From b6a84118410a60430c6f9cb525ece628c974467d Mon Sep 17 00:00:00 2001
From: Nikita Galaiko <nikita@galaiko.rocks>
Date: Thu, 21 Dec 2023 11:43:48 +0100
Subject: [PATCH] lock::Dir implementation

---
 gitbutler-app/src/lib.rs  |   1 +
 gitbutler-app/src/lock.rs | 158 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 159 insertions(+)
 create mode 100644 gitbutler-app/src/lock.rs

diff --git a/gitbutler-app/src/lib.rs b/gitbutler-app/src/lib.rs
index 698a487ab..071ffdb5f 100644
--- a/gitbutler-app/src/lib.rs
+++ b/gitbutler-app/src/lib.rs
@@ -15,6 +15,7 @@ pub mod gb_repository;
 pub mod git;
 pub mod github;
 pub mod keys;
+pub mod lock;
 pub mod logs;
 pub mod menu;
 pub mod paths;
diff --git a/gitbutler-app/src/lock.rs b/gitbutler-app/src/lock.rs
new file mode 100644
index 000000000..7cb6fb040
--- /dev/null
+++ b/gitbutler-app/src/lock.rs
@@ -0,0 +1,158 @@
+use std::sync::{Arc, Mutex};
+
+#[derive(Debug, Clone)]
+pub struct Dir {
+    inner: Arc<Inner>,
+}
+
+impl Dir {
+    pub fn new<P: AsRef<std::path::Path>>(path: P) -> Result<Self, OpenError> {
+        Inner::new(path).map(Arc::new).map(|inner| Self { inner })
+    }
+
+    pub fn batch<R, E>(
+        &self,
+        action: impl FnOnce(&std::path::Path) -> Result<R, E>,
+    ) -> Result<R, BatchError<E>> {
+        self.inner.batch(action)
+    }
+}
+
+#[derive(Debug)]
+struct Inner {
+    path: std::path::PathBuf,
+    flock: Mutex<fslock::LockFile>,
+}
+
+impl Inner {
+    fn new<P: AsRef<std::path::Path>>(path: P) -> Result<Self, OpenError> {
+        let path = path.as_ref().to_path_buf();
+        if !path.is_dir() {
+            return Err(OpenError::NotDirectory(path));
+        }
+        let flock = fslock::LockFile::open(&path.with_extension("lock")).map(Mutex::new)?;
+        Ok(Self { path, flock })
+    }
+
+    fn batch<R, E>(
+        &self,
+        action: impl FnOnce(&std::path::Path) -> Result<R, E>,
+    ) -> Result<R, BatchError<E>> {
+        let mut flock = self.flock.lock().unwrap();
+
+        flock.lock()?;
+        let result = action(&self.path).map_err(BatchError::Batch);
+        flock.unlock()?;
+
+        result
+    }
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum OpenError {
+    #[error("{0} is not a directory")]
+    NotDirectory(std::path::PathBuf),
+    #[error(transparent)]
+    Io(#[from] std::io::Error),
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum BatchError<E> {
+    #[error(transparent)]
+    Io(#[from] std::io::Error),
+    #[error(transparent)]
+    Batch(E),
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::test_utils::temp_dir;
+
+    #[tokio::test]
+    async fn test_lock_same_instance() {
+        let dir_path = temp_dir();
+        std::fs::write(dir_path.join("file.txt"), "").unwrap();
+        let dir = Dir::new(&dir_path).unwrap();
+
+        let (tx, rx) = std::sync::mpsc::sync_channel(1);
+
+        // spawn a task that will signal right after aquireing the lock
+        let _ = tokio::spawn({
+            let dir = dir.clone();
+            async move {
+                dir.batch(|root| {
+                    tx.send(()).unwrap();
+                    assert_eq!(
+                        std::fs::read_to_string(root.join("file.txt")).unwrap(),
+                        String::new()
+                    );
+                    std::fs::write(root.join("file.txt"), "1")
+                })
+            }
+        })
+        .await
+        .unwrap();
+
+        // then we wait until the lock is aquired
+        rx.recv().unwrap();
+
+        // and immidiately try to lock again
+        dir.batch(|root| {
+            assert_eq!(std::fs::read_to_string(root.join("file.txt")).unwrap(), "1");
+            std::fs::write(root.join("file.txt"), "2")
+        })
+        .unwrap();
+
+        assert_eq!(
+            std::fs::read_to_string(dir_path.join("file.txt")).unwrap(),
+            "2"
+        );
+    }
+
+    #[tokio::test]
+    async fn test_lock_different_instances() {
+        let dir_path = temp_dir();
+        std::fs::write(dir_path.join("file.txt"), "").unwrap();
+
+        let (tx, rx) = std::sync::mpsc::sync_channel(1);
+
+        // spawn a task that will signal right after aquireing the lock
+        let _ = tokio::spawn({
+            let dir_path = dir_path.clone();
+            async move {
+                // one dir instance is created on a separate thread
+                let dir = Dir::new(&dir_path).unwrap();
+                dir.batch(|root| {
+                    tx.send(()).unwrap();
+                    assert_eq!(
+                        std::fs::read_to_string(root.join("file.txt")).unwrap(),
+                        String::new()
+                    );
+                    std::fs::write(root.join("file.txt"), "1")
+                })
+            }
+        })
+        .await
+        .unwrap();
+
+        // another dir instance is created on the main thread
+        let dir = Dir::new(&dir_path).unwrap();
+
+        // then we wait until the lock is aquired
+        rx.recv().unwrap();
+
+        // and immidiately try to lock again
+        dir.batch(|root| {
+            assert_eq!(std::fs::read_to_string(root.join("file.txt")).unwrap(), "1");
+            std::fs::write(root.join("file.txt"), "2")
+        })
+        .unwrap();
+
+        assert_eq!(
+            std::fs::read_to_string(dir_path.join("file.txt")).unwrap(),
+            "2"
+        );
+    }
+}