cranpose_ui/text/

measure.rs

use crate::text_layout_result::TextLayoutResult;
use std::cell::RefCell;

use super::layout_options::{TextLayoutOptions, TextOverflow};
use super::paragraph::{Hyphens, LineBreak};
use super::style::TextStyle;

const ELLIPSIS: &str = "\u{2026}";
const WRAP_EPSILON: f32 = 0.5;
const AUTO_HYPHEN_MIN_SEGMENT_CHARS: usize = 2;
const AUTO_HYPHEN_MIN_TRAILING_CHARS: usize = 3;
const AUTO_HYPHEN_PREFERRED_TRAILING_CHARS: usize = 4;

#[derive(Clone, Copy, Debug, PartialEq)]
pub struct TextMetrics {
    pub width: f32,
    pub height: f32,
    /// Height of a single line of text
    pub line_height: f32,
    /// Number of lines in the text
    pub line_count: usize,
}

#[derive(Clone, Debug, PartialEq)]
pub struct PreparedTextLayout {
    pub text: crate::text::AnnotatedString,
    pub metrics: TextMetrics,
    pub did_overflow: bool,
}

pub trait TextMeasurer: 'static {
    fn measure(&self, text: &crate::text::AnnotatedString, style: &TextStyle) -> TextMetrics;

    fn get_offset_for_position(
        &self,
        text: &crate::text::AnnotatedString,
        style: &TextStyle,
        x: f32,
        y: f32,
    ) -> usize;

    fn get_cursor_x_for_offset(
        &self,
        text: &crate::text::AnnotatedString,
        style: &TextStyle,
        offset: usize,
    ) -> f32;

    fn layout(&self, text: &crate::text::AnnotatedString, style: &TextStyle) -> TextLayoutResult;

    /// Returns an alternate break boundary for `Hyphens::Auto` when a greedy break
    /// split lands in the middle of a word.
    ///
    /// `segment_start_char` and `measured_break_char` are character-boundary indices
    /// in `line` (not byte offsets). Return `None` to delegate to fallback behavior.
    fn choose_auto_hyphen_break(
        &self,
        _line: &str,
        _style: &TextStyle,
        _segment_start_char: usize,
        _measured_break_char: usize,
    ) -> Option<usize> {
        None
    }

    fn measure_with_options(
        &self,
        text: &crate::text::AnnotatedString,
        style: &TextStyle,
        options: TextLayoutOptions,
        max_width: Option<f32>,
    ) -> TextMetrics {
        self.prepare_with_options(text, style, options, max_width)
            .metrics
    }

    fn prepare_with_options(
        &self,
        text: &crate::text::AnnotatedString,
        style: &TextStyle,
        options: TextLayoutOptions,
        max_width: Option<f32>,
    ) -> PreparedTextLayout {
        prepare_text_layout_fallback(self, text, style, options, max_width)
    }
}

#[derive(Default)]
struct MonospacedTextMeasurer;

impl MonospacedTextMeasurer {
    const DEFAULT_SIZE: f32 = 14.0;
    const CHAR_WIDTH_RATIO: f32 = 0.6; // Width is 0.6 of Height

    fn get_metrics(style: &TextStyle) -> (f32, f32) {
        let font_size = style.resolve_font_size(Self::DEFAULT_SIZE);
        let line_height = style.resolve_line_height(Self::DEFAULT_SIZE, font_size);
        let letter_spacing = style.resolve_letter_spacing(Self::DEFAULT_SIZE).max(0.0);
        (
            (font_size * Self::CHAR_WIDTH_RATIO) + letter_spacing,
            line_height,
        )
    }
}

impl TextMeasurer for MonospacedTextMeasurer {
    fn measure(&self, text: &crate::text::AnnotatedString, style: &TextStyle) -> TextMetrics {
        let (char_width, line_height) = Self::get_metrics(style);

        let lines: Vec<&str> = text.text.split('\n').collect();
        let line_count = lines.len().max(1);

        let width = lines
            .iter()
            .map(|line| line.chars().count() as f32 * char_width)
            .fold(0.0_f32, f32::max);

        TextMetrics {
            width,
            height: line_count as f32 * line_height,
            line_height,
            line_count,
        }
    }

    fn get_offset_for_position(
        &self,
        text: &crate::text::AnnotatedString,
        style: &TextStyle,
        x: f32,
        y: f32,
    ) -> usize {
        let (char_width, line_height) = Self::get_metrics(style);

        if text.text.is_empty() {
            return 0;
        }

        let line_index = (y / line_height).floor().max(0.0) as usize;
        let lines: Vec<&str> = text.text.split('\n').collect();
        let target_line = line_index.min(lines.len().saturating_sub(1));

        let mut line_start_byte = 0;
        for line in lines.iter().take(target_line) {
            line_start_byte += line.len() + 1;
        }

        let line_text = lines.get(target_line).unwrap_or(&"");
        let char_index = (x / char_width).round() as usize;
        let line_char_count = line_text.chars().count();
        let clamped_index = char_index.min(line_char_count);

        let offset_in_line = line_text
            .char_indices()
            .nth(clamped_index)
            .map(|(i, _)| i)
            .unwrap_or(line_text.len());

        line_start_byte + offset_in_line
    }

    fn get_cursor_x_for_offset(
        &self,
        text: &crate::text::AnnotatedString,
        style: &TextStyle,
        offset: usize,
    ) -> f32 {
        let (char_width, _) = Self::get_metrics(style);

        let clamped_offset = offset.min(text.text.len());
        let char_count = text.text[..clamped_offset].chars().count();
        char_count as f32 * char_width
    }

    fn layout(&self, text: &crate::text::AnnotatedString, style: &TextStyle) -> TextLayoutResult {
        let (char_width, line_height) = Self::get_metrics(style);
        TextLayoutResult::monospaced(&text.text, char_width, line_height)
    }
}

