import json
import os
import subprocess

from prometheus_client.core import REGISTRY
from prometheus_client.exposition import start_http_server
from prometheus_client.metrics_core import GaugeMetricFamily

import rawfile_util
from rawfile_util import attached_loops


class VolumeStatsCollector(object):
    def collect(self):
        VOLUME_ID = "volume_id"
        fs_size = GaugeMetricFamily(
            "rawfile_filesystem_size_bytes",
            "Filesystem size in bytes.",
            labels=[VOLUME_ID],
        )
        fs_free = GaugeMetricFamily(
            "rawfile_filesystem_avail_bytes",
            "Filesystem free space in bytes",
            labels=[VOLUME_ID],
        )
        dev_size = GaugeMetricFamily(
            "rawfile_device_size_bytes", "Device size in bytes.", labels=[VOLUME_ID]
        )
        dev_free = GaugeMetricFamily(
            "rawfile_device_free_bytes",
            "Device free space in bytes.",
            labels=[VOLUME_ID],
        )

        for volume_id in rawfile_util.list_all_volumes():
            img_file = rawfile_util.img_file(volume_id)
            labels = [volume_id]
            dev_stat = img_file.stat()
            dev_size.add_metric(labels, dev_stat.st_size)
            dev_free.add_metric(labels, dev_stat.st_size - dev_stat.st_blocks * 512)
            mountpoint = volume_to_mountpoint(img_file)
            if mountpoint is not None:
                fs_stat = os.statvfs(mountpoint)
                fs_size.add_metric(labels, fs_stat.f_frsize * fs_stat.f_blocks)
                fs_free.add_metric(labels, fs_stat.f_frsize * fs_stat.f_bfree)

        return [fs_size, fs_free, dev_size, dev_free]


def volume_to_mountpoint(img_file):
    for dev in attached_loops(img_file):
        mountpoint = dev_to_mountpoint(dev)
        if mountpoint is not None:
            return mountpoint
    return None


def dev_to_mountpoint(dev_name):
    try:
        output = subprocess.run(
            f"findmnt --json --first-only {dev_name}",
            shell=True,
            check=True,
            capture_output=True,
        ).stdout.decode()
        data = json.loads(output)
        return data["filesystems"][0]["target"]
    except subprocess.CalledProcessError:
        return None


def expose_metrics():
    REGISTRY.register(VolumeStatsCollector())
    start_http_server(9100)