bat: add custom themes

Add the ability to add custom theme files to bat.

Co-Authored-By: Robert Helgesson <robert@rycee.net>

modules/programs/bat.nix

@@ -24,14 +24,35 @@ in {
       '';
     };
 
+    themes = mkOption {
+      type = types.attrsOf types.lines;
+      default = { };
+      example = literalExample ''
+        {
+          dracula = builtins.readFile (pkgs.fetchFromGitHub {
+            owner = "dracula";
+            repo = "sublime"; # Bat uses sublime syntax for its themes
+            rev = "26c57ec282abcaa76e57e055f38432bd827ac34e";
+            sha256 = "019hfl4zbn4vm4154hh3bwk6hm7bdxbr1hdww83nabxwjn99ndhv";
+          } + "/Dracula.tmTheme");
+        }
+      '';
+      description = ''
+        Additional themes to provide.
+      '';
+    };
+
   };
 
   config = mkIf cfg.enable {
     home.packages = [ pkgs.bat ];
 
-    xdg.configFile."bat/config" = mkIf (cfg.config != { }) {
+    xdg.configFile = mkMerge ([{
+      "bat/config" = mkIf (cfg.config != { }) {
         text = concatStringsSep "\n"
           (mapAttrsToList (n: v: ''--${n}="${v}"'') cfg.config);
       };
+    }] ++ flip mapAttrsToList cfg.themes
+      (name: body: { "bat/themes/${name}.tmTheme" = { text = body; }; }));
   };
 }