slint/internal/core/textlayout/linebreak_simple.rs

// Copyright © SixtyFPS GmbH <info@slint-ui.com>
// SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-commercial

#[derive(Copy, Clone)]
pub enum BreakOpportunity {
    Allowed,
    Mandatory,
}

pub struct LineBreakIterator<'a> {
    it: core::str::CharIndices<'a>,
    last_ch: Option<char>,
}

impl<'a> LineBreakIterator<'a> {
    pub fn new(text: &'a str) -> Self {
        Self { it: text.char_indices(), last_ch: None }
    }
}

impl<'a> Iterator for LineBreakIterator<'a> {
    type Item = (usize, BreakOpportunity);

    fn next(&mut self) -> Option<Self::Item> {
        while let Some((byte_offset, char)) = self.it.next() {
            let maybe_opportunity = match char {
                '\u{2028}' | '\u{2029}' => Some(BreakOpportunity::Mandatory), // unicode line- and paragraph separators
                '\n' => Some(BreakOpportunity::Mandatory),                    // ascii line break
                _ if self.last_ch.map_or(false, |c| c.is_ascii_whitespace()) => {
                    Some(BreakOpportunity::Allowed)
                }
                _ => None,
            };
            self.last_ch = Some(char);

            if let Some(opportunity) = maybe_opportunity {
                return Some((byte_offset, opportunity));
            }
        }

        None
    }
}