"""Background-generation safety: a player interrupt aborts an in-flight generation call
between tokens and frees the single-flight lock immediately.
"""

from __future__ import annotations

import threading

import pytest

from case_zero.api.runtime import _SharedLockBackend
from case_zero.llm.backend import GenParams, LLMError


class _SlowStreamBackend:
    """Yields tokens one by one; records how many were consumed."""

    def __init__(self, tokens: list[str]) -> None:
        self.tokens = tokens
        self.consumed = 0

    def generate(self, prompt: str, params: GenParams) -> str:
        return "".join(self.tokens)

    def stream(self, prompt: str, params: GenParams):
        for t in self.tokens:
            self.consumed += 1
            yield t


def test_uninterrupted_generate_joins_stream() -> None:
    inner = _SlowStreamBackend(["a", "b", "c"])
    lock = threading.Lock()
    wrapped = _SharedLockBackend(inner, lock, threading.Event())
    assert wrapped.generate("p", GenParams()) == "abc"
    assert not lock.locked(), "lock must be released after the call"


def test_interrupt_aborts_between_tokens_and_frees_lock() -> None:
    inner = _SlowStreamBackend(["a", "b", "c", "d", "e"])
    lock = threading.Lock()
    interrupt = threading.Event()

    class _TripWire(_SlowStreamBackend):
        def stream(self, prompt: str, params: GenParams):
            for i, t in enumerate(self.tokens):
                if i == 2:
                    interrupt.set()  # the player shows up mid-stream
                self.consumed += 1
                yield t

    tripwire = _TripWire(["a", "b", "c", "d", "e"])
    wrapped = _SharedLockBackend(tripwire, lock, interrupt)
    with pytest.raises(LLMError, match="interrupted"):
        wrapped.generate("p", GenParams())
    assert tripwire.consumed <= 3, "must abort within ~a token of the interrupt"
    assert not lock.locked(), "lock must be freed for the player immediately"
    assert inner.consumed == 0


def test_no_interrupt_event_uses_plain_generate() -> None:
    inner = _SlowStreamBackend(["x", "y"])
    wrapped = _SharedLockBackend(inner, threading.Lock(), None)
    assert wrapped.generate("p", GenParams()) == "xy"
    assert inner.consumed == 0, "plain path must not stream"