1 files changed, 128 insertions, 0 deletions
diff --git a/src/watch.rs b/src/watch.rs
new file mode 100644
index 0000000..d20e552
--- /dev/null
+++ b/src/watch.rs
@@ -0,0 +1,128 @@
+use anyhow::{Error, Result};
+use notify_debouncer_mini::{
+    new_debouncer,
+    notify::{self, RecursiveMode},
+};
+use std::{
+    io::{self, Write},
+    path::Path,
+    sync::mpsc::channel,
+    thread,
+    time::Duration,
+};
+
+mod notify_event;
+mod state;
+mod terminal_event;
+
+use crate::app_state::{AppState, ExercisesProgress};
+
+use self::{
+    notify_event::DebounceEventHandler,
+    state::WatchState,
+    terminal_event::{terminal_event_handler, InputEvent},
+};
+
+enum WatchEvent {
+    Input(InputEvent),
+    FileChange { exercise_ind: usize },
+    TerminalResize,
+    NotifyErr(notify::Error),
+    TerminalEventErr(io::Error),
+}
+
+/// Returned by the watch mode to indicate what to do afterwards.
+#[must_use]
+pub enum WatchExit {
+    /// Exit the program.
+    Shutdown,
+    /// Enter the list mode and restart the watch mode afterwards.
+    List,
+}
+
+pub fn watch(
+    app_state: &mut AppState,
+    notify_exercise_paths: Option<&'static [&'static str]>,
+) -> Result<WatchExit> {
+    let (tx, rx) = channel();
+
+    let mut manual_run = false;
+    // Prevent dropping the guard until the end of the function.
+    // Otherwise, the file watcher exits.
+    let _debouncer_guard = if let Some(exercise_paths) = notify_exercise_paths {
+        let mut debouncer = new_debouncer(
+            Duration::from_secs(1),
+            DebounceEventHandler {
+                tx: tx.clone(),
+                exercise_paths,
+            },
+        )
+        .inspect_err(|_| eprintln!("{NOTIFY_ERR}"))?;
+        debouncer
+            .watcher()
+            .watch(Path::new("exercises"), RecursiveMode::Recursive)
+            .inspect_err(|_| eprintln!("{NOTIFY_ERR}"))?;
+
+        Some(debouncer)
+    } else {
+        manual_run = true;
+        None
+    };
+
+    let mut watch_state = WatchState::new(app_state, manual_run);
+
+    watch_state.run_current_exercise()?;
+
+    thread::spawn(move || terminal_event_handler(tx, manual_run));
+
+    while let Ok(event) = rx.recv() {
+        match event {
+            WatchEvent::Input(InputEvent::Next) => match watch_state.next_exercise()? {
+                ExercisesProgress::AllDone => break,
+                ExercisesProgress::Pending => watch_state.run_current_exercise()?,
+            },
+            WatchEvent::Input(InputEvent::Hint) => {
+                watch_state.show_hint()?;
+            }
+            WatchEvent::Input(InputEvent::List) => {
+                return Ok(WatchExit::List);
+            }
+            WatchEvent::Input(InputEvent::Quit) => {
+                watch_state.into_writer().write_all(QUIT_MSG)?;
+                break;
+            }
+            WatchEvent::Input(InputEvent::Run) => watch_state.run_current_exercise()?,
+            WatchEvent::Input(InputEvent::Unrecognized(cmd)) => {
+                watch_state.handle_invalid_cmd(&cmd)?;
+            }
+            WatchEvent::FileChange { exercise_ind } => {
+                watch_state.run_exercise_with_ind(exercise_ind)?;
+            }
+            WatchEvent::TerminalResize => {
+                watch_state.render()?;
+            }
+            WatchEvent::NotifyErr(e) => {
+                watch_state.into_writer().write_all(NOTIFY_ERR.as_bytes())?;
+                return Err(Error::from(e));
+            }
+            WatchEvent::TerminalEventErr(e) => {
+                return Err(Error::from(e).context("Terminal event listener failed"));
+            }
+        }
+    }
+
+    Ok(WatchExit::Shutdown)
+}
+
+const QUIT_MSG: &[u8] = b"
+We hope you're enjoying learning Rust!
+If you want to continue working on the exercises at a later point, you can simply run `rustlings` again.
+";
+
+const NOTIFY_ERR: &str = "
+The automatic detection of exercise file changes failed :(
+Please try running `rustlings` again.
+
+If you keep getting this error, run `rustlings --manual-run` to deactivate the file watcher.
+You need to manually trigger running the current exercise using `r` or `run` then.
+";