commit 8bb508f3db92f515fc60c1f2dee206c3a6f1d21f
Author: Edward Betts <edward@4angle.com>
Date:   Sat Apr 8 08:53:28 2023 +0100

    Initial commit.

diff --git a/watch.py b/watch.py
new file mode 100755
index 0000000..17381ea
--- /dev/null
+++ b/watch.py
@@ -0,0 +1,102 @@
+#!/usr/bin/python3
+"""Watch for HDMI connection state change and update screen layout."""
+
+import json
+import os
+import subprocess
+import sys
+import time
+from typing import Any
+
+import pyudev
+
+context = pyudev.Context()
+monitor = pyudev.Monitor.from_netlink(context)
+
+# description of an HDMI connection state change
+want = {
+    "action": "change",
+    "device_node": "/dev/dri/card0",
+    "device_type": "drm_minor",
+    "sys_path": "/sys/devices/pci0000:00/0000:00:02.0/drm/card0",
+    "sys_name": "card0",
+}
+
+
+def run_swaymsg() -> bytes:
+    """Run swaymsg to get list of outputs."""
+    p = subprocess.run(["swaymsg", "-r", "-t", "get_outputs"], capture_output=True)
+    return p.stdout
+
+
+def get_outputs(attempts: int = 10) -> dict[str, dict[str, Any]] | None:
+    """Ask sway for the current list of outputs."""
+    for attempt in range(attempts):
+        outputs = run_swaymsg()
+        if outputs.strip() == b"":
+            return None
+        try:
+            json_data = json.loads(outputs)
+            break
+        except json.decoder.JSONDecodeError:
+            print("JSON parse error")
+            print(outputs)
+            if attempt == attempts - 1:
+                raise
+            time.sleep(1)
+
+    return {o["name"]: o for o in json_data}
+
+
+def is_sony_tv(output: dict[str, Any]) -> bool:
+    """Is a given output a Sony TV."""
+    return bool(output["make"] == "Sony" and output["model"] == "SONY TV")
+
+
+def sony_tv_connected() -> None:
+    """Run command when HDMI is connected."""
+    subprocess.run([os.path.expanduser("~/bin/desk")])
+
+
+def hdmi_disconnected() -> None:
+    """Run command when HDMI is disconnected."""
+    subprocess.run([os.path.expanduser("~/bin/unplugged")])
+
+
+def is_output_connected(name: str) -> bool:
+    """Is HDMI connected."""
+    state = open(f"/sys/class/drm/card0-{name}/status").read()
+    states = {"connected\n": True, "disconnected\n": False}
+    if state not in states:
+        print(f"unknown state: [{state}]")
+        sys.exit(1)
+    return states[state]
+
+
+def handle_state_change() -> str:
+    """Something happened, check and handle state change."""
+    hdmi_name = "HDMI-A-1"
+    if not is_output_connected(hdmi_name):
+        hdmi_disconnected()
+        return "HDMI disconnected, switching to laptop screen."
+
+    hdmi = get_outputs().get(hdmi_name)
+
+    if hdmi and is_sony_tv(hdmi):
+        sony_tv_connected()
+        return "Sony TV connected to HDMI, switching to desk layout."
+
+    return "Unknown device connected to HDMI, doing nothing."
+
+
+def watch() -> None:
+    """Watch for state change and respond."""
+    d: pyudev.Device
+    for d in iter(monitor.poll, None):
+        if all(getattr(d, key) == value for key, value in want.items()):
+            print(handle_state_change())
+
+
+if __name__ == "__main__":
+    handle_state_change()
+    watch()