import os
from distutils.dist import Distribution

__metaclass__ = type

class EnvironmentConfig:
    def __init__(self, distutils_section='DEFAULT', **kw):
        self._distutils_section = distutils_section
        self._conf_keys = kw
        self._conf = None
        self._hook_handler = None

    def __getattr__(self, name):
        try:
            conf_desc = self._conf_keys[name]
        except KeyError:
            raise AttributeError(name)
        return self._get_var(name, conf_desc)

    def get(self, name, default=None):
        try:
            conf_desc = self._conf_keys[name]
        except KeyError:
            return default
        var = self._get_var(name, conf_desc)
        if var is None:
            var = default
        return var

    def _get_var(self, name, conf_desc):
        hook, envvar, confvar = conf_desc
        var = self._hook_handler(name, hook)
        if envvar is not None:
            var = os.environ.get(envvar, var)
        if confvar is not None and self._conf:
            var = self._conf.get(confvar, (None, var))[1]
        return var

    def clone(self, hook_handler):
        ec = self.__class__(distutils_section=self._distutils_section,
                            **self._conf_keys)
        ec._hook_handler = hook_handler
        return ec

    def use_distribution(self, dist):
        if isinstance(dist, Distribution):
            self._conf = dist.get_option_dict(self._distutils_section)
        else:
            self._conf = dist