from collections import Counter

from django.core.management.base import BaseCommand
from django.db import transaction
from django.utils import timezone

from apps.events.models import Registration
from apps.gamification.rules import ACTIVITY_BADGES, LEVELS, POINTS, level_for_points
from apps.gamification.services import sync_registration_attendance


class Command(BaseCommand):
    help = "Report or backfill lifetime points from existing attended event registrations."

    def add_arguments(self, parser):
        parser.add_argument(
            "--apply",
            action="store_true",
            help="Write historical attendance provenance and ledger awards; default is read-only.",
        )

    def handle(self, *args, **options):
        registrations = list(
            Registration.objects.filter(status=Registration.StatusChoices.ATTENDED)
            .select_related("user")
            .order_by("user_id", "id")
        )
        attendance_counts = Counter(registration.user_id for registration in registrations)
        level_counts = Counter()
        for count in attendance_counts.values():
            level_counts[level_for_points(count * POINTS["attendance"])["id"]] += 1

        self.stdout.write(f"Attended registrations eligible: {len(registrations)}")
        self.stdout.write(f"Users with attended registrations: {len(attendance_counts)}")
        self.stdout.write("Projected level distribution (event history only):")
        for level in LEVELS:
            self.stdout.write(f"  {level['id']}: {level_counts[level['id']]}")
        self.stdout.write("Projected attendance badges (threshold -> users):")
        for badge in ACTIVITY_BADGES["attendance"]:
            members = sum(count >= badge["threshold"] for count in attendance_counts.values())
            self.stdout.write(f"  {badge['threshold']}: {members}")

        if not options["apply"]:
            self.stdout.write(self.style.WARNING("Dry run only; no records were changed. Pass --apply to backfill."))
            return

        verified_at = timezone.now()
        with transaction.atomic():
            for registration in registrations:
                if not registration.attendance_verified_at:
                    registration.attendance_verified_at = verified_at
                    registration.attendance_verification_source = Registration.AttendanceVerificationSource.HISTORICAL
                    registration.save(update_fields=[
                        "attendance_verified_at",
                        "attendance_verification_source",
                        "updated_at",
                    ])
                sync_registration_attendance(registration, trust_legacy=True)

        self.stdout.write(self.style.SUCCESS(f"Backfilled {len(registrations)} attended registrations."))