//! Renderer-oriented scene snapshot types.

use std::ops::{Deref, Range};
use std::sync::Arc;

use cosmic_text::CacheKey;
use tracing::debug;

use crate::ImageResource;
use crate::text::TextSelectionStyle;
use crate::trace_targets;
use crate::tree::{BoxShadowKind, ElementId};

pub type SceneVersion = u64;

#[derive(Clone, Copy, Debug, PartialEq)]
pub struct Point {
    pub x: f32,
    pub y: f32,
}

impl Point {
    pub const fn new(x: f32, y: f32) -> Self {
        Self { x, y }
    }
}

#[derive(Clone, Copy, Debug, PartialEq)]
pub struct UiSize {
    pub width: f32,
    pub height: f32,
}

impl UiSize {
    pub const fn new(width: f32, height: f32) -> Self {
        Self { width, height }
    }
}

#[derive(Clone, Copy, Debug, PartialEq)]
pub struct Rect {
    pub origin: Point,
    pub size: UiSize,
}

impl Rect {
    pub const fn new(x: f32, y: f32, width: f32, height: f32) -> Self {
        Self {
            origin: Point::new(x, y),
            size: UiSize::new(width, height),
        }
    }

    pub fn contains(self, point: Point) -> bool {
        point.x >= self.origin.x
            && point.y >= self.origin.y
            && point.x < self.origin.x + self.size.width
            && point.y < self.origin.y + self.size.height
    }

    pub fn intersects(self, other: Rect) -> bool {
        self.origin.x < other.origin.x + other.size.width
            && self.origin.x + self.size.width > other.origin.x
            && self.origin.y < other.origin.y + other.size.height
            && self.origin.y + self.size.height > other.origin.y
    }
}

#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
pub struct Color {
    pub r: u8,
    pub g: u8,
    pub b: u8,
    pub a: u8,
}

impl Color {
    /// Sentinel value meaning "use the PreparedText default_color at render time".
    /// Fully transparent black (a == 0) is never a useful visible color, so it is
    /// safe to reserve as a sentinel.  No user-facing API sets this value directly.
    pub const SENTINEL: Self = Self::rgba(0, 0, 0, 0);

    pub const fn rgba(r: u8, g: u8, b: u8, a: u8) -> Self {
        Self { r, g, b, a }
    }

    pub const fn rgb(r: u8, g: u8, b: u8) -> Self {
        Self::rgba(r, g, b, 255)
    }

    /// Returns `true` when this color is the sentinel "use default" marker.
    #[inline]
    pub const fn is_sentinel(self) -> bool {
        self.a == 0
    }
}

#[derive(Clone, Copy, Debug, PartialEq)]
pub struct Translation {
    pub x: f32,
    pub y: f32,
}

impl Translation {
    pub const fn new(x: f32, y: f32) -> Self {
        Self { x, y }
    }
}

#[derive(Clone, Copy, Debug, PartialEq)]
pub struct Quad {
    pub rect: Rect,
    pub color: Color,
}

impl Quad {
    pub const fn new(rect: Rect, color: Color) -> Self {
        Self { rect, color }
    }
}

#[derive(Clone, Copy, Debug, PartialEq)]
pub struct RoundedRect {
    pub rect: Rect,
    pub fill: Option<Color>,
    pub border_color: Option<Color>,
    pub border_width: f32,
    pub radius: f32,
}

#[derive(Clone, Copy, Debug, PartialEq)]
pub struct ShadowRect {
    pub rect: Rect,
    pub source_rect: Rect,
    pub color: Color,
    pub blur: f32,
    pub radius: f32,
    pub source_radius: f32,
    pub kind: BoxShadowKind,
}

#[derive(Clone, Copy, Debug, PartialEq)]
pub struct ClipRegion {
    pub rect: Rect,
    pub radius: f32,
}

#[derive(Clone, Debug, PartialEq)]
pub struct GlyphInstance {
    pub position: Point,
    pub advance: f32,
    /// Glyph color.  When equal to `Color::SENTINEL` the renderer uses the
    /// enclosing `PreparedText::default_color`.  This allows the text layout
    /// cache to be color-independent: the same shaped data can be reused for
    /// the same text displayed in different colors.
    pub color: Color,
    pub cache_key: Option<CacheKey>,
    pub text_start: usize,
    pub text_end: usize,
}

