use std::{io, path::PathBuf};
use file_mmap::FileMmap;
const U32_SIZE: usize = std::mem::size_of::<u32>();
pub struct RowFragment {
filemmap: FileMmap,
}
impl RowFragment {
pub fn new(path: PathBuf) -> io::Result<Self> {
let mut filemmap = FileMmap::new(path)?;
if filemmap.len()? == 0 {
filemmap.set_len(U32_SIZE as u64)?;
}
Ok(Self { filemmap })
}
fn blank_count(&self) -> u64 {
self.filemmap.len().unwrap() / U32_SIZE as u64 - 1
}
pub fn insert_blank(&mut self, row: u32) -> io::Result<u64> {
self.filemmap.append(&row.to_ne_bytes())
}
pub fn pop(&mut self) -> io::Result<Option<u32>> {
let count = self.blank_count();
Ok(if count > 0 {
let last = unsafe { *(self.filemmap.as_ptr() as *mut u32).offset(count as isize) };
self.filemmap.set_len(count * U32_SIZE as u64)?;
Some(last)
} else {
None
})
}
pub fn serial_increment(&mut self) -> u32 {
let blank_list = unsafe { &mut *(self.filemmap.as_ptr() as *mut u32) };
*blank_list += 1;
*blank_list
}
}