Pusing up the first page code

src/engine/io/index_formats.rs

@@ -6,6 +6,10 @@ mod btree_branch;
 pub use btree_branch::BTreeBranch;
 pub use btree_branch::BTreeBranchError;
 
+mod btree_first_page;
+pub use btree_first_page::BTreeFirstPage;
+pub use btree_first_page::BTreeFirstPageError;
+
 mod btree_leaf;
 pub use btree_leaf::BTreeLeaf;
 pub use btree_leaf::BTreeLeafError;

src/engine/io/index_formats/btree_first_page.rs

@@ -0,0 +1,57 @@
+use crate::engine::io::{
+    format_traits::{Parseable, Serializable},
+    page_formats::{PageOffset, PageOffsetError},
+};
+use bytes::BufMut;
+use thiserror::Error;
+
+/// Special page that points to where the root page of the index is really located
+#[derive(Debug, PartialEq)]
+pub struct BTreeFirstPage {
+    pub root_offset: PageOffset,
+}
+
+impl Parseable<BTreeFirstPageError> for BTreeFirstPage {
+    type Output = Self;
+    fn parse(buffer: &mut impl bytes::Buf) -> Result<Self::Output, BTreeFirstPageError> {
+        let root_offset = PageOffset::parse(buffer)?;
+        Ok(BTreeFirstPage { root_offset })
+    }
+}
+
+impl Serializable for BTreeFirstPage {
+    fn serialize(&self, buffer: &mut impl BufMut) {
+        self.root_offset.serialize(buffer);
+    }
+}
+
+#[derive(Debug, Error)]
+pub enum BTreeFirstPageError {
+    #[error(transparent)]
+    PageOffsetError(#[from] PageOffsetError),
+}
+
+#[cfg(test)]
+mod tests {
+    use bytes::BytesMut;
+
+    use crate::constants::PAGE_SIZE;
+
+    use super::*;
+
+    #[test]
+    fn test_roundtrip() -> Result<(), Box<dyn std::error::Error>> {
+        let first = BTreeFirstPage {
+            root_offset: PageOffset(1),
+        };
+
+        let mut buffer = BytesMut::with_capacity(PAGE_SIZE as usize);
+        first.serialize(&mut buffer);
+
+        let result = BTreeFirstPage::parse(&mut buffer)?;
+
+        assert_eq!(first, result);
+
+        Ok(())
+    }
+}