// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.

use kurbo::{ParamCurveArclen, ParamCurve, ParamCurveDeriv};
use unicode_vo::Orientation as CharOrientation;
use unicode_script::UnicodeScript;
use ttf_parser::GlyphId;

use crate::{CubicBezExt, FuzzyZero, IsValidLength, PathData, PathSegment, Transform, converter};
use super::convert::{ByteIndex, CharacterPosition, TextAnchor, TextChunk, TextFlow, TextPath, WritingMode};
use super::fontdb_ext::{self, DatabaseExt};


/// A glyph.
///
/// Basically, a glyph ID and it's metrics.
#[derive(Clone)]
struct Glyph {
    /// The glyph ID in the font.
    id: GlyphId,

    /// Position in bytes in the original string.
    ///
    /// We use it to match a glyph with a character in the text chunk and therefore with the style.
    byte_idx: ByteIndex,

    /// The glyph offset in font units.
    dx: i32,

    /// The glyph offset in font units.
    dy: i32,

    /// The glyph width / X-advance in font units.
    width: i32,

    /// Reference to the source font.
    ///
    /// Each glyph can have it's own source font.
    font: fontdb_ext::Font,
}

impl Glyph {
    fn is_missing(&self) -> bool {
        self.id.0 == 0
    }
}

/// An outlined cluster.
///
/// Cluster/grapheme is a single, unbroken, renderable character.
/// It can be positioned, rotated, spaced, etc.
///
/// Let's say we have `й` which is *CYRILLIC SMALL LETTER I* and *COMBINING BREVE*.
/// It consists of two code points, will be shaped (via harfbuzz) as two glyphs into one cluster,
/// and then will be combined into the one `OutlinedCluster`.
#[derive(Clone)]
pub struct OutlinedCluster {
    /// Position in bytes in the original string.
    ///
    /// We use it to match a cluster with a character in the text chunk and therefore with the style.
    pub byte_idx: ByteIndex,

    /// Cluster's original codepoint.
    ///
    /// Technically, a cluster can contain multiple codepoints,
    /// but we are storing only the first one.
    pub codepoint: char,

    /// Cluster's width.
    ///
    /// It's different from advance in that it's not affected by letter spacing and word spacing.
    pub width: f64,

    /// An advance along the X axis.
    ///
    /// Can be negative.
    pub advance: f64,

    /// An ascent in SVG coordinates.
    pub ascent: f64,

    /// A descent in SVG coordinates.
    pub descent: f64,

    /// A x-height in SVG coordinates.
    pub x_height: f64,

    /// Indicates that this cluster was affected by the relative shift (via dx/dy attributes)
    /// during the text layouting. Which breaks the `text-decoration` line.
    ///
    /// Used during the `text-decoration` processing.
    pub has_relative_shift: bool,

    /// An actual outline.
    pub path: PathData,

    /// A cluster's transform that contains it's position, rotation, etc.
    pub transform: Transform,

    /// Not all clusters should be rendered.
    ///
    /// For example, if a cluster is outside the text path than it should not be rendered.
    pub visible: bool,
}

impl OutlinedCluster {
    pub fn height(&self) -> f64 {
        self.ascent - self.descent
    }
}


/// An iterator over glyph clusters.
///
/// Input:  0 2 2 2 3 4 4 5 5
/// Result: 0 1     4 5   7
struct GlyphClusters<'a> {
    data: &'a [Glyph],
    idx: usize,
}

impl<'a> GlyphClusters<'a> {
    fn new(data: &'a [Glyph]) -> Self {
        GlyphClusters { data, idx: 0 }
    }
}

impl<'a> Iterator for GlyphClusters<'a> {
    type Item = (std::ops::Range<usize>, ByteIndex);

    fn next(&mut self) -> Option<Self::Item> {
        if self.idx == self.data.len() {
            return None;
        }

        let start = self.idx;
        let cluster = self.data[self.idx].byte_idx;
        for g in &self.data[self.idx..] {
            if g.byte_idx != cluster {
                break;
            }

            self.idx += 1;
        }

        Some((start..self.idx, cluster))
    }
}


/// Converts a text chunk into a list of outlined clusters.
///
/// This function will do the BIDI reordering, text shaping and glyphs outlining,
/// but not the text layouting. So all clusters are in the 0x0 position.
pub fn outline_chunk(
    chunk: &TextChunk,
    state: &converter::State,
) -> Vec<OutlinedCluster> {
    let mut glyphs = Vec::new();
    for span in &chunk.spans {
        let tmp_glyphs = shape_text(&chunk.text, span.font, span.small_caps, state);

