set-kodi-display

#!/usr/bin/env python3
"""
*** ANSIBLE MANAGED FILE ***
template: /home/alexander/yavdr-ansible/roles/kodi/templates/set-kodi-display.j2

This Script changes the monitor in KODI's guisettings.xml to the wanted output
according to the DISPLAY environment variable. It works with KODI 18 (not KODI 17!).

In order to change the display we need to modify the settings/videoscreen nodes.

Basic algorithm:
    - get the current videoscreen.monitor
    - check if it needs to be changed
    - create a backup of the videoscreen nodes in /var/lib/vdr/.kodi/.display_cache/{CONNETOR}-videoscreen.xml
    - check if there is an existing backup for the new CONNECTOR
    - parse the backup of the videoscreen nodes
    - replace the videoscreen nodes with the backup data
"""

import copy
import logging
import os
import sys
import subprocess
import traceback
from lxml import etree as ET

logging.basicConfig(format='%(levelname)s:%(message)s', level=logging.DEBUG)
GUISETTINGS = '/var/lib/vdr/.kodi/userdata/guisettings.xml'
CACHE_DIR = '/var/lib/vdr/.kodi/.display_cache'
VIDEOSCREEN_TEMPLATE = """<settings version="2">
    <setting id="videoscreen.monitor">{}</setting>
</settings>"""


def create_cache_dir():
    try:
        os.makedirs(CACHE_DIR, exist_ok=True)
    except PermissionError:
        sys.exit(f"Error: insufficient permissions to create cachedir {CACHE_DIR}")
    except Exception:
        logging.exception(f"Unexpected Error when trying to create {CACHE_DIR}:")
        sys.exit(1)



def get_output_name():
    """
    get display name from xrandr output for given DISPLAY environment variable
    """
    try:
        xrandr_output = [
            l for l in subprocess.check_output(
                ["xrandr"],
                env={"DISPLAY": os.environ["DISPLAY"]}
            ).decode("utf-8").splitlines()
        ]
        return next(l.split()[0] for l in xrandr_output if " connected " in l)
    except Exception:
        logging.exception("could not determine output name")
        sys.exit("output name unknown, exiting early")


def parse_template(template_path, template, output=""):
    """read videoscreen settings from backup or create a stub file"""
    def xml_tree_from_template(template, output):
        xml_template = ET.fromstring(template.format(output))
        xml_tree = ET.ElementTree(xml_template)
        return xml_tree

    try:
        xml_tree = ET.parse(template_path)
    except OSError:
        logging.debug(f"{template_path} not found, creating stub file")
        xml_tree = xml_tree_from_template(template, output)
    except ET.XMLSyntaxError as e:
        if e.msg.startswith('Document is empty'):
            logging.info(f"{template_path} is empty, creating stub file")
            xml_tree = xml_tree_from_template(template, output)
        else:
            sys.exit(f"Could not parse {template_path}, please fix file or remove it")
    finally:
        xml_tree.write(template_path)
    return xml_tree


def main(output):
    guisettings = parse_template(GUISETTINGS, VIDEOSCREEN_TEMPLATE, "Default")

    # parse guisettings Etree for display name an backup videoscreen data
    root = guisettings.getroot()
    old_output = root.find("./setting[@id='videoscreen.monitor']").text
    if old_output == output:
        logging.debug("no changes necessary, exiting")
        sys.exit()

    # create a minimal guisettings etree
    xml_path = os.path.join(CACHE_DIR, f'{old_output}-videoscreen.xml')
    base_tree = ET.fromstring('<settings version="2"></settings>')
    xml_tree = ET.ElementTree(base_tree)
    backup_root = xml_tree.getroot()

    # copy videoscreen elements to backup etree
    videoscreen_elements = root.xpath(
            "./setting[starts-with(@id, 'videoscreen.')]")
    for element in videoscreen_elements:
        backup_root.append(copy.deepcopy(element))
        element.getparent().remove(element)
    xml_tree.write(xml_path)
    logging.debug(f"written backup for {old_output} to {xml_path}")

    # change videoscreen node to content of backup file
    xml_path = os.path.join(CACHE_DIR, f'{output}-videoscreen.xml')
    videodir_xml = parse_template(xml_path, VIDEOSCREEN_TEMPLATE, output)
    videodir_root = videodir_xml.getroot()
    videoscreen = videodir_root.find("./setting[@id='videoscreen.monitor']")
    # copy videoscreen.* elements from Backup
    videoscreen_elements = videodir_root.xpath(
            "./setting[starts-with(@id, 'videoscreen.')]")
    for element in videoscreen_elements:
        new_element = copy.deepcopy(element)
        root.append(new_element)
    guisettings.write(GUISETTINGS)


if __name__ == '__main__':
    create_cache_dir()
    output = get_output_name()
    try:
        main(output)
    except Exception:
        logging.exception("Could not change videoscreen.* settings")