use crate::lib::fmt::{self, Write};

use crate::lib::str;

pub(super) struct Buf<'a> {

    bytes: &'a mut [u8],

    offset: usize,

}

impl<'a> Buf<'a> {

    pub fn new(bytes: &'a mut [u8]) -> Self {

        Buf { bytes, offset: 0 }

    }

    pub fn as_str(&self) -> &str {

        let slice = &self.bytes[..self.offset];

        unsafe { str::from_utf8_unchecked(slice) }

    }

}

impl<'a> Write for Buf<'a> {

    fn write_str(&mut self, s: &str) -> fmt::Result {

        if self.offset + s.len() > self.bytes.len() {

            Err(fmt::Error)

        } else {

            self.bytes[self.offset..self.offset + s.len()].copy_from_slice(s.as_bytes());

            self.offset += s.len();

            Ok(())

        }

    }

}