Add asynchronous file loading and load default file

src/main.rs

@@ -1,12 +1,15 @@
+use std::{io, path::Path, sync::Arc};
+
 use iced::{
     executor,
     widget::{column, text, text_editor},
-    Application, Command, Element, Result, Settings, Theme,
+    Application, Command, Element, Settings, Theme,
 };
 
 #[derive(Debug, Clone)]
 enum Message {
     Edit(text_editor::Action),
+    FileOpened(Result<Arc<String>, io::ErrorKind>),
 }
 
 struct BookManagerApp {
@@ -24,7 +27,10 @@ impl Application for BookManagerApp {
             Self {
                 book_content: text_editor::Content::new(),
             },
-            Command::none(),
+            Command::perform(
+                load_file(format!("{}/src/main.rs", env!("CARGO_MANIFEST_DIR"))),
+                Message::FileOpened,
+            ),
         )
     }
 
@@ -35,6 +41,11 @@ impl Application for BookManagerApp {
     fn update(&mut self, message: Self::Message) -> Command<Self::Message> {
         match message {
             Message::Edit(action) => self.book_content.perform(action),
+            Message::FileOpened(result) => {
+                if let Ok(content) = result {
+                    self.book_content = text_editor::Content::with_text(&content);
+                }
+            }
         }
 
         Command::none()
@@ -55,6 +66,13 @@ impl Application for BookManagerApp {
     }
 }
 
-fn main() -> Result {
+fn main() -> iced::Result {
     BookManagerApp::run(Settings::default())
 }
+
+async fn load_file(path: impl AsRef<Path>) -> Result<Arc<String>, io::ErrorKind> {
+    tokio::fs::read_to_string(path)
+        .await
+        .map(Arc::new)
+        .map_err(|error| error.kind())
+}