import os
from typing import Callable, Iterable, Optional, Union

from .metrics_core import CounterMetricFamily, GaugeMetricFamily, Metric
from .registry import Collector, CollectorRegistry, REGISTRY

try:
    import resource

    _PAGESIZE = resource.getpagesize()
except ImportError:
    # Not Unix
    _PAGESIZE = 4096


class ProcessCollector(Collector):
    """Collector for Standard Exports such as cpu and memory."""

    def __init__(self,
                 namespace: str = '',
                 pid: Callable[[], Union[int, str]] = lambda: 'self',
                 proc: str = '/proc',
                 registry: Optional[CollectorRegistry] = REGISTRY):
        self._namespace = namespace
        self._pid = pid
        self._proc = proc
        if namespace:
            self._prefix = namespace + '_process_'
        else:
            self._prefix = 'process_'
        self._ticks = 100.0
        try:
            self._ticks = os.sysconf('SC_CLK_TCK')
        except (ValueError, TypeError, AttributeError, OSError):
            pass

        self._pagesize = _PAGESIZE

        # This is used to test if we can access /proc.
        self._btime = 0
        try:
            self._btime = self._boot_time()
        except OSError:
            pass
        if registry:
            registry.register(self)

    def _boot_time(self):
        with open(os.path.join(self._proc, 'stat'), 'rb') as stat:
            for line in stat:
                if line.startswith(b'btime '):
                    return float(line.split()[1])

    def collect(self) -> Iterable[Metric]:
        if not self._btime:
            return []

        pid = os.path.join(self._proc, str(self._pid()).strip())

        result = []
        try:
            with open(os.path.join(pid, 'stat'), 'rb') as stat:
                parts = (stat.read().split(b')')[-1].split())

            vmem = GaugeMetricFamily(self._prefix + 'virtual_memory_bytes',
                                     'Virtual memory size in bytes.', value=float(parts[20]))
            rss = GaugeMetricFamily(self._prefix + 'resident_memory_bytes', 'Resident memory size in bytes.',
                                    value=float(parts[21]) * self._pagesize)
            start_time_secs = float(parts[19]) / self._ticks
            start_time = GaugeMetricFamily(self._prefix + 'start_time_seconds',
                                           'Start time of the process since unix epoch in seconds.',
                                           value=start_time_secs + self._btime)
            utime = float(parts[11]) / self._ticks
            stime = float(parts[12]) / self._ticks
            cpu = CounterMetricFamily(self._prefix + 'cpu_seconds_total',
                                      'Total user and system CPU time spent in seconds.',
                                      value=utime + stime)
            result.extend([vmem, rss, start_time, cpu])
        except OSError:
            pass

        try:
            with open(os.path.join(pid, 'limits'), 'rb') as limits:
                for line in limits:
                    if line.startswith(b'Max open file'):
                        max_fds = GaugeMetricFamily(self._prefix + 'max_fds',
                                                    'Maximum number of open file descriptors.',
                                                    value=float(line.split()[3]))
                        break
            open_fds = GaugeMetricFamily(self._prefix + 'open_fds',
                                         'Number of open file descriptors.',
                                         len(os.listdir(os.path.join(pid, 'fd'))))
            result.extend([open_fds, max_fds])
        except OSError:
            pass

        return result


PROCESS_COLLECTOR = ProcessCollector()
"""Default ProcessCollector in default Registry REGISTRY."""