1 files changed, 63 insertions, 19 deletions

diff --git a/src/main/rust/main.rs b/src/main/rust/main.rs
index 4796c46..5b13d2a 100644
--- a/src/main/rust/main.rs
+++ b/src/main/rust/main.rs
@@ -1,4 +1,5 @@
 use crossterm::event::{self, Event, KeyCode, KeyEvent, KeyEventKind};
+use miette::{Diagnostic, IntoDiagnostic, Result};
 use ratatui::{
     DefaultTerminal, Frame,
     buffer::Buffer,
@@ -8,7 +9,7 @@ use ratatui::{
     text::{Line, Text},
     widgets::{Block, Paragraph, Widget},
 };
-use std::io::Result;
+use thiserror::Error;
 
 #[derive(Debug, Default)]
 pub struct App {
@@ -16,6 +17,13 @@ pub struct App {
     exit: bool,
 }
 
+#[derive(Diagnostic, Debug, Error, PartialEq)]
+#[error("An overflow error occurred")]
+#[diagnostic()]
+pub struct OverflowError {
+    msg: String,
+}
+
 fn main() -> Result<()> {
     ratatui::run(|term| App::default().run(term))
 }
@@ -24,7 +32,7 @@ impl App {
     /// runs the application's main loop until the user quits
     pub fn run(&mut self, terminal: &mut DefaultTerminal) -> Result<()> {
         while !self.exit {
-            terminal.draw(|frame| self.draw(frame))?;
+            terminal.draw(|frame| self.draw(frame)).into_diagnostic()?;
             self.handle_events()?;
         }
         Ok(())
@@ -35,36 +43,45 @@ impl App {
     }
 
     fn handle_events(&mut self) -> Result<()> {
-        match event::read()? {
+        match event::read().into_diagnostic()? {
             // it's important to check that the event is a key press event as
             // crossterm also emits key release and repeat events on Windows.
             Event::Key(key_event) if key_event.kind == KeyEventKind::Press => {
                 self.handle_key_event(key_event)
             }
-            _ => {}
-        };
-        Ok(())
+            _ => Ok(()),
+        }
     }
 
-    fn handle_key_event(&mut self, key_event: KeyEvent) {
+    fn handle_key_event(&mut self, key_event: KeyEvent) -> Result<()> {
         match key_event.code {
-            KeyCode::Char('q') => self.exit(),
-            KeyCode::Left => self.decrement_counter(),
-            KeyCode::Right => self.increment_counter(),
+            KeyCode::Char('q') => self.exit()?,
+            KeyCode::Left => self.decrement_counter()?,
+            KeyCode::Right => self.increment_counter()?,
             _ => {}
-        }
+        };
+        Ok(())
     }
 
-    fn exit(&mut self) {
+    fn exit(&mut self) -> Result<()> {
         self.exit = true;
+        Ok(())
     }
 
-    fn decrement_counter(&mut self) {
-        self.counter -= 1;
+    fn decrement_counter(&mut self) -> Result<(), OverflowError> {
+        if self.counter == 0 {
+            Err(OverflowError {
+                msg: "Overflow error occurred!".into(),
+            })
+        } else {
+            self.counter -= 1;
+            Ok(())
+        }
     }
 
-    fn increment_counter(&mut self) {
+    fn increment_counter(&mut self) -> Result<()> {
         self.counter += 1;
+        Ok(())
     }
 }
 
@@ -128,16 +145,43 @@ mod tests {
     }
 
     #[test]
-    fn handle_key_event() {
+    fn handle_key_event_inc_dec() {
         let mut app = App::default();
-        app.handle_key_event(KeyCode::Right.into());
+        let res = app.handle_key_event(KeyCode::Right.into());
+        assert!(res.is_ok());
         assert_eq!(app.counter, 1);
 
-        app.handle_key_event(KeyCode::Left.into());
+        let res = app.handle_key_event(KeyCode::Left.into());
+        assert!(res.is_ok());
         assert_eq!(app.counter, 0);
+    }
 
+    #[test]
+    fn handle_key_event_exit() {
         let mut app = App::default();
-        app.handle_key_event(KeyCode::Char('q').into());
+        let res = app.handle_key_event(KeyCode::Char('q').into());
+        assert!(res.is_ok());
         assert!(app.exit);
     }
+
+    #[test]
+    fn handle_key_event_dec_error() {
+        let mut app = App::default();
+        let res = app.handle_key_event(KeyCode::Left.into());
+
+        assert!(res.is_err());
+        let res_err = res.unwrap_err();
+        let casted_val = res_err
+            .downcast_ref::<OverflowError>()
+            .expect("something bad occurred");
+
+        let expected_err_msg: String = "Overflow error occurred!".into();
+        assert_eq!(casted_val.msg, expected_err_msg);
+        assert_eq!(
+            *casted_val,
+            OverflowError {
+                msg: expected_err_msg,
+            },
+        );
+    }
 }