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+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0-only
+# udt-tv: send the wallpaper accent to the tv-debloat launcher on the TV.
+# Copyright (C) 2026 Danilo M. <danix@danix.xyz>
+# Licensed under the GNU General Public License v2 only.
+"""Tint the TV launcher's focus highlight, pills and title glow in the accent.
+
+Usage: udt-tv              send the window border's three hues
+       udt-tv --selftest
+
+The colours are the three udt-accent wrote for the window border, the accent
+between its two hue neighbours: the launcher draws its focus highlight's edge
+as a gradient of all three and uses the middle one everywhere else. One UDP
+datagram to the launcher's port 47800, "<#a,#b,#c> <unix seconds> <hex
+HMAC-SHA256 of the first two fields>", keyed with the secret the launcher was
+deployed with. The launcher drops anything unsigned, more than a minute off
+its clock, or not newer than the last one it took, and sends no reply, so
+this cannot tell whether the TV took it (a TV in standby or a launcher that
+Android killed misses it; the launcher keeps the last colour it got).
+
+The TV's address comes from ~/.config/udt/tv.json ({"host": "<ip>"}), the
+secret from ~/.config/tv-debloat/accent.secret, the file tv-debloat's
+deploy-launcher.sh pushes to the TV. Without either, this does nothing.
+"""
+import hashlib
+import hmac
+import json
+import re
+import socket
+import sys
+import time
+from pathlib import Path
+
+CONFIG = Path.home() / ".config/udt/tv.json"
+SECRET = Path.home() / ".config/tv-debloat/accent.secret"
+BORDER = Path.home() / ".cache/udt/udt-border.lua"
+PORT = 47800
+
+
+def colours(border):
+    """The border's rgb(rrggbb) hues as the launcher's "#a,#b,#c" field."""
+    return ",".join("#" + h for h in re.findall(r"rgb\(([0-9a-fA-F]{6})\)", border))
+
+
+def message(field, secret, now):
+    body = f"{field} {now}"
+    return f"{body} {hmac.new(secret, body.encode(), hashlib.sha256).hexdigest()}"
+
+
+def selftest():
+    border = 'return { "rgb(fcd317)", "rgb(36d190)", "rgb(37daea)" }'
+    assert colours(border) == "#fcd317,#36d190,#37daea"
+    msg = message("#fcd317,#36d190,#37daea", b"k", 1700000000)
+    field, ts, mac = msg.split(" ")
+    assert (field, ts) == ("#fcd317,#36d190,#37daea", "1700000000")
+    assert mac == hmac.new(b"k", f"{field} {ts}".encode(), hashlib.sha256).hexdigest()
+    print("ok")
+
+
+def main():
+    args = sys.argv[1:]
+    if args == ["--selftest"]:
+        return selftest()
+    if args:
+        sys.exit(__doc__.split("\n\n")[1])
+    try:
+        host = json.loads(CONFIG.read_text())["host"]
+        secret = SECRET.read_text().strip().encode()
+        field = colours(BORDER.read_text())
+    except (OSError, ValueError, KeyError):
+        return
+    # The launcher takes one colour or three; anything else it would drop.
+    if field.count(",") not in (0, 2) or not field or not secret:
+        return
+    with socket.socket(socket.AF_INET, socket.SOCK_DGRAM) as s:
+        try:
+            s.sendto(message(field, secret, int(time.time())).encode(), (host, PORT))
+        except OSError as e:
+            print(f"udt-tv: {host}: {e}", file=sys.stderr)
+
+
+if __name__ == "__main__":
+    main()