# Licensed under the GPL: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
# For details: https://github.com/PyCQA/pylint/blob/main/LICENSE
# Copyright (c) https://github.com/PyCQA/pylint/blob/main/CONTRIBUTORS.txt

"""Ellipsis checker for Python code."""
from typing import TYPE_CHECKING

from astroid import nodes

from pylint.checkers import BaseChecker
from pylint.checkers.utils import check_messages
from pylint.interfaces import IAstroidChecker

if TYPE_CHECKING:
    from pylint.lint import PyLinter


class EllipsisChecker(BaseChecker):
    __implements__ = (IAstroidChecker,)
    name = "unnecessary_ellipsis"
    msgs = {
        "W2301": (
            "Unnecessary ellipsis constant",
            "unnecessary-ellipsis",
            "Used when the ellipsis constant is encountered and can be avoided. "
            "A line of code consisting of an ellipsis is unnecessary if "
            "there is a docstring on the preceding line or if there is a "
            "statement in the same scope.",
        )
    }

    @check_messages("unnecessary-ellipsis")
    def visit_const(self, node: nodes.Const) -> None:
        """Check if the ellipsis constant is used unnecessarily.

        Emits a warning when:
         - A line consisting of an ellipsis is preceded by a docstring.
         - A statement exists in the same scope as the ellipsis.
           For example: A function consisting of an ellipsis followed by a
           return statement on the next line.
        """
        if (
            node.pytype() == "builtins.Ellipsis"
            and not isinstance(
                node.parent,
                (
                    nodes.AnnAssign,
                    nodes.Arguments,
                    nodes.Assign,
                    nodes.BaseContainer,
                    nodes.Call,
                    nodes.Lambda,
                ),
            )
            and (
                len(node.parent.parent.child_sequence(node.parent)) > 1
                or (
                    isinstance(node.parent.parent, (nodes.ClassDef, nodes.FunctionDef))
                    and node.parent.parent.doc_node
                )
            )
        ):
            self.add_message("unnecessary-ellipsis", node=node)


def register(linter: "PyLinter") -> None:
    linter.register_checker(EllipsisChecker(linter))