        // Do nothing with the first run.
        if glyphs.is_empty() {
            glyphs = tmp_glyphs;
            continue;
        }

        // We assume, that shaping with an any font will produce the same amount of glyphs.
        // Otherwise an error.
        if glyphs.len() != tmp_glyphs.len() {
            log::warn!("Text layouting failed.");
            return Vec::new();
        }

        // Copy span's glyphs.
        for (i, glyph) in tmp_glyphs.iter().enumerate() {
            if span.contains(glyph.byte_idx) {
                glyphs[i] = glyph.clone();
            }
        }
    }

    // Convert glyphs to clusters.
    let mut clusters = Vec::new();
    for (range, byte_idx) in GlyphClusters::new(&glyphs) {
        if let Some(span) = chunk.span_at(byte_idx) {
            let db = &state.opt.fontdb;
            clusters.push(outline_cluster(&glyphs[range], &chunk.text, span.font_size, db));
        }
    }

    clusters
}

/// Text shaping with font fallback.
fn shape_text(
    text: &str,
    font: fontdb_ext::Font,
    small_caps: bool,
    state: &converter::State,
) -> Vec<Glyph> {
    let mut glyphs = shape_text_with_font(text, font, small_caps, state).unwrap_or_default();

    // Remember all fonts used for shaping.
    let mut used_fonts = vec![font.id];

    // Loop until all glyphs become resolved or until no more fonts are left.
    'outer: loop {
        let mut missing = None;
        for glyph in &glyphs {
            if glyph.is_missing() {
                missing = Some(glyph.byte_idx.char_from(text));
                break;
            }
        }

        if let Some(c) = missing {
            let fallback_font = match find_font_for_char(c, &used_fonts, state) {
                Some(v) => v,
                None => break 'outer,
            };

            // Shape again, using a new font.
            let fallback_glyphs = shape_text_with_font(text, fallback_font, small_caps, state)
                .unwrap_or_default();

            let all_matched = fallback_glyphs.iter().all(|g| !g.is_missing());
            if all_matched {
                // Replace all glyphs when all of them were matched.
                glyphs = fallback_glyphs;
                break 'outer;
            }

            // We assume, that shaping with an any font will produce the same amount of glyphs.
            // This is incorrect, but good enough for now.
            if glyphs.len() != fallback_glyphs.len() {
                break 'outer;
            }

            // TODO: Replace clusters and not glyphs. This should be more accurate.

            // Copy new glyphs.
            for i in 0..glyphs.len() {
                if glyphs[i].is_missing() && !fallback_glyphs[i].is_missing() {
                    glyphs[i] = fallback_glyphs[i].clone();
                }
            }

            // Remember this font.
            used_fonts.push(fallback_font.id);
        } else {
            break 'outer;
        }
    }

    // Warn about missing glyphs.
    for glyph in &glyphs {
        if glyph.is_missing() {
            let c = glyph.byte_idx.char_from(text);
            // TODO: print a full grapheme
            log::warn!("No fonts with a {}/U+{:X} character were found.", c, c as u32);
        }
    }

    glyphs
}

/// Converts a text into a list of glyph IDs.
///
/// This function will do the BIDI reordering and text shaping.
fn shape_text_with_font(
    text: &str,
    font: fontdb_ext::Font,
    small_caps: bool,
    state: &converter::State,
) -> Option<Vec<Glyph>> {
    state.opt.fontdb.with_face_data(font.id, |font_data, face_index| -> Option<Vec<Glyph>> {
        let rb_font = rustybuzz::Face::from_slice(font_data, face_index)?;

        let bidi_info = unicode_bidi::BidiInfo::new(text, Some(unicode_bidi::Level::ltr()));
        let paragraph = &bidi_info.paragraphs[0];
        let line = paragraph.range.clone();

        let mut glyphs = Vec::new();

        let (levels, runs) = bidi_info.visual_runs(paragraph, line);
        for run in runs.iter() {
            let sub_text = &text[run.clone()];
            if sub_text.is_empty() {
                continue;
            }

            let hb_direction = if levels[run.start].is_rtl() {
                rustybuzz::Direction::RightToLeft
            } else {
                rustybuzz::Direction::LeftToRight
            };

