#!/usr/bin/env python3

import sys

import gi
gi.require_version('Gst', '1.0')
from gi.repository import Gst
Gst.init(None)

from gi.repository import GLib


# The following pipeline works
PIPELINE = """
videotestsrc pattern=0 ! selector.
videotestsrc pattern=18 background-color=4294901760 ! selector.
input-selector name=selector ! autovideosink
"""


class Player:
    def __init__(self):
        self.loop = GLib.MainLoop()
        self.pipeline = Gst.parse_launch(PIPELINE)
        self.selector = self.pipeline.get_by_name('selector')

        pad = self.selector.get_static_pad("sink_0")
        self.selector.set_property("active-pad", pad)
        print("n-pads: %d" % self.selector.get_property("n-pads"))

        bus = self.pipeline.get_bus()
        bus.add_signal_watch()
        bus.connect('message::eos', self.on_eos)
        bus.connect('message::error', self.on_error)
        bus.connect('message::state-changed', self.on_state_changed)

    def run(self):
        self.pipeline.set_state(Gst.State.PLAYING)
        self.loop.run()

    def quit(self):
        self.pipeline.set_state(Gst.State.NULL)
        self.loop.quit()

    def on_switch(self):
        active_pad = self.selector.get_property("active-pad")
        if active_pad.get_name() == "sink_0":
            new_pad = self.selector.get_static_pad("sink_1")
        else:
            new_pad = self.selector.get_static_pad("sink_0")

        print("switching from %s to %s" % (active_pad.get_name(),
                                           new_pad.get_name()))

        self.selector.set_property("active-pad", new_pad)

    def on_eos(self, bus, msg):
        self.quit()

    def on_error(self, bus, msg):
        (err, debug) = msg.parse_error()
        print("Error: %s" % err)
        self.quit()

    def on_state_changed(self, bus, msg):
        if msg.src != self.pipeline:
            return

        old_state, new_state, pending = msg.parse_state_changed()
        print("%s from %s to %s" % (msg.src.get_name(), old_state, new_state))


def main():
    player = Player()

    def stdin_cb(source, condition):
        source.readline()
        player.on_switch()
        return True

    GLib.io_add_watch(sys.stdin, GLib.IO_IN, stdin_cb)

    print("\nPress Enter to switch the source\n")
    player.run()


if __name__ == '__main__':
    sys.exit(main())