# Convert Site.site_id from BigAutoField to name-based SlugField PK with numeric suffix.
# atomic=False: PostgreSQL cannot ALTER TABLE in the same transaction after PK UPDATEs.

from django.db import migrations, models
import django.db.models.deletion
from django.utils.text import slugify


def _unique_slug(site_name: str, old_pk: str, used: set[str]) -> str:
    base = slugify(str(site_name or "").strip())[:55] or f"site-{old_pk}"[:55]
    try:
        seed = int(old_pk) % 10000
    except ValueError:
        seed = sum(ord(c) for c in old_pk) % 10000
    for i in range(10000):
        code = f"{base}-{(seed + i) % 10000:04d}"
        if code not in used:
            used.add(code)
            return code
    raise RuntimeError(f"Could not allocate site id for {old_pk}")


def forwards_slug_pks(apps, schema_editor):
    Site = apps.get_model("farms", "Site")
    Kandang = apps.get_model("farms", "Kandang")
    PusatRegistration = apps.get_model("farms", "PusatRegistration")

    used: set[str] = set()
    mapping: dict[str, str] = {}
    for site in Site.objects.all().order_by("site_id"):
        old = str(site.site_id)
        mapping[old] = _unique_slug(site.site_name, old, used)

    for old_id, new_id in mapping.items():
        if old_id == new_id:
            continue
        Kandang.objects.filter(site_id=old_id).update(site_id=new_id)
        PusatRegistration.objects.filter(site_id=old_id).update(site_id=new_id)
        Site.objects.filter(site_id=old_id).update(site_id=new_id)

    # Ensure site names are unique before adding the constraint.
    seen_names: dict[str, int] = {}
    for site in Site.objects.all().order_by("site_id"):
        name = site.site_name
        count = seen_names.get(name, 0)
        seen_names[name] = count + 1
        if count == 0:
            continue
        suffix = f"-{count + 1}"
        site.site_name = f"{name[: 30 - len(suffix)]}{suffix}"
        site.save(update_fields=["site_name"])


def noop_reverse(apps, schema_editor):
    raise RuntimeError("Cannot reverse site_id slug migration.")


class Migration(migrations.Migration):

    atomic = False

    dependencies = [
        ("farms", "0016_pusat_registration"),
    ]

    operations = [
        migrations.AlterField(
            model_name="kandang",
            name="site",
            field=models.ForeignKey(
                db_constraint=False,
                on_delete=django.db.models.deletion.CASCADE,
                related_name="kandangs",
                to="farms.site",
            ),
        ),
        migrations.AlterField(
            model_name="pusatregistration",
            name="site",
            field=models.OneToOneField(
                db_constraint=False,
                on_delete=django.db.models.deletion.CASCADE,
                related_name="pusat_registration",
                to="farms.site",
            ),
        ),
        migrations.AlterField(
            model_name="site",
            name="site_id",
            field=models.CharField(max_length=64, primary_key=True, serialize=False),
        ),
        migrations.RunPython(forwards_slug_pks, noop_reverse),
        migrations.AlterField(
            model_name="site",
            name="site_id",
            field=models.SlugField(max_length=64, primary_key=True, serialize=False),
        ),
        migrations.AlterField(
            model_name="site",
            name="site_name",
            field=models.CharField(max_length=30, unique=True),
        ),
        migrations.AlterField(
            model_name="kandang",
            name="site",
            field=models.ForeignKey(
                on_delete=django.db.models.deletion.CASCADE,
                related_name="kandangs",
                to="farms.site",
            ),
        ),
        migrations.AlterField(
            model_name="pusatregistration",
            name="site",
            field=models.OneToOneField(
                on_delete=django.db.models.deletion.CASCADE,
                related_name="pusat_registration",
                to="farms.site",
            ),
        ),
    ]