            let mut buffer = rustybuzz::UnicodeBuffer::new();
            buffer.push_str(sub_text);
            buffer.set_direction(hb_direction);

            let mut features = Vec::new();
            if small_caps {
                features.push(rustybuzz::Feature::new(rustybuzz::Tag::from_bytes(b"smcp"), 1, ..));
            }

            let output = rustybuzz::shape(&rb_font, &features, buffer);

            let positions = output.glyph_positions();
            let infos = output.glyph_infos();

            for (pos, info) in positions.iter().zip(infos) {
                let idx = run.start + info.cluster as usize;
                debug_assert!(text.get(idx..).is_some());

                glyphs.push(Glyph {
                    byte_idx: ByteIndex::new(idx),
                    id: GlyphId(info.glyph_id as u16),
                    dx: pos.x_offset,
                    dy: pos.y_offset,
                    width: pos.x_advance,
                    font,
                });
            }
        }

        Some(glyphs)
    })?
}

/// Outlines a glyph cluster.
///
/// Uses one or more `Glyph`s to construct an `OutlinedCluster`.
fn outline_cluster(
    glyphs: &[Glyph],
    text: &str,
    font_size: f64,
    db: &fontdb::Database,
) -> OutlinedCluster {
    debug_assert!(!glyphs.is_empty());

    let mut path = PathData::new();
    let mut width = 0.0;
    let mut x = 0.0;

    for glyph in glyphs {
        let mut outline = db.outline(glyph.font.id, glyph.id).unwrap_or_default();

        let sx = glyph.font.scale(font_size);

        if !outline.is_empty() {
            // By default, glyphs are upside-down, so we have to mirror them.
            let mut ts = Transform::new_scale(1.0, -1.0);

            // Scale to font-size.
            ts.scale(sx, sx);

            // Apply offset.
            //
            // The first glyph in the cluster will have an offset from 0x0,
            // but the later one will have an offset from the "current position".
            // So we have to keep an advance.
            // TODO: should be done only inside a single text span
            ts.translate(x + glyph.dx as f64, glyph.dy as f64);

            outline.transform(ts);

            path.extend_from_slice(&outline);
        }

        x += glyph.width as f64;

        let glyph_width = glyph.width as f64 * sx;
        if glyph_width > width {
            width = glyph_width;
        }
    }

    let byte_idx = glyphs[0].byte_idx;
    let font = glyphs[0].font;
    OutlinedCluster {
        byte_idx,
        codepoint: byte_idx.char_from(text),
        width,
        advance: width,
        ascent: font.ascent(font_size),
        descent: font.descent(font_size),
        x_height: font.x_height(font_size),
        has_relative_shift: false,
        path,
        transform: Transform::default(),
        visible: true,
    }
}

/// Finds a font with a specified char.
///
/// This is a rudimentary font fallback algorithm.
fn find_font_for_char(
    c: char,
    exclude_fonts: &[fontdb::ID],
    state: &converter::State,
) -> Option<fontdb_ext::Font> {
    let base_font_id = exclude_fonts[0];

    // Iterate over fonts and check if any of them support the specified char.
    for face in state.opt.fontdb.faces() {
        // Ignore fonts, that were used for shaping already.
        if exclude_fonts.contains(&face.id) {
            continue;
        }

        // Check that the new face has the same style.
        let base_face = state.opt.fontdb.face(base_font_id)?;
        if  base_face.style != face.style &&
            base_face.weight != face.weight &&
            base_face.stretch != face.stretch
        {
            continue;
        }

        if !state.opt.fontdb.has_char(face.id, c) {
            continue;
        }

        log::warn!("Fallback from {} to {}.", base_face.family, face.family);
        return state.opt.fontdb.load_font(face.id);
    }

    None
}

/// Resolves clusters positions.
///
/// Mainly sets the `transform` property.
///
/// Returns the last text position. The next text chunk should start from that position.
pub fn resolve_clusters_positions(
    chunk: &TextChunk,
    char_offset: usize,
    pos_list: &[CharacterPosition],
    rotate_list: &[f64],
    writing_mode: WritingMode,
    ts: Transform,
    clusters: &mut [OutlinedCluster],
) -> (f64, f64) {
    match chunk.text_flow {
        TextFlow::Horizontal => {
            resolve_clusters_positions_horizontal(
                chunk, char_offset, pos_list, rotate_list, writing_mode, clusters,
            )
        }
        TextFlow::Path(ref path) => {
            resolve_clusters_positions_path(
                chunk, char_offset, path, pos_list, rotate_list, writing_mode, ts, clusters,
            )
        }
    }
}

