''' Configuration subsystem '''

from    typing      import MutableMapping, Any

from    sys         import  argv,  executable, stdout
from    os          import  environ, getcwd, sep as psep
from    os.path     import  dirname, abspath, join as joinpath, \
                            expanduser, splitdrive, isfile

from    copy                            import deepcopy

import  logging
import  pprint

import  asyncio

from    apscheduler.triggers.cron       import CronTrigger      # type: ignore
from    apscheduler.triggers.interval   import IntervalTrigger  # type: ignore

from    zasd.log    import log
from    zasd.util   import ifenv, uniq, find_file

import  zasd.config as _config

#
# Constants

_CONFIG_BASENAME  = 'zasd.conf.py'
_CONFIG_FILENAMES = [_CONFIG_BASENAME, '.' + _CONFIG_BASENAME]

_WARNING_WAIT = 3
#_WARNING_WAIT = 10

# Default configuration
_DEFAULT_CONFIG = dict(
    zfs_path        = '/usr/local/bin/zfs',
    fswatch_path    = '/usr/local/bin/fswatch',

    tab_size        = 2,

    log_level       = logging.INFO,
    log_format      = '%(asctime)s %(name)s [%(levelname)-8s]: %(message)s',
    log_date_format = '%a, %d %b %Y, %H:%M:%S',

    separator       = ':',
    destroy_trigger = CronTrigger.from_crontab('* * * * *'),

    # Defaults will take a snapshot every 12 hours
    # and keep them for a week, so if the config file
    # should disappear for some reason, there will
    # at least be _some_ recoverable snapshots
    defaults = dict(
        disabled    = False,
        filesystems = ['tank'],
        recursive   = True,
        tag         = 'zasd',
        trigger     = IntervalTrigger(hours=12),
        if_modified = False,
        priority    = 1,
        keep        = 14
    ),

    schedules       = [{}]
)

async def load_config():
    ''' Load configuration file '''

    if len(argv) > 1:
        # Configuration pathname given as first argument
        if isfile(argv[1]):
            config_pathname = argv[1]
        else:
            log.warning('Could not find configuration file %s', argv[1])
            return await _warn_default()
    else:
        # No configuration pathname given; attempt to find it:

        # Get root of system partition
        sys_root_path = environ.get('SystemDrive', splitdrive(executable)[0] + psep)

        # Get system configuration directory
        sys_conf_path = joinpath(
            *ifenv(
                'SystemRoot',
                lambda path:    [path,          'System32', 'drivers', 'etc'],
                lambda:         [sys_root_path, 'etc']))

        # Get user home directory
        user_home_path = expanduser('~')

        # Get path of this Python file
        if '__file__' in globals():
            script_path = dirname(abspath(__file__))
        else:
            script_path = dirname(abspath(argv[0]))

        # Build list of configuration file pathnames to search
        config_paths = uniq([
            getcwd(),
            user_home_path,
            joinpath(user_home_path, '.config'),
            joinpath(user_home_path, '.local', 'share'),
            sys_conf_path,
            script_path])
        config_pathnames = list(joinpath(p, f) for p in config_paths for f in _CONFIG_FILENAMES)

        # Attempt to find a config file
        config_pathname = find_file(config_pathnames)

        if config_pathname is None:
            log.warning('Unable to find a config file at:')
            for pathname in config_pathnames:
                log.warning('  %s', pathname)

            await _warn_default()
            return

    with open(config_pathname, 'rt', encoding='utf-8') as f:
        config_source = f.read()

    # Create configuration file scopes

    global_scope = dict(
        CRITICAL    = logging.CRITICAL,
        ERROR       = logging.ERROR,
        WARNING     = logging.WARNING,
        INFO        = logging.INFO,
        DEBUG       = logging.DEBUG,
        NOTSET      = logging.NOTSET,

        crontab     = CronTrigger.from_crontab,
        cron        = CronTrigger.from_crontab,

        interval    = IntervalTrigger,
        every       = IntervalTrigger)

    local_scope: MutableMapping[str, Any] = dict()

    # Execute configuration file
    exec(config_source, global_scope, local_scope)

    # Merge configuration with default configuration
    _config.change(_merge_configs(_DEFAULT_CONFIG, local_scope))

    log.debug('Loaded configuration')

    if _config.get('log_level') <= logging.DEBUG:
        log.debug('')
        for line in pprint.pformat(_config).split('\n'):
            logging.debug(_config.get('tab_size') * ' ' + line)
        log.debug('')

async def _warn_default():
    log.warning('')
    log.warning(
        'Waiting %s seconds before loading default configuration...',
        _WARNING_WAIT)
    log.warning('')
    await asyncio.sleep(_WARNING_WAIT)
    stdout.write('\r')
    log.warning('Loading default configuration')
    log.warning('')
    _config.change(deepcopy(_DEFAULT_CONFIG))

# pylint: disable=dangerous-default-value
def _merge_configs(base, diff, path=[]):
    ''' Deep merge configuration dictionaries '''

    base = base if len(path) == 0 else deepcopy(base)
    for key, value in diff.items():
        if not key in base:
            base[key] = value
        elif not isinstance(value, type(base[key])):
            log.error('Cannot merge diff type %s with base %s type at %s.%s',
                      type(value), type(base[key]), '.'.join(path), key)
            return None
        elif isinstance(value, dict):
            merged = _merge_configs(base[key], value, path + [key])
            if merged is None:
                return None
            base[key] = merged
        else:
            base[key] = value
    return base