from django.db import migrations, models


def _table_columns(schema_editor, table):
    connection = schema_editor.connection
    with connection.cursor() as cursor:
        return {
            col.name
            for col in connection.introspection.get_table_description(cursor, table)
        }


def _ensure_varchar_column(schema_editor, table, column, max_length):
    """Add a non-null varchar column with empty default when missing; else clear NULLs."""
    connection = schema_editor.connection
    q_table = connection.ops.quote_name(table)
    q_column = connection.ops.quote_name(column)

    if column in _table_columns(schema_editor, table):
        with connection.cursor() as cursor:
            cursor.execute(
                f"UPDATE {q_table} SET {q_column} = '' WHERE {q_column} IS NULL"
            )
        return

    with connection.cursor() as cursor:
        cursor.execute(
            f"ALTER TABLE {q_table} "
            f"ADD COLUMN {q_column} varchar({max_length}) DEFAULT '' NOT NULL"
        )


def add_treasury_event_name(apps, schema_editor):
    """
    Add TreasuryTxn.event_name when missing.
    Safe for fresh DBs and for DBs that already have the column from older deploys.
    """
    _ensure_varchar_column(schema_editor, 'accounting_treasury_txns', 'event_name', 200)


class Migration(migrations.Migration):

    dependencies = [
        ('accounting', '0008_invoice_cancelled_status'),
    ]

    operations = [
        migrations.SeparateDatabaseAndState(
            state_operations=[
                migrations.AddField(
                    model_name='treasurytxn',
                    name='event_name',
                    field=models.CharField(blank=True, default='', max_length=200),
                ),
            ],
            database_operations=[
                migrations.RunPython(add_treasury_event_name, migrations.RunPython.noop),
            ],
        ),
    ]