"""Optical drive helpers for the Ekklesia Classroom shell.

Everything here is deliberately dependency free and non-blocking so the
dock can poll drive state from its GTK main loop without stalling and
without spinning the drive up.
"""

import fcntl
import glob
import os

# linux/cdrom.h
CDROM_DRIVE_STATUS = 0x5326
CDROM_DISC_STATUS = 0x5327
CDROMEJECT = 0x5309
CDROMCLOSETRAY = 0x5319

# CDSL_CURRENT: "whatever slot is loaded right now".
CDSL_CURRENT = 0x7FFFFFFF

# Drive status values.
CDS_NO_INFO = 0
CDS_NO_DISC = 1
CDS_TRAY_OPEN = 2
CDS_DRIVE_NOT_READY = 3
CDS_DISC_OK = 4

# Disc status values.
CDS_AUDIO = 100
CDS_DATA_1 = 101
CDS_DATA_2 = 102
CDS_XA_2_1 = 103
CDS_XA_2_2 = 104
CDS_MIXED = 105


def devices():
    """Every optical device node currently present."""
    return sorted(glob.glob("/dev/sr[0-9]*"))


def default_device():
    """The optical device the classroom should use, if any."""
    found = devices()

    if not found:
        return None

    return found[0]


def _ioctl(device, request, argument=CDSL_CURRENT):
    """Run a CD-ROM ioctl, returning None when the drive cannot be read."""
    try:
        fd = os.open(device, os.O_RDONLY | os.O_NONBLOCK)
    except OSError:
        return None

    try:
        return fcntl.ioctl(fd, request, argument)
    except OSError:
        return None
    finally:
        os.close(fd)


def drive_status(device=None):
    """CDS_* drive status, or None when there is no readable drive."""
    if device is None:
        device = default_device()

    if device is None:
        return None

    return _ioctl(device, CDROM_DRIVE_STATUS)


def disc_status(device=None):
    """CDS_* disc type. Only call this once a disc has become ready."""
    if device is None:
        device = default_device()

    if device is None:
        return None

    return _ioctl(device, CDROM_DISC_STATUS)


def has_disc(device=None):
    """True when a disc is loaded and the drive has finished reading it."""
    return drive_status(device) == CDS_DISC_OK


def eject(device=None):
    """Open the tray. Returns True when the drive accepted the request."""
    if device is None:
        device = default_device()

    if device is None:
        return False

    return _ioctl(device, CDROMEJECT, 0) is not None


def close_tray(device=None):
    """Close the tray. Returns True when the drive accepted the request."""
    if device is None:
        device = default_device()

    if device is None:
        return False

    return _ioctl(device, CDROMCLOSETRAY, 0) is not None


def describe(status):
    """Human readable drive status, used by classroom-dvd status."""
    return {
        None: "no drive",
        CDS_NO_INFO: "unknown",
        CDS_NO_DISC: "no disc",
        CDS_TRAY_OPEN: "tray open",
        CDS_DRIVE_NOT_READY: "drive not ready",
        CDS_DISC_OK: "disc ready",
    }.get(status, "unknown")