Split cursor capabilities

storage_engine/src/cursor_capabilities/header_access.rs

@@ -0,0 +1,230 @@
+use tokio::io::AsyncReadExt;
+use async_trait::async_trait;
+
+use bincode;
+use bincode::{Decode, Encode};
+use crate::binary_coding::{encode, decode};
+
+use crate::error::{Error, DecodeErrorKind};
+use crate::segments::entry::{Entry, EntryDetailed};
+use crate::segments::entry_header::EntryHeaderWithDataSize;
+use crate::segments::store_header::StoreHeader;
+use crate::storage_engine::{FilePosition, Column, Result};
+use crate::cursor_capabilities::primitive::{CursorCanRead, CursorCanWrite};
+
+#[async_trait]
+pub trait CursorCanReadHeader<T>: CursorCanRead<T> {
+    fn header(&self) -> &StoreHeader;
+
+    async fn seek_to_start_of_data(&mut self) -> Result<FilePosition> {
+        self.seek_to(StoreHeader::size(self.header().number_of_columns) as u64).await
+    }
+
+    async fn read_entry_header(&mut self) -> Result<EntryHeaderWithDataSize> {
+        let number_of_columns: usize = self.header().number_of_columns;
+        let mut header_bytes: Vec<u8> = vec![0; EntryHeaderWithDataSize::size(number_of_columns)];
+        self.read_bytes(&mut header_bytes).await?;
+        let header = EntryHeaderWithDataSize::decode(&mut header_bytes[..], number_of_columns)?;
+
+        Ok(header)
+    }
+
+    async fn read_entry_header_at(&mut self, file_position: FilePosition) -> Result<EntryHeaderWithDataSize>  {
+        self.seek_to(file_position).await?;
+        self.read_entry_header().await
+    }
+
+    // Returns None when file_position == eof_file_position
+    async fn read_entry_at(&mut self, file_position: FilePosition) -> Result<Option<EntryDetailed<T>>> 
+        where T: Decode
+    {
+        self.seek_to(file_position).await?;
+        self.next().await
+    }
+
+    // ===Iteration===
+    // The following functions assume that the current file position is at a valid entry or EOF.
+
+
+    // WARNING: This moves the file_position to start of the data, so you can't just call
+    //    next_entry_header() a bunch of times. You must move the cursor!
+    async fn next_entry_header(&mut self) -> Result<Option<EntryHeaderWithDataSize>> {
+        if self.is_at_eof().await? {
+            return Ok(None)
+        }
+
+        let entry_header = self.read_entry_header().await?;
+
+        Ok(Some(entry_header))
+    }
+
+    // This is meant to be used after next_entry_header() is called.
+    async fn jump_from_start_of_entry_data_to_next_entry(&mut self, entry_header: &EntryHeaderWithDataSize) -> Result<FilePosition>{
+        let file_position = self.seek_by(entry_header.size_of_data() as i64).await?;
+        Ok(file_position)
+    }
+
+    async fn next(&mut self) -> Result<Option<EntryDetailed<T>>> 
+        where T: Decode
+    {
+        let file_position = self.current_file_position().await?;
+        let Some(entry_header) = self.next_entry_header().await? else { return Ok(None) };
+
+        let mut data_bytes: Vec<u8> = vec![0; entry_header.size_of_data()];
+        self.read_bytes(&mut data_bytes).await?;
+        let entry: EntryDetailed<T> =
+            EntryDetailed::decode(entry_header, file_position, self.header().number_of_columns, &mut data_bytes)?;
+
+        Ok(Some(entry))
+    }
+
+    // Like next, but only reads the column, not the whole entry. 
+    async fn next_at_column(&mut self, column: Column) -> Result<Option<(EntryHeaderWithDataSize, FilePosition, T)>> 
+        where T: Decode + Send
+    {
+        let file_position = self.current_file_position().await?;
+        let Some(entry_header) = self.next_entry_header().await? else { return Ok(None) };
+        let file_position_at_start_of_data = self.current_file_position().await?;
+
+        // figuring out how much to decode
+        let column_offset = entry_header.offset_of_column(column);
+        self.seek_by(column_offset as i64).await?;
+
+        // reading and decoding
+        let mut bytes: Vec<u8> = vec![0; entry_header.data_sizes[column as usize]];
+        self.read_bytes(&mut bytes).await?;
+        let (value, _) =
+            decode::<T>(&bytes[..])
