//! niri's fill/clear/continue row. Repaints never consume a sample twice.
use unicode_segmentation::UnicodeSegmentation;
use unicode_width::UnicodeWidthStr;
#[derive(Default)]
pub struct CodeLine {
    source: String,
    width: usize,
    line: String,
}
impl CodeLine {
    pub fn advance(&mut self, code: &str, width: usize) -> &str {
        let continued = self.width == width && code.starts_with(&self.source);
        let start = if continued {
            self.source.len()
        } else {
            self.line.clear();
            0
        };
        for grapheme in code[start..].graphemes(true) {
            let safe: String = grapheme
                .chars()
                .map(|c| if c.is_control() { ' ' } else { c })
                .collect();
            if self.line.width() + safe.width() > width {
                self.line.clear();
            }
            if safe.width() <= width {
                self.line.push_str(&safe);
            }
        }
        self.source.clear();
        self.source.push_str(code);
        self.width = width;
        &self.line
    }
}
#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn fill_clear_continue_repaint_resize_and_correction() {
        let mut row = CodeLine::default();
        assert_eq!(row.advance("abcdef", 5), "f");
        assert_eq!(row.advance("abcdef", 5), "f");
        assert_eq!(row.advance("abcdef\ng", 5), "f g");
        assert_eq!(row.advance("abcdef\ng", 4), "ef g");
        assert_eq!(row.advance("界界é", 4), "é");
        assert_eq!(row.advance("x", 0), "");
    }
}