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

from __future__ import annotations

from typing import TYPE_CHECKING

from astroid import nodes

from pylint.checkers import BaseChecker
from pylint.checkers.utils import only_required_for_messages

if TYPE_CHECKING:
    from pylint.lint import PyLinter


class ConfusingConsecutiveElifChecker(BaseChecker):
    """Checks if "elif" is used right after an indented block that finishes with "if" or
    "elif" itself.
    """

    name = "confusing_elif"
    msgs = {
        "R5601": (
            "Consecutive elif with differing indentation level, consider creating a function to separate the inner"
            " elif",
            "confusing-consecutive-elif",
            "Used when an elif statement follows right after an indented block which itself ends with if or elif. "
            "It may not be obvious if the elif statement was willingly or mistakenly unindented. "
            "Extracting the indented if statement into a separate function might avoid confusion and prevent "
            "errors.",
        )
    }

    @only_required_for_messages("confusing-consecutive-elif")
    def visit_if(self, node: nodes.If) -> None:
        body_ends_with_if = isinstance(
            node.body[-1], nodes.If
        ) and self._has_no_else_clause(node.body[-1])
        if node.has_elif_block() and body_ends_with_if:
            self.add_message("confusing-consecutive-elif", node=node.orelse[0])

    @staticmethod
    def _has_no_else_clause(node: nodes.If) -> bool:
        orelse = node.orelse
        while orelse and isinstance(orelse[0], nodes.If):
            orelse = orelse[0].orelse
        if not orelse or isinstance(orelse[0], nodes.If):
            return True
        return False


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