"""Import currency exchange rates."""

import os

from accounting import config
from accounting.adapters.file import read_exchange_rate_file
from accounting.adapters.log import getlogger
from accounting.data import get_db_adapter

SELECT_SQL = (
    'SELECT '
    'COUNT(*) as count '
    'FROM `currency_exchange_rates` '
    'WHERE `period_id` = {:d}')

INSERT_SQL = (
    'INSERT INTO `currency_exchange_rates` '
    '(`period_id`, `currency_from_id`, `currency_to_id`, `exchange_rate`) '
    'VALUES {}')

VALUE_SQL = (
    '({period_id}, {currency_from_id}, {currency_to_id}, {exchange_rate})')

ALREADY_EXISTS_TEXT = (
    'Exchange rates already exist for period {:d}. '
    'Canceling import.')

MISMATCH_TEXT = (
    'Import period id does not match current period id. '
    'Given {:d}, expecting {:d}. '
    'Canceling import.')

IMPORT_TEXT = 'Importing currency exchange rates for period {:d}'


def import_exchange_rates():
    """Import currency exchange rates.

    Performs checks that the given period id does not already exist in the db.
    Checks that the imported period_id matches the current period_id.

    Raises:
        Exception: Exchange rates already exist for the current period.

    """
    db_adapter = get_db_adapter()
    logger = getlogger()

    if check_rates_exist_for_period(config.PERIOD_ID):
        raise Exception(ALREADY_EXISTS_TEXT.format(config.PERIOD_ID))

    logger.info(IMPORT_TEXT.format(config.PERIOD_ID))
    db_adapter.execute(get_sql(
        os.environ.get('CURRENCY_EXCHANGE_RATES_FILE'), config.PERIOD_ID))


def check_rates_exist_for_period(period_id):
    """Check if currency exchange rates exist for the given period.

    Args:
        period_id (int): Current period id.

    Returns:
        bool: if rows exist for the given period.

    """
    db_adapter = get_db_adapter()
    row = db_adapter.fetch_rows(SELECT_SQL.format(period_id))
    return row[0][0] > 0


def get_sql(filename, period_id):
    """Build insert sql for exchange rates.

    Args:
        filename (str): Path to exchange rates file.
        period_id (int): Current period id.

    Returns:
        str: Insert SQL for exchange rates.

    """
    value_list = []
    for rate in read_exchange_rate_file(filename):
        if period_id != rate['period_id']:
            raise Exception(MISMATCH_TEXT.format(rate['period_id'], period_id))
        value_list.append(VALUE_SQL.format(**rate))
    return INSERT_SQL.format(', '.join(value_list))