Add applyTheme API and apply theme immediately after save

- Add PluginCommand::ApplyTheme variant to plugin API
- Add op_fresh_apply_theme operation in Deno runtime
- Update apply_theme() to also persist theme to config file
- Update theme_editor.ts to use applyTheme API

This allows the theme editor to apply theme changes immediately
without requiring a restart.

Author: claude

docs/plugin-api.md

@@ -567,6 +567,22 @@ setPromptSuggestions(suggestions: PromptSuggestion[]): boolean
 
 ### Buffer Mutations
 
+#### `applyTheme`
+
+Apply a theme by name
+Loads and applies the specified theme immediately. The theme can be a built-in
+theme name or a custom theme from the themes directory.
+
+```typescript
+applyTheme(theme_name: string): void
+```
+
+**Parameters:**
+
+| Name | Type | Description |
+|------|------|-------------|
+| `theme_name` | `string` | Name of the theme to apply (e.g., "dark", "light", "my-custom-theme") |
+
 #### `setClipboard`
 
 Copy text to the system clipboard

plugins/lib/fresh.d.ts

@@ -395,6 +395,14 @@ interface EditorAPI {
   setPromptSuggestions(suggestions: PromptSuggestion[]): boolean;
 
   // === Buffer Mutations ===
+  /**
+   * Apply a theme by name
+   *
+   * Loads and applies the specified theme immediately. The theme can be a built-in
+   * theme name or a custom theme from the themes directory.
+   * @param theme_name - Name of the theme to apply (e.g., "dark", "light", "my-custom-theme")
+   */
+  applyTheme(theme_name: string): void;
   /**
    * Copy text to the system clipboard
    *

plugins/theme_editor.ts

@@ -993,37 +993,15 @@ async function saveTheme(name?: string): Promise<boolean> {
 }
 
 /**
- * Set a theme as the default in config
+ * Set a theme as the default in config and apply it immediately
  */
 async function setThemeAsDefault(themeName: string): Promise<void> {
-  // Find config file
-  const home = editor.getEnv("HOME");
-  let configPath = editor.pathJoin(editor.getCwd(), "config.json");
-
-  if (home) {
-    const userConfig = editor.pathJoin(home, ".config", "fresh", "config.json");
-    if (editor.fileExists(userConfig)) {
-      configPath = userConfig;
-    }
-  }
-
   try {
-    let config: Record<string, unknown> = {};
-
-    if (editor.fileExists(configPath)) {
-      const content = await editor.readFile(configPath);
-      config = JSON.parse(content);
-    }
-
-    config.theme = themeName;
-    const content = JSON.stringify(config, null, 2);
-    await editor.writeFile(configPath, content);
-
-    // Note: The plugin API doesn't currently support applying themes at runtime.
-    // Users need to restart or use the Select Theme command (Ctrl+P -> "Select Theme")
-    editor.setStatus(`Default theme set to "${themeName}". Use 'Select Theme' command or restart to apply.`);
+    // Use the editor API to apply and persist the theme
+    editor.applyTheme(themeName);
+    editor.setStatus(`Theme "${themeName}" applied and saved as default.`);
   } catch (e) {
-    editor.setStatus(`Failed to update config: ${e}`);
+    editor.setStatus(`Failed to apply theme: ${e}`);
   }
 }
 

src/app/input.rs

@@ -3611,14 +3611,44 @@ impl Editor {
         }
     }
 
-    /// Apply a theme by name
-    fn apply_theme(&mut self, theme_name: &str) {
+    /// Apply a theme by name and persist it to config
+    pub(super) fn apply_theme(&mut self, theme_name: &str) {
         if !theme_name.is_empty() {
             self.theme = crate::view::theme::Theme::from_name(theme_name);
+
+            // Update the config in memory
+            self.config.theme = self.theme.name.clone();
+
+            // Persist to config file
+            self.save_theme_to_config();
+
             self.set_status_message(format!("Theme changed to '{}'", self.theme.name));
         }
     }
 
+    /// Save the current theme setting to the user's config file
+    fn save_theme_to_config(&mut self) {
+        // Find the config path
+        let config_dir = if let Some(home) = dirs::home_dir() {
+            home.join(".config").join("fresh")
+        } else {
+            std::env::current_dir().unwrap_or_else(|_| std::path::PathBuf::from("."))
+        };
+
+        let config_path = config_dir.join("config.json");
+
+        // Create the directory if it doesn't exist
+        if let Err(e) = std::fs::create_dir_all(&config_dir) {
+            tracing::warn!("Failed to create config directory: {}", e);
+            return;
+        }
+
+        // Save the config
+        if let Err(e) = self.config.save_to_file(&config_path) {
+            tracing::warn!("Failed to save theme to config: {}", e);
+        }
+    }
+
     /// Switch to the previously active tab in the current split
     fn switch_to_previous_tab(&mut self) {
         let active_split = self.split_manager.active_split();

src/app/mod.rs

@@ -4516,6 +4516,9 @@ impl Editor {
             PluginCommand::SetStatus { message } => {
                 self.handle_set_status(message);
             }
+            PluginCommand::ApplyTheme { theme_name } => {
+                self.apply_theme(&theme_name);
+            }
             PluginCommand::StartPrompt { label, prompt_type } => {
                 self.handle_start_prompt(label, prompt_type);
             }

src/services/plugins/api.rs

@@ -242,6 +242,9 @@ pub enum PluginCommand {
     /// Set status message
     SetStatus { message: String },
 
+    /// Apply a theme by name
+    ApplyTheme { theme_name: String },
+
     /// Register a custom command
     RegisterCommand { command: Command },
 

src/services/plugins/runtime.rs

@@ -178,6 +178,22 @@ fn op_fresh_set_status(state: &mut OpState, #[string] message: String) {
     tracing::info!("TypeScript plugin set_status: {}", message);
 }
 
+/// Apply a theme by name
+///
+/// Loads and applies the specified theme immediately. The theme can be a built-in
+/// theme name or a custom theme from the themes directory.
+/// @param theme_name - Name of the theme to apply (e.g., "dark", "light", "my-custom-theme")
+#[op2(fast)]
+fn op_fresh_apply_theme(state: &mut OpState, #[string] theme_name: String) {
+    if let Some(runtime_state) = state.try_borrow::<Rc<RefCell<TsRuntimeState>>>() {
+        let runtime_state = runtime_state.borrow();
+        let _ = runtime_state.command_sender.send(PluginCommand::ApplyTheme {
+            theme_name: theme_name.clone(),
+        });
+    }
+    tracing::info!("TypeScript plugin apply_theme: {}", theme_name);
+}
+
 /// Log a debug message to the editor's trace output
 ///
 /// Messages appear in stderr when running with RUST_LOG=debug.
@@ -2625,6 +2641,7 @@ extension!(
     fresh_runtime,
     ops = [
         op_fresh_set_status,
+        op_fresh_apply_theme,
         op_fresh_debug,
         op_fresh_set_clipboard,
         op_fresh_get_active_buffer_id,