use alloc::collections::VecDeque;
#[cfg(feature = "std")]
use std::io;

use super::Buf;

impl Buf for VecDeque<u8> {
    fn remaining(&self) -> usize {
        self.len()
    }

    fn chunk(&self) -> &[u8] {
        let (s1, s2) = self.as_slices();
        if s1.is_empty() {
            s2
        } else {
            s1
        }
    }

    #[cfg(feature = "std")]
    fn chunks_vectored<'a>(&'a self, dst: &mut [io::IoSlice<'a>]) -> usize {
        if self.is_empty() || dst.is_empty() {
            return 0;
        }

        let (s1, s2) = self.as_slices();
        dst[0] = io::IoSlice::new(s1);
        if s2.is_empty() || dst.len() == 1 {
            return 1;
        }

        dst[1] = io::IoSlice::new(s2);
        2
    }

    fn advance(&mut self, cnt: usize) {
        self.drain(..cnt);
    }
}