document main.rs

clock-tui/src/bin/main.rs

@@ -30,29 +30,44 @@ fn run_app<B: Backend>(
             return Ok(());
         }
 
+        // draw the TUI using the `tui` library
         terminal.draw(|f| app.ui(f))?;
 
         let timeout = tick_rate
-            .checked_sub(last_tick.elapsed())
-            .unwrap_or(Duration::ZERO);
+            .checked_sub(last_tick.elapsed()) // substraction, is None if would underflow (be negative)
+            .unwrap_or(Duration::ZERO); // if it was `None`, it was longer than `tick_rate` since the
+                                        // `last_tick`. We set the timeout to `DURATION::ZERO` so
+                                        // that `event::poll` will return instantly with success
+
+        // wait up to 100 ms for the timeout Duration. This ensures that we do not loop very fast,
+        // which would cause high cpu load. If the Duration is less than 100 ms, we enter the if
+        // clause. An event describes some kind of user interaction: Mouse actions, Key Presses, or
+        // Resizing of the Terminal
         if event::poll(timeout)? {
+            // we only care about pressed keys
             if let Event::Key(key) = event::read()? {
                 match key.code {
+                    // exit the application if the user presses the 'q' key
                     KeyCode::Char('q') => {
                         return Ok(());
                     }
+                    // otherwise, let the app handle it the key that was pressed
                     key => app.on_key(key),
                 }
             }
         }
 
+        // has it been longer since the last tick than the duration of the `tick_rate`?
         if last_tick.elapsed() >= tick_rate {
+            // if so, we want to substract with NOW when we calculate the new timeout.
             last_tick = Instant::now();
         }
     }
 }
 
+// entry point into the program
 fn main() -> Result<(), Box<dyn Error>> {
+    // Parse the cli arguments
     let mut app = App::parse();
     app.init_app();