import os
import threading
import time

from .interfaces import IFileMonitor


class PollingFileMonitor(threading.Thread, IFileMonitor):
    """
    An :class:`hupper.interfaces.IFileMonitor` that stats the files
    at periodic intervals.

    ``callback`` is a callable that accepts a path to a changed file.

    ``interval`` is a value in seconds between scans of the files on disk.
    Do not set this too low or it will eat your CPU and kill your drive.

    """

    def __init__(self, callback, interval=1, **kw):
        super(PollingFileMonitor, self).__init__()
        self.callback = callback
        self.poll_interval = interval
        self.paths = set()
        self.mtimes = {}
        self.lock = threading.Lock()
        self.enabled = True

    def add_path(self, path):
        with self.lock:
            self.paths.add(path)

    def run(self):
        while self.enabled:
            with self.lock:
                paths = list(self.paths)
            self.check_reload(paths)
            time.sleep(self.poll_interval)

    def stop(self):
        self.enabled = False

    def check_reload(self, paths):
        changes = set()
        for path in paths:
            mtime = get_mtime(path)
            if path not in self.mtimes:
                self.mtimes[path] = mtime
            elif self.mtimes[path] < mtime:
                self.mtimes[path] = mtime
                changes.add(path)
        for path in sorted(changes):
            self.callback(path)


def get_mtime(path):
    try:
        stat = os.stat(path)
        if stat:
            return stat.st_mtime
    except (OSError, IOError):  # pragma: no cover
        pass
    return 0