Simplify the state file

src/app_state.rs

@@ -4,15 +4,14 @@ use crossterm::{
     terminal::{Clear, ClearType},
     ExecutableCommand,
 };
-use std::io::{StdoutLock, Write};
-
-mod state_file;
+use std::{
+    fs::{self, File},
+    io::{Read, StdoutLock, Write},
+};
 
 use crate::{exercise::Exercise, info_file::InfoFile, FENISH_LINE};
 
-use self::state_file::{write, StateFileDeser};
-
-const STATE_FILE_NAME: &str = ".rustlings-state.json";
+const STATE_FILE_NAME: &str = ".rustlings-state.txt";
 const BAD_INDEX_ERR: &str = "The current exercise index is higher than the number of exercises";
 
 #[must_use]
@@ -27,11 +26,51 @@ pub struct AppState {
     n_done: u16,
     welcome_message: String,
     final_message: String,
+    file_buf: Vec<u8>,
 }
 
 impl AppState {
+    fn update_from_file(&mut self) {
+        self.file_buf.clear();
+        self.n_done = 0;
+
+        if File::open(STATE_FILE_NAME)
+            .and_then(|mut file| file.read_to_end(&mut self.file_buf))
+            .is_ok()
+        {
+            let mut lines = self.file_buf.split(|c| *c == b'\n');
+            let Some(current_exercise_name) = lines.next() else {
+                return;
+            };
+
+            if lines.next().is_none() {
+                return;
+            }
+
+            let mut done_exercises = hashbrown::HashSet::with_capacity(self.exercises.len());
+
+            for done_exerise_name in lines {
+                if done_exerise_name.is_empty() {
+                    break;
+                }
+                done_exercises.insert(done_exerise_name);
+            }
+
+            for (ind, exercise) in self.exercises.iter_mut().enumerate() {
+                if done_exercises.contains(exercise.name.as_bytes()) {
+                    exercise.done = true;
+                    self.n_done += 1;
+                }
+
+                if exercise.name.as_bytes() == current_exercise_name {
+                    self.current_exercise_ind = ind;
+                }
+            }
+        }
+    }
+
     pub fn new(info_file: InfoFile) -> Self {
-        let mut exercises = info_file
+        let exercises = info_file
             .exercises
             .into_iter()
             .map(|mut exercise_info| {
@@ -55,42 +94,18 @@ impl AppState {
             })
             .collect::<Vec<_>>();
 
-        let (current_exercise_ind, n_done) = StateFileDeser::read().map_or((0, 0), |state_file| {
-            let mut state_file_exercises =
-                hashbrown::HashMap::with_capacity(state_file.exercises.len());
-
-            for (ind, exercise_state) in state_file.exercises.into_iter().enumerate() {
-                state_file_exercises.insert(
-                    exercise_state.name,
-                    (ind == state_file.current_exercise_ind, exercise_state.done),
-                );
-            }
-
-            let mut current_exercise_ind = 0;
-            let mut n_done = 0;
-            for (ind, exercise) in exercises.iter_mut().enumerate() {
-                if let Some((current, done)) = state_file_exercises.get(exercise.name) {
-                    if *done {
-                        exercise.done = true;
-                        n_done += 1;
-                    }
-
-                    if *current {
-                        current_exercise_ind = ind;
-                    }
-                }
-            }
-
-            (current_exercise_ind, n_done)
-        });
-
-        Self {
-            current_exercise_ind,
+        let mut slf = Self {
+            current_exercise_ind: 0,
             exercises,
-            n_done,
+            n_done: 0,
             welcome_message: info_file.welcome_message.unwrap_or_default(),
             final_message: info_file.final_message.unwrap_or_default(),
-        }
+            file_buf: Vec::with_capacity(2048),
+        };
+
+        slf.update_from_file();
+
+        slf
     }
 
     #[inline]
@@ -120,7 +135,7 @@ impl AppState {
 
         self.current_exercise_ind = ind;
 
-        write(self)
+        self.write()
     }
 
     pub fn set_current_exercise_by_name(&mut self, name: &str) -> Result<()> {
@@ -132,7 +147,7 @@ impl AppState {
             .position(|exercise| exercise.name == name)
             .with_context(|| format!("No exercise found for '{name}'!"))?;
 
-        write(self)
+        self.write()
     }
 
     pub fn set_pending(&mut self, ind: usize) -> Result<()> {
@@ -141,7 +156,7 @@ impl AppState {
         if exercise.done {
             exercise.done = false;
             self.n_done -= 1;
-            write(self)?;
+            self.write()?;
         }
 
         Ok(())
@@ -193,7 +208,7 @@ impl AppState {
                     self.exercises[exercise_ind].done = false;
                     self.n_done -= 1;
 
-                    write(self)?;
+                    self.write()?;
 
                     return Ok(ExercisesProgress::Pending);
                 }
@@ -213,6 +228,31 @@ impl AppState {
 
         Ok(ExercisesProgress::Pending)
     }
+
+    // Write the state file.
+    // The file's format is very simple:
+    // - The first line is the name of the current exercise.
+    // - The second line is an empty line.
+    // - All remaining lines are the names of done exercises.
+    fn write(&mut self) -> Result<()> {
+        self.file_buf.clear();
+
+        self.file_buf
+            .extend_from_slice(self.current_exercise().name.as_bytes());
+        self.file_buf.extend_from_slice(b"\n\n");
+
+        for exercise in &self.exercises {
+            if exercise.done {
+                self.file_buf.extend_from_slice(exercise.name.as_bytes());
+                self.file_buf.extend_from_slice(b"\n");
+            }
+        }
+
+        fs::write(STATE_FILE_NAME, &self.file_buf)
+            .with_context(|| format!("Failed to write the state file {STATE_FILE_NAME}"))?;
+
+        Ok(())
+    }
 }
 
 const RERUNNING_ALL_EXERCISES_MSG: &[u8] = b"