//! Buffer structures to enable decoding strings without allocating.
use std::str;

/// UTF-8 encoding buffer over an u8-slice.
pub struct Utf8Buffer<'r> {
    buf: &'r mut [u8],
    idx: usize
}

impl<'r> Utf8Buffer<'r> {
    pub fn new(b: &'r mut [u8]) -> Utf8Buffer<'r> {
        Utf8Buffer { buf: b, idx: 0 }
    }

    pub fn reset(&mut self) {
        self.idx = 0
    }

    pub fn as_str(&self) -> &str {
        unsafe { str::from_utf8_unchecked(&self.buf[0 .. self.idx]) }
    }

    pub fn is_full(&self) -> bool {
        self.idx >= self.buf.len()
    }

    pub fn push(&mut self, c: char) {
        let len = c.len_utf8();
        if self.idx + len > self.buf.len() {
            return ()
        }
        self.idx += c.encode_utf8(&mut self.buf[self.idx ..]).len()
    }
}

pub trait Buffer {
    fn push(&mut self, c: char);
    fn is_full(&self) -> bool;
}

impl Buffer for String {
    fn push(&mut self, c: char) { self.push(c) }
    fn is_full(&self) -> bool   { false }
}

impl<'r> Buffer for Utf8Buffer<'r> {
    fn push(&mut self, c: char) { self.push(c)   }
    fn is_full(&self) -> bool   { self.is_full() }
}