"""Settings and configuration handlers.

Settings will be loaded from several .conf files
and any user provided settings file.
"""

# pylint: disable=invalid-name

import copy
import os
import re
import logging
import pprint
#import ast
#import netaddr

_LOGGER = logging.getLogger(__name__)

_PARSE_PATTERN = r'(#[A-Z]+)(\(([^(),]+)(,([0-9]+))?\))?'

class Settings(object):
    """Holding class for settings.
    """
    def __init__(self):
        pass

    def _eval_param(self, param):
        # pylint: disable=invalid-name
        """ Helper function for expansion of references to parameters
        """
        if isinstance(param, str):
            # evaluate every #PARAM reference inside parameter itself
            macros = re.findall(r'#PARAM\((([\w\-]+)(\[[\w\[\]\-\'\"]+\])*)\)', param)
            if macros:
                for macro in macros:
                    # pylint: disable=eval-used
                    try:
                        tmp_val = str(eval("self.getValue('{}'){}".format(macro[1], macro[2])))
                        param = param.replace('#PARAM({})'.format(macro[0]), tmp_val)
                    # silently ignore that option required by PARAM macro can't be evaluated;
                    # It is possible, that referred parameter will be constructed during runtime
                    # and re-read later.
                    except IndexError:
                        pass
                    except AttributeError:
                        pass
            return param
        elif isinstance(param, (list, tuple)):
            tmp_list = []
            for item in param:
                tmp_list.append(self._eval_param(item))
            return tmp_list
        elif isinstance(param, dict):
            tmp_dict = {}
            for (key, value) in param.items():
                tmp_dict[key] = self._eval_param(value)
            return tmp_dict
        else:
            return param

    def getValue(self, attr):
        """Return a settings item value
        """
        if attr in self.__dict__:
            master_value = getattr(self, attr)
            return self._eval_param(master_value)
        else:
            raise AttributeError("%r object has no attribute %r" %
                                 (self.__class__, attr))

    def hasValue(self, attr):
        """Return true if key exists
        """
        if attr in self.__dict__:
            return True
        return False

    def __setattr__(self, name, value):
        """Set a value
        """
        # skip non-settings. this should exclude built-ins amongst others
        if not name.isupper():
            return

        # we can assume all uppercase keys are valid settings
        super(Settings, self).__setattr__(name, value)

    def setValue(self, name, value):
        """Set a value
        """
        if name is not None and value is not None:
            super(Settings, self).__setattr__(name, value)


    def load_from_file(self, path):
        """Update ``settings`` with values found in module at ``path``.
        """
        import imp

        custom_settings = imp.load_source('custom_settings', path)

        for key in dir(custom_settings):
            if getattr(custom_settings, key) is not None:
                setattr(self, key, getattr(custom_settings, key))

    def load_from_dir(self, dir_path):
        """Update ``settings`` with contents of the .conf files at ``path``.

        Each file must be named Nfilename.conf, where N is a single or
        multi-digit decimal number.  The files are loaded in ascending order of
        N - so if a configuration item exists in more that one file the setting
        in the file with the largest value of N takes precedence.

        :param dir_path: The full path to the dir from which to load the .conf
            files.

        :returns: None
        """
        regex = re.compile("^(?P<digit_part>[0-9]+)(?P<alfa_part>[a-z]?)_.*.conf$")

        def get_prefix(filename):
            """
            Provide a suitable function for sort's key arg
            """
            match_object = regex.search(os.path.basename(filename))
            return [int(match_object.group('digit_part')),
                    match_object.group('alfa_part')]

        # get full file path to all files & dirs in dir_path
        file_paths = os.listdir(dir_path)
        file_paths = [os.path.join(dir_path, x) for x in file_paths]

        # filter to get only those that are a files, with a leading
        # digit and end in '.conf'
        file_paths = [x for x in file_paths if os.path.isfile(x) and
                      regex.search(os.path.basename(x))]

        # sort ascending on the leading digits and afla (e.g. 03_, 05a_)
        file_paths.sort(key=get_prefix)

        # load settings from each file in turn
        for filepath in file_paths:
            self.load_from_file(filepath)

    def load_from_dict(self, conf):
        """
        Update ``settings`` with values found in ``conf``.

        Unlike the other loaders, this is case insensitive.
        """
        for key in conf:
            if conf[key] is not None:
                if isinstance(conf[key], dict):
                    # recursively update dict items
                    setattr(self, key.upper(),
                            merge_spec(getattr(self, key.upper()), conf[key]))
                else:
                    setattr(self, key.upper(), conf[key])

    def restore_from_dict(self, conf):
        """
        Restore ``settings`` with values found in ``conf``.

        Method will drop all configuration options and restore their
        values from conf dictionary
        """
        self.__dict__.clear()
        tmp_conf = copy.deepcopy(conf)
        for key in tmp_conf:
            self.setValue(key, tmp_conf[key])

    def load_from_env(self):
        """
        Update ``settings`` with values found in the environment.
        """
        for key in os.environ:
            setattr(self, key, os.environ[key])

    def __str__(self):
        """Provide settings as a human-readable string.

        This can be useful for debug.

        Returns:
            A human-readable string.
        """
        tmp_dict = {}
        for key in self.__dict__:
            tmp_dict[key] = self.getValue(key)

        return pprint.pformat(tmp_dict)


settings = Settings()

def merge_spec(orig, new):
    """Merges ``new`` dict with ``orig`` dict, and returns orig.

    This takes into account nested dictionaries. Example:

        >>> old = {'foo': 1, 'bar': {'foo': 2, 'bar': 3}}
        >>> new = {'foo': 6, 'bar': {'foo': 7}}
        >>> merge_spec(old, new)
        {'foo': 6, 'bar': {'foo': 7, 'bar': 3}}

    You'll notice that ``bar.bar`` is not removed. This is the desired result.
    """
    for key in orig:
        if key not in new:
            continue

        # Not allowing derived dictionary types for now
        # pylint: disable=unidiomatic-typecheck
        if type(orig[key]) == dict:
            orig[key] = merge_spec(orig[key], new[key])
        else:
            orig[key] = new[key]

    for key in new:
        if key not in orig:
            orig[key] = new[key]

    return orig