import os
import time
from threading import Thread, Lock

import sentry_sdk
from sentry_sdk.utils import logger
from sentry_sdk._types import TYPE_CHECKING

if TYPE_CHECKING:
    from typing import Optional


class Monitor(object):
    """
    Performs health checks in a separate thread once every interval seconds
    and updates the internal state. Other parts of the SDK only read this state
    and act accordingly.
    """

    name = "sentry.monitor"

    def __init__(self, transport, interval=10):
        # type: (sentry_sdk.transport.Transport, float) -> None
        self.transport = transport  # type: sentry_sdk.transport.Transport
        self.interval = interval  # type: float

        self._healthy = True
        self._downsample_factor = 1  # type: int

        self._thread = None  # type: Optional[Thread]
        self._thread_lock = Lock()
        self._thread_for_pid = None  # type: Optional[int]
        self._running = True

    def _ensure_running(self):
        # type: () -> None
        if self._thread_for_pid == os.getpid() and self._thread is not None:
            return None

        with self._thread_lock:
            if self._thread_for_pid == os.getpid() and self._thread is not None:
                return None

            def _thread():
                # type: (...) -> None
                while self._running:
                    time.sleep(self.interval)
                    if self._running:
                        self.run()

            thread = Thread(name=self.name, target=_thread)
            thread.daemon = True
            thread.start()
            self._thread = thread
            self._thread_for_pid = os.getpid()

        return None

    def run(self):
        # type: () -> None
        self.check_health()
        self.set_downsample_factor()

    def set_downsample_factor(self):
        # type: () -> None
        if self._healthy:
            if self._downsample_factor > 1:
                logger.debug(
                    "[Monitor] health check positive, reverting to normal sampling"
                )
            self._downsample_factor = 1
        else:
            self._downsample_factor *= 2
            logger.debug(
                "[Monitor] health check negative, downsampling with a factor of %d",
                self._downsample_factor,
            )

    def check_health(self):
        # type: () -> None
        """
        Perform the actual health checks,
        currently only checks if the transport is rate-limited.
        TODO: augment in the future with more checks.
        """
        self._healthy = self.transport.is_healthy()

    def is_healthy(self):
        # type: () -> bool
        self._ensure_running()
        return self._healthy

    @property
    def downsample_factor(self):
        # type: () -> int
        self._ensure_running()
        return self._downsample_factor

    def kill(self):
        # type: () -> None
        self._running = False

    def __del__(self):
        # type: () -> None
        self.kill()