#[derive(Clone, Debug, PartialEq)]
pub struct PreparedTextLine {
    pub rect: Rect,
    pub text_start: usize,
    pub text_end: usize,
    pub glyph_start: usize,
    pub glyph_end: usize,
}

/// Shaped, positioned text ready for rendering.
///
/// Glyphs and line rects are stored in **local (origin-relative) coordinates**:
/// add `self.origin` to convert to absolute window coords.  This keeps the
/// `Arc<TextLayoutData>` from the text shape cache shareable across different
/// on-screen positions — no per-frame translation is required.
///
/// The `lines` and `glyphs` are stored behind an `Arc` so that cloning a
/// `PreparedText` (e.g. to put the same shaped text into both the scene
/// snapshot and the interaction tree) is O(1).  The `Arc` is shared as long
/// as no mutation is needed; `apply_selected_text_color` uses
/// `Arc::make_mut` and clones on first write.
///
/// Glyph colors may be `Color::SENTINEL` — the renderer substitutes
/// `default_color` for those glyphs.
#[derive(Clone, Debug, PartialEq)]
pub struct PreparedText {
    pub element_id: Option<ElementId>,
    pub text: String,
    pub origin: Point,
    pub bounds: Option<UiSize>,
    pub font_size: f32,
    pub line_height: f32,
    /// Default color applied to sentinel-colored glyphs at render time.
    pub default_color: Color,
    pub selectable: bool,
    pub selection_style: TextSelectionStyle,
    layout: Arc<TextLayoutData>,
}

/// Shaped glyph and line data shared between scene and interaction-tree copies
/// of the same `PreparedText`.  Coordinates are LOCAL (relative to `PreparedText::origin`).
/// Add `origin` to convert to absolute window coords.
#[derive(Clone, Debug, PartialEq)]
pub struct TextLayoutData {
    pub lines: Vec<PreparedTextLine>,
    pub glyphs: Vec<GlyphInstance>,
    /// Measured (unclamped) size of the laid-out text.
    pub size: UiSize,
}

impl Deref for PreparedText {
    type Target = TextLayoutData;

    fn deref(&self) -> &TextLayoutData {
        &self.layout
    }
}

impl PreparedText {
    /// Construct a `PreparedText` from shaped data.  Called by `TextSystem::prepare_spans`.
    pub(crate) fn from_layout(
        element_id: Option<ElementId>,
        text: String,
        origin: Point,
        bounds: Option<UiSize>,
        font_size: f32,
        line_height: f32,
        default_color: Color,
        selectable: bool,
        selection_style: TextSelectionStyle,
        layout: Arc<TextLayoutData>,
    ) -> Self {
        Self {
            element_id,
            text,
            origin,
            bounds,
            font_size,
            line_height,
            default_color,
            selectable,
            selection_style,
            layout,
        }
    }

    /// Returns a raw pointer to the underlying `TextLayoutData` allocation.
    /// Used in tests to verify Arc sharing between PreparedTexts.
    #[cfg(test)]
    pub(crate) fn layout_ptr(&self) -> *const TextLayoutData {
        Arc::as_ptr(&self.layout)
    }

    /// Create a monospace `PreparedText` without going through the text system.
    /// Used for testing and low-level terminal-style rendering.
    pub fn monospace(
        text: impl Into<String>,
        origin: Point,
        font_size: f32,
        advance: f32,
        color: Color,
    ) -> Self {
        let text = text.into();
        // Glyphs are stored in LOCAL (origin-relative) coordinates.
        let mut local_x = 0.0f32;
        let mut glyphs = Vec::with_capacity(text.chars().count());
        for (text_start, ch) in text.char_indices() {
            let text_end = text_start + ch.len_utf8();
            // monospace() builds glyphs directly; use the actual color (not sentinel)
            // because this path does not go through the text cache.
            glyphs.push(GlyphInstance {
                position: Point::new(local_x, 0.0),
                advance,
                color,
                cache_key: None,
                text_start,
                text_end,
            });
            local_x += advance;
        }
        let line = PreparedTextLine {
            rect: Rect::new(0.0, 0.0, local_x, font_size),
            text_start: 0,
            text_end: glyphs.last().map_or(0, |glyph| glyph.text_end),
            glyph_start: 0,
            glyph_end: glyphs.len(),
        };
        let size = UiSize::new(local_x, font_size);
        Self {
            element_id: None,
            text,
            origin,
            bounds: None,
            font_size,
            line_height: font_size,
            default_color: color,
            selectable: true,
            selection_style: TextSelectionStyle::DEFAULT,
            layout: Arc::new(TextLayoutData {
                lines: vec![line],
                glyphs,
                size,
            }),
        }
    }