+                .map_err(|e| Error::DecodeError(DecodeErrorKind::EntryIsDeleted, e))?;
+
+        // jumping to next entry
+        self.seek_to(file_position_at_start_of_data).await?;
+        self.jump_from_start_of_entry_data_to_next_entry(&entry_header).await?;
+
+        Ok(Some((entry_header, file_position, value)))
+    }
+
+    async fn next_alive_at_column(&mut self, column: Column) -> Result<Option<(EntryHeaderWithDataSize, FilePosition, T)>> 
+        where T: Decode + Send
+    {
+        while let Some((header, file_position, t)) = self.next_at_column(column).await? {
+            if !header.is_deleted  {
+                return Ok(Some((header, file_position, t)))
+            }
+        }
+        Ok(None)
+    } 
+
+    async fn next_alive(&mut self) -> Result<Option<EntryDetailed<T>>> 
+        where T: Decode
+    {
+        while let Some(entry) = self.next().await? {
+            if !entry.header.is_deleted  {
+                return Ok(Some(entry))
+            }
+        }
+        Ok(None)
+    }
+
+    // ===Search===
+    async fn find_first_eq_bruteforce(&mut self, column: Column, t0: &T) -> Result<Option<EntryDetailed<T>>> 
+        where T: Decode + PartialEq + Send + Sync
+    {
+        let mut file_position = self.current_file_position().await?;
+        while let Some((_, _, t)) = self.next_alive_at_column(column).await? {
+            if &t == t0  {
+                // go back and decode the whole entry
+                self.seek_to(file_position).await?;
+                return self.next().await
+            } else {
+                file_position = self.current_file_position().await?;
+            }
+        }
+        Ok(None)
+    }
+
+    async fn find_all_eq_bruteforce(&mut self, column: Column, t0: &T) -> Result<Vec<EntryDetailed<T>>> 
+        where T: Decode + PartialEq + Send + Sync
+    {
+        let mut entries = vec![];
+        while let Some(entry) = self.find_first_eq_bruteforce(column, t0).await? {
+            entries.push(entry)
+        }
+        Ok(entries)
+    }
+
+    // ===Debugging===
+    async fn read_entries(&mut self) -> Result<()> 
+        where T: Decode + std::fmt::Debug
+    {
+        self.seek_to_start_of_data().await?;
+        while let Some(entry) = self.next().await? {
+            println!("{:?}", entry);
+        }
+        println!("END of entries.");
+        Ok(())
+    }
+
+    async fn read_all_bytes(&mut self) -> std::result::Result<Vec<u8>, std::io::Error> {
+        let mut bytes: Vec<u8> = vec![];
+        self.seek_to_start().await.map_err(|e| e.to_io_or_panic())?;
+        self.file().read_to_end(&mut bytes).await?;
+        Ok(bytes)
+    }
+}
+
+#[async_trait]
+pub trait CursorCanWriteHeader<T>: CursorCanReadHeader<T> + CursorCanWrite<T> {
+    fn header_mut(&mut self) -> &mut StoreHeader;
+    fn set_eof_file_position(&mut self, new_file_position: FilePosition);
+
+    // ===Store Header Manipulation===
+    async fn increment_total_count(&mut self) -> Result<()> 
+        where T: Send
+    {
+        self.seek_to_start().await?;
+        self.seek_to(StoreHeader::TOTAL_COUNT_OFFSET as u64).await?;
+        let new_count = self.header_mut().increment_total_count();
+        self.write_bytes(&encode::<usize>(&new_count)?).await?;
+        Ok(())
+    }
+
+    async fn increment_deleted_count(&mut self) -> Result<()> 
+        where T: Send
+    {
+        self.seek_to_start().await?;
+        self.seek_to(StoreHeader::DELETED_COUNT_OFFSET as u64).await?;
+        let new_count = self.header_mut().increment_deleted_count();
+        self.write_bytes(&encode::<usize>(&new_count)?).await?;
+        Ok(())
+    }
+
+    async fn set_header(&mut self, header: &StoreHeader) -> Result<()> 
+        where T: Send
+    {
+        self.seek_to_start().await?;
+        let encoded_header: Vec<u8> = header.encode()?;
+        self.write_bytes(&encoded_header).await?;
+
+        Ok(())
+    }
+
+    // ===Append Entry===
+
+    // Moves cursor to the end.
+    // Returns file position to the start of the new entry.
+    async fn append_entry_no_indexing(&mut self, entry: &Entry<T>) -> Result<FilePosition> 
+        where T: Encode + Send + Sync
+    {
+        self.increment_total_count().await?;
+
+        let encoded_entry: Vec<u8> = entry.encode()?;
+        let file_position = self.seek_to_end().await?;
+        self.write_bytes(&encoded_entry).await?;
+
+        let eof_file_position: FilePosition = self.current_file_position().await?;
+        self.set_eof_file_position(eof_file_position);
+
+        Ok(file_position)
+    }
+}