"""Backfill `VerifiedEmail` from any historical submission that already had
`email_confirmed=True` (i.e. the user clicked the confirmation link before
the trust list existed). One-shot; safe to re-run thanks to
`update_or_create`."""

from django.db import migrations


def backfill_verified_emails(apps, schema_editor):
    Submission = apps.get_model("submissions", "Submission")
    VerifiedEmail = apps.get_model("submissions", "VerifiedEmail")

    # `update_or_create` keeps the migration idempotent.
    seen: set[str] = set()
    qs = Submission.objects.filter(email_confirmed=True).exclude(
        guest_email__isnull=True
    ).exclude(guest_email="").values_list("guest_email", flat=True)
    for email in qs:
        email = email.strip().lower()
        if not email or email in seen:
            continue
        seen.add(email)
        VerifiedEmail.objects.update_or_create(email=email)


def noop_reverse(apps, schema_editor):
    """We don't try to undo the backfill -- the trust list is a forward-only
    derived artefact; rolling back the migration leaves the rows alone."""


class Migration(migrations.Migration):

    dependencies = [
        ("submissions", "0002_verifiedemail"),
    ]

    operations = [
        migrations.RunPython(backfill_verified_emails, noop_reverse),
    ]