]),
            models.Index(fields=["actor_id", "occurred_at"]),
            models.Index(fields=["object_type", "object_id"]),
        ]

    def save(self, *args, **kwargs):
        if self.pk and AuditEvent.objects.filter(pk=self.pk).exists():
            raise IntegrityError("AuditEvent records are immutable")
        super().save(*args, **kwargs)

    def delete(self, *args, **kwargs):
        raise IntegrityError("AuditEvent records cannot be deleted via ORM")

    def __str__(self):
        return f"{self.event_type} @ {self.occurred_at}"


# ── Dwell-time tracking ───────────────────────────────────────────────────────

class Enrollment(models.Model):
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    user = models.ForeignKey(User, on_delete=models.CASCADE, related_name="enrollments")
    course = models.ForeignKey(Course, on_delete=models.CASCADE, related_name="enrollments")
    org_id = models.UUIDField(db_index=True)
    enrolled_at = models.DateTimeField(auto_now_add=True)
    completed_at = models.DateTimeField(null=True, blank=True)

    class Meta:
        constraints = [
            models.UniqueConstraint(
                fields=["user", "course"], name="unique_user_course_enrollment"
            )
        ]
        ordering = ["-enrolled_at"]

    def __str__(self):
        return f"{self.user_id} → {self.course_id}"


class PageProgress(models.Model):
    """Accumulated dwell-time and completion state for a single (enrollment, page) pair."""

    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    enrollment = models.ForeignKey(
        Enrollment, on_delete=models.CASCADE, related_name="page_progresses"
    )
    page = models.ForeignKey(Page, on_delete=models.CASCADE, related_name="progresses")
    accumulated_seconds = models.PositiveIntegerField(default=0)
    is_complete = models.BooleanField(default=False)
    last_seen_at = models.DateTimeField(null=True, blank=True)
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)

    class Meta:
        constraints = [
            models.UniqueConstraint(
                fields=["enrollment", "page"], name="unique_enrollment_page_progress"
            )
        ]
        ordering = ["-updated_at"]

    @property
    def can_advance(self) -> bool:
        """True when accumulated dwell satisfies the page's required_seconds threshold."""
        return self.accumulated_seconds >= self.page.required_seconds

    def __str__(self):
        return f"progress({self.enrollment_id}/{self.page_id} {self.accumulated_seconds}s)"


class DwellEvent(models.Model):
    """
    Raw contiguous window during which the learner was active on a page.

    The service layer coalesces events within RECONNECT_TOLERANCE_SECONDS and
    applies MAX_VALID_EVENT_SECONDS anti-idle capping before crediting
    PageProgress.accumulated_seconds.
    """

    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    page_progress = models.ForeignKey(
        PageProgress, on_delete=models.CASCADE, related_name="dwell_events"
    )
    started_at = models.DateTimeField()
    ended_at = models.DateTimeField(null=True, blank=True)
    raw_seconds = models.PositiveIntegerField(default=0)
    # Set False when the event is determined to be an idle/bot artifact.
    is_valid = models.BooleanField(default=True)
    created_at = models.DateTimeField(auto_now_add=True)

    class Meta:
        ordering = ["started_at"]

    def __str__(self):
        return f"dwell({self.page_progress_id} {self.started_at}–{self.ended_at})"