thread_local! {
    static TEXT_MEASURER: RefCell<Box<dyn TextMeasurer>> = RefCell::new(Box::new(MonospacedTextMeasurer));
}

pub fn set_text_measurer<M: TextMeasurer>(measurer: M) {
    TEXT_MEASURER.with(|m| {
        *m.borrow_mut() = Box::new(measurer);
    });
}

pub fn measure_text(text: &crate::text::AnnotatedString, style: &TextStyle) -> TextMetrics {
    TEXT_MEASURER.with(|m| m.borrow().measure(text, style))
}

pub fn measure_text_with_options(
    text: &crate::text::AnnotatedString,
    style: &TextStyle,
    options: TextLayoutOptions,
    max_width: Option<f32>,
) -> TextMetrics {
    TEXT_MEASURER.with(|m| {
        m.borrow()
            .measure_with_options(text, style, options.normalized(), max_width)
    })
}

pub fn prepare_text_layout(
    text: &crate::text::AnnotatedString,
    style: &TextStyle,
    options: TextLayoutOptions,
    max_width: Option<f32>,
) -> PreparedTextLayout {
    TEXT_MEASURER.with(|m| {
        m.borrow()
            .prepare_with_options(text, style, options.normalized(), max_width)
    })
}

pub fn get_offset_for_position(
    text: &crate::text::AnnotatedString,
    style: &TextStyle,
    x: f32,
    y: f32,
) -> usize {
    TEXT_MEASURER.with(|m| m.borrow().get_offset_for_position(text, style, x, y))
}

pub fn get_cursor_x_for_offset(
    text: &crate::text::AnnotatedString,
    style: &TextStyle,
    offset: usize,
) -> f32 {
    TEXT_MEASURER.with(|m| m.borrow().get_cursor_x_for_offset(text, style, offset))
}

pub fn layout_text(text: &crate::text::AnnotatedString, style: &TextStyle) -> TextLayoutResult {
    TEXT_MEASURER.with(|m| m.borrow().layout(text, style))
}

fn prepare_text_layout_fallback<M: TextMeasurer + ?Sized>(
    measurer: &M,
    text: &crate::text::AnnotatedString,
    style: &TextStyle,
    options: TextLayoutOptions,
    max_width: Option<f32>,
) -> PreparedTextLayout {
    let opts = options.normalized();
    let max_width = normalize_max_width(max_width);
    let wrap_width = (opts.soft_wrap && opts.overflow != TextOverflow::Visible)
        .then_some(max_width)
        .flatten();
    let line_break_mode = style
        .paragraph_style
        .line_break
        .take_or_else(|| LineBreak::Simple);
    let hyphens_mode = style.paragraph_style.hyphens.take_or_else(|| Hyphens::None);

    let mut lines = split_text_lines(text.text.as_str());
    let mut annotated_lines = split_annotated_lines(text);
    if let Some(width_limit) = wrap_width {
        let mut wrapped = Vec::with_capacity(lines.len());
        let mut wrapped_annotated = Vec::with_capacity(lines.len());
        for line in &annotated_lines {
            let wrapped_lines = wrap_line_to_width(
                measurer,
                line,
                style,
                width_limit,
                line_break_mode,
                hyphens_mode,
            );
            for wrapped_line in wrapped_lines {
                wrapped.push(wrapped_line.text.clone());
                wrapped_annotated.push(wrapped_line);
            }
        }
        lines = wrapped;
        annotated_lines = wrapped_annotated;
    }

    let mut did_overflow = false;
    let mut visible_lines = lines.clone();
    let mut visible_annotated_lines = annotated_lines.clone();

    if opts.overflow != TextOverflow::Visible && visible_lines.len() > opts.max_lines {
        did_overflow = true;
        visible_lines.truncate(opts.max_lines);
        visible_annotated_lines.truncate(opts.max_lines);
        if let Some(last_line) = visible_lines.last_mut() {
            *last_line =
                apply_line_overflow(measurer, last_line, style, max_width, opts, true, true);
            if let Some(last_annotated_line) = visible_annotated_lines.last_mut() {
                *last_annotated_line =
                    remap_annotated_for_display(last_annotated_line, last_line.as_str());
            }
        }
    }

    if let Some(width_limit) = max_width {
        let single_line_ellipsis = opts.max_lines == 1 || !opts.soft_wrap;
        let visible_len = visible_lines.len();
        for (line_index, line) in visible_lines.iter_mut().enumerate() {
            let width = visible_annotated_lines
                .get(line_index)
                .map(|annotated_line| measurer.measure(annotated_line, style).width)
                .unwrap_or_default();
            if width > width_limit + WRAP_EPSILON {
                if opts.overflow == TextOverflow::Visible {
                    continue;
                }
                did_overflow = true;
                *line = apply_line_overflow(
                    measurer,
                    line,
                    style,
                    Some(width_limit),
                    opts,
                    line_index + 1 == visible_len,
                    single_line_ellipsis,
                );
                if let Some(annotated_line) = visible_annotated_lines.get_mut(line_index) {
                    *annotated_line = remap_annotated_for_display(annotated_line, line.as_str());
                }
            }
        }
    }

    let display_annotated = join_annotated_lines(&visible_annotated_lines);
    debug_assert_eq!(display_annotated.text, visible_lines.join("\n"));
    let line_height = measurer.measure(text, style).line_height.max(0.0);
    let display_line_count = visible_lines.len().max(1);
    let layout_line_count = display_line_count.max(opts.min_lines);

    let measured_width = if visible_annotated_lines.is_empty() {
        0.0
    } else {
        visible_annotated_lines
            .iter()
            .map(|line| measurer.measure(line, style).width)
            .fold(0.0_f32, f32::max)
    };
    let width = if opts.overflow == TextOverflow::Visible {
        measured_width
    } else if let Some(width_limit) = max_width {
        measured_width.min(width_limit)
    } else {
        measured_width
    };

