nixos/mpd: Add a settings option per RFC42

nixos/modules/services/audio/mpd.nix

@@ -6,6 +6,17 @@
 }:
 let
 
+  inherit (lib)
+    isList
+    isBool
+    isAttrs
+    concatStringsSep
+    optionalString
+    foldlAttrs
+    boolToString
+    literalExpression
+    ;
+
   name = "mpd";
 
   uid = config.ids.uids.mpd;
@@ -17,41 +28,83 @@ let
     let
       placeholders = (
         lib.imap0 (
-          i: c: ''password "{{password-${toString i}}}@${lib.concatStringsSep "," c.permissions}"''
+          i: c: ''password "{{password-${toString i}}}@${concatStringsSep "," c.permissions}"''
         ) creds
       );
     in
-    lib.concatStringsSep "\n" placeholders
+    concatStringsSep "\n" placeholders
   );
 
-  mpdConf = pkgs.writeText "mpd.conf" ''
-    # This file was automatically generated by NixOS. Edit mpd's configuration
-    # via NixOS' configuration.nix, as this file will be rewritten upon mpd's
-    # restart.
-
-    music_directory     "${cfg.musicDirectory}"
-    playlist_directory  "${cfg.playlistDirectory}"
-    ${lib.optionalString (cfg.dbFile != null) ''
-      db_file             "${cfg.dbFile}"
-    ''}
-    state_file          "${cfg.dataDir}/state"
-    sticker_file        "${cfg.dataDir}/sticker.sql"
-
-    ${lib.optionalString (
-      cfg.network.listenAddress != "any"
-    ) ''bind_to_address "${cfg.network.listenAddress}"''}
-    ${lib.optionalString (cfg.network.port != 6600) ''port "${toString cfg.network.port}"''}
-    ${lib.optionalString (cfg.fluidsynth) ''
-      decoder {
-              plugin "fluidsynth"
-              soundfont "${pkgs.soundfont-fluid}/share/soundfonts/FluidR3_GM2-2.sf2"
-      }
-    ''}
-
-    ${lib.optionalString (cfg.credentials != [ ]) (credentialsPlaceholder cfg.credentials)}
-
-    ${cfg.extraConfig}
-  '';
+  mpdConf =
+    let
+      mkSetting =
+        with builtins;
+        k: v:
+        if isAttrs v then
+          ''
+            ${k} {
+            ${foldlAttrs (
+              acc: name: value:
+              "${acc}     ${mkSetting name value}"
+            ) "" v}
+            }
+          ''
+        else if isList v then
+          foldl' (acc: elem: acc + mkSetting k elem) "" v
+        else if isBool v then
+          ''
+            ${k} "${boolToString v}"
+          ''
+        else
+          ''
+            ${k} "${toString v}"
+          '';
+    in
+    pkgs.writeText "mpd.conf" ''
+      # This file was automatically generated by NixOS. Edit mpd's configuration
+      # via NixOS' configuration.nix, as this file will be rewritten upon mpd's
+      # restart.
+
+      music_directory     "${cfg.musicDirectory}"
+      playlist_directory  "${cfg.playlistDirectory}"
+      ${optionalString (cfg.dbFile != null) ''
+        db_file             "${cfg.dbFile}"
+      ''}
+      state_file          "${cfg.dataDir}/state"
+      sticker_file        "${cfg.dataDir}/sticker.sql"
+
+      ${optionalString (
+        cfg.network.listenAddress != "any"
+      ) ''bind_to_address "${cfg.network.listenAddress}"''}
+      ${optionalString (cfg.network.port != 6600) ''port "${toString cfg.network.port}"''}
+      ${optionalString (cfg.fluidsynth) ''
+        decoder {
+                plugin "fluidsynth"
+                soundfont "${pkgs.soundfont-fluid}/share/soundfonts/FluidR3_GM2-2.sf2"
+        }
+      ''}
+
+      ${optionalString (cfg.credentials != [ ]) (credentialsPlaceholder cfg.credentials)}
+
+      ${optionalString (!isNull cfg.settings) (
+        foldlAttrs (
+          acc: name: value:
+          acc + mkSetting name value
+        ) "" cfg.settings
+      )}
+
+      ${cfg.extraConfig}
+    '';
+
+  baseType =
+    with lib.types;
+    oneOf [
+      str
+      bool
+      int
+      float
+      path
+    ];
 
 in
 {
@@ -195,7 +248,7 @@ in
                   default = [ "read" ];
                   description = ''
                     List of permissions that are granted with this password.
-                    Permissions can be "${lib.concatStringsSep "\", \"" perms}".
+                    Permissions can be "${lib.concatStringsSep ''", "'' perms}".
                   '';
                 };
             };
@@ -229,6 +282,42 @@ in
           If set, add fluidsynth soundfont and configure the plugin.
         '';
       };
+
+      settings = lib.mkOption {
+        type =
+          with lib.types;
+          nullOr (
+            attrsOf (oneOf [
+              baseType
+              (listOf baseType)
+              (attrsOf baseType)
+              (listOf (attrsOf baseType))
+            ])
+          );
+        default = null;
+        description = ''
+          Manages the configuration file declaratively.
+        '';
+        example = literalExpression ''
+          {
+            # Configure two outputs; Both Pipewire and PulseAudio, the latter being disabled by default
+            audio_output = [
+              { name = "Pipewire"; type = "pipewire"; }
+              { name = "PulseAudio"; type = "pulse"; enabled = false; }
+            ];
+
+            # Configure one input. Can also be multiple inputs by using a list of attribute sets like audio_output above
+            input = { plugin = "curl"; proxy = "proxy.local"; };
+
+            # Configuring a database plugin
+            database = { plugin = "simple"; path = /var/lib/mpd/db; };
+
+            # Set a replay gain
+            replaygain = "album";
+            replaygain_preamp = 5;
+          }
+        '';
+      };
     };
 
   };
@@ -245,7 +334,7 @@ in
       listenStreams = [
         "" # Note: this is needed to override the upstream unit
         (
-          if pkgs.lib.hasPrefix "/" cfg.network.listenAddress then
+          if lib.hasPrefix "/" cfg.network.listenAddress then
             cfg.network.listenAddress
           else
             "${
@@ -267,7 +356,7 @@ in
           lib.concatStringsSep "\n" (
             lib.imap0 (
               i: c:
-              ''${pkgs.replace-secret}/bin/replace-secret '{{password-${toString i}}}' '${c.passwordFile}' /run/mpd/mpd.conf''
+              "${pkgs.replace-secret}/bin/replace-secret '{{password-${toString i}}}' '${c.passwordFile}' /run/mpd/mpd.conf"
             ) cfg.credentials
           )
         );
@@ -304,9 +393,7 @@ in
       };
     };
 
-    users.groups = lib.optionalAttrs (cfg.group == name) {
-      ${name}.gid = gid;
-    };
+    users.groups = lib.optionalAttrs (cfg.group == name) { ${name}.gid = gid; };
   };
 
 }