feat: adds basic mpd server

modules/services/mpd.nix

@@ -0,0 +1,22 @@
+{ username, config, ... }:
+{
+  services.mpd = {
+    enable = true;
+    musicDirectory = "/dandelion/home/liv/music";
+    extraConfig = ''
+      audio_output {
+        type "pipewire"
+      	name "pipewire"
+      }
+    '';
+    user = "${username}"; # PipeWire requires this as it runs as the normal user and mpd normally runs as a system user.
+
+    # Optional:
+    # network.listenAddress = "any"; # if you want to allow non-localhost connections
+    network.startWhenNeeded = false; # systemd feature: only start MPD service upon connection to its socket
+  };
+  systemd.services.mpd.environment = {
+    # see: https://gitlab.freedesktop.org/pipewire/pipewire/-/issues/609
+    XDG_RUNTIME_DIR = "/run/user/${toString config.users.users.userRunningPipeWire.uid}"; # User-id must match above user. MPD will look inside this directory for the PipeWire socket.
+  };
+}