    /// Translate this text by `offset`.  O(1): only `self.origin` is updated.
    /// Glyphs are stored in local coords and are unaffected.
    pub fn translated(mut self, offset: Point) -> Self {
        self.origin.x += offset.x;
        self.origin.y += offset.y;
        self
    }

    /// Return the byte offset within `self.text` for an absolute window-space point.
    pub fn byte_offset_for_position(&self, point: Point) -> usize {
        // Convert to local coords before delegating to the local-space helpers.
        let local_x = point.x - self.origin.x;
        let local_y = point.y - self.origin.y;
        let Some(line) = self.line_for_position(local_y) else {
            return 0;
        };
        self.byte_offset_for_line_position(line, local_x)
    }

    pub fn selection_range(&self, start: usize, end: usize) -> Range<usize> {
        let start = start.min(self.text.len());
        let end = end.min(self.text.len());
        if start <= end { start..end } else { end..start }
    }

    pub fn selected_text(&self, start: usize, end: usize) -> Option<&str> {
        let range = self.selection_range(start, end);
        self.text.get(range)
    }

    pub fn selection_rects(&self, start: usize, end: usize) -> Vec<Rect> {
        let range = self.selection_range(start, end);
        if range.is_empty() {
            return Vec::new();
        }

        let mut rects = Vec::new();
        for line in &self.lines {
            let mut left = None::<f32>;
            let mut right = None::<f32>;
            for glyph in &self.glyphs[line.glyph_start..line.glyph_end] {
                if glyph.text_end <= range.start || glyph.text_start >= range.end {
                    continue;
                }
                let glyph_left = glyph.position.x;
                let glyph_right = glyph.position.x + glyph.advance.max(0.0);
                left = Some(left.map_or(glyph_left, |current| current.min(glyph_left)));
                right = Some(right.map_or(glyph_right, |current| current.max(glyph_right)));
            }

            if let (Some(left), Some(right)) = (left, right) {
                // Glyph x/y and line rect are in local coords; add origin for absolute result.
                rects.push(Rect::new(
                    self.origin.x + left,
                    self.origin.y + line.rect.origin.y,
                    (right - left).max(0.0),
                    line.rect.size.height,
                ));
            }
        }
        rects
    }

    pub fn caret_rect(&self, offset: usize, width: f32) -> Option<Rect> {
        let width = width.max(0.0);
        let line = self.line_for_offset(offset)?;
        // caret_x_for_line_offset returns local x; add origin for absolute result.
        let local_x = self.caret_x_for_line_offset(line, offset);
        Some(Rect::new(
            self.origin.x + local_x,
            self.origin.y + line.rect.origin.y,
            width,
            line.rect.size.height,
        ))
    }

    pub fn previous_char_boundary(&self, offset: usize) -> usize {
        let offset = offset.min(self.text.len());
        self.text[..offset]
            .char_indices()
            .last()
            .map(|(index, _)| index)
            .unwrap_or(0)
    }

    pub fn next_char_boundary(&self, offset: usize) -> usize {
        let offset = offset.min(self.text.len());
        if offset >= self.text.len() {
            return self.text.len();
        }
        self.text
            .char_indices()
            .find_map(|(index, _)| (index > offset).then_some(index))
            .unwrap_or(self.text.len())
    }

    pub fn line_start_offset(&self, offset: usize) -> Option<usize> {
        Some(self.line_for_offset(offset)?.text_start)
    }

    pub fn line_end_offset(&self, offset: usize) -> Option<usize> {
        Some(self.line_for_offset(offset)?.text_end)
    }

