mpv: add mpv-websocket support

Note that we use a simplified version of run_websocket_server.lua since
we don't depend on toggling functionality.

home/mpv.nix

@@ -1,5 +1,18 @@
-{ lib, pkgs, ... }:
+{
+  lib,
+  pkgs,
+  nixosConfig,
+  ...
+}:
 
+let
+  inherit (nixosConfig._module.specialArgs) nix-config;
+
+  inherit (lib) getExe;
+  inherit (nix-config.packages.${pkgs.system}) mpv-websocket;
+
+  input-ipc-server = "/tmp/mpv-socket";
+in
 {
   programs.mpv = {
     enable = true;
@@ -33,6 +46,8 @@
       osd-duration = 750;
 
       autofit = "65%";
+
+      inherit input-ipc-server;
     };
 
     bindings = {
@@ -42,7 +57,26 @@
     };
   };
 
-  xdg.configFile."mpv/script-opts/uosc.conf".text = lib.concatStrings [
+  xdg.configFile = {
+    "mpv/scripts/run_websocket_server.lua".text = # lua
+      ''
+        mp.command_native_async({
+          name = "subprocess",
+          playback_only = false,
+          capture_stdout = true,
+          capture_stderr = true,
+
+          args = {
+            "${getExe mpv-websocket}",
+            "-m",
+            "${input-ipc-server}",
+            "-w",
+            "6677",
+          },
+        })
+      '';
+
+    "mpv/script-opts/uosc.conf".text = lib.concatStrings [
       "opacity="
       ",timeline=0.1"
       ",position=0.2"
@@ -63,4 +97,5 @@
       ",buffering_indicator=0.3"
       ",playlist_position=0.8"
     ];
+  };
 }