Support reset to undo all snapshots

Cargo.toml

@@ -2,7 +2,7 @@ workspace = { members = ["example"] }
 
 [package]
 name = "spacedb"
-version = "0.0.11"
+version = "0.0.12"
 edition = "2021"
 description = "A cryptographically verifiable data store and universal accumulator for the Spaces protocol."
 repository = "https://github.com/spacesprotocol/spacedb"

src/db.rs

@@ -207,6 +207,14 @@ impl<H: NodeHasher> Database<H> {
         Ok(save_point)
     }
 
+    pub fn reset(&self) -> Result<()> {
+        let mut header = self.header.lock().expect("acquire lock");
+        *header = DatabaseHeader::new();
+        self.write_header(&header)?;
+        self.file.set_len(header.len())?;
+        Ok(())
+    }
+
     pub fn begin_write(&self) -> Result<WriteTransaction<'_, H>> {
         Ok(WriteTransaction::new(self))
     }

tests/integration_test.rs

@@ -1359,3 +1359,43 @@ fn read_only_while_writer_holds_db() {
     drop(db);
     let _ = fs::remove_file(&db_path);
 }
+
+#[test]
+fn reset_to_empty() {
+    let db = Database::memory().unwrap();
+    let empty_root = db.begin_read().unwrap().compute_root().unwrap();
+
+    // Insert data across multiple snapshots
+    let mut write = db.begin_write().unwrap();
+    for i in 0u8..10 {
+        let mut k = [0u8; 32];
+        k[0] = i;
+        write = write.insert(k, vec![i]).unwrap();
+    }
+    write.commit().unwrap();
+
+    db.begin_write().unwrap()
+        .insert([0xFFu8; 32], vec![0xFF]).unwrap()
+        .commit().unwrap();
+
+    assert_eq!(db.iter().count(), 2, "should have 2 snapshots");
+    assert_ne!(db.begin_read().unwrap().compute_root().unwrap(), empty_root);
+
+    // Reset to empty
+    db.reset().unwrap();
+
+    // Should behave like a fresh database
+    let mut snapshot = db.begin_read().unwrap();
+    assert_eq!(snapshot.compute_root().unwrap(), empty_root);
+    assert_eq!(snapshot.get(&[0u8; 32]).unwrap(), None);
+    assert_eq!(db.iter().count(), 0, "should have 0 snapshots after reset");
+
+    // Should be able to write again after reset
+    db.begin_write().unwrap()
+        .insert([0x42u8; 32], vec![1, 2, 3]).unwrap()
+        .commit().unwrap();
+
+    let mut snapshot = db.begin_read().unwrap();
+    assert_eq!(snapshot.get(&[0x42u8; 32]).unwrap(), Some(vec![1, 2, 3]));
+    assert_ne!(snapshot.compute_root().unwrap(), empty_root);
+}