    pub fn vertical_offset(&self, offset: usize, line_delta: isize) -> Option<usize> {
        if line_delta == 0 {
            return Some(offset.min(self.text.len()));
        }
        let offset = offset.min(self.text.len());
        let line = self.line_for_offset(offset)?;
        let current_index = self.lines.iter().position(|candidate| candidate == line)?;
        let next_index = current_index.checked_add_signed(line_delta)?;
        let next_line = self.lines.get(next_index)?;
        let target_x = self.caret_x_for_line_offset(line, offset);
        Some(self.byte_offset_for_line_position(next_line, target_x))
    }

    pub fn word_range_for_offset(&self, offset: usize) -> Range<usize> {
        if self.text.is_empty() {
            return 0..0;
        }
        let offset = offset.min(self.text.len());
        let target = self.word_class_offset(offset);
        let Some((target_start, target_ch)) = self.char_at(target) else {
            return 0..self.text.len();
        };
        let target_class = classify_word_char(target_ch);

        let mut start = target_start;
        while let Some((previous_start, previous_ch)) = self.char_before(start) {
            if classify_word_char(previous_ch) != target_class {
                break;
            }
            start = previous_start;
        }

        let mut end = target_start + target_ch.len_utf8();
        while let Some((next_start, next_ch)) = self.char_at(end) {
            if classify_word_char(next_ch) != target_class {
                break;
            }
            end = next_start + next_ch.len_utf8();
        }

        start..end
    }

    /// Apply `selection_style.text_color` to glyphs in `[start, end)`.
    /// Clones the inner `Arc<TextLayoutData>` on first call if it is shared.
    pub fn apply_selected_text_color(&mut self, start: usize, end: usize) {
        let Some(selected_color) = self.selection_style.text_color else {
            return;
        };
        let range = self.selection_range(start, end);
        if range.is_empty() {
            return;
        }
        for glyph in Arc::make_mut(&mut self.layout).glyphs.iter_mut() {
            if glyph.text_end > range.start && glyph.text_start < range.end {
                glyph.color = selected_color;
            }
        }
    }

    fn line_for_position(&self, y: f32) -> Option<&PreparedTextLine> {
        let mut lines = self.lines.iter();
        let first = lines.next()?;
        if y < first.rect.origin.y {
            return Some(first);
        }

        let mut last = first;
        for line in std::iter::once(first).chain(lines) {
            last = line;
            if y < line.rect.origin.y + line.rect.size.height {
                return Some(line);
            }
        }
        Some(last)
    }

    fn line_for_offset(&self, offset: usize) -> Option<&PreparedTextLine> {
        let offset = offset.min(self.text.len());
        let mut lines = self.lines.iter();
        let first = lines.next()?;
        for line in std::iter::once(first).chain(lines) {
            if offset <= line.text_end {
                return Some(line);
            }
        }
        Some(self.lines.last().unwrap_or(first))
    }

    fn byte_offset_for_line_position(&self, line: &PreparedTextLine, x: f32) -> usize {
        if line.glyph_start == line.glyph_end {
            return line.text_start;
        }

        let line_glyphs = &self.glyphs[line.glyph_start..line.glyph_end];
        let first_glyph = &line_glyphs[0];
        if x <= first_glyph.position.x {
            return first_glyph.text_start;
        }

        for glyph in line_glyphs {
            let glyph_left = glyph.position.x;
            let glyph_right = glyph.position.x + glyph.advance.max(0.0);
            let midpoint = glyph_left + glyph.advance.max(0.0) * 0.5;
            if x < midpoint {
                return glyph.text_start;
            }
            if x < glyph_right {
                return glyph.text_end;
            }
        }

        line.text_end
    }

    fn caret_x_for_line_offset(&self, line: &PreparedTextLine, offset: usize) -> f32 {
        if line.glyph_start == line.glyph_end {
            return line.rect.origin.x;
        }

        let offset = offset.min(self.text.len());
        let line_glyphs = &self.glyphs[line.glyph_start..line.glyph_end];
        let first_glyph = &line_glyphs[0];
        if offset <= first_glyph.text_start {
            return first_glyph.position.x;
        }

        for glyph in line_glyphs {
            if offset <= glyph.text_start {
                return glyph.position.x;
            }
            if offset <= glyph.text_end {
                return glyph.position.x + glyph.advance.max(0.0);
            }
        }

