import base64
from itertools import count
from pathlib import Path
from textwrap import indent
from typing import NamedTuple

import httpx
from httpx import HTTPStatusError

from backend.constants import SNEKBOX_URL
from backend.models import Form, FormResponse

with Path("resources/unittest_template.py").open(encoding="utf8") as file:
    TEST_TEMPLATE = file.read()


class BypassDetectedError(Exception):
    """Detected an attempt at bypassing the unittests."""


class UnittestResult(NamedTuple):
    question_id: str
    question_index: int
    return_code: int
    passed: bool
    result: str


def filter_unittests(form: Form) -> Form:
    """
    Replace the unittest data section of code questions with the number of test cases.

    This is used to redact the exact tests when sending the form back to the frontend.
    """
    for question in form.questions:
        if question.type == "code" and question.data["unittests"] is not None:
            question.data["unittests"]["tests"] = len(question.data["unittests"]["tests"])

    return form


def _make_unit_code(units: dict[str, str]) -> str:
    """Compose a dict mapping unit names to their code into an actual class body."""
    result = ""

    for unit_name, unit_code in units.items():
        # Function definition
        if unit_name == "setUp":
            result += "\ndef setUp(self):"
        elif unit_name == "tearDown":
            result += "\ndef tearDown(self):"
        else:
            name = f"test_{unit_name.removeprefix("#").removeprefix("test_")}"
            result += f"\nasync def {name}(self):"

        # Unite code
        result += f"\n{indent(unit_code, "    ")}"

    return indent(result, "    ")


def _make_user_code(code: str) -> str:
    """Compose the user code into an actual base64-encoded string variable."""
    code = base64.b64encode(code.encode("utf8")).decode("utf8")
    return f'USER_CODE = b"{code}"'


async def _post_eval(code: str) -> dict[str, str]:
    """Post the eval to snekbox and return the response."""
    async with httpx.AsyncClient() as client:
        data = {"input": code}
        response = await client.post(SNEKBOX_URL, json=data, timeout=10)

        response.raise_for_status()
        return response.json()


async def execute_unittest(
    form_response: FormResponse,
    form: Form,
) -> tuple[list[UnittestResult], list[BypassDetectedError]]:
    """Execute all the unittests in this form and return the results."""
    unittest_results = []
    errors = []

    for index, question in enumerate(form.questions):
        if question.type == "code":
            # Exit early if the suite doesn't have any tests
            if question.data["unittests"] is None:
                unittest_results.append(
                    UnittestResult(
                        question_id=question.id,
                        question_index=index,
                        return_code=0,
                        passed=True,
                        result="",
                    )
                )
                continue

            passed = False

            # Tests starting with an hashtag should have censored names.
            hidden_test_counter = count(1)
            hidden_tests = {
                test.removeprefix("#").removeprefix("test_"): next(hidden_test_counter)
                for test in question.data["unittests"]["tests"]
                if test.startswith("#")
            }

            # Compose runner code
            unit_code = _make_unit_code(question.data["unittests"]["tests"])
            user_code = _make_user_code(form_response.response[question.id])

            code = TEST_TEMPLATE.replace("### USER CODE", user_code)
            code = code.replace("### UNIT CODE", unit_code)

            try:
                try:
                    response = await _post_eval(code)
                except HTTPStatusError:
                    return_code = 99
                    result = "Unable to contact code runner."
                else:
                    return_code = int(response["returncode"])

                    # Parse the stdout if the tests ran successfully
                    if return_code == 0:
                        stdout = response["stdout"]
                        try:
                            passed = bool(int(stdout[0]))
                        except ValueError:
                            msg = "Detected a bypass when reading result code."
                            raise BypassDetectedError(msg)

                        if passed and stdout.strip() != "1":
                            # Most likely a bypass attempt
                            # A 1 was written to stdout to indicate success,
                            # followed by the actual output
                            msg = "Detected improper value for stdout in unittest."
                            raise BypassDetectedError(msg)

                        # If the test failed, we have to populate the result string.
                        if not passed:
                            failed_tests = stdout[1:].strip().split(";")

                            # Redact failed hidden tests
                            for i, failed_test in enumerate(failed_tests.copy()):
                                if failed_test in hidden_tests:
                                    failed_tests[i] = f"hidden_test_{hidden_tests[failed_test]}"

                            result = ";".join(failed_tests)
                        else:
                            result = ""
                    elif return_code in {5, 6, 99}:
                        result = response["stdout"]
                    # Killed by NsJail
                    elif return_code == 137:
                        return_code = 7
                        result = "Timed out or ran out of memory."
                    # Another code has been returned by CPython because of another failure.
                    else:
                        return_code = 99
                        result = "Internal error."
            except BypassDetectedError as error:
                return_code = 10
                result = "Bypass attempt detected, aborting."
                errors.append(error)
                passed = False

            unittest_results.append(
                UnittestResult(
                    question_id=question.id,
                    question_index=index,
                    return_code=return_code,
                    passed=passed,
                    result=result,
                )
            )

    return unittest_results, errors