from collections.abc import Generator
from dataclasses import dataclass

from mypy.nodes import Block, FuncItem, IfStmt, MatchStmt, ReturnStmt, Statement, WithStmt
from mypy.patterns import AsPattern

from refurb.error import Error


@dataclass
class ErrorInfo(Error):
    """
    Don't explicitly return if you are already at the end of the control flow
    for the current function:

    Bad:

    ```
    def func():
        print("hello world!")

        return

    def func2(x):
        if x == 1:
            print("x is 1")

        else:
            print("x is not 1")

            return
    ```

    Good:

    ```
    def func():
        print("hello world!")

    def func2(x):
        if x == 1:
            print("x is 1")

        else:
            print("x is not 1")
    ```
    """

    name = "no-redundant-return"
    code = 125
    msg: str = "Return is redundant here"
    categories = ("control-flow", "readability")


def get_trailing_return(node: Statement) -> Generator[Statement, None, None]:
    match node:
        case ReturnStmt(expr=None):
            yield node

        case MatchStmt(bodies=bodies, patterns=patterns):
            for body, pattern in zip(bodies, patterns):
                match (body.body, pattern):
                    case _, AsPattern(pattern=None, name=None):
                        pass

                    case [ReturnStmt()], _:
                        continue

                yield from get_trailing_return(body.body[-1])

        case IfStmt(else_body=Block(body=[*_, stmt])) | WithStmt(body=Block(body=[*_, stmt])):
            yield from get_trailing_return(stmt)


def check(node: FuncItem, errors: list[Error]) -> None:
    match node:
        case FuncItem(body=Block(body=[*prev, stmt])):
            if not prev and isinstance(stmt, ReturnStmt):
                return

            errors.extend(ErrorInfo.from_node(x) for x in get_trailing_return(stmt))
