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use euclid::{
    default::{Transform2D, Transform3D},
    Angle,
};
use lyon_geom::vector;
use svgtypes::{Align, AspectRatio, TransformListToken, ViewBox};

/// <https://www.w3.org/TR/SVG/coords.html#ComputingAViewportsTransform>
pub fn get_viewport_transform(
    view_box: ViewBox,
    preserve_aspect_ratio: Option<AspectRatio>,
    viewport_size: [f64; 2],
    viewport_pos: [Option<f64>; 2],
) -> Transform2D<f64> {
    let [element_width, element_height] = viewport_size;
    let [element_x, element_y] = viewport_pos.map(|pos| pos.unwrap_or(0.));

    let preserve_aspect_ratio = preserve_aspect_ratio.unwrap_or(AspectRatio {
        defer: false,
        align: Align::XMidYMid,
        slice: false,
    });

    let mut scale_x = element_width / view_box.w;
    let mut scale_y = element_height / view_box.h;
    if preserve_aspect_ratio.align != Align::None {
        if preserve_aspect_ratio.slice {
            scale_x = scale_x.max(scale_y);
        } else {
            scale_x = scale_x.min(scale_y);
        }
        scale_y = scale_x;
    }
    let mut translate_x = element_x - (view_box.x * scale_x);
    let mut translate_y = element_y - (view_box.y * scale_y);
    match preserve_aspect_ratio.align {
        Align::XMidYMax | Align::XMidYMid | Align::XMidYMin => {
            translate_x += (element_width - view_box.w * scale_x) / 2.;
        }
        Align::XMaxYMax | Align::XMaxYMid | Align::XMaxYMin => {
            translate_x += element_width - view_box.w * scale_x;
        }
        Align::None | Align::XMinYMin | Align::XMinYMid | Align::XMinYMax => {}
    }
    match preserve_aspect_ratio.align {
        Align::XMinYMid | Align::XMidYMid | Align::XMaxYMid => {
            translate_y += (element_height - view_box.h * scale_y) / 2.;
        }
        Align::XMinYMax | Align::XMidYMax | Align::XMaxYMax => {
            translate_y += element_height - view_box.h * scale_y;
        }
        Align::None | Align::XMinYMin | Align::XMidYMin | Align::XMaxYMin => {}
    }
    Transform2D::scale(scale_x, scale_y).then_translate(vector(translate_x, translate_y))
}

pub fn svg_transform_into_euclid_transform(svg_transform: TransformListToken) -> Transform2D<f64> {
    use TransformListToken::*;
    match svg_transform {
        Matrix { a, b, c, d, e, f } => Transform2D::new(a, b, c, d, e, f),
        Translate { tx, ty } => Transform2D::translation(tx, ty),
        Scale { sx, sy } => Transform2D::scale(sx, sy),
        Rotate { angle } => Transform2D::rotation(Angle::degrees(angle)),
        // https://drafts.csswg.org/css-transforms/#SkewXDefined
        SkewX { angle } => Transform3D::skew(Angle::degrees(angle), Angle::zero()).to_2d(),
        // https://drafts.csswg.org/css-transforms/#SkewYDefined
        SkewY { angle } => Transform3D::skew(Angle::zero(), Angle::degrees(angle)).to_2d(),
    }
}