    PreparedTextLayout {
        text: display_annotated,
        metrics: TextMetrics {
            width,
            height: layout_line_count as f32 * line_height,
            line_height,
            line_count: layout_line_count,
        },
        did_overflow,
    }
}

fn split_text_lines(text: &str) -> Vec<String> {
    if text.is_empty() {
        return vec![String::new()];
    }
    text.split('\n').map(ToString::to_string).collect()
}

fn split_annotated_lines(text: &crate::text::AnnotatedString) -> Vec<crate::text::AnnotatedString> {
    if text.text.is_empty() {
        return vec![crate::text::AnnotatedString::from("")];
    }

    let mut out = Vec::new();
    let mut start = 0usize;
    for (idx, ch) in text.text.char_indices() {
        if ch == '\n' {
            out.push(text.subsequence(start..idx));
            start = idx + ch.len_utf8();
        }
    }
    out.push(text.subsequence(start..text.text.len()));
    out
}

fn join_annotated_lines(lines: &[crate::text::AnnotatedString]) -> crate::text::AnnotatedString {
    if lines.is_empty() {
        return crate::text::AnnotatedString::from("");
    }

    let mut text = String::new();
    let mut span_styles = Vec::new();
    let mut paragraph_styles = Vec::new();
    let mut offset = 0usize;

    for (idx, line) in lines.iter().enumerate() {
        text.push_str(line.text.as_str());
        for span in &line.span_styles {
            span_styles.push(crate::text::RangeStyle {
                item: span.item.clone(),
                range: (span.range.start + offset)..(span.range.end + offset),
            });
        }
        for span in &line.paragraph_styles {
            paragraph_styles.push(crate::text::RangeStyle {
                item: span.item.clone(),
                range: (span.range.start + offset)..(span.range.end + offset),
            });
        }

        offset += line.text.len();
        if idx + 1 < lines.len() {
            text.push('\n');
            offset += 1;
        }
    }

    crate::text::AnnotatedString {
        text,
        span_styles,
        paragraph_styles,
    }
}

fn trim_segment_end_whitespace(line: &str, start: usize, mut end: usize) -> usize {
    while end > start {
        let Some((idx, ch)) = line[start..end].char_indices().next_back() else {
            break;
        };
        if ch.is_whitespace() {
            end = start + idx;
        } else {
            break;
        }
    }
    end
}

fn remap_annotated_for_display(
    source: &crate::text::AnnotatedString,
    display_text: &str,
) -> crate::text::AnnotatedString {
    if source.text == display_text {
        return source.clone();
    }

    let display_chars = map_display_chars_to_source(source.text.as_str(), display_text);
    crate::text::AnnotatedString {
        text: display_text.to_string(),
        span_styles: remap_range_styles(&source.span_styles, &display_chars),
        paragraph_styles: remap_range_styles(&source.paragraph_styles, &display_chars),
    }
}

#[derive(Clone, Copy)]
struct DisplayCharMap {
    display_start: usize,
    display_end: usize,
    source_start: Option<usize>,
}

fn map_display_chars_to_source(source: &str, display: &str) -> Vec<DisplayCharMap> {
    let source_chars: Vec<(usize, char)> = source.char_indices().collect();
    let mut source_index = 0usize;
    let mut maps = Vec::with_capacity(display.chars().count());

    for (display_start, display_char) in display.char_indices() {
        let display_end = display_start + display_char.len_utf8();
        let mut source_start = None;
        while source_index < source_chars.len() {
            let (candidate_start, candidate_char) = source_chars[source_index];
            source_index += 1;
            if candidate_char == display_char {
                source_start = Some(candidate_start);
                break;
            }
        }
        maps.push(DisplayCharMap {
            display_start,
            display_end,
            source_start,
        });
    }

    maps
}

fn remap_range_styles<T: Clone>(
    styles: &[crate::text::RangeStyle<T>],
    display_chars: &[DisplayCharMap],
) -> Vec<crate::text::RangeStyle<T>> {
    let mut remapped = Vec::new();

    for style in styles {
        let mut range_start = None;
        let mut range_end = 0usize;

        for map in display_chars {
            let in_range = map.source_start.is_some_and(|source_start| {
                source_start >= style.range.start && source_start < style.range.end
            });

            if in_range {
                if range_start.is_none() {
                    range_start = Some(map.display_start);
                }
                range_end = map.display_end;
                continue;
            }

            if let Some(start) = range_start.take() {
                if start < range_end {
                    remapped.push(crate::text::RangeStyle {
                        item: style.item.clone(),
                        range: start..range_end,
                    });
                }
            }
        }

        if let Some(start) = range_start.take() {
            if start < range_end {
                remapped.push(crate::text::RangeStyle {
                    item: style.item.clone(),
                    range: start..range_end,
                });
            }
        }
    }

    remapped
}

fn normalize_max_width(max_width: Option<f32>) -> Option<f32> {
    match max_width {
        Some(width) if width.is_finite() && width > 0.0 => Some(width),
        _ => None,
    }
}

fn wrap_line_to_width<M: TextMeasurer + ?Sized>(
    measurer: &M,
    line: &crate::text::AnnotatedString,
    style: &TextStyle,
    max_width: f32,
    line_break: LineBreak,
    hyphens: Hyphens,
) -> Vec<crate::text::AnnotatedString> {
    if line.text.is_empty() {
        return vec![crate::text::AnnotatedString::from("")];
    }

