1 files changed, 205 insertions, 0 deletions
diff --git a/src/main/rust/app.rs b/src/main/rust/app.rs
new file mode 100644
index 0000000..d6e84e1
--- /dev/null
+++ b/src/main/rust/app.rs
@@ -0,0 +1,205 @@
+use crate::store::{Context, Store};
+use miette::{Diagnostic, Result};
+use thiserror::Error;
+
+#[derive(Default)]
+pub struct App {
+    context: Context,
+    exit: bool,
+}
+
+#[derive(Diagnostic, Debug, Error, PartialEq)]
+#[error("An overflow error occurred")]
+#[diagnostic()]
+pub struct OverflowError {
+    #[help]
+    pub _msg: String,
+}
+
+impl App {
+    /// Build context in App and pass it forward
+    pub fn init_context(&mut self) -> Result<&mut Self> {
+        let store = self.context.unwrap_store();
+
+        store.init()?;
+        Ok(self)
+    }
+
+    pub fn get_exit_status(&self) -> bool {
+        self.exit
+    }
+
+    pub fn exit(&mut self) -> Result<()> {
+        self.exit = true;
+        Ok(())
+    }
+
+    pub fn decrement_counter(&mut self) -> Result<()> {
+        let store = self.context.unwrap_store();
+        let count = store.get_counter()?;
+
+        if count == 0 {
+            Err(OverflowError {
+                _msg: "Cannot count below 0".into(),
+            }
+            .into())
+        } else {
+            store.set_counter(count - 1)?;
+            Ok(())
+        }
+    }
+
+    pub fn increment_counter(&mut self) -> Result<()> {
+        let store = self.context.unwrap_store();
+        let count = store.get_counter()?;
+
+        if count == u8::MAX {
+            Err(OverflowError {
+                _msg: "Cannot count above u8::MAX".into(),
+            }
+            .into())
+        } else {
+            store.set_counter(count + 1)?;
+            Ok(())
+        }
+    }
+
+    pub fn display_counter(&self) -> String {
+        self.context
+            .get_store()
+            .get_counter()
+            .map(|u| u.to_string())
+            .unwrap_or("Error".into())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::store::ContextError;
+
+    fn get_count(app: &App) -> Result<u8, ContextError> {
+        app.context.get_store().get_counter()
+    }
+
+    #[test]
+    fn display_counter_inited() {
+        let mut app = App::default();
+        assert!(app.init_context().is_ok());
+
+        let count = app.display_counter();
+
+        assert_eq!(count, "0");
+    }
+
+    #[test]
+    fn display_counter_noninited() {
+        let app = App::default();
+
+        let count = app.display_counter();
+
+        assert_eq!(count, "Error");
+    }
+
+    #[test]
+    fn increment_decrement() {
+        let mut app = App::default();
+        assert!(app.init_context().is_ok());
+
+        let res = app.increment_counter();
+        assert!(res.is_ok());
+        assert_eq!(get_count(&app).unwrap(), 1);
+
+        let res = app.decrement_counter();
+        assert!(res.is_ok());
+        assert_eq!(get_count(&app).unwrap(), 0);
+    }
+
+    #[test]
+    fn increment_n() {
+        let mut app = App::default();
+        assert!(app.init_context().is_ok());
+        let n = 8;
+
+        for i in 1..=n {
+            let res = app.increment_counter();
+            assert!(res.is_ok());
+            assert_eq!(get_count(&app).unwrap(), i);
+        }
+        assert_eq!(get_count(&app).unwrap(), n);
+    }
+
+    #[test]
+    fn increment_n_decrement() {
+        let mut app = App::default();
+        assert!(app.init_context().is_ok());
+        let n = 8;
+
+        for i in 1..=n {
+            let res = app.increment_counter();
+            assert!(res.is_ok());
+            assert_eq!(get_count(&app).unwrap(), i);
+        }
+        assert_eq!(get_count(&app).unwrap(), n);
+
+        let res = app.decrement_counter();
+        assert!(res.is_ok());
+        assert_eq!(get_count(&app).unwrap(), n - 1);
+    }
+
+    #[test]
+    fn exit() {
+        let mut app = App::default();
+        assert!(app.init_context().is_ok());
+
+        let res = app.exit();
+
+        assert!(res.is_ok());
+        assert!(app.exit);
+    }
+
+    #[test]
+    fn decrement_counter_error() {
+        let mut app = App::default();
+        assert!(app.init_context().is_ok());
+        let res = app.decrement_counter();
+
+        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 = "Cannot count below 0".into();
+        assert_eq!(casted_val._msg, expected_err_msg);
+        assert_eq!(
+            *casted_val,
+            OverflowError {
+                _msg: expected_err_msg,
+            },
+        );
+    }
+
+    #[test]
+    fn increment_counter_error() {
+        let mut app = App::default();
+        assert!(app.init_context().is_ok());
+        assert!(app.context.unwrap_store().set_counter(u8::MAX).is_ok());
+        let res = app.increment_counter();
+
+        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 = "Cannot count above u8::MAX".into();
+        assert_eq!(casted_val._msg, expected_err_msg);
+        assert_eq!(
+            *casted_val,
+            OverflowError {
+                _msg: expected_err_msg,
+            },
+        );
+    }
+}