#!/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). Other mpv instances (not started
by umpv) are ignored, and the script doesn't know about them.

This only takes filenames as arguments. Custom options can't be used; the script
interprets them as filenames. If mpv is already running, the files passed to
umpv are appended to mpv's internal playlist. If a 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. It will not write output to stdout/stderr, because this
will typically just fill ~/.xsession-errors with garbage.

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-
writable), and checks that it's really a FIFO. This is important for security,
because the FIFO allows anyone with write access to run arbitrary commands
in mpv's context using the "run" input command. If you are worried about
security, you should verify that the code handles these concerns correctly.
"""

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", "--really-quiet", "--force-window",
                           "--input-file=" + FIFO, "--"] + files)