    if matches!(line_break, LineBreak::Heading | LineBreak::Paragraph)
        && line.text.chars().any(char::is_whitespace)
    {
        if let Some(balanced) =
            wrap_line_with_word_balance(measurer, line, style, max_width, line_break)
        {
            return balanced;
        }
    }

    wrap_line_greedy(measurer, line, style, max_width, line_break, hyphens)
}

fn wrap_line_greedy<M: TextMeasurer + ?Sized>(
    measurer: &M,
    line: &crate::text::AnnotatedString,
    style: &TextStyle,
    max_width: f32,
    line_break: LineBreak,
    hyphens: Hyphens,
) -> Vec<crate::text::AnnotatedString> {
    let line_text = line.text.as_str();
    let boundaries = char_boundaries(line_text);
    let mut wrapped = Vec::new();
    let mut start_idx = 0usize;

    while start_idx < boundaries.len() - 1 {
        let mut low = start_idx + 1;
        let mut high = boundaries.len() - 1;
        let mut best = start_idx + 1;

        while low <= high {
            let mid = (low + high) / 2;
            let segment = line.subsequence(boundaries[start_idx]..boundaries[mid]);
            let width = measurer.measure(&segment, style).width;
            if width <= max_width + WRAP_EPSILON || mid == start_idx + 1 {
                best = mid;
                low = mid + 1;
            } else {
                if mid == 0 {
                    break;
                }
                high = mid - 1;
            }
        }

        let wrap_idx = choose_wrap_break(line_text, &boundaries, start_idx, best, line_break);
        let mut effective_wrap_idx = wrap_idx;
        let can_hyphenate = hyphens == Hyphens::Auto
            && wrap_idx == best
            && best < boundaries.len() - 1
            && is_break_inside_word(line_text, &boundaries, wrap_idx);
        if can_hyphenate {
            effective_wrap_idx = resolve_auto_hyphen_break(
                measurer,
                line_text,
                style,
                &boundaries,
                start_idx,
                wrap_idx,
            );
        }

        let segment_start = boundaries[start_idx];
        let mut segment_end = boundaries[effective_wrap_idx];
        if wrap_idx != best {
            segment_end = trim_segment_end_whitespace(line_text, segment_start, segment_end);
        }
        wrapped.push(line.subsequence(segment_start..segment_end));

        start_idx = if wrap_idx != best {
            skip_leading_whitespace(line_text, &boundaries, wrap_idx)
        } else {
            effective_wrap_idx
        };
    }

    if wrapped.is_empty() {
        wrapped.push(crate::text::AnnotatedString::from(""));
    }

    wrapped
}

fn wrap_line_with_word_balance<M: TextMeasurer + ?Sized>(
    measurer: &M,
    line: &crate::text::AnnotatedString,
    style: &TextStyle,
    max_width: f32,
    line_break: LineBreak,
) -> Option<Vec<crate::text::AnnotatedString>> {
    let line_text = line.text.as_str();
    let boundaries = char_boundaries(line_text);
    let breakpoints = collect_word_breakpoints(line_text, &boundaries);
    if breakpoints.len() <= 2 {
        return None;
    }

    let node_count = breakpoints.len();
    let mut best_cost = vec![f32::INFINITY; node_count];
    let mut next_index = vec![None; node_count];
    best_cost[node_count - 1] = 0.0;

    for start in (0..node_count - 1).rev() {
        for end in start + 1..node_count {
            let start_byte = boundaries[breakpoints[start]];
            let end_byte = boundaries[breakpoints[end]];
            let trimmed_end = trim_segment_end_whitespace(line_text, start_byte, end_byte);
            if trimmed_end <= start_byte {
                continue;
            }
            let segment = line.subsequence(start_byte..trimmed_end);
            let segment_width = measurer.measure(&segment, style).width;
            if segment_width > max_width + WRAP_EPSILON {
                continue;
            }
            if !best_cost[end].is_finite() {
                continue;
            }
            let slack = (max_width - segment_width).max(0.0);
            let is_last = end == node_count - 1;
            let segment_cost = match line_break {
                LineBreak::Heading => slack * slack,
                LineBreak::Paragraph => {
                    if is_last {
                        slack * slack * 0.16
                    } else {
                        slack * slack
                    }
                }
                LineBreak::Simple | LineBreak::Unspecified => slack * slack,
            };
            let candidate = segment_cost + best_cost[end];
            if candidate < best_cost[start] {
                best_cost[start] = candidate;
                next_index[start] = Some(end);
            }
        }
    }

    let mut wrapped = Vec::new();
    let mut current = 0usize;
    while current < node_count - 1 {
        let next = next_index[current]?;
        let start_byte = boundaries[breakpoints[current]];
        let end_byte = boundaries[breakpoints[next]];
        let trimmed_end = trim_segment_end_whitespace(line_text, start_byte, end_byte);
        if trimmed_end <= start_byte {
            return None;
        }
        wrapped.push(line.subsequence(start_byte..trimmed_end));
        current = next;
    }

    if wrapped.is_empty() {
        return None;
    }

    Some(wrapped)
}

fn collect_word_breakpoints(line: &str, boundaries: &[usize]) -> Vec<usize> {
    let mut points = vec![0usize];
    for idx in 1..boundaries.len() - 1 {
        let prev = &line[boundaries[idx - 1]..boundaries[idx]];
        let current = &line[boundaries[idx]..boundaries[idx + 1]];
        if prev.chars().all(char::is_whitespace) && !current.chars().all(char::is_whitespace) {
            points.push(idx);
        }
    }
    let end = boundaries.len() - 1;
    if points.last().copied() != Some(end) {
        points.push(end);
    }
    points
}

fn choose_wrap_break(
    line: &str,
    boundaries: &[usize],
    start_idx: usize,
    best: usize,
    _line_break: LineBreak,
) -> usize {
    if best >= boundaries.len() - 1 {
        return best;
    }