fn resolve_clusters_positions_horizontal(
    chunk: &TextChunk,
    offset: usize,
    pos_list: &[CharacterPosition],
    rotate_list: &[f64],
    writing_mode: WritingMode,
    clusters: &mut [OutlinedCluster],
) -> (f64, f64) {
    let mut x = process_anchor(chunk.anchor, clusters_length(clusters));
    let mut y = 0.0;

    for cluster in clusters {
        let cp = offset + cluster.byte_idx.code_point_at(&chunk.text);
        if let Some(pos) = pos_list.get(cp) {
            if writing_mode == WritingMode::LeftToRight {
                x += pos.dx.unwrap_or(0.0);
                y += pos.dy.unwrap_or(0.0);
            } else {
                y -= pos.dx.unwrap_or(0.0);
                x += pos.dy.unwrap_or(0.0);
            }
            cluster.has_relative_shift = pos.dx.is_some() || pos.dy.is_some();
        }

        cluster.transform.translate(x, y);

        if let Some(angle) = rotate_list.get(cp).cloned() {
            if !angle.is_fuzzy_zero() {
                cluster.transform.rotate(angle);
                cluster.has_relative_shift = true;
            }
        }

        x += cluster.advance;
    }

    (x, y)
}

fn resolve_clusters_positions_path(
    chunk: &TextChunk,
    char_offset: usize,
    path: &TextPath,
    pos_list: &[CharacterPosition],
    rotate_list: &[f64],
    writing_mode: WritingMode,
    ts: Transform,
    clusters: &mut [OutlinedCluster],
) -> (f64, f64) {
    let mut last_x = 0.0;
    let mut last_y = 0.0;

    let mut dy = 0.0;

    // In the text path mode, chunk's x/y coordinates provide an additional offset along the path.
    // The X coordinate is used in a horizontal mode, and Y in vertical.
    let chunk_offset = match writing_mode {
        WritingMode::LeftToRight => chunk.x.unwrap_or(0.0),
        WritingMode::TopToBottom => chunk.y.unwrap_or(0.0),
    };

    let start_offset = chunk_offset + path.start_offset
        + process_anchor(chunk.anchor, clusters_length(clusters));

    let normals = collect_normals(
        chunk, clusters, &path.path, pos_list, char_offset, start_offset, ts,
    );
    for (cluster, normal) in clusters.iter_mut().zip(normals) {
        let (x, y, angle) = match normal {
            Some(normal) => {
                (normal.x, normal.y, normal.angle)
            }
            None => {
                // Hide clusters that are outside the text path.
                cluster.visible = false;
                continue;
            }
        };

        // We have to break a decoration line for each cluster during text-on-path.
        cluster.has_relative_shift = true;

        // Clusters should be rotated by the x-midpoint x baseline position.
        let half_width = cluster.width / 2.0;
        cluster.transform.translate(x - half_width, y);
        cluster.transform.rotate_at(angle, half_width, 0.0);

        let cp = char_offset + cluster.byte_idx.code_point_at(&chunk.text);
        if let Some(pos) = pos_list.get(cp) {
            dy += pos.dy.unwrap_or(0.0);
        }

        let baseline_shift = chunk.span_at(cluster.byte_idx)
            .map(|span| span.baseline_shift)
            .unwrap_or(0.0);

        // Shift only by `dy` since we already applied `dx`
        // during offset along the path calculation.
        if !dy.is_fuzzy_zero() || !baseline_shift.is_fuzzy_zero() {
            let shift = kurbo::Vec2::new(0.0, dy - baseline_shift);
            cluster.transform.translate(shift.x, shift.y);
        }

        if let Some(angle) = rotate_list.get(cp).cloned() {
            if !angle.is_fuzzy_zero() {
                cluster.transform.rotate(angle);
            }
        }

        last_x = x + cluster.advance;
        last_y = y;
    }

    (last_x, last_y)
}

fn clusters_length(clusters: &[OutlinedCluster]) -> f64 {
    clusters.iter().fold(0.0, |w, cluster| w + cluster.advance)
}

fn process_anchor(
    a: TextAnchor,
    text_width: f64,
) -> f64 {
    match a {
        TextAnchor::Start   => 0.0, // Nothing.
        TextAnchor::Middle  => -text_width / 2.0,
        TextAnchor::End     => -text_width,
    }
}

