from django.db import migrations, models


def forwards(apps, schema_editor):
    Dinosaur = apps.get_model('cards', 'Dinosaur')
    # Constants must match those used in models at conversion time
    SPEED_MAX_KMH = 60.0
    WEIGHT_MAX_KG = 15000.0
    HEIGHT_MAX_M = 12.0

    for obj in Dinosaur.objects.all():
        try:
            # previous values were 0-100 percentages
            old_speed = getattr(obj, 'speed', None)
            old_weight = getattr(obj, 'weight', None)
            old_height = getattr(obj, 'height', None)
            if old_speed is not None:
                new_speed = int(round(float(old_speed) / 100.0 * SPEED_MAX_KMH))
                obj.speed = new_speed
            if old_weight is not None:
                new_weight = int(round(float(old_weight) / 100.0 * WEIGHT_MAX_KG))
                obj.weight = new_weight
            if old_height is not None:
                new_height = round(float(old_height) / 100.0 * HEIGHT_MAX_M, 1)
                # assign as string to avoid Decimal conversion issues
                obj.height = new_height
            obj.save(update_fields=['speed', 'weight', 'height'])
        except Exception:
            # skip errors during migration for safety; admins can fix manually
            continue


def reverse(apps, schema_editor):
    # Not reversible automatically
    pass


class Migration(migrations.Migration):

    dependencies = [
        ('cards', '0003_dinosaur_facts'),
    ]

    operations = [
        migrations.AlterField(
            model_name='dinosaur',
            name='speed',
            field=models.PositiveIntegerField(default=30, help_text='Speed in km/h'),
        ),
        migrations.AlterField(
            model_name='dinosaur',
            name='weight',
            field=models.PositiveIntegerField(default=1000, help_text='Weight in kg'),
        ),
        migrations.AlterField(
            model_name='dinosaur',
            name='height',
            field=models.DecimalField(default=1.5, max_digits=5, decimal_places=1, help_text='Height in metres'),
        ),
        migrations.RunPython(forwards, reverse_code=migrations.RunPython.noop),
    ]