        line_glyphs
            .last()
            .map(|glyph| glyph.position.x + glyph.advance.max(0.0))
            .unwrap_or(line.rect.origin.x)
    }

    fn char_at(&self, offset: usize) -> Option<(usize, char)> {
        if offset >= self.text.len() {
            return None;
        }
        self.text[offset..].chars().next().map(|ch| (offset, ch))
    }

    fn char_before(&self, offset: usize) -> Option<(usize, char)> {
        let offset = offset.min(self.text.len());
        self.text[..offset].char_indices().last()
    }

    fn word_class_offset(&self, offset: usize) -> usize {
        if offset >= self.text.len() {
            return self.previous_char_boundary(offset);
        }
        if offset > 0
            && let (Some((_, previous)), Some((_, current))) =
                (self.char_before(offset), self.char_at(offset))
            && classify_word_char(current) == WordClass::Whitespace
            && classify_word_char(previous) == WordClass::Word
        {
            return self.previous_char_boundary(offset);
        }
        offset
    }
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
enum WordClass {
    Word,
    Whitespace,
    Punctuation,
}

fn classify_word_char(ch: char) -> WordClass {
    if ch.is_whitespace() {
        WordClass::Whitespace
    } else if ch.is_alphanumeric() || ch == '_' {
        WordClass::Word
    } else {
        WordClass::Punctuation
    }
}

#[derive(Clone, Debug, PartialEq)]
pub struct PreparedImage {
    pub element_id: Option<ElementId>,
    pub resource: ImageResource,
    pub rect: Rect,
    pub uv_rect: (f32, f32, f32, f32),
}

#[derive(Clone, Debug, PartialEq)]
pub enum DisplayItem {
    Quad(Quad),
    RoundedRect(RoundedRect),
    ShadowRect(ShadowRect),
    Image(PreparedImage),
    Text(PreparedText),
    PushClip(ClipRegion),
    PopClip,
    PushTransform(Translation),
    PopTransform,
    LayerBegin { opacity: f32 },
    LayerEnd,
}

impl DisplayItem {
    /// Return a copy of this item with all positions shifted by `offset`.
    pub fn translated(&self, offset: Point) -> Self {
        fn translate_rect(r: Rect, o: Point) -> Rect {
            Rect::new(r.origin.x + o.x, r.origin.y + o.y, r.size.width, r.size.height)
        }
        match self {
            Self::Quad(q) => Self::Quad(Quad { rect: translate_rect(q.rect, offset), ..*q }),
            Self::RoundedRect(r) => Self::RoundedRect(RoundedRect {
                rect: translate_rect(r.rect, offset),
                ..*r
            }),
            Self::ShadowRect(s) => Self::ShadowRect(ShadowRect {
                rect: translate_rect(s.rect, offset),
                source_rect: translate_rect(s.source_rect, offset),
                ..*s
            }),
            Self::Image(img) => Self::Image(PreparedImage {
                rect: translate_rect(img.rect, offset),
                ..img.clone()
            }),
            Self::Text(text) => Self::Text(text.clone().translated(offset)),
            Self::PushClip(clip) => Self::PushClip(ClipRegion {
                rect: translate_rect(clip.rect, offset),
                ..*clip
            }),
            // These items carry no position data or are balanced markers.
            Self::PopClip => Self::PopClip,
            Self::PushTransform(t) => Self::PushTransform(*t),
            Self::PopTransform => Self::PopTransform,
            Self::LayerBegin { opacity } => Self::LayerBegin { opacity: *opacity },
            Self::LayerEnd => Self::LayerEnd,
        }
    }
}

