#!/usr/bin/env python3

import os
import sys
import subprocess
import xml.etree.ElementTree as ET


guisettings = '/var/lib/vdr/.kodi/userdata/guisettings.xml'
cache_dir = '/var/lib/vdr/.kodi/.display_cache'
videoscreen_template = """<settings>
  <videoscreen>
    <monitor>{}</monitor>
  </videoscreen>
</settings>"""


def get_output_names():
    """
    get connected display names from xrandr for a given DISPLAY 
    environment variable
    """
    output = subprocess.check_output(
      ["xrandr"],
      env={"DISPLAY": os.environ["DISPLAY"]}
    ).decode("utf-8").splitlines()
    return [l.split()[0] for l in output if " connected " in l]


def parse_template(template_path, template, output=""):
    """read videoscreen settings from backup or create a stub file"""
    try:
        xml_tree = ET.parse(template_path)
    except FileNotFoundError:
        print("{} not found, creating stub file".format(template_path))
        xml_template = ET.fromstring(template.format(output))
        xml_tree = ET.ElementTree(xml_template)
    finally:
        xml_tree.write(template_path)
    return xml_tree


def backup_videoscreen():
    """parse guisettings.xml for display name an backup videoscreen data"""
    tree = parse_template(guisettings, videoscreen_template, "Default")
    root = tree.getroot()
    videoscreen = root.find('videoscreen')
    output = videoscreen.find('monitor').text
    xml_path = os.path.join(cache_dir, '{}-videodevice.xml'.format(output))
    base_tree = ET.fromstring('<settings></settings>')
    xml_tree = ET.ElementTree(base_tree)
    backup_root = xml_tree.getroot()
    backup_root.insert(0, videoscreen)
    xml_tree.write(xml_path)
    print("written backup for {} to {}".format(output, xml_path))


def change_videoscreen(output, new_videoscreen):
    """change videoscreen node to content of backup file"""
    tree = parse_template(guisettings, videoscreen_template, output)
    root = tree.getroot()
    videoscreen = root.find('videoscreen')
    root.insert(0, new_videoscreen)
    root.remove(videoscreen)
    tree.write(guisettings)
    return tree

if __name__ == '__main__':
    output = get_output_names()[0]
    if not output:
        sys.exit("Error: no screen name found")
    try:
        os.makedirs(cache_dir, exist_ok=True)
    except PermissionError:
        sys.exit("Error: insufficient permissions to create cachedir {}".format(
            cache_dir))
    try:
        backup_videoscreen()
    except FileNotFoundError:
        print("{} does not exist".format(guisettings))
    xml_path = os.path.join(cache_dir, '{}-videodevice.xml'.format(output))
    videodir_xml = parse_template(xml_path, videoscreen_template, output)
    videodir_xml.getroot()
    new_videoscreen = videodir_xml.find('videoscreen')
    guisettings_xml = change_videoscreen(output, new_videoscreen)