feat: implementation of M1

crates/bds-core/src/util/atomic_write.rs

@@ -0,0 +1,53 @@
+use std::fs;
+use std::io::{self, Write};
+use std::path::Path;
+
+/// Write `content` to `path` atomically: write to a temp file in the same
+/// directory, then rename. Creates parent directories if missing.
+pub fn atomic_write(path: &Path, content: &[u8]) -> io::Result<()> {
+    if let Some(parent) = path.parent() {
+        fs::create_dir_all(parent)?;
+    }
+    let tmp_path = path.with_extension("tmp");
+    let mut file = fs::File::create(&tmp_path)?;
+    file.write_all(content)?;
+    file.sync_all()?;
+    fs::rename(&tmp_path, path)?;
+    Ok(())
+}
+
+/// Convenience wrapper for UTF-8 string content.
+pub fn atomic_write_str(path: &Path, content: &str) -> io::Result<()> {
+    atomic_write(path, content.as_bytes())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use tempfile::TempDir;
+
+    #[test]
+    fn write_and_read_back() {
+        let dir = TempDir::new().unwrap();
+        let path = dir.path().join("test.txt");
+        atomic_write_str(&path, "hello world").unwrap();
+        assert_eq!(fs::read_to_string(&path).unwrap(), "hello world");
+    }
+
+    #[test]
+    fn creates_parent_directories() {
+        let dir = TempDir::new().unwrap();
+        let path = dir.path().join("a").join("b").join("c.txt");
+        atomic_write_str(&path, "nested").unwrap();
+        assert_eq!(fs::read_to_string(&path).unwrap(), "nested");
+    }
+
+    #[test]
+    fn overwrites_existing() {
+        let dir = TempDir::new().unwrap();
+        let path = dir.path().join("test.txt");
+        atomic_write_str(&path, "v1").unwrap();
+        atomic_write_str(&path, "v2").unwrap();
+        assert_eq!(fs::read_to_string(&path).unwrap(), "v2");
+    }
+}