ic-host-text 0.31.2

//! Pure clipping to a caller-selected terminal column allowance.
use unicode_width::UnicodeWidthChar;

use crate::escape::escaped_chars;

// One scalar-column policy for clipping, tables and progress erasure.
pub(crate) fn scalar_width(character: char) -> usize {
    character.width().unwrap_or(0)
}

pub(crate) fn display_width(text: &str) -> usize {
    text.chars().map(scalar_width).sum()
}

/// Escape controls and fit one line within `columns`, adding `…` when clipped.
///
/// Zero columns return an empty string. Width is the sum of Unicode scalar
/// widths, conservatively counting joined emoji separately. Clipping preserves
/// UTF-8 boundaries, but does not promise grapheme-cluster boundaries. This is
/// display text, not an identity-preserving encoding or an ANSI parser.
/// Escaping stops once clipping is established; no complete escaped copy is built.
/// Callers own input byte limits, terminal dimensions, output and redraw policy.
#[must_use]
pub fn fit_line(line: &str, columns: usize) -> String {
    if columns == 0 {
        return String::new();
    }
    let mut width = 0;
    let mut text = String::new();
    let mut clip_at = None;
    for ch in escaped_chars(line) {
        let next = scalar_width(ch);
        let remaining = columns - width;
        if next > remaining {
            text.truncate(clip_at.unwrap_or(text.len()));
            text.push('…');
            return text;
        }
        if next == remaining && clip_at.is_none() {
            // Reserve the same prefix as clipping with one column for the ellipsis.
            // Keep it only if a later character proves that clipping is necessary.
            clip_at = Some(text.len());
        }
        text.push(ch);
        width += next;
    }
    text
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn exact_width_and_small_allowances() {
        for (text, columns, expected) in [
            ("", 0, ""),
            ("", usize::MAX, ""),
            ("abc", 0, ""),
            ("abc", 1, "…"),
            ("abc", 2, "a…"),
            ("abc", 3, "abc"),
            ("abc", usize::MAX, "abc"),
            ("界界", 3, "界…"),
            ("e\u{301}x", 2, "e\u{301}x"),
            ("a\u{301}", 1, "a\u{301}"),
            ("a\u{301}x", 1, "…"),
            ("\u{301}界", 1, "\u{301}…"),
            ("界\u{301}", 2, "界\u{301}"),
            ("界\u{301}x", 2, "…"),
            ("a\u{200d}b", 2, "a\u{200d}b"),
            ("a\u{200d}bc", 2, "a\u{200d}…"),
            ("\u{202e}", 8, "\\u{202e}"),
            ("\u{202e}", 7, "\\u{202…"),
        ] {
            assert_eq!(fit_line(text, columns), expected);
        }
    }

    #[test]
    fn controls_are_visible_before_width_admission() {
        assert_eq!(fit_line("a\nb", 4), "a\\nb");
        assert_eq!(fit_line("a\nb", 3), "a\\…");
        assert_eq!(fit_line("\x1b[31m", 40), "\\u{1b}[31m");
    }

    #[test]
    fn unicode_output_obeys_each_selected_allowance() {
        for input in ["界界界", "e\u{301}e\u{301}xx", "👩‍💻 ready", "\n\t\u{202e}"] {
            for columns in 0..32 {
                let fitted = fit_line(input, columns);
                assert!(
                    fitted
                        .chars()
                        .map(|ch| ch.width().unwrap_or(0))
                        .sum::<usize>()
                        <= columns
                );
                assert!(!fitted.chars().any(char::is_control));
            }
        }
    }
}