"""
`Fish-style <http://fishshell.com/>`_  like auto-suggestion.

While a user types input in a certain buffer, suggestions are generated
(asynchronously.) Usually, they are displayed after the input. When the cursor
presses the right arrow and the cursor is at the end of the input, the
suggestion will be inserted.

If you want the auto suggestions to be asynchronous (in a background thread),
because they take too much time, and could potentially block the event loop,
then wrap the :class:`.AutoSuggest` instance into a
:class:`.ThreadedAutoSuggest`.
"""
from abc import ABCMeta, abstractmethod
from typing import TYPE_CHECKING, Callable, Optional, Union

from prompt_toolkit.eventloop import run_in_executor_with_context

from .document import Document
from .filters import Filter, to_filter

if TYPE_CHECKING:
    from .buffer import Buffer

__all__ = [
    "Suggestion",
    "AutoSuggest",
    "ThreadedAutoSuggest",
    "DummyAutoSuggest",
    "AutoSuggestFromHistory",
    "ConditionalAutoSuggest",
    "DynamicAutoSuggest",
]


class Suggestion:
    """
    Suggestion returned by an auto-suggest algorithm.

    :param text: The suggestion text.
    """

    def __init__(self, text: str) -> None:
        self.text = text

    def __repr__(self) -> str:
        return "Suggestion(%s)" % self.text


class AutoSuggest(metaclass=ABCMeta):
    """
    Base class for auto suggestion implementations.
    """

    @abstractmethod
    def get_suggestion(
        self, buffer: "Buffer", document: Document
    ) -> Optional[Suggestion]:
        """
        Return `None` or a :class:`.Suggestion` instance.

        We receive both :class:`~prompt_toolkit.buffer.Buffer` and
        :class:`~prompt_toolkit.document.Document`. The reason is that auto
        suggestions are retrieved asynchronously. (Like completions.) The
        buffer text could be changed in the meantime, but ``document`` contains
        the buffer document like it was at the start of the auto suggestion
        call. So, from here, don't access ``buffer.text``, but use
        ``document.text`` instead.

        :param buffer: The :class:`~prompt_toolkit.buffer.Buffer` instance.
        :param document: The :class:`~prompt_toolkit.document.Document` instance.
        """

    async def get_suggestion_async(
        self, buff: "Buffer", document: Document
    ) -> Optional[Suggestion]:
        """
        Return a :class:`.Future` which is set when the suggestions are ready.
        This function can be overloaded in order to provide an asynchronous
        implementation.
        """
        return self.get_suggestion(buff, document)


class ThreadedAutoSuggest(AutoSuggest):
    """
    Wrapper that runs auto suggestions in a thread.
    (Use this to prevent the user interface from becoming unresponsive if the
    generation of suggestions takes too much time.)
    """

    def __init__(self, auto_suggest: AutoSuggest) -> None:
        self.auto_suggest = auto_suggest

    def get_suggestion(
        self, buff: "Buffer", document: Document
    ) -> Optional[Suggestion]:
        return self.auto_suggest.get_suggestion(buff, document)

    async def get_suggestion_async(
        self, buff: "Buffer", document: Document
    ) -> Optional[Suggestion]:
        """
        Run the `get_suggestion` function in a thread.
        """

        def run_get_suggestion_thread() -> Optional[Suggestion]:
            return self.get_suggestion(buff, document)

        return await run_in_executor_with_context(run_get_suggestion_thread)


class DummyAutoSuggest(AutoSuggest):
    """
    AutoSuggest class that doesn't return any suggestion.
    """

    def get_suggestion(
        self, buffer: "Buffer", document: Document
    ) -> Optional[Suggestion]:
        return None  # No suggestion


class AutoSuggestFromHistory(AutoSuggest):
    """
    Give suggestions based on the lines in the history.
    """

    def get_suggestion(
        self, buffer: "Buffer", document: Document
    ) -> Optional[Suggestion]:
        history = buffer.history

        # Consider only the last line for the suggestion.
        text = document.text.rsplit("\n", 1)[-1]

        # Only create a suggestion when this is not an empty line.
        if text.strip():
            # Find first matching line in history.
            for string in reversed(list(history.get_strings())):
                for line in reversed(string.splitlines()):
                    if line.startswith(text):
                        return Suggestion(line[len(text) :])

        return None


class ConditionalAutoSuggest(AutoSuggest):
    """
    Auto suggest that can be turned on and of according to a certain condition.
    """

    def __init__(self, auto_suggest: AutoSuggest, filter: Union[bool, Filter]) -> None:

        self.auto_suggest = auto_suggest
        self.filter = to_filter(filter)

    def get_suggestion(
        self, buffer: "Buffer", document: Document
    ) -> Optional[Suggestion]:
        if self.filter():
            return self.auto_suggest.get_suggestion(buffer, document)

        return None


class DynamicAutoSuggest(AutoSuggest):
    """
    Validator class that can dynamically returns any Validator.

    :param get_validator: Callable that returns a :class:`.Validator` instance.
    """

    def __init__(self, get_auto_suggest: Callable[[], Optional[AutoSuggest]]) -> None:
        self.get_auto_suggest = get_auto_suggest

    def get_suggestion(
        self, buff: "Buffer", document: Document
    ) -> Optional[Suggestion]:
        auto_suggest = self.get_auto_suggest() or DummyAutoSuggest()
        return auto_suggest.get_suggestion(buff, document)

    async def get_suggestion_async(
        self, buff: "Buffer", document: Document
    ) -> Optional[Suggestion]:
        auto_suggest = self.get_auto_suggest() or DummyAutoSuggest()
        return await auto_suggest.get_suggestion_async(buff, document)