    if best <= start_idx + 1 {
        return best;
    }

    for idx in (start_idx + 1..best).rev() {
        let prev = &line[boundaries[idx - 1]..boundaries[idx]];
        if prev.chars().all(char::is_whitespace) {
            return idx;
        }
    }
    best
}

fn is_break_inside_word(line: &str, boundaries: &[usize], break_idx: usize) -> bool {
    if break_idx == 0 || break_idx >= boundaries.len() - 1 {
        return false;
    }
    let prev = &line[boundaries[break_idx - 1]..boundaries[break_idx]];
    let next = &line[boundaries[break_idx]..boundaries[break_idx + 1]];
    !prev.chars().all(char::is_whitespace) && !next.chars().all(char::is_whitespace)
}

fn resolve_auto_hyphen_break<M: TextMeasurer + ?Sized>(
    measurer: &M,
    line: &str,
    style: &TextStyle,
    boundaries: &[usize],
    start_idx: usize,
    break_idx: usize,
) -> usize {
    if let Some(candidate) = measurer.choose_auto_hyphen_break(line, style, start_idx, break_idx) {
        if is_valid_auto_hyphen_break(line, boundaries, start_idx, break_idx, candidate) {
            return candidate;
        }
    }
    choose_auto_hyphen_break_fallback(boundaries, start_idx, break_idx)
}

fn is_valid_auto_hyphen_break(
    line: &str,
    boundaries: &[usize],
    start_idx: usize,
    break_idx: usize,
    candidate_idx: usize,
) -> bool {
    let end_idx = boundaries.len().saturating_sub(1);
    candidate_idx > start_idx
        && candidate_idx < end_idx
        && candidate_idx <= break_idx
        && candidate_idx >= start_idx + AUTO_HYPHEN_MIN_SEGMENT_CHARS
        && is_break_inside_word(line, boundaries, candidate_idx)
}

fn choose_auto_hyphen_break_fallback(
    boundaries: &[usize],
    start_idx: usize,
    break_idx: usize,
) -> usize {
    let end_idx = boundaries.len().saturating_sub(1);
    if break_idx >= end_idx {
        return break_idx;
    }
    let trailing_len = end_idx.saturating_sub(break_idx);
    if trailing_len > 2 || break_idx <= start_idx + AUTO_HYPHEN_MIN_SEGMENT_CHARS {
        return break_idx;
    }

    let min_break = start_idx + AUTO_HYPHEN_MIN_SEGMENT_CHARS;
    let max_break = break_idx.saturating_sub(1);
    if min_break > max_break {
        return break_idx;
    }

    let mut best_break = break_idx;
    let mut best_penalty = usize::MAX;
    for idx in min_break..=max_break {
        let candidate_trailing_len = end_idx.saturating_sub(idx);
        let candidate_prefix_len = idx.saturating_sub(start_idx);
        if candidate_prefix_len < AUTO_HYPHEN_MIN_SEGMENT_CHARS
            || candidate_trailing_len < AUTO_HYPHEN_MIN_TRAILING_CHARS
        {
            continue;
        }

        let penalty = candidate_trailing_len.abs_diff(AUTO_HYPHEN_PREFERRED_TRAILING_CHARS);
        if penalty < best_penalty {
            best_penalty = penalty;
            best_break = idx;
            if penalty == 0 {
                break;
            }
        }
    }
    best_break
}

fn skip_leading_whitespace(line: &str, boundaries: &[usize], mut idx: usize) -> usize {
    while idx < boundaries.len() - 1 {
        let ch = &line[boundaries[idx]..boundaries[idx + 1]];
        if !ch.chars().all(char::is_whitespace) {
            break;
        }
        idx += 1;
    }
    idx
}

fn apply_line_overflow<M: TextMeasurer + ?Sized>(
    measurer: &M,
    line: &str,
    style: &TextStyle,
    max_width: Option<f32>,
    options: TextLayoutOptions,
    is_last_visible_line: bool,
    single_line_ellipsis: bool,
) -> String {
    if options.overflow == TextOverflow::Clip || !is_last_visible_line {
        return line.to_string();
    }

    let Some(width_limit) = max_width else {
        return match options.overflow {
            TextOverflow::Ellipsis => format!("{line}{ELLIPSIS}"),
            TextOverflow::StartEllipsis => format!("{ELLIPSIS}{line}"),
            TextOverflow::MiddleEllipsis => format!("{ELLIPSIS}{line}"),
            TextOverflow::Clip | TextOverflow::Visible => line.to_string(),
        };
    };

    match options.overflow {
        TextOverflow::Clip | TextOverflow::Visible => line.to_string(),
        TextOverflow::Ellipsis => fit_end_ellipsis(measurer, line, style, width_limit),
        TextOverflow::StartEllipsis => {
            if single_line_ellipsis {
                fit_start_ellipsis(measurer, line, style, width_limit)
            } else {
                line.to_string()
            }
        }
        TextOverflow::MiddleEllipsis => {
            if single_line_ellipsis {
                fit_middle_ellipsis(measurer, line, style, width_limit)
            } else {
                line.to_string()
            }
        }
    }
}

fn fit_end_ellipsis<M: TextMeasurer + ?Sized>(
    measurer: &M,
    line: &str,
    style: &TextStyle,
    max_width: f32,
) -> String {
    if measurer
        .measure(&crate::text::AnnotatedString::from(line), style)
        .width
        <= max_width + WRAP_EPSILON
    {
        return line.to_string();
    }

    let ellipsis_width = measurer
        .measure(&crate::text::AnnotatedString::from(ELLIPSIS), style)
        .width;
    if ellipsis_width > max_width + WRAP_EPSILON {
        return String::new();
    }

