#!/usr/bin/env python

"""
This script emulates "unique application" functionality on Linux. When starting
playback with this script, it will try to reuse an already running instance of
mpv (but only if that was started with umpv).

This script only uses mpv instances started with umpv. Other instances are
ignored, and don't exist for the script.

This only takes filenames as arguments. If mpv is already running, they are
appended to mpv's internal playlist. If the file does not exist or is otherwise
not playable, mpv will skip the playlist entry when attempting to play it (from
the GUI perspective, it's silently ignored).

If mpv isn't running yet, this script will start mpv and let it control the
current terminal. If you play an audio-only file, mpv will not open a window
(that is its normal behavior; but it might not be what a user expects if this
script is used in a GUI setting).

mpv will terminate if there are no more files to play, and running the umpv
script after that will start a new mpv instance.

Note that you can control the mpv instance by writing to the command fifo:

    echo "cycle fullscreen" > /tmp/umpv-fifo-*

Warning:

The script attempts to make sure the FIFO is safely created (i.e. not world-
readable, not trying to open a bogus
"""

import sys
import os
import errno
import subprocess
import fcntl
import stat

if len(sys.argv) < 2:
    print("error: needs at least one file as argument.")
    sys.exit(1)
files = sys.argv[1:]
# make them absolute; also makes them safe against interpretation as options
files = [os.path.abspath(f) for f in files]

FIFO = "/tmp/umpv-fifo-" + os.getenv("USER")

fifo_fd = -1
try:
    fifo_fd = os.open(FIFO, os.O_NONBLOCK | os.O_WRONLY)
except OSError as e:
    if e.errno == errno.ENXIO:
        pass  # pipe has no writer
    elif e.errno == errno.ENOENT:
        pass # doesn't exist
    else:
        raise e

if fifo_fd >= 0:
    st = os.fstat(fifo_fd)
    if (((st.st_mode & (stat.S_IRWXG | stat.S_IRWXO)) != 0) or
        (not stat.S_ISFIFO(st.st_mode)) or
        (st.st_uid != os.getuid())):
        print("error: command FIFO is not a FIFO or has bogus permissions")
        sys.exit(1)

if fifo_fd >= 0:
    # Unhandled race condition: what if mpv is terminating right now?
    fcntl.fcntl(fifo_fd, fcntl.F_SETFL, 0) # set blocking mode
    fifo = os.fdopen(fifo_fd, "w")
    for f in files:
        # escape: \ \n "
        f = f.replace("\\", "\\\\").replace("\"", "\\\"").replace("\n", "\\n")
        f = "\"" + f + "\""
        fifo.write("raw loadfile " + f + " append\n")
else:
    # Recreate pipe if it doesn't already exist.
    # Also makes sure it's safe, and no other user can create a bogus pipe
    # that breaks security.
    try:
        os.unlink(FIFO)
    except OSError as e:
        if e.errno == errno.ENOENT:
            pass
        else:
            raise e
    os.mkfifo(FIFO, 0600)

    subprocess.check_call(["mpv", "--input-file=" + FIFO] + files)