/*
 * Copyright (c) 2023, MacDue <macdue@dueutil.tech>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <LibWeb/Bindings/Intrinsics.h>
#include <LibWeb/Bindings/SVGGradientElementPrototype.h>
#include <LibWeb/DOM/Document.h>
#include <LibWeb/Painting/PaintStyle.h>
#include <LibWeb/SVG/AttributeNames.h>
#include <LibWeb/SVG/SVGGradientElement.h>
#include <LibWeb/SVG/SVGGraphicsElement.h>

namespace Web::SVG {

SVGGradientElement::SVGGradientElement(DOM::Document& document, DOM::QualifiedName qualified_name)
    : SVGElement(document, move(qualified_name))
{
}

void SVGGradientElement::attribute_changed(FlyString const& name, Optional<String> const& old_value, Optional<String> const& value, Optional<FlyString> const& namespace_)
{
    Base::attribute_changed(name, old_value, value, namespace_);

    if (name == AttributeNames::gradientUnits) {
        m_gradient_units = AttributeParser::parse_units(value.value_or(String {}));
    } else if (name == AttributeNames::spreadMethod) {
        m_spread_method = AttributeParser::parse_spread_method(value.value_or(String {}));
    } else if (name == AttributeNames::gradientTransform) {
        if (auto transform_list = AttributeParser::parse_transform(value.value_or(String {})); transform_list.has_value()) {
            m_gradient_transform = transform_from_transform_list(*transform_list);
        } else {
            m_gradient_transform = {};
        }
    }
}

GradientUnits SVGGradientElement::gradient_units() const
{
    HashTable<SVGGradientElement const*> seen_gradients;
    return gradient_units_impl(seen_gradients);
}

GradientUnits SVGGradientElement::gradient_units_impl(HashTable<SVGGradientElement const*>& seen_gradients) const
{
    if (m_gradient_units.has_value())
        return *m_gradient_units;
    if (auto gradient = linked_gradient(seen_gradients))
        return gradient->gradient_units_impl(seen_gradients);
    return GradientUnits::ObjectBoundingBox;
}

SpreadMethod SVGGradientElement::spread_method() const
{
    HashTable<SVGGradientElement const*> seen_gradients;
    return spread_method_impl(seen_gradients);
}

SpreadMethod SVGGradientElement::spread_method_impl(HashTable<SVGGradientElement const*>& seen_gradients) const
{
    if (m_spread_method.has_value())
        return *m_spread_method;
    if (auto gradient = linked_gradient(seen_gradients))
        return gradient->spread_method_impl(seen_gradients);
    return SpreadMethod::Pad;
}

Optional<Gfx::AffineTransform> SVGGradientElement::gradient_transform() const
{
    HashTable<SVGGradientElement const*> seen_gradients;
    return gradient_transform_impl(seen_gradients);
}

Optional<Gfx::AffineTransform> SVGGradientElement::gradient_transform_impl(HashTable<SVGGradientElement const*>& seen_gradients) const
{
    if (m_gradient_transform.has_value())
        return m_gradient_transform;
    if (auto gradient = linked_gradient(seen_gradients))
        return gradient->gradient_transform_impl(seen_gradients);
    return {};
}

// The gradient transform, appropriately scaled and combined with the paint transform.
Gfx::AffineTransform SVGGradientElement::gradient_paint_transform(SVGPaintContext const& paint_context) const
{
    Gfx::AffineTransform gradient_paint_transform = paint_context.paint_transform;
    auto const& bounding_box = paint_context.path_bounding_box;

    if (gradient_units() == SVGUnits::ObjectBoundingBox) {
        // Scale points from 0..1 to bounding box coordinates:
        gradient_paint_transform.scale(bounding_box.width(), bounding_box.height());
    } else {
        // Translate points from viewport to bounding box coordinates:
        gradient_paint_transform.translate(paint_context.viewport.location() - bounding_box.location());
    }

    if (auto transform = gradient_transform(); transform.has_value())
        gradient_paint_transform.multiply(transform.value());

    return gradient_paint_transform;
}

void SVGGradientElement::add_color_stops(Painting::SVGGradientPaintStyle& paint_style) const
{
    auto largest_offset = 0.0f;
    for_each_color_stop([&](auto& stop) {
        // https://svgwg.org/svg2-draft/pservers.html#StopNotes
        // Gradient offset values less than 0 (or less than 0%) are rounded up to 0%.
        // Gradient offset values greater than 1 (or greater than 100%) are rounded down to 100%.
        float stop_offset = AK::clamp(stop.stop_offset().value(), 0.0f, 1.0f);

        // Each gradient offset value is required to be equal to or greater than the previous gradient
        // stop's offset value. If a given gradient stop's offset value is not equal to or greater than all
        // previous offset values, then the offset value is adjusted to be equal to the largest of all previous
        // offset values.
        stop_offset = AK::max(stop_offset, largest_offset);
        largest_offset = stop_offset;

        paint_style.add_color_stop(stop_offset, stop.stop_color().with_opacity(stop.stop_opacity()));
    });
}

GC::Ptr<SVGGradientElement const> SVGGradientElement::linked_gradient(HashTable<SVGGradientElement const*>& seen_gradients) const
{
    // FIXME: This entire function is an ad-hoc hack!
    // It can only resolve #<ids> in the same document.

    auto link = has_attribute(AttributeNames::href) ? get_attribute(AttributeNames::href) : get_attribute("xlink:href"_fly_string);
    if (auto href = link; href.has_value() && !link->is_empty()) {
        auto url = document().encoding_parse_url(*href);
        if (!url.has_value())
            return {};
        auto id = url->fragment();
        if (!id.has_value() || id->is_empty())
            return {};
        auto element = document().get_element_by_id(id.value());
        if (!element)
            return {};
        if (element == this)
            return {};
        if (!is<SVGGradientElement>(*element))
            return {};
        if (seen_gradients.set(&as<SVGGradientElement>(*element)) != AK::HashSetResult::InsertedNewEntry)
            return {};
        return &as<SVGGradientElement>(*element);
    }
    return {};
}

void SVGGradientElement::initialize(JS::Realm& realm)
{
    Base::initialize(realm);
    WEB_SET_PROTOTYPE_FOR_INTERFACE(SVGGradientElement);
}

void SVGGradientElement::visit_edges(Cell::Visitor& visitor)
{
    Base::visit_edges(visitor);
    SVGURIReferenceMixin::visit_edges(visitor);
}

}