#[derive(Clone, Debug, PartialEq)]
pub struct SceneSnapshot {
    pub version: SceneVersion,
    pub logical_size: UiSize,
    pub items: Vec<DisplayItem>,
}

impl SceneSnapshot {
    pub fn new(version: SceneVersion, logical_size: UiSize) -> Self {
        debug!(
            target: trace_targets::SCENE,
            event = "create_scene",
            version,
            width = logical_size.width,
            height = logical_size.height,
            "creating scene snapshot"
        );
        Self {
            version,
            logical_size,
            items: Vec::new(),
        }
    }

    pub fn item_count(&self) -> usize {
        self.items.len()
    }

    pub fn push_item(&mut self, item: DisplayItem) -> &mut Self {
        self.items.push(item);
        self
    }

    pub fn push_quad(&mut self, rect: Rect, color: Color) -> &mut Self {
        self.push_item(DisplayItem::Quad(Quad::new(rect, color)))
    }

    pub fn push_rounded_rect(&mut self, rounded_rect: RoundedRect) -> &mut Self {
        self.push_item(DisplayItem::RoundedRect(rounded_rect))
    }

    pub fn push_shadow_rect(&mut self, shadow_rect: ShadowRect) -> &mut Self {
        self.push_item(DisplayItem::ShadowRect(shadow_rect))
    }

    pub fn push_text(&mut self, text: PreparedText) -> &mut Self {
        self.push_item(DisplayItem::Text(text))
    }

    pub fn push_image(&mut self, image: PreparedImage) -> &mut Self {
        self.push_item(DisplayItem::Image(image))
    }

    pub fn push_clip(&mut self, rect: Rect, radius: f32) -> &mut Self {
        self.push_item(DisplayItem::PushClip(ClipRegion { rect, radius }))
    }

    pub fn pop_clip(&mut self) -> &mut Self {
        self.push_item(DisplayItem::PopClip)
    }

    pub fn push_transform(&mut self, translation: Translation) -> &mut Self {
        self.push_item(DisplayItem::PushTransform(translation))
    }

    pub fn pop_transform(&mut self) -> &mut Self {
        self.push_item(DisplayItem::PopTransform)
    }

    pub fn begin_layer(&mut self, opacity: f32) -> &mut Self {
        self.push_item(DisplayItem::LayerBegin { opacity })
    }

    pub fn end_layer(&mut self) -> &mut Self {
        self.push_item(DisplayItem::LayerEnd)
    }
}

// ---------------------------------------------------------------------------
// Hash implementations for f32-containing types.

impl std::hash::Hash for Point {
    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
        self.x.to_bits().hash(state);
        self.y.to_bits().hash(state);
    }
}

impl std::hash::Hash for UiSize {
    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
        self.width.to_bits().hash(state);
        self.height.to_bits().hash(state);
    }
}

#[cfg(test)]
mod tests {
    use super::{Color, Point, PreparedText, Rect};
    use crate::TextSelectionStyle;
    use crate::{TextStyle, TextSystem, TextWrap};

    #[test]
    fn prepared_text_hit_testing_clamps_to_nearest_cluster_boundary() {
        let text = PreparedText::monospace(
            "abcd",
            Point::new(10.0, 20.0),
            16.0,
            8.0,
            Color::rgb(0xFF, 0xFF, 0xFF),
        );

        assert_eq!(text.byte_offset_for_position(Point::new(6.0, 24.0)), 0);
        assert_eq!(text.byte_offset_for_position(Point::new(13.0, 24.0)), 0);
        assert_eq!(text.byte_offset_for_position(Point::new(17.0, 24.0)), 1);
        assert_eq!(text.byte_offset_for_position(Point::new(33.0, 24.0)), 3);
        assert_eq!(text.byte_offset_for_position(Point::new(50.0, 24.0)), 4);
    }

    #[test]
    fn prepared_text_selection_rects_cover_selected_glyphs() {
        let mut text = PreparedText::monospace(
            "abcd",
            Point::new(10.0, 20.0),
            16.0,
            8.0,
            Color::rgb(0xFF, 0xFF, 0xFF),
        );
        text.selection_style = TextSelectionStyle::new(Color::rgba(0x44, 0x66, 0xFF, 0xAA))
            .with_text_color(Color::rgb(0x11, 0x12, 0x1A));

        assert_eq!(
            text.selection_rects(1, 3),
            vec![Rect::new(18.0, 20.0, 16.0, 16.0)]
        );
        assert_eq!(text.selected_text(1, 3), Some("bc"));
        text.apply_selected_text_color(1, 3);
        assert_eq!(text.glyphs[0].color, Color::rgb(0xFF, 0xFF, 0xFF));
        assert_eq!(text.glyphs[1].color, Color::rgb(0x11, 0x12, 0x1A));
        assert_eq!(text.glyphs[2].color, Color::rgb(0x11, 0x12, 0x1A));
    }

