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_missing_columns(apps, schema_editor):
    """
    Ensure schema columns match current models.
    Idempotent for local/prod DBs that already have some of these columns.
    Also re-checks treasury event_name in case an older 0009 only updated state.
    """
    specs = [
        ('accounting_vouchers', 'regarding', 255),
        ('accounting_invoice_lines', 'event_name', 255),
        ('accounting_treasury_txns', 'event_name', 200),
    ]
    for table, column, max_length in specs:
        _ensure_varchar_column(schema_editor, table, column, max_length)


class Migration(migrations.Migration):

    dependencies = [
        ('accounting', '0009_treasury_event_name'),
    ]

    operations = [
        migrations.SeparateDatabaseAndState(
            state_operations=[
                migrations.AddField(
                    model_name='invoiceline',
                    name='event_name',
                    field=models.CharField(blank=True, default='', max_length=255),
                ),
                migrations.AddField(
                    model_name='voucher',
                    name='regarding',
                    field=models.CharField(blank=True, default='', max_length=255),
                ),
                migrations.AlterField(
                    model_name='party',
                    name='external_source',
                    field=models.CharField(
                        blank=True,
                        choices=[
                            ('', 'Manual'),
                            ('funzone_customer', 'FunZone Customer'),
                            ('funzone_owner', 'FunZone Owner'),
                        ],
                        default='',
                        max_length=30,
                    ),
                ),
            ],
            database_operations=[
                migrations.RunPython(add_missing_columns, migrations.RunPython.noop),
            ],
        ),
    ]