    let boundaries = char_boundaries(line);
    let mut low = 0usize;
    let mut high = boundaries.len() - 1;
    let mut best = 0usize;

    while low <= high {
        let mid = (low + high) / 2;
        let prefix = &line[..boundaries[mid]];
        let candidate = format!("{prefix}{ELLIPSIS}");
        let width = measurer
            .measure(
                &crate::text::AnnotatedString::from(candidate.as_str()),
                style,
            )
            .width;
        if width <= max_width + WRAP_EPSILON {
            best = mid;
            low = mid + 1;
        } else if mid == 0 {
            break;
        } else {
            high = mid - 1;
        }
    }

    format!("{}{}", &line[..boundaries[best]], ELLIPSIS)
}

fn fit_start_ellipsis<M: TextMeasurer + ?Sized>(
    measurer: &M,
    line: &str,
    style: &TextStyle,
    max_width: f32,
) -> String {
    if measurer
        .measure(&crate::text::AnnotatedString::from(line), style)
        .width
        <= max_width + WRAP_EPSILON
    {
        return line.to_string();
    }

    let ellipsis_width = measurer
        .measure(&crate::text::AnnotatedString::from(ELLIPSIS), style)
        .width;
    if ellipsis_width > max_width + WRAP_EPSILON {
        return String::new();
    }

    let boundaries = char_boundaries(line);
    let mut low = 0usize;
    let mut high = boundaries.len() - 1;
    let mut best = boundaries.len() - 1;

    while low <= high {
        let mid = (low + high) / 2;
        let suffix = &line[boundaries[mid]..];
        let candidate = format!("{ELLIPSIS}{suffix}");
        let width = measurer
            .measure(
                &crate::text::AnnotatedString::from(candidate.as_str()),
                style,
            )
            .width;
        if width <= max_width + WRAP_EPSILON {
            best = mid;
            if mid == 0 {
                break;
            }
            high = mid - 1;
        } else {
            low = mid + 1;
        }
    }

    format!("{ELLIPSIS}{}", &line[boundaries[best]..])
}

fn fit_middle_ellipsis<M: TextMeasurer + ?Sized>(
    measurer: &M,
    line: &str,
    style: &TextStyle,
    max_width: f32,
) -> String {
    if measurer
        .measure(&crate::text::AnnotatedString::from(line), style)
        .width
        <= max_width + WRAP_EPSILON
    {
        return line.to_string();
    }

    let ellipsis_width = measurer
        .measure(&crate::text::AnnotatedString::from(ELLIPSIS), style)
        .width;
    if ellipsis_width > max_width + WRAP_EPSILON {
        return String::new();
    }

    let boundaries = char_boundaries(line);
    let total_chars = boundaries.len().saturating_sub(1);
    for keep in (0..=total_chars).rev() {
        let keep_start = keep.div_ceil(2);
        let keep_end = keep / 2;
        let start = &line[..boundaries[keep_start]];
        let end_start = boundaries[total_chars.saturating_sub(keep_end)];
        let end = &line[end_start..];
        let candidate = format!("{start}{ELLIPSIS}{end}");
        if measurer
            .measure(
                &crate::text::AnnotatedString::from(candidate.as_str()),
                style,
            )
            .width
            <= max_width + WRAP_EPSILON
        {
            return candidate;
        }
    }

    ELLIPSIS.to_string()
}

fn char_boundaries(text: &str) -> Vec<usize> {
    let mut out = Vec::with_capacity(text.chars().count() + 1);
    out.push(0);
    for (idx, _) in text.char_indices() {
        if idx != 0 {
            out.push(idx);
        }
    }
    out.push(text.len());
    out
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::text::{Hyphens, LineBreak, ParagraphStyle, TextUnit};
    use crate::text_layout_result::TextLayoutResult;

    struct ContractBreakMeasurer {
        retreat: usize,
    }

    impl TextMeasurer for ContractBreakMeasurer {
        fn measure(&self, text: &crate::text::AnnotatedString, style: &TextStyle) -> TextMetrics {
            MonospacedTextMeasurer.measure(
                &crate::text::AnnotatedString::from(text.text.as_str()),
                style,
            )
        }

        fn get_offset_for_position(
            &self,
            text: &crate::text::AnnotatedString,
            style: &TextStyle,
            x: f32,
            y: f32,
        ) -> usize {
            MonospacedTextMeasurer.get_offset_for_position(
                &crate::text::AnnotatedString::from(text.text.as_str()),
                style,
                x,
                y,
            )
        }

        fn get_cursor_x_for_offset(
            &self,
            text: &crate::text::AnnotatedString,
            style: &TextStyle,
            offset: usize,
        ) -> f32 {
            MonospacedTextMeasurer.get_cursor_x_for_offset(
                &crate::text::AnnotatedString::from(text.text.as_str()),
                style,
                offset,
            )
        }

        fn layout(
            &self,
            text: &crate::text::AnnotatedString,
            style: &TextStyle,
        ) -> TextLayoutResult {
            MonospacedTextMeasurer.layout(
                &crate::text::AnnotatedString::from(text.text.as_str()),
                style,
            )
        }

        fn choose_auto_hyphen_break(
            &self,
            _line: &str,
            _style: &TextStyle,
            _segment_start_char: usize,
            measured_break_char: usize,
        ) -> Option<usize> {
            measured_break_char.checked_sub(self.retreat)
        }
    }

    fn style_with_line_break(line_break: LineBreak) -> TextStyle {
        TextStyle {
            span_style: crate::text::SpanStyle {
                font_size: TextUnit::Sp(10.0),
                ..Default::default()
            },
            paragraph_style: ParagraphStyle {
                line_break,
                ..Default::default()
            },
        }
    }

    fn style_with_hyphens(hyphens: Hyphens) -> TextStyle {
        TextStyle {
            span_style: crate::text::SpanStyle {
                font_size: TextUnit::Sp(10.0),
                ..Default::default()
            },
            paragraph_style: ParagraphStyle {
                hyphens,
                ..Default::default()
            },
        }
    }

