feat(syncthing): set up LAN-only sync for 'readings'

modules/syncthing/default.nix

@@ -3,9 +3,42 @@
 let
   cfg = config.syncthing;
   inherit (config.host) username;
+
+  deviceRegistry = import ./devices.nix;
+  deviceName = lib.types.enum (builtins.attrNames deviceRegistry);
+  referencedDevices = lib.unique (
+    lib.concatMap (folder: folder.devices) (lib.attrValues cfg.folders)
+  );
 in
 {
-  options.syncthing.enable = lib.mkEnableOption "syncthing";
+  options.syncthing = {
+    enable = lib.mkEnableOption "syncthing";
+    folders = lib.mkOption {
+      default = { };
+      type = lib.types.attrsOf (
+        lib.types.submodule {
+          options = {
+            path = lib.mkOption {
+              type = lib.types.str;
+            };
+            type = lib.mkOption {
+              type = lib.types.enum [
+                "sendreceive"
+                "sendonly"
+                "receiveonly"
+                "receiveencrypted"
+              ];
+              default = "sendreceive";
+            };
+            devices = lib.mkOption {
+              type = lib.types.listOf deviceName;
+              default = [ ];
+            };
+          };
+        }
+      );
+    };
+  };
 
   config = lib.mkIf cfg.enable {
     users.groups.${username} = { };
@@ -17,6 +50,21 @@ in
       group = username;
       configDir = "/home/${username}/.local/state/syncthing";
       openDefaultPorts = true;
+      settings = {
+        devices = lib.getAttrs referencedDevices deviceRegistry;
+        folders = lib.mapAttrs (_: folder: {
+          inherit (folder)
+            path
+            type
+            devices
+            ;
+        }) cfg.folders;
+        options = {
+          globalAnnounceEnabled = false;
+          localAnnounceEnabled = true;
+          relaysEnabled = false;
+        };
+      };
     };
   };
 }