Add helper to format theme name for theme changer

src/renderer/html_handlebars/hbs_renderer.rs

@@ -214,6 +214,7 @@ impl HtmlHandlebars {
         );
         handlebars.register_helper("previous", Box::new(helpers::navigation::previous));
         handlebars.register_helper("next", Box::new(helpers::navigation::next));
+        handlebars.register_helper("theme_option", Box::new(helpers::theme::theme_option));
     }
 
     /// Copy across any additional CSS and JavaScript files which the book

src/renderer/html_handlebars/helpers/mod.rs

@@ -1,2 +1,3 @@
 pub mod navigation;
 pub mod toc;
+pub mod theme;

src/renderer/html_handlebars/helpers/theme.rs

@@ -0,0 +1,30 @@
+use handlebars::{Context, Handlebars, Helper, Output, RenderContext, RenderError};
+
+pub fn theme_option(
+    h: &Helper,
+    _r: &Handlebars,
+    ctx: &Context,
+    rc: &mut RenderContext,
+    out: &mut Output,
+) -> Result<(), RenderError> {
+    trace!("theme_option (handlebars helper)");
+
+    let param = h
+        .param(0)
+        .and_then(|v| v.value().as_str())
+        .ok_or(RenderError::new(
+            "Param 0 with String type is required for theme_option helper.",
+        ))?;
+
+    let theme_name = rc
+        .evaluate_absolute(ctx, "default_theme", true)?
+        .as_str()
+        .ok_or_else(|| RenderError::new("Type error for `default_theme`, string expected"))?;
+
+    out.write(param)?;
+    if param.to_lowercase() == theme_name.to_lowercase() {
+        out.write(" (default)")?;
+    }
+
+    Ok(())
+}

src/theme/index.hbs

@@ -97,11 +97,11 @@
                                 <i class="fa fa-paint-brush"></i>
                             </button>
                             <ul id="theme-list" class="theme-popup" aria-label="Themes" role="menu">
-                                <li role="none"><button role="menuitem" class="theme" id="light">Light</button></li>
+                                <li role="none"><button role="menuitem" class="theme" id="light">{{ theme_option "Light" }}</button></li>
-                                <li role="none"><button role="menuitem" class="theme" id="rust">Rust</button></li>
+                                <li role="none"><button role="menuitem" class="theme" id="rust">{{ theme_option "Rust" }}</button></li>
-                                <li role="none"><button role="menuitem" class="theme" id="coal">Coal</button></li>
+                                <li role="none"><button role="menuitem" class="theme" id="coal">{{ theme_option "Coal" }}</button></li>
-                                <li role="none"><button role="menuitem" class="theme" id="navy">Navy</button></li>
+                                <li role="none"><button role="menuitem" class="theme" id="navy">{{ theme_option "Navy" }}</button></li>
-                                <li role="none"><button role="menuitem" class="theme" id="ayu">Ayu</button></li>
+                                <li role="none"><button role="menuitem" class="theme" id="ayu">{{ theme_option "Ayu" }}</button></li>
                             </ul>
                             {{#if search_enabled}}
                             <button id="search-toggle" class="icon-button" type="button" title="Search. (Shortkey: s)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="S" aria-controls="searchbar">