    #[test]
    fn text_layout_options_wraps_and_limits_lines() {
        let style = TextStyle {
            span_style: crate::text::SpanStyle {
                font_size: TextUnit::Sp(10.0),
                ..Default::default()
            },
            ..Default::default()
        };
        let options = TextLayoutOptions {
            overflow: TextOverflow::Clip,
            soft_wrap: true,
            max_lines: 2,
            min_lines: 1,
        };

        let prepared = prepare_text_layout(
            &crate::text::AnnotatedString::from("A B C D E F"),
            &style,
            options,
            Some(24.0), // roughly 4 chars in monospaced fallback
        );

        assert!(prepared.did_overflow);
        assert!(prepared.metrics.line_count <= 2);
    }

    #[test]
    fn text_layout_options_end_ellipsis_applies() {
        let style = TextStyle {
            span_style: crate::text::SpanStyle {
                font_size: TextUnit::Sp(10.0),
                ..Default::default()
            },
            ..Default::default()
        };
        let options = TextLayoutOptions {
            overflow: TextOverflow::Ellipsis,
            soft_wrap: false,
            max_lines: 1,
            min_lines: 1,
        };

        let prepared = prepare_text_layout(
            &crate::text::AnnotatedString::from("Long long line"),
            &style,
            options,
            Some(20.0),
        );
        assert!(prepared.did_overflow);
        assert!(prepared.text.text.contains(ELLIPSIS));
    }

    #[test]
    fn text_layout_options_visible_keeps_full_text() {
        let style = TextStyle {
            span_style: crate::text::SpanStyle {
                font_size: TextUnit::Sp(10.0),
                ..Default::default()
            },
            ..Default::default()
        };
        let options = TextLayoutOptions {
            overflow: TextOverflow::Visible,
            soft_wrap: false,
            max_lines: 1,
            min_lines: 1,
        };

        let input = "This should remain unchanged";
        let prepared = prepare_text_layout(
            &crate::text::AnnotatedString::from(input),
            &style,
            options,
            Some(10.0),
        );
        assert_eq!(prepared.text.text, input);
    }

    #[test]
    fn text_layout_options_respects_min_lines() {
        let style = TextStyle {
            span_style: crate::text::SpanStyle {
                font_size: TextUnit::Sp(10.0),
                ..Default::default()
            },
            ..Default::default()
        };
        let options = TextLayoutOptions {
            overflow: TextOverflow::Clip,
            soft_wrap: true,
            max_lines: 4,
            min_lines: 3,
        };

        let prepared = prepare_text_layout(
            &crate::text::AnnotatedString::from("short"),
            &style,
            options,
            Some(100.0),
        );
        assert_eq!(prepared.metrics.line_count, 3);
    }

    #[test]
    fn text_layout_options_middle_ellipsis_for_single_line() {
        let style = TextStyle {
            span_style: crate::text::SpanStyle {
                font_size: TextUnit::Sp(10.0),
                ..Default::default()
            },
            ..Default::default()
        };
        let options = TextLayoutOptions {
            overflow: TextOverflow::MiddleEllipsis,
            soft_wrap: false,
            max_lines: 1,
            min_lines: 1,
        };

        let prepared = prepare_text_layout(
            &crate::text::AnnotatedString::from("abcdefghijk"),
            &style,
            options,
            Some(24.0),
        );
        assert!(prepared.text.text.contains(ELLIPSIS));
        assert!(prepared.did_overflow);
    }

    #[test]
    fn text_layout_options_does_not_wrap_on_tiny_width_delta() {
        let style = TextStyle {
            span_style: crate::text::SpanStyle {
                font_size: TextUnit::Sp(10.0),
                ..Default::default()
            },
            ..Default::default()
        };
        let options = TextLayoutOptions {
            overflow: TextOverflow::Clip,
            soft_wrap: true,
            max_lines: usize::MAX,
            min_lines: 1,
        };

        let text = "if counter % 2 == 0";
        let exact_width = measure_text(&crate::text::AnnotatedString::from(text), &style).width;
        let prepared = prepare_text_layout(
            &crate::text::AnnotatedString::from(text),
            &style,
            options,
            Some(exact_width - 0.1),
        );

        assert!(
            !prepared.text.text.contains('\n'),
            "unexpected line split: {:?}",
            prepared.text
        );
    }

    #[test]
    fn line_break_mode_changes_wrap_strategy_contract() {
        let text = "This is an example text";
        let options = TextLayoutOptions {
            overflow: TextOverflow::Clip,
            soft_wrap: true,
            max_lines: usize::MAX,
            min_lines: 1,
        };

        let simple = prepare_text_layout(
            &crate::text::AnnotatedString::from(text),
            &style_with_line_break(LineBreak::Simple),
            options,
            Some(120.0),
        );
        let heading = prepare_text_layout(
            &crate::text::AnnotatedString::from(text),
            &style_with_line_break(LineBreak::Heading),
            options,
            Some(120.0),
        );
        let paragraph = prepare_text_layout(
            &crate::text::AnnotatedString::from(text),
            &style_with_line_break(LineBreak::Paragraph),
            options,
            Some(50.0),
        );

        assert_eq!(
            simple.text.text.lines().collect::<Vec<_>>(),
            vec!["This is an example", "text"]
        );
        assert_eq!(
            heading.text.text.lines().collect::<Vec<_>>(),
            vec!["This is an", "example text"]
        );
        assert_eq!(
            paragraph.text.text.lines().collect::<Vec<_>>(),
            vec!["This", "is an", "example", "text"]
        );
    }

