from __future__ import absolute_import, unicode_literals

from abc import ABCMeta, abstractmethod

from six import add_metaclass


@add_metaclass(ABCMeta)
class Discover(object):
    """Discover and provide the requested Python interpreter"""

    @classmethod
    def add_parser_arguments(cls, parser):
        """Add CLI arguments for this discovery mechanisms.

        :param parser: the CLI parser
        """
        raise NotImplementedError

    # noinspection PyUnusedLocal
    def __init__(self, options):
        """Create a new discovery mechanism.

        :param options: the parsed options as defined within :meth:`add_parser_arguments`
        """
        self._has_run = False
        self._interpreter = None

    @abstractmethod
    def run(self):
        """Discovers an interpreter.


        :return: the interpreter ready to use for virtual environment creation
        """
        raise NotImplementedError

    @property
    def interpreter(self):
        """
        :return: the interpreter as returned by :meth:`run`, cached
        """
        if self._has_run is False:
            self._interpreter = self.run()
            self._has_run = True
        return self._interpreter
