"""Neo4J cluster verification logic."""

from constants import neo4j_errors
from constants import neo4j_queries

QUERIES_TO_VERIFY = {
    'GET_SERVERS': neo4j_queries.GET_SERVERS_QUERY
}


class VerifyNeo4JException(Exception):
    """Error that is raised if neo4j verification fails."""

    pass


def verify_write_node_exists(query_result):
    """Verify that we have at least one write node in a cluster.

    Args:
        query_result (dict):

    Returns:
        dict or None: dictionary with error description or None
    """
    if not any(
            server for server in query_result.get('servers', [])
            if server['role'] == 'WRITE'):
        return {
            'query_result': query_result,
            'error': neo4j_errors.WRITE_NODE_NOT_AVAILABLE
        }

    return None


VERIFICATION_FUNCTIONS = {
    'GET_SERVERS': verify_write_node_exists
}


def verify_neo4j_cluster(driver):
    """Make a number of queries to Neo4J cluster and verify the results.

    Args:
        driver: Neo4J driver instance

    Returns:
        list: a list with errors found.
    """
    errors = []
    with driver.session() as session:
        for query_name, query in QUERIES_TO_VERIFY.items():
            neo4j_result = session.run(query)
            data = neo4j_result.data()[0]
            verify_result = VERIFICATION_FUNCTIONS[query_name](data)
            if verify_result is not None:
                errors.append(verify_result)
    return errors