"""One observation deadline shared with synchronous screen-client worker threads."""

from contextvars import ContextVar
from dataclasses import dataclass, field
from threading import Event
from time import monotonic


class ObservationExpired(TimeoutError):
    """The shared observation deadline has elapsed."""


class ObservationCancelled(RuntimeError):
    """The owning driver has ended this observation."""


@dataclass
class ObservationBudget:
    deadline: float
    cancelled: Event = field(default_factory=Event)
    phase: str = "获取屏幕"
    last_failure: str | None = None

    def remaining(self) -> float:
        if self.cancelled.is_set():
            raise ObservationCancelled("设备观测已取消，禁止继续重连")
        remaining = self.deadline - monotonic()
        if remaining <= 0:
            raise ObservationExpired(f"设备观测预算耗尽：{self.detail}")
        return remaining

    @property
    def detail(self) -> str:
        return self.phase + (f"；最近错误：{self.last_failure}" if self.last_failure else "")


current_observation: ContextVar[ObservationBudget | None] = ContextVar(
    "screen_observation_budget", default=None
)


def check_observation(phase: str | None = None, failure: BaseException | None = None) -> None:
    budget = current_observation.get()
    if budget is not None:
        if failure is not None and not isinstance(
            failure, (ObservationExpired, ObservationCancelled)
        ):
            budget.last_failure = f"{type(failure).__name__}: {failure}"
        budget.remaining()
        if phase is not None:
            budget.phase = phase