"""
`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 __future__ import unicode_literals

from abc import ABCMeta, abstractmethod

from six import with_metaclass

from .eventloop import Future, run_in_executor
from .filters import to_filter

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


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

    :param text: The suggestion text.
    """
    def __init__(self, text):
        self.text = text

    def __repr__(self):
        return 'Suggestion(%s)' % self.text


class AutoSuggest(with_metaclass(ABCMeta, object)):
    """
    Base class for auto suggestion implementations.
    """
    @abstractmethod
    def get_suggestion(self, buffer, document):
        """
        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.
        """

    def get_suggestion_future(self, buff, document):
        """
        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 Future.succeed(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):
        assert isinstance(auto_suggest, AutoSuggest)
        self.auto_suggest = auto_suggest

    def get_suggestion(self, buff, document):
        return self.auto_suggest.get_suggestion(buff, document)

    def get_suggestion_future(self, buff, document):
        """
        Run the `get_suggestion` function in a thread.
        """
        def run_get_suggestion_thread():
            return self.get_suggestion(buff, document)
        f = run_in_executor(run_get_suggestion_thread)
        return f


class DummyAutoSuggest(AutoSuggest):
    """
    AutoSuggest class that doesn't return any suggestion.
    """
    def get_suggestion(self, buffer, document):
        return  # No suggestion


class AutoSuggestFromHistory(AutoSuggest):
    """
    Give suggestions based on the lines in the history.
    """
    def get_suggestion(self, buffer, document):
        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):])


class ConditionalAutoSuggest(AutoSuggest):
    """
    Auto suggest that can be turned on and of according to a certain condition.
    """
    def __init__(self, auto_suggest, filter):
        assert isinstance(auto_suggest, AutoSuggest)

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

    def get_suggestion(self, buffer, document):
        if self.filter():
            return self.auto_suggest.get_suggestion(buffer, document)


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):
        assert callable(get_auto_suggest)
        self.get_auto_suggest = get_auto_suggest

    def get_suggestion(self, buff, document):
        auto_suggest = self.get_auto_suggest() or DummyAutoSuggest()
        assert isinstance(auto_suggest, AutoSuggest)
        return auto_suggest.get_suggestion(buff, document)

    def get_suggestion_future(self, buff, document):
        auto_suggest = self.get_auto_suggest() or DummyAutoSuggest()
        assert isinstance(auto_suggest, AutoSuggest)
        return auto_suggest.get_suggestion_future(buff, document)
