"""Helper utilities for integrating argcomplete with traitlets"""

# Copyright (c) IPython Development Team.
# Distributed under the terms of the Modified BSD License.
from __future__ import annotations

import argparse
import os
import typing as t

try:
    import argcomplete
    from argcomplete import CompletionFinder  # type:ignore[attr-defined]
except ImportError:
    # This module and its utility methods are written to not crash even
    # if argcomplete is not installed.
    class StubModule:
        def __getattr__(self, attr: str) -> t.Any:
            if not attr.startswith("__"):
                raise ModuleNotFoundError("No module named 'argcomplete'")
            raise AttributeError(f"argcomplete stub module has no attribute '{attr}'")

    argcomplete = StubModule()  # type:ignore[assignment]
    CompletionFinder = object  # type:ignore[assignment, misc]


def get_argcomplete_cwords() -> list[str] | None:
    """Get current words prior to completion point

    This is normally done in the `argcomplete.CompletionFinder` constructor,
    but is exposed here to allow `traitlets` to follow dynamic code-paths such
    as determining whether to evaluate a subcommand.
    """
    if "_ARGCOMPLETE" not in os.environ:
        return None

    comp_line = os.environ["COMP_LINE"]
    comp_point = int(os.environ["COMP_POINT"])
    # argcomplete.debug("splitting COMP_LINE for:", comp_line, comp_point)
    comp_words: list[str]
    try:
        (
            _cword_prequote,
            _cword_prefix,
            _cword_suffix,
            comp_words,
            _last_wordbreak_pos,
        ) = argcomplete.split_line(comp_line, comp_point)  # type:ignore[attr-defined,no-untyped-call]
    except ModuleNotFoundError:
        return None

    # _ARGCOMPLETE is set by the shell script to tell us where comp_words
    # should start, based on what we're completing.
    # 1: <script> [args]
    # 2: python <script> [args]
    # 3: python -m <module> [args]
    start = int(os.environ["_ARGCOMPLETE"]) - 1
    comp_words = comp_words[start:]

    # argcomplete.debug("prequote=", _cword_prequote, "prefix=", _cword_prefix, "suffix=", _cword_suffix, "words=", comp_words, "last=", _last_wordbreak_pos)
    return comp_words


def increment_argcomplete_index() -> None:
    """Assumes ``$_ARGCOMPLETE`` is set and `argcomplete` is importable

    Increment the index pointed to by ``$_ARGCOMPLETE``, which is used to
    determine which word `argcomplete` should start evaluating the command-line.
    This may be useful to "inform" `argcomplete` that we have already evaluated
    the first word as a subcommand.
    """
    try:
        os.environ["_ARGCOMPLETE"] = str(int(os.environ["_ARGCOMPLETE"]) + 1)
    except Exception:
        try:
            argcomplete.debug("Unable to increment $_ARGCOMPLETE", os.environ["_ARGCOMPLETE"])  # type:ignore[attr-defined,no-untyped-call]
        except (KeyError, ModuleNotFoundError):
            pass


class ExtendedCompletionFinder(CompletionFinder):
    """An extension of CompletionFinder which dynamically completes class-trait based options

    This finder adds a few functionalities:

    1. When completing options, it will add ``--Class.`` to the list of completions, for each
    class in `Application.classes` that could complete the current option.
    2. If it detects that we are currently trying to complete an option related to ``--Class.``,
    it will add the corresponding config traits of Class to the `ArgumentParser` instance,
    so that the traits' completers can be used.
    3. If there are any subcommands, they are added as completions for the first word

    Note that we are avoiding adding all config traits of all classes to the `ArgumentParser`,
    which would be easier but would add more runtime overhead and would also make completions
    appear more spammy.

    These changes do require using the internals of `argcomplete.CompletionFinder`.
    """

    _parser: argparse.ArgumentParser
    config_classes: list[t.Any] = []  # Configurables
    subcommands: list[str] = []

    def match_class_completions(self, cword_prefix: str) -> list[tuple[t.Any, str]]:
        """Match the word to be completed against our Configurable classes

        Check if cword_prefix could potentially match against --{class}. for any class
        in Application.classes.
        """
        class_completions = [(cls, f"--{cls.__name__}.") for cls in self.config_classes]
        matched_completions = class_completions
        if "." in cword_prefix:
            cword_prefix = cword_prefix[: cword_prefix.index(".") + 1]
            matched_completions = [(cls, c) for (cls, c) in class_completions if c == cword_prefix]
        elif len(cword_prefix) > 0:
            matched_completions = [
                (cls, c) for (cls, c) in class_completions if c.startswith(cword_prefix)
            ]
        return matched_completions

    def inject_class_to_parser(self, cls: t.Any) -> None:
        """Add dummy arguments to our ArgumentParser for the traits of this class

        The argparse-based loader currently does not actually add any class traits to
        the constructed ArgumentParser, only the flags & aliaes. In order to work nicely
        with argcomplete's completers functionality, this method adds dummy arguments
        of the form --Class.trait to the ArgumentParser instance.

