"""
Utilities for monitoring the LMS
"""
import logging
import re
from django.conf import settings

log = logging.getLogger(__name__)


def get_code_owner_from_module(module):
    """
    Attempts lookup of code_owner based on a code module,
    finding the most specific match. If no match, returns None.

    For example, if the module were 'openedx.features.discounts.views',
    this lookup would match on 'openedx.features.discounts' before
    'openedx.features', because the former is more specific.

    """
    assert _PATH_TO_CODE_OWNER_MAPPINGS != _INVALID_CODE_OWNER_MAPPING,\
        'CODE_OWNER_MAPPINGS django setting set with invalid configuration. See logs for details.'

    module_parts = module.split('.')
    # To make the most specific match, start with the max number of parts
    for number_of_parts in range(len(module_parts), 0, -1):
        partial_path = '.'.join(module_parts[0:number_of_parts])
        if partial_path in _PATH_TO_CODE_OWNER_MAPPINGS:
            code_owner = _PATH_TO_CODE_OWNER_MAPPINGS[partial_path]
            return code_owner
    return None


def is_code_owner_mappings_configured():
    """
    Returs True if code owner mappings were configured, and False otherwise.
    """
    return bool(_PATH_TO_CODE_OWNER_MAPPINGS)


def _process_code_owner_mappings():
    """
    Processes the CODE_OWNER_MAPPINGS Django Setting and returns a dict optimized
    for efficient lookup by path.

    Returns:
         (dict): optimized dict for success processing, None if there are no
            configured mappings, or _INVALID_CODE_OWNER_MAPPING if there is an
            error processing the setting.

    Example CODE_OWNER_MAPPINGS Django Setting::

        CODE_OWNER_MAPPINGS = {
            'team-red': [
                'xblock_django',
                'openedx.core.djangoapps.xblock',
            ],
            'team-blue': [
                'badges',
            ],
        }

    Example return value::

        {
            'xblock_django': 'team-red',
            'openedx.core.djangoapps.xblock': 'team-red',
            'badges': 'team-blue',
        }

    """
    _CODE_OWNER_MAPPINGS = getattr(settings, 'CODE_OWNER_MAPPINGS', None)
    if not _CODE_OWNER_MAPPINGS:
        return None

    try:
        path_to_code_owner_mappings = {}
        for code_owner in _CODE_OWNER_MAPPINGS:
            path_list = _CODE_OWNER_MAPPINGS[code_owner]
            for path in path_list:
                path_to_code_owner_mappings[path] = code_owner
                optional_module_prefix_match = _OPTIONAL_MODULE_PREFIX_PATTERN.match(path)
                # if path has an optional prefix, also add the module name without the prefix
                if optional_module_prefix_match:
                    path_without_prefix = path[optional_module_prefix_match.end():]
                    path_to_code_owner_mappings[path_without_prefix] = code_owner

        return path_to_code_owner_mappings
    except Exception as e:
        log.exception('Error processing code_owner_mappings. {}'.format(e))
        # errors should be unlikely due do scripting the setting values.
        # this will trigger an error custom metric that can be alerted on.
        return _INVALID_CODE_OWNER_MAPPING

# .. toggle_name: CODE_OWNER_MAPPINGS
# .. toggle_implementation: DjangoSetting
# .. toggle_default: None
# .. toggle_description: Used to set monitoring custom metrics for owner. Dict with keys of code owner and value as list of dotted path module names owned by code owner.
# .. toggle_category: monitoring
# .. toggle_use_cases: open_edx
# .. toggle_creation_date: 2020-05-29
# .. toggle_expiration_date: None
# .. toggle_tickets: None
# .. toggle_status: supported
# .. toggle_warnings: None
# Set to settings.CODE_OWNER_MAPPINGS during processing for simpler testing
_CODE_OWNER_MAPPINGS = None

# The following module prefixes are optional in a view's reported module:
#   'common.djangoapps.', 'lms.djangoapps.', 'openedx.core.djangoapps.'
_OPTIONAL_MODULE_PREFIX_PATTERN = re.compile(r'^(lms|common|openedx\.core)\.djangoapps\.')
_INVALID_CODE_OWNER_MAPPING = 'invalid-code-owner-mapping'
# lookup table for code owner given a module path
_PATH_TO_CODE_OWNER_MAPPINGS = _process_code_owner_mappings()