    #[test]
    fn hyphens_mode_changes_wrap_strategy_contract() {
        let text = "Transformation";
        let options = TextLayoutOptions {
            overflow: TextOverflow::Clip,
            soft_wrap: true,
            max_lines: usize::MAX,
            min_lines: 1,
        };

        let auto = prepare_text_layout(
            &crate::text::AnnotatedString::from(text),
            &style_with_hyphens(Hyphens::Auto),
            options,
            Some(24.0),
        );
        let none = prepare_text_layout(
            &crate::text::AnnotatedString::from(text),
            &style_with_hyphens(Hyphens::None),
            options,
            Some(24.0),
        );

        assert_eq!(
            auto.text.text.lines().collect::<Vec<_>>(),
            vec!["Tran", "sfor", "ma", "tion"]
        );
        assert_eq!(
            none.text.text.lines().collect::<Vec<_>>(),
            vec!["Tran", "sfor", "mati", "on"]
        );
        assert!(
            !auto.text.text.contains('-'),
            "automatic hyphenation should influence breaks without mutating source text content"
        );
    }

    #[test]
    fn hyphens_auto_uses_measurer_hyphen_contract_when_valid() {
        let text = "Transformation";
        let style = style_with_hyphens(Hyphens::Auto);
        let options = TextLayoutOptions {
            overflow: TextOverflow::Clip,
            soft_wrap: true,
            max_lines: usize::MAX,
            min_lines: 1,
        };

        let prepared = prepare_text_layout_fallback(
            &ContractBreakMeasurer { retreat: 1 },
            &crate::text::AnnotatedString::from(text),
            &style,
            options,
            Some(24.0),
        );

        assert_eq!(
            prepared.text.text.lines().collect::<Vec<_>>(),
            vec!["Tra", "nsf", "orm", "ati", "on"]
        );
    }

    #[test]
    fn hyphens_auto_falls_back_when_measurer_hyphen_contract_is_invalid() {
        let text = "Transformation";
        let style = style_with_hyphens(Hyphens::Auto);
        let options = TextLayoutOptions {
            overflow: TextOverflow::Clip,
            soft_wrap: true,
            max_lines: usize::MAX,
            min_lines: 1,
        };

        let prepared = prepare_text_layout_fallback(
            &ContractBreakMeasurer { retreat: 10 },
            &crate::text::AnnotatedString::from(text),
            &style,
            options,
            Some(24.0),
        );

        assert_eq!(
            prepared.text.text.lines().collect::<Vec<_>>(),
            vec!["Tran", "sfor", "ma", "tion"]
        );
    }

    #[test]
    fn transformed_text_keeps_span_ranges_within_display_bounds() {
        let style = TextStyle {
            span_style: crate::text::SpanStyle {
                font_size: TextUnit::Sp(10.0),
                ..Default::default()
            },
            ..Default::default()
        };
        let options = TextLayoutOptions {
            overflow: TextOverflow::Ellipsis,
            soft_wrap: false,
            max_lines: 1,
            min_lines: 1,
        };
        let annotated = crate::text::AnnotatedString::builder()
            .push_style(crate::text::SpanStyle {
                font_weight: Some(crate::text::FontWeight::BOLD),
                ..Default::default()
            })
            .append("Styled overflow text sample")
            .pop()
            .to_annotated_string();

        let prepared = prepare_text_layout(&annotated, &style, options, Some(40.0));
        assert!(prepared.did_overflow);
        for span in &prepared.text.span_styles {
            assert!(span.range.start < span.range.end);
            assert!(span.range.end <= prepared.text.text.len());
            assert!(prepared.text.text.is_char_boundary(span.range.start));
            assert!(prepared.text.text.is_char_boundary(span.range.end));
        }
    }

    #[test]
    fn wrapped_text_splits_styles_around_inserted_newlines() {
        let style = TextStyle {
            span_style: crate::text::SpanStyle {
                font_size: TextUnit::Sp(10.0),
                ..Default::default()
            },
            ..Default::default()
        };
        let options = TextLayoutOptions {
            overflow: TextOverflow::Clip,
            soft_wrap: true,
            max_lines: usize::MAX,
            min_lines: 1,
        };
        let annotated = crate::text::AnnotatedString::builder()
            .push_style(crate::text::SpanStyle {
                text_decoration: Some(crate::text::TextDecoration::UNDERLINE),
                ..Default::default()
            })
            .append("Wrapped style text example")
            .pop()
            .to_annotated_string();

        let prepared = prepare_text_layout(&annotated, &style, options, Some(32.0));
        assert!(prepared.text.text.contains('\n'));
        assert!(!prepared.text.span_styles.is_empty());
        for span in &prepared.text.span_styles {
            assert!(span.range.end <= prepared.text.text.len());
        }
    }

    #[test]
    fn mixed_font_size_segments_wrap_without_truncation() {
        let style = TextStyle {
            span_style: crate::text::SpanStyle {
                font_size: TextUnit::Sp(14.0),
                ..Default::default()
            },
            ..Default::default()
        };
        let options = TextLayoutOptions {
            overflow: TextOverflow::Clip,
            soft_wrap: true,
            max_lines: usize::MAX,
            min_lines: 1,
        };
        let annotated = crate::text::AnnotatedString::builder()
            .append("You can also ")
            .push_style(crate::text::SpanStyle {
                font_size: TextUnit::Sp(22.0),
                ..Default::default()
            })
            .append("change font size")
            .pop()
            .append(" dynamically mid-sentence!")
            .to_annotated_string();

        let prepared = prepare_text_layout(&annotated, &style, options, Some(260.0));
        assert!(prepared.text.text.contains('\n'));
        assert!(prepared.text.text.contains("mid-sentence!"));
        assert!(!prepared.did_overflow);
    }
}