nimrodshn-btree 0.1.0

use crate::error::Error;
use crate::node_type::Offset;
use crate::page_layout::PTR_SIZE;
use std::convert::TryFrom;
use std::fs::{File, OpenOptions};
use std::io::{Read, Seek, SeekFrom, Write};
use std::path::PathBuf;

pub struct Wal {
    file: File,
}

impl Wal {
    pub fn new(parent_directoy: PathBuf) -> Result<Self, Error> {
        let fd = OpenOptions::new()
            .create(true)
            .read(true)
            .write(true)
            .truncate(true)
            .open(parent_directoy.join("wal"))?;

        Ok(Self { file: fd })
    }

    pub fn get_root(&mut self) -> Result<Offset, Error> {
        let mut buff: [u8; PTR_SIZE] = [0x00; PTR_SIZE];
        let file_len = self.file.seek(SeekFrom::End(0))? as usize;
        let mut root_offset: usize = 0;
        if file_len > 0 {
            root_offset = (file_len / PTR_SIZE - 1) * PTR_SIZE;
        }
        self.file.seek(SeekFrom::Start(root_offset as u64))?;
        self.file.read_exact(&mut buff)?;
        Offset::try_from(buff)
    }

    pub fn set_root(&mut self, offset: Offset) -> Result<(), Error> {
        self.file.seek(SeekFrom::End(0))?;
        self.file.write_all(&offset.0.to_be_bytes())?;
        Ok(())
    }
}