//! Extends the BufReader Lines to support summing based on newlines.
use std::io::BufRead;
use std::io::Lines;

pub struct Accumulator<B> {
    lines: Lines<B>,
    current: u32,
}

pub trait Elvish<B> {
    fn elf(self) -> Accumulator<B>;
}

impl<B> Elvish<B> for Lines<B> {
    fn elf(self) -> Accumulator<B> {
        Accumulator {
            lines: self,
            current: 0,
        }
    }
}

impl<B: BufRead> Iterator for Accumulator<B> {
    type Item = u32;

    fn next(&mut self) -> Option<Self::Item> {
        while let Some(Ok(line)) = self.lines.next() {
            let line = line.trim();
            if line.is_empty() {
                let result = self.current;
                self.current = 0;
                return Some(result);
            } else {
                self.current += line.parse::<u32>().unwrap();
            }
        }
        None
    }
}