from django.db import migrations, models
from django.db.models import Count, F


def reconcile_schema(apps, schema_editor):
    """Réconcilie la base réelle après les changements d'état seuls de 0004."""
    entry = apps.get_model('time_tracking', 'TimeEntry')
    rows = entry.objects.using(schema_editor.connection.alias)
    # Ne jamais inventer une heure ni supprimer un doublon historique.
    if rows.filter(start_time__isnull=True).exists():
        raise RuntimeError('Corrigez les pointages sans heure d’entrée avant la migration 0005.')
    if rows.values('user_id', 'start_date', 'start_time').annotate(n=Count('pk')).filter(n__gt=1).exists():
        raise RuntimeError('Corrigez les doublons de pointages avant la migration 0005.')
    rows.filter(end_date__isnull=True).update(end_date=F('start_date'))

    connection = schema_editor.connection
    with connection.cursor() as cursor:
        columns = {
            column.name: column
            for column in connection.introspection.get_table_description(cursor, entry._meta.db_table)
        }
        constraints = connection.introspection.get_constraints(cursor, entry._meta.db_table)

    for field_name in ('start_time', 'end_date'):
        if columns[field_name].null_ok:
            old_field = entry._meta.get_field(field_name).clone()
            old_field.set_attributes_from_name(field_name)
            old_field.model = entry
            old_field.null = True
            new_field = old_field.clone()
            new_field.set_attributes_from_name(field_name)
            new_field.model = entry
            new_field.null = False
            schema_editor.alter_field(entry, old_field, new_field, strict=True)

    fields = ['user', 'start_date', 'start_time']
    target = 'unique_time_entry_start'
    if target not in constraints:
        schema_editor.add_constraint(entry, models.UniqueConstraint(fields=fields, name=target))
    # L'ancien unique_together a été retiré de l'état, mais peut encore exister en SQL.
    for name, constraint in constraints.items():
        if (name != target and constraint['unique']
                and constraint['columns'] == ['user_id', 'start_date', 'start_time']):
            schema_editor.remove_constraint(entry, models.UniqueConstraint(fields=fields, name=name))


class Migration(migrations.Migration):
    atomic = False
    dependencies = [('time_tracking', '0004_alter_timeentry_options_and_more')]

    operations = [
        migrations.SeparateDatabaseAndState(
            database_operations=[migrations.RunPython(reconcile_schema, atomic=False)],
            state_operations=[
                migrations.AlterField(model_name='timeentry', name='end_date', field=models.DateField()),
                migrations.AddConstraint(
                    model_name='timeentry',
                    constraint=models.UniqueConstraint(
                        fields=('user', 'start_date', 'start_time'), name='unique_time_entry_start',
                    ),
                ),
            ],
        ),
    ]