use std::io;

pub struct LineColIterator<I> {
    iter: I,

    /// Index of the current line. Characters in the first line of the input
    /// (before the first newline character) are in line 1.
    line: usize,

    /// Index of the current column. The first character in the input and any
    /// characters immediately following a newline character are in column 1.
    /// The column is 0 immediately after a newline character has been read.
    col: usize,

    /// Byte offset of the start of the current line. This is the sum of lenghts
    /// of all previous lines. Keeping track of things this way allows efficient
    /// computation of the current line, column, and byte offset while only
    /// updating one of the counters in `next()` in the common case.
    start_of_line: usize,
}

impl<I> LineColIterator<I>
where
    I: Iterator<Item = io::Result<u8>>,
{
    pub fn new(iter: I) -> LineColIterator<I> {
        LineColIterator {
            iter: iter,
            line: 1,
            col: 0,
            start_of_line: 0,
        }
    }

    pub fn line(&self) -> usize {
        self.line
    }

    pub fn col(&self) -> usize {
        self.col
    }

    pub fn byte_offset(&self) -> usize {
        self.start_of_line + self.col
    }
}

impl<I> Iterator for LineColIterator<I>
where
    I: Iterator<Item = io::Result<u8>>,
{
    type Item = io::Result<u8>;

    fn next(&mut self) -> Option<io::Result<u8>> {
        match self.iter.next() {
            None => None,
            Some(Ok(b'\n')) => {
                self.start_of_line += self.col + 1;
                self.line += 1;
                self.col = 0;
                Some(Ok(b'\n'))
            }
            Some(Ok(c)) => {
                self.col += 1;
                Some(Ok(c))
            }
            Some(Err(e)) => Some(Err(e)),
        }
    }
}
