from abc import ABC, abstractmethod
from typing import Dict, Optional
from gettext import NullTranslations

from public import public


@public
class TranslationContextManager(ABC):
    """Context manager for translations in a particular language."""

    @abstractmethod
    def __enter__(self):
        pass                                        # pragma: nocover

    @abstractmethod
    def __exit__(self, *exc_info):
        pass                                        # pragma nocover


@public
class RuntimeTranslator(ABC):
    @abstractmethod
    def __call__(self,
                 original: str,
                 extras: Optional[Dict[str, str]] = None
                 ) -> str:
        """Translate the string into the language of the current context.

        This is the primary method for the runtime behavior or translating a
        source string.

        :param original: The original string to translate.
        :param extras: Extra substitution mapping, elements of which override
            the locals and globals.
        :return: The translated string.
        """

    @abstractmethod
    def using(self, language_code: str) -> TranslationContextManager:
        """Create a context manager for temporary translation.

        While in this context manager, translations use the given language
        code.  When the with statement exits, the original language is
        restored.  These are nestable.

        :param language_code: The language code for the translation context.
        :return: The new translation context.
        """

    @abstractmethod
    def defer_translation(self) -> TranslationContextManager:
        """Push a NullTranslations onto the stack.

        This is useful for when you want to mark strings statically for
        extraction but you want to defer translation of the string until
        later.

        :return: The NULLTranslations context.
        """

    @abstractmethod
    def push(self, language_code: str) -> None:
        """Push a new catalog onto the stack.

        The translation catalog associated with the language code now becomes
        the currently active translation context.

        :param language_code: The language code for the translation context.
        """

    @abstractmethod
    def pop(self) -> None:
        """Pop the current catalog off the translation stack.

        No exception is raised for under-runs.  In that case, pop() just
        no-ops and the null translation becomes the current translation
        context.
        """

    @property
    def default(self) -> Optional[str]:
        """Return the default language code.

        :return: The default language code, or None if there is no default
            language.
        """

    # 2020-07-06(warsaw): Despite the recommendations in
    #
    # https://docs.python.org/3/library/abc.html#abc.abstractproperty
    #
    # says for adding @abstractmethod to @property's, mypy does not support
    # this.
    #
    # https://github.com/python/mypy/issues/1362

    @default.setter
    def default(self, language_code: str) -> None:
        """Set the default language code.

        :param language_code: The language code for the default translation
            context.
        """

    @default.deleter                                # type: ignore
    def default(self) -> None:
        """Reset the default language to the null translator."""

    @property
    def code(self) -> Optional[str]:
        """The language code currently in effect, if there is one."""


@public
class TranslationStrategy(ABC):
    def __call__(self,
                 language_code: Optional[str] = None
                 ) -> NullTranslations:
        """Find the catalog for the language.

        :param language_code: The language code to find.  If None, then the
            default gettext language code lookup scheme is used.
        :return: A `gettext` catalog.
        """

    @property
    def name(self) -> str:
        """The application's name."""
