import logging

import pkg_resources
import pykwalify.core
import pykwalify.errors
from ruamel import yaml


logger = logging.getLogger(__name__)


def schema_filename():
    '''
    Path to the installed YAML configuration schema file, used to validate and parse the
    configuration.
    '''
    return pkg_resources.resource_filename('borgmatic', 'config/schema.yaml')


class Validation_error(ValueError):
    '''
    A collection of error message strings generated when attempting to validate a particular
    configurartion file.
    '''

    def __init__(self, config_filename, error_messages):
        self.config_filename = config_filename
        self.error_messages = error_messages

    def __str__(self):
        '''
        Render a validation error as a user-facing string.
        '''
        return 'An error occurred while parsing a configuration file at {}:\n'.format(
            self.config_filename
        ) + '\n'.join(self.error_messages)


def apply_logical_validation(config_filename, parsed_configuration):
    '''
    Given a parsed and schematically valid configuration as a data structure of nested dicts (see
    below), run through any additional logical validation checks. If there are any such validation
    problems, raise a Validation_error.
    '''
    archive_name_format = parsed_configuration.get('storage', {}).get('archive_name_format')
    prefix = parsed_configuration.get('retention', {}).get('prefix')

    if archive_name_format and not prefix:
        raise Validation_error(
            config_filename,
            ('If you provide an archive_name_format, you must also specify a retention prefix.',),
        )

    location_repositories = parsed_configuration.get('location', {}).get('repositories')
    check_repositories = parsed_configuration.get('consistency', {}).get('check_repositories', [])
    for repository in check_repositories:
        if repository not in location_repositories:
            raise Validation_error(
                config_filename,
                (
                    'Unknown repository in the consistency section\'s check_repositories: {}'.format(
                        repository
                    ),
                ),
            )

    consistency_prefix = parsed_configuration.get('consistency', {}).get('prefix')
    if archive_name_format and not consistency_prefix:
        logger.warning(
            'Since version 1.1.16, if you provide `archive_name_format`, you should also'
            ' specify `consistency.prefix`.'
        )


def parse_configuration(config_filename, schema_filename):
    '''
    Given the path to a config filename in YAML format and the path to a schema filename in
    pykwalify YAML schema format, return the parsed configuration as a data structure of nested
    dicts and lists corresponding to the schema. Example return value:

       {'location': {'source_directories': ['/home', '/etc'], 'repository': 'hostname.borg'},
       'retention': {'keep_daily': 7}, 'consistency': {'checks': ['repository', 'archives']}}

    Raise FileNotFoundError if the file does not exist, PermissionError if the user does not
    have permissions to read the file, or Validation_error if the config does not match the schema.
    '''
    logging.getLogger('pykwalify').setLevel(logging.ERROR)

    try:
        config = yaml.safe_load(open(config_filename))
        schema = yaml.safe_load(open(schema_filename))
    except yaml.error.YAMLError as error:
        raise Validation_error(config_filename, (str(error),))

    # pykwalify gets angry if the example field is not a string. So rather than bend to its will,
    # simply remove all examples before passing the schema to pykwalify.
    for section_name, section_schema in schema['map'].items():
        for field_name, field_schema in section_schema['map'].items():
            field_schema.pop('example', None)

    validator = pykwalify.core.Core(source_data=config, schema_data=schema)
    parsed_result = validator.validate(raise_exception=False)

    if validator.validation_errors:
        raise Validation_error(config_filename, validator.validation_errors)

    apply_logical_validation(config_filename, parsed_result)

    return parsed_result