Introduce total_count

storage_engine/src/storage_engine.rs

@@ -36,11 +36,17 @@ pub struct Store<T> {
 pub struct StoreHeader {
     number_of_columns: usize,
     deleted_count: usize,
+    total_count: usize,
 }
 impl StoreHeader {
     const NUMBER_OF_COLUMNS_SIZE: usize = size_of::<usize>();
     const DELETED_COUNT_SIZE: usize = size_of::<usize>();
-    const SIZE: usize = Self::NUMBER_OF_COLUMNS_SIZE + Self::DELETED_COUNT_SIZE;
+    const TOTAL_COUNT_SIZE: usize = size_of::<usize>();
+    const SIZE: usize = Self::NUMBER_OF_COLUMNS_SIZE + Self::DELETED_COUNT_SIZE + Self::TOTAL_COUNT_SIZE;
+
+    const NUMBER_OF_COLUMNS_OFFSET: usize = 0;
+    const DELETED_COUNT_OFFSET: usize  = Self::NUMBER_OF_COLUMNS_OFFSET + Self::NUMBER_OF_COLUMNS_SIZE;
+    const TOTAL_COUNT_OFFSET: usize = Self::DELETED_COUNT_OFFSET + Self::DELETED_COUNT_SIZE;
 }
 
 #[derive(Debug)]
@@ -153,6 +159,7 @@ impl <T>Store<T> {
         let header = StoreHeader {
             number_of_columns,
             deleted_count: 0,
+            total_count: 0,
         };
         let encoded_header: Vec<u8> = header.encode()?;
 
@@ -192,17 +199,46 @@ impl <T>Store<T> {
     }
 
     // ===Append Entry===
+    async fn increment_total_count(&mut self) -> Result<()> {
+        self.seek_to_start().await?;
+        self.seek_to(StoreHeader::TOTAL_COUNT_OFFSET as u64).await?;
+        let new_count = self.header.increment_total_count();
+        self.write_bytes(&encode::<usize>(&new_count)?).await?;
+        Ok(())
+    }
+
+    async fn increment_deleted_count(&mut self) -> Result<()> {
+        self.seek_to_start().await?;
+        self.seek_to(StoreHeader::DELETED_COUNT_OFFSET as u64).await?;
+        let new_count = self.header.increment_deleted_count();
+        self.write_bytes(&encode::<usize>(&new_count)?).await?;
+        Ok(())
+    }
+
     // Moves cursor to the end.
     pub async fn append_entry(&mut self, entry: &Entry<T>) -> Result<Cursor> 
         where T: Encode
     {
+        self.increment_total_count().await?;
+
         let encoded_entry: Vec<u8> = entry.encode()?;
         self.seek_to_end().await?;
         let cursor: Cursor = self.current_cursor().await?;
         self.write_bytes(&encoded_entry).await?;
+
         Ok(cursor)
     }
 
+    // ===Deletion===
+    pub async fn mark_deleted_at(&mut self, cursor: Cursor) -> Result<()> {
+        self.increment_deleted_count().await?;
+
+        self.seek_to(cursor).await?;
+
+        // TODO: Now you need to mutate the entry itself
+        todo!()
+    }
+
 
     // ===Lookup===
     // WARNING: The cursor has to be at the start of an entry. Otherwise garbage data will be
@@ -266,6 +302,7 @@ impl StoreHeader {
         // FORMAT: First Number of Columns, Then Deleted Count.
         let mut result = encode(&self.number_of_columns)?;
         result.append(&mut encode(&self.deleted_count)?);
+        result.append(&mut encode(&self.total_count)?);
         Ok(result)
     }
 
@@ -274,20 +311,35 @@ impl StoreHeader {
     }
 
     async fn decode(result: &mut [u8]) -> Result<StoreHeader> {
-        let offset = 0;
-        let (number_of_columns, offset) =
-            decode::<usize>(&result[offset..offset + Self::NUMBER_OF_COLUMNS_SIZE])
+        let (number_of_columns, _) =
+            decode::<usize>(&result[Self::NUMBER_OF_COLUMNS_OFFSET..Self::NUMBER_OF_COLUMNS_OFFSET + Self::NUMBER_OF_COLUMNS_SIZE])
                 .map_err(|e| Error::DecodeError(DecodeErrorKind::StoreHeaderNumberOfColumns, e))?;
         let (deleted_count, _) =
-            decode::<usize>(&result[offset..offset + Self::DELETED_COUNT_SIZE])
+            decode::<usize>(&result[Self::DELETED_COUNT_OFFSET..Self::DELETED_COUNT_OFFSET + Self::DELETED_COUNT_SIZE])
                 .map_err(|e| Error::DecodeError(DecodeErrorKind::StoreHeaderDeletedCount, e))?;
+        let (total_count, _offset) =
+            decode::<usize>(&result[Self::TOTAL_COUNT_OFFSET..Self::TOTAL_COUNT_OFFSET + Self::TOTAL_COUNT_SIZE])
+                .map_err(|e| Error::DecodeError(DecodeErrorKind::StoreHeaderTotalCount, e))?;
         let header = StoreHeader {
             number_of_columns,
             deleted_count,
+            total_count,
         };
 
         Ok(header)
     }
+
+    // returns new count
+    fn increment_total_count(&mut self) -> usize {
+        self.total_count += 1;
+        self.total_count
+    }
+
+    // returns new count
+    fn increment_deleted_count(&mut self) -> usize {
+        self.deleted_count += 1;
+        self.deleted_count
+    }
 }
 
 // ====Entry====