//! Terminal-cell-safe plain-text fitting shared by HUD and terminal chrome.

use unicode_width::UnicodeWidthChar;

/// Sanitize controls and fit plain text to exactly `width` terminal cells.
///
/// C0 controls and DEL become spaces. Characters that would cross the cell
/// boundary are omitted without splitting UTF-8. Zero-width characters are
/// retained only after a visible base character, preventing detached leading
/// combining marks. This is scalar-width fitting, not full grapheme shaping.
#[must_use]
pub fn fit_terminal_cells(value: &str, width: usize) -> String {
    let mut output = String::new();
    let mut cells = 0usize;
    let mut has_base = false;

    for mut character in value.chars() {
        if character <= '\u{1f}' || character == '\u{7f}' {
            character = ' ';
        }
        let character_width = UnicodeWidthChar::width(character).unwrap_or(0);
        if character_width == 0 {
            if has_base {
                output.push(character);
            }
            continue;
        }
        if cells.saturating_add(character_width) > width {
            break;
        }
        output.push(character);
        cells += character_width;
        has_base = true;
    }
    while cells < width {
        output.push(' ');
        cells += 1;
    }
    output
}

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

    #[test]
    fn fits_ascii_controls_wide_and_combining_scalars() {
        assert_eq!(fit_terminal_cells("lamp\u{1b}[31m", 8), "lamp [31");
        assert_eq!(fit_terminal_cells("深淵灯", 2), "深");
        assert_eq!(fit_terminal_cells("深淵灯", 5), "深淵 ");
        assert_eq!(fit_terminal_cells("e\u{301}lan", 3), "e\u{301}la");
        assert_eq!(fit_terminal_cells("\u{301}a", 1), "a");
        assert_eq!(fit_terminal_cells("ignored", 0), "");
        for value in ["plain", "深淵灯", "e\u{301}lan", "\u{301}a"] {
            for width in 0..8 {
                let fitted = fit_terminal_cells(value, width);
                assert_eq!(UnicodeWidthStr::width(fitted.as_str()), width);
            }
        }
    }
}