from __future__ import annotations

import ast
import sys
from typing import Any
from typing import Generator

YTT101 = 'YTT101 `sys.version[:3]` referenced (python3.10), use `sys.version_info`'  # noqa: E501
YTT102 = 'YTT102 `sys.version[2]` referenced (python3.10), use `sys.version_info`'  # noqa: E501
YTT103 = 'YTT103 `sys.version` compared to string (python3.10), use `sys.version_info`'  # noqa: E501
YTT201 = 'YTT201 `sys.version_info[0] == 3` referenced (python4), use `>=`'
YTT202 = 'YTT202 `six.PY3` referenced (python4), use `not six.PY2`'
YTT203 = 'YTT203 `sys.version_info[1]` compared to integer (python4), compare `sys.version_info` to tuple'  # noqa: E501
YTT204 = 'YTT204 `sys.version_info.minor` compared to integer (python4), compare `sys.version_info` to tuple'  # noqa: E501
YTT301 = 'YTT301 `sys.version[0]` referenced (python10), use `sys.version_info`'  # noqa: E501
YTT302 = 'YTT302 `sys.version` compared to string (python10), use `sys.version_info`'  # noqa: E501
YTT303 = 'YTT303 `sys.version[:1]` referenced (python10), use `sys.version_info`'  # noqa: E501


def _is_index(node: ast.Subscript, n: int) -> bool:
    if sys.version_info >= (3, 9):  # pragma: >=3.9 cover
        node_slice = node.slice
    elif isinstance(node.slice, ast.Index):  # pragma: <3.9 cover
        node_slice = node.slice.value
    else:  # pragma: <3.9 cover
        return False

    return isinstance(node_slice, ast.Constant) and node_slice.value == n


class Visitor(ast.NodeVisitor):
    def __init__(self) -> None:
        self.errors: list[tuple[int, int, str]] = []
        self._from_imports: dict[str, str] = {}

    def visit_ImportFrom(self, node: ast.ImportFrom) -> None:
        for alias in node.names:
            if node.module is not None and not alias.asname:
                self._from_imports[alias.name] = node.module
        self.generic_visit(node)

    def _is_sys(self, attr: str, node: ast.AST) -> bool:
        return (
            # subscripting `sys.<thing>`
            isinstance(node, ast.Attribute) and
            isinstance(node.value, ast.Name) and
            node.value.id == 'sys' and
            node.attr == attr
        ) or (
            isinstance(node, ast.Name) and
            node.id == attr and
            self._from_imports.get(node.id) == 'sys'
        )

    def _is_sys_version_upper_slice(self, node: ast.Subscript, n: int) -> bool:
        return (
            self._is_sys('version', node.value) and
            isinstance(node.slice, ast.Slice) and
            node.slice.lower is None and
            isinstance(node.slice.upper, ast.Constant) and
            node.slice.upper.value == n and
            node.slice.step is None
        )

    def visit_Subscript(self, node: ast.Subscript) -> None:
        if self._is_sys_version_upper_slice(node, 1):
            self.errors.append((
                node.value.lineno, node.value.col_offset, YTT303,
            ))
        elif self._is_sys_version_upper_slice(node, 3):
            self.errors.append((
                node.value.lineno, node.value.col_offset, YTT101,
            ))
        elif self._is_sys('version', node.value) and _is_index(node, n=2):
            self.errors.append((
                node.value.lineno, node.value.col_offset, YTT102,
            ))
        elif self._is_sys('version', node.value) and _is_index(node, n=0):
            self.errors.append((
                node.value.lineno, node.value.col_offset, YTT301,
            ))

        self.generic_visit(node)

    def visit_Compare(self, node: ast.Compare) -> None:
        if (
                isinstance(node.left, ast.Subscript) and
                self._is_sys('version_info', node.left.value) and
                _is_index(node.left, n=0) and
                len(node.ops) == 1 and
                isinstance(node.ops[0], (ast.Eq, ast.NotEq)) and
                isinstance(node.comparators[0], ast.Constant) and
                node.comparators[0].value == 3
        ):
            self.errors.append((
                node.left.lineno, node.left.col_offset, YTT201,
            ))
        elif (
                self._is_sys('version', node.left) and
                len(node.ops) == 1 and
                isinstance(node.ops[0], (ast.Lt, ast.LtE, ast.Gt, ast.GtE)) and
                isinstance(node.comparators[0], ast.Constant) and
                isinstance(node.comparators[0].value, str)
        ):
            if len(node.comparators[0].value) == 1:
                code = YTT302
            else:
                code = YTT103
            self.errors.append((
                node.left.lineno, node.left.col_offset, code,
            ))
        elif (
                isinstance(node.left, ast.Subscript) and
                self._is_sys('version_info', node.left.value) and
                _is_index(node.left, n=1) and
                len(node.ops) == 1 and
                isinstance(node.ops[0], (ast.Lt, ast.LtE, ast.Gt, ast.GtE)) and
                isinstance(node.comparators[0], ast.Constant) and
                isinstance(node.comparators[0].value, (int, float))
        ):
            self.errors.append((
                node.lineno, node.col_offset, YTT203,
            ))
        elif (
                isinstance(node.left, ast.Attribute) and
                self._is_sys('version_info', node.left.value) and
                node.left.attr == 'minor' and
                len(node.ops) == 1 and
                isinstance(node.ops[0], (ast.Lt, ast.LtE, ast.Gt, ast.GtE)) and
                isinstance(node.comparators[0], ast.Constant) and
                isinstance(node.comparators[0].value, (int, float))
        ):
            self.errors.append((
                node.lineno, node.col_offset, YTT204,
            ))
        self.generic_visit(node)

    def visit_Attribute(self, node: ast.Attribute) -> None:
        if (
                isinstance(node.value, ast.Name) and
                node.value.id == 'six' and
                node.attr == 'PY3'
        ):
            self.errors.append((node.lineno, node.col_offset, YTT202))
        self.generic_visit(node)

    def visit_Name(self, node: ast.Name) -> None:
        if node.id == 'PY3' and self._from_imports.get(node.id) == 'six':
            self.errors.append((node.lineno, node.col_offset, YTT202))
        self.generic_visit(node)


class Plugin:
    def __init__(self, tree: ast.AST):
        self._tree = tree

    def run(self) -> Generator[tuple[int, int, str, type[Any]], None, None]:
        visitor = Visitor()
        visitor.visit(self._tree)

        for line, col, msg in visitor.errors:
            yield line, col, msg, type(self)