    #[test]
    fn prepared_text_caret_rect_tracks_cluster_boundaries() {
        let text = PreparedText::monospace(
            "abcd",
            Point::new(10.0, 20.0),
            16.0,
            8.0,
            Color::rgb(0xFF, 0xFF, 0xFF),
        );

        assert_eq!(
            text.caret_rect(0, 2.0),
            Some(Rect::new(10.0, 20.0, 2.0, 16.0))
        );
        assert_eq!(
            text.caret_rect(2, 2.0),
            Some(Rect::new(26.0, 20.0, 2.0, 16.0))
        );
        assert_eq!(
            text.caret_rect(4, 2.0),
            Some(Rect::new(42.0, 20.0, 2.0, 16.0))
        );
    }

    #[test]
    fn prepared_text_word_range_tracks_words_and_punctuation() {
        let text = PreparedText::monospace(
            "alpha beta, gamma",
            Point::new(10.0, 20.0),
            16.0,
            8.0,
            Color::rgb(0xFF, 0xFF, 0xFF),
        );

        assert_eq!(text.word_range_for_offset(1), 0..5);
        assert_eq!(text.word_range_for_offset(6), 6..10);
        assert_eq!(text.word_range_for_offset(10), 10..11);
        assert_eq!(text.word_range_for_offset(text.text.len()), 12..17);
    }

    #[test]
    fn prepared_text_vertical_offset_moves_between_lines() {
        use std::sync::Arc;
        use super::{PreparedTextLine, TextLayoutData};

        let mut text = PreparedText::monospace(
            "abcdwxyz",
            Point::new(10.0, 20.0),
            16.0,
            8.0,
            Color::rgb(0xFF, 0xFF, 0xFF),
        );
        // Lines and glyphs use LOCAL (origin-relative) coordinates.
        let lines = vec![
            PreparedTextLine {
                rect: Rect::new(0.0, 0.0, 32.0, 16.0),
                text_start: 0,
                text_end: 4,
                glyph_start: 0,
                glyph_end: 4,
            },
            PreparedTextLine {
                rect: Rect::new(0.0, 16.0, 32.0, 16.0),
                text_start: 4,
                text_end: 8,
                glyph_start: 4,
                glyph_end: 8,
            },
        ];
        let mut glyphs = text.glyphs.to_vec();
        for (index, glyph) in glyphs.iter_mut().enumerate() {
            if index >= 4 {
                glyph.position.y = 16.0;
                glyph.position.x = (index - 4) as f32 * 8.0;
            }
        }
        let orig_size = text.layout.size;
        text.layout = Arc::new(TextLayoutData { lines, glyphs, size: orig_size });

        assert_eq!(text.vertical_offset(2, 1), Some(6));
        assert_eq!(text.vertical_offset(6, -1), Some(2));
        assert_eq!(text.line_start_offset(6), Some(4));
        assert_eq!(text.line_end_offset(2), Some(4));
    }

    #[test]
    fn prepared_text_multiline_selection_stays_on_target_line() {
        let mut text_system = TextSystem::new();
        let style = TextStyle::new(16.0, Color::rgb(0xFF, 0xFF, 0xFF)).with_wrap(TextWrap::None);
        let text = text_system.prepare("ab\ncd\nef", Point::new(10.0, 20.0), &style);

        assert_eq!(text.lines.len(), 3);

        let target_line = &text.lines[1];
        // Lines store LOCAL coords; add text.origin to get absolute window coords for the query.
        let y = text.origin.y + target_line.rect.origin.y + target_line.rect.size.height * 0.5;
        let start = text.byte_offset_for_position(Point::new(text.origin.x + target_line.rect.origin.x, y));
        let end = text.byte_offset_for_position(Point::new(text.origin.x + target_line.rect.origin.x + 16.0, y));
        let rects = text.selection_rects(start, end);

        assert_eq!(rects.len(), 1);
        // selection_rects returns absolute coords; compare against absolute line y.
        assert_eq!(rects[0].origin.y, text.origin.y + target_line.rect.origin.y);
    }
}