from __future__ import division

import os
import re
import codecs

from twisted.python.compat import _PY3


# List of filesystem types authorized when generating disk use statistics.
STABLE_FILESYSTEMS = frozenset(
    ["ext", "ext2", "ext3", "ext4", "reiserfs", "ntfs", "msdos", "dos", "vfat",
     "xfs", "hpfs", "jfs", "ufs", "hfs", "hfsplus", "simfs"])


EXTRACT_DEVICE = re.compile("([a-z]+)[0-9]*")


def get_mount_info(mounts_file, statvfs_,
                   filesystems_whitelist=STABLE_FILESYSTEMS):
    """
    This is a generator that yields information about mounted filesystems.

    @param mounts_file: A file with information about mounted filesystems,
        such as C{/proc/mounts}.
    @param statvfs_: A function to get file status information.
    @param filesystems_whitelist: Optionally, a list of which filesystems to
        stat.
    @return: A C{dict} with C{device}, C{mount-point}, C{filesystem},
        C{total-space} and C{free-space} keys. If the filesystem information
        is not available, C{None} is returned. Both C{total-space} and
        C{free-space} are in megabytes.
    """
    for line in open(mounts_file):
        try:
            device, mount_point, filesystem = line.split()[:3]
            if _PY3:
                mount_point = codecs.decode(mount_point, "unicode_escape")
            else:
                mount_point = codecs.decode(mount_point, "string_escape")
        except ValueError:
            continue
        if (filesystems_whitelist is not None and
            filesystem not in filesystems_whitelist
            ):
            continue
        megabytes = 1024 * 1024
        try:
            stats = statvfs_(mount_point)
        except OSError:
            continue
        block_size = stats.f_bsize
        total_space = (stats.f_blocks * block_size) // megabytes
        free_space = (stats.f_bfree * block_size) // megabytes
        yield {"device": device, "mount-point": mount_point,
               "filesystem": filesystem, "total-space": total_space,
               "free-space": free_space}


def get_filesystem_for_path(path, mounts_file, statvfs_):
    """
    Tries to determine to which of the mounted filesystem C{path} belongs to,
    and then returns information about that filesystem or C{None} if it
    couldn't be determined.

    @param path: The path we want filesystem information about.
    @param mounts_file: A file with information about mounted filesystems,
        such as C{/proc/mounts}.
    @param statvfs_: A function to get file status information.
    @return: A C{dict} with C{device}, C{mount-point}, C{filesystem},
        C{total-space} and C{free-space} keys. If the filesystem information
        is not available, C{None} is returned. Both C{total-space} and
        C{free-space} are in megabytes.
    """
    candidate = None
    path = os.path.realpath(path)
    path_segments = path.split("/")
    for info in get_mount_info(mounts_file, statvfs_):
        mount_segments = info["mount-point"].split("/")
        if path.startswith(info["mount-point"]):
            if ((not candidate) or
                path_segments[:len(mount_segments)] == mount_segments
                ):
                candidate = info
    return candidate


def is_device_removable(device):
    """
    This function returns whether a given device is removable or not by looking
    at the corresponding /sys/block/<device>/removable file

    @param device: The filesystem path to the device, e.g. /dev/sda1
    """
    # Shortcut the case where the device an SD card. The kernel/udev currently
    # consider SD cards (mmcblk devices) to be non-removable.
    if os.path.basename(device).startswith("mmcblk"):
        return True

    path = _get_device_removable_file_path(device)

    if not path:
        return False

    contents = None
    try:
        with open(path, "r") as f:
            contents = f.readline()
    except IOError:
        return False

    if contents.strip() == "1":
        return True
    return False


def _get_device_removable_file_path(device):
    """
    Get a device's "removable" file path.

    This function figures out the C{/sys/block/<device>/removable} path
    associated with the given device. The file at that path contains either
    a "0" if the device is not removable, or a "1" if it is.

    @param device: File system path of the device.
    """
    # The device will be a symlink if the disk is mounted by uuid or by label.
    if os.path.islink(device):
        # Paths are in the form "/dev/disk/by-uuid/<uuid>" and symlink
        # to the device file under /dev
        device = os.readlink(device)  # /dev/disk/by-uuid/<uuid> -> ../../sda1

    [device_name] = device.split("/")[-1:]  # /dev/sda1 -> sda1

    matched = EXTRACT_DEVICE.match(device_name)  # sda1 -> sda

    if not matched:
        return None

    device_name = matched.groups()[0]

    removable_file = os.path.join("/sys/block/", device_name, "removable")
    return removable_file