        This method should be called selectively to reduce runtime overhead and to avoid
        spamming options across all of Application.classes.
        """
        try:
            for traitname, trait in cls.class_traits(config=True).items():
                completer = trait.metadata.get("argcompleter") or getattr(
                    trait, "argcompleter", None
                )
                multiplicity = trait.metadata.get("multiplicity")
                self._parser.add_argument(  # type: ignore[attr-defined]
                    f"--{cls.__name__}.{traitname}",
                    type=str,
                    help=trait.help,
                    nargs=multiplicity,
                    # metavar=traitname,
                ).completer = completer
                # argcomplete.debug(f"added --{cls.__name__}.{traitname}")
        except AttributeError:
            pass

    def _get_completions(self, comp_words: list[str], cword_prefix: str, *args: t.Any) -> list[str]:
        """Overridden to dynamically append --Class.trait arguments if appropriate

        Warning:
            This does not (currently) support completions of the form
            --Class1.Class2.<...>.trait, although this is valid for traitlets.
            Part of the reason is that we don't currently have a way to identify
            which classes may be used with Class1 as a parent.

        Warning:
            This is an internal method in CompletionFinder and so the API might
            be subject to drift.
        """
        # Try to identify if we are completing something related to --Class. for
        # a known Class, if we are then add the Class config traits to our ArgumentParser.
        prefix_chars = self._parser.prefix_chars
        is_option = len(cword_prefix) > 0 and cword_prefix[0] in prefix_chars
        if is_option:
            # If we are currently completing an option, check if it could
            # match with any of the --Class. completions. If there's exactly
            # one matched class, then expand out the --Class.trait options.
            matched_completions = self.match_class_completions(cword_prefix)
            if len(matched_completions) == 1:
                matched_cls = matched_completions[0][0]
                self.inject_class_to_parser(matched_cls)
        elif len(comp_words) > 0 and "." in comp_words[-1] and not is_option:
            # If not an option, perform a hacky check to see if we are completing
            # an argument for an already present --Class.trait option. Search backwards
            # for last option (based on last word starting with prefix_chars), and see
            # if it is of the form --Class.trait. Note that if multiplicity="+", these
            # arguments might conflict with positional arguments.
            for prev_word in comp_words[::-1]:
                if len(prev_word) > 0 and prev_word[0] in prefix_chars:
                    matched_completions = self.match_class_completions(prev_word)
                    if matched_completions:
                        matched_cls = matched_completions[0][0]
                        self.inject_class_to_parser(matched_cls)
                    break

        completions: list[str]
        completions = super()._get_completions(comp_words, cword_prefix, *args)  # type:ignore[no-untyped-call]

        # For subcommand-handling: it is difficult to get this to work
        # using argparse subparsers, because the ArgumentParser accepts
        # arbitrary extra_args, which ends up masking subparsers.
        # Instead, check if comp_words only consists of the script,
        # if so check if any subcommands start with cword_prefix.
        if self.subcommands and len(comp_words) == 1:
            argcomplete.debug("Adding subcommands for", cword_prefix)  # type:ignore[attr-defined,no-untyped-call]
            completions.extend(subc for subc in self.subcommands if subc.startswith(cword_prefix))

        return completions

    def _get_option_completions(
        self, parser: argparse.ArgumentParser, cword_prefix: str
    ) -> list[str]:
        """Overridden to add --Class. completions when appropriate"""
        completions: list[str]
        completions = super()._get_option_completions(parser, cword_prefix)  # type:ignore[no-untyped-call]
        if cword_prefix.endswith("."):
            return completions

        matched_completions = self.match_class_completions(cword_prefix)
        if len(matched_completions) > 1:
            completions.extend(opt for cls, opt in matched_completions)
        # If there is exactly one match, we would expect it to have already
        # been handled by the options dynamically added in _get_completions().
        # However, maybe there's an edge cases missed here, for example if the
        # matched class has no configurable traits.
        return completions