struct PathNormal {
    x: f64,
    y: f64,
    angle: f64,
}

fn collect_normals(
    chunk: &TextChunk,
    clusters: &[OutlinedCluster],
    path: &PathData,
    pos_list: &[CharacterPosition],
    char_offset: usize,
    offset: f64,
    ts: Transform,
) -> Vec<Option<PathNormal>> {
    debug_assert!(!path.is_empty());

    let mut offsets = Vec::with_capacity(clusters.len());
    let mut normals = Vec::with_capacity(clusters.len());
    {
        let mut advance = offset;
        for cluster in clusters {
            // Clusters should be rotated by the x-midpoint x baseline position.
            let half_width = cluster.width / 2.0;

            // Include relative position.
            let cp = char_offset + cluster.byte_idx.code_point_at(&chunk.text);
            if let Some(pos) = pos_list.get(cp) {
                advance += pos.dx.unwrap_or(0.0);
            }

            let offset = advance + half_width;

            // Clusters outside the path have no normals.
            if offset < 0.0 {
                normals.push(None);
            }

            offsets.push(offset);
            advance += cluster.advance;
        }
    }

    let (mut prev_mx, mut prev_my, mut prev_x, mut prev_y) = {
        if let PathSegment::MoveTo { x, y } = path[0] {
            (x, y, x, y)
        } else {
            unreachable!();
        }
    };

    fn create_curve_from_line(px: f64, py: f64, x: f64, y: f64) -> kurbo::CubicBez {
        let line = kurbo::Line::new(kurbo::Point::new(px, py), kurbo::Point::new(x, y));
        let p1 = line.eval(0.33);
        let p2 = line.eval(0.66);
        kurbo::CubicBez::from_points(px, py, p1.x, p1.y, p2.x, p2.y, x, y)
    }

    let mut length = 0.0;
    for seg in path.iter() {
        let curve = match *seg {
            PathSegment::MoveTo { x, y } => {
                prev_mx = x;
                prev_my = y;
                prev_x = x;
                prev_y = y;
                continue;
            }
            PathSegment::LineTo { x, y } => {
                create_curve_from_line(prev_x, prev_y, x, y)
            }
            PathSegment::CurveTo { x1, y1, x2, y2, x, y } => {
                kurbo::CubicBez::from_points(prev_x, prev_y, x1, y1, x2, y2, x, y)
            }
            PathSegment::ClosePath => {
                create_curve_from_line(prev_x, prev_y, prev_mx, prev_my)
            }
        };

        let arclen_accuracy = {
            let base_arclen_accuracy = 0.5;
            // Accuracy depends on a current scale.
            // When we have a tiny path scaled by a large value,
            // we have to increase out accuracy accordingly.
            let (sx, sy) = ts.get_scale();
            // 1.0 acts as a threshold to prevent division by 0 and/or low accuracy.
            base_arclen_accuracy / (sx * sy).sqrt().max(1.0)
        };

        let curve_len = curve.arclen(arclen_accuracy);

        for offset in &offsets[normals.len()..] {
            if *offset >= length && *offset <= length + curve_len {
                let mut offset = curve.inv_arclen(offset - length, arclen_accuracy);
                // some rounding error may occur, so we give offset a little tolerance
                debug_assert!((-1.0e-3..=1.0 + 1.0e-3).contains(&offset));
                offset = offset.min(1.0).max(0.0);

                let pos = curve.eval(offset);
                let d = curve.deriv().eval(offset);
                let d = kurbo::Vec2::new(-d.y, d.x); // tangent
                let angle = d.atan2().to_degrees() - 90.0;

                normals.push(Some(PathNormal {
                    x: pos.x,
                    y: pos.y,
                    angle,
                }));

                if normals.len() == offsets.len() {
                    break;
                }
            }
        }

        length += curve_len;
        prev_x = curve.p3.x;
        prev_y = curve.p3.y;
    }

    // If path ended and we still have unresolved normals - set them to `None`.
    for _ in 0..(offsets.len() - normals.len()) {
        normals.push(None);
    }

    normals
}

/// Applies the `letter-spacing` property to a text chunk clusters.
///
/// [In the CSS spec](https://www.w3.org/TR/css-text-3/#letter-spacing-property).
pub fn apply_letter_spacing(
    chunk: &TextChunk,
    clusters: &mut [OutlinedCluster],
) {
    // At least one span should have a non-zero spacing.
    if !chunk.spans.iter().any(|span| !span.letter_spacing.is_fuzzy_zero()) {
        return;
    }

    let num_clusters = clusters.len();
    for (i, cluster) in clusters.iter_mut().enumerate() {
        // Spacing must be applied only to characters that belongs to the script
        // that supports spacing.
        // We are checking only the first code point, since it should be enough.
        let script = cluster.codepoint.script();
        if script_supports_letter_spacing(script) {
            if let Some(span) = chunk.span_at(cluster.byte_idx) {
                // A space after the last cluster should be ignored,
                // since it affects the bbox and text alignment.
                if i != num_clusters - 1 {
                    cluster.advance += span.letter_spacing;
                }

                // If the cluster advance became negative - clear it.
                // This is an UB so we can do whatever we want, and we mimic Chrome's behavior.
                if !cluster.advance.is_valid_length() {
                    cluster.width = 0.0;
                    cluster.advance = 0.0;
                    cluster.path.clear();
                }
            }
        }
    }
}

/// Checks that selected script supports letter spacing.
///
/// [In the CSS spec](https://www.w3.org/TR/css-text-3/#cursive-tracking).
///
/// The list itself is from: https://github.com/harfbuzz/harfbuzz/issues/64
fn script_supports_letter_spacing(script: unicode_script::Script) -> bool {
    use unicode_script::Script;

    !matches!(script,
          Script::Arabic
        | Script::Syriac
        | Script::Nko
        | Script::Manichaean
        | Script::Psalter_Pahlavi
        | Script::Mandaic
        | Script::Mongolian
        | Script::Phags_Pa
        | Script::Devanagari
        | Script::Bengali
        | Script::Gurmukhi
        | Script::Modi
        | Script::Sharada
        | Script::Syloti_Nagri
        | Script::Tirhuta
        | Script::Ogham)
}

/// Applies the `word-spacing` property to a text chunk clusters.
///
/// [In the CSS spec](https://www.w3.org/TR/css-text-3/#propdef-word-spacing).
pub fn apply_word_spacing(
    chunk: &TextChunk,
    clusters: &mut [OutlinedCluster],
) {
    // At least one span should have a non-zero spacing.
    if !chunk.spans.iter().any(|span| !span.word_spacing.is_fuzzy_zero()) {
        return;
    }

    for cluster in clusters {
        if is_word_separator_characters(cluster.codepoint) {
            if let Some(span) = chunk.span_at(cluster.byte_idx) {
                // Technically, word spacing 'should be applied half on each
                // side of the character', but it doesn't affect us in any way,
                // so we are ignoring this.
                cluster.advance += span.word_spacing;

                // After word spacing, `advance` can be negative.
            }
        }
    }
}

/// Checks that the selected character is a word separator.
///
/// According to: https://www.w3.org/TR/css-text-3/#word-separator
fn is_word_separator_characters(c: char) -> bool {
    matches!(c as u32, 0x0020 | 0x00A0 | 0x1361 | 0x010100 | 0x010101 | 0x01039F | 0x01091F)
}

/// Rotates clusters according to
/// [Unicode Vertical_Orientation Property](https://www.unicode.org/reports/tr50/tr50-19.html).
pub fn apply_writing_mode(
    writing_mode: WritingMode,
    clusters: &mut [OutlinedCluster],
) {
    if writing_mode != WritingMode::TopToBottom {
        return;
    }

    for cluster in clusters {
        let orientation = unicode_vo::char_orientation(cluster.codepoint);
        if orientation == CharOrientation::Upright {
            // Additional offset. Not sure why.
            let dy = cluster.width - cluster.height();

            // Rotate a cluster 90deg counter clockwise by the center.
            let mut ts = Transform::default();
            ts.translate(cluster.width / 2.0, 0.0);
            ts.rotate(-90.0);
            ts.translate(-cluster.width / 2.0, -dy);
            cluster.path.transform(ts);

            // Move "baseline" to the middle and make height equal to width.
            cluster.ascent = cluster.width / 2.0;
            cluster.descent = -cluster.width / 2.0;
        } else {
            // Could not find a spec that explains this,
            // but this is how other applications are shifting the "rotated" characters
            // in the top-to-bottom mode.
            cluster.transform.translate(0.0, cluster.x_height / 2.0);
        }
    }
}