/*
 * Copyright (c) 2018-2022, Andreas Kling <kling@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <AK/StringBuilder.h>
#include <LibJS/Interpreter.h>
#include <LibJS/Parser.h>
#include <LibWeb/DOM/Document.h>
#include <LibWeb/DOM/IDLEventListener.h>
#include <LibWeb/HTML/BrowsingContext.h>
#include <LibWeb/HTML/BrowsingContextContainer.h>
#include <LibWeb/HTML/EventHandler.h>
#include <LibWeb/HTML/HTMLAnchorElement.h>
#include <LibWeb/HTML/HTMLBodyElement.h>
#include <LibWeb/HTML/HTMLElement.h>
#include <LibWeb/HTML/Window.h>
#include <LibWeb/Layout/Box.h>
#include <LibWeb/Layout/BreakNode.h>
#include <LibWeb/Layout/TextNode.h>
#include <LibWeb/Painting/PaintableBox.h>
#include <LibWeb/UIEvents/EventNames.h>
#include <LibWeb/UIEvents/FocusEvent.h>
#include <LibWeb/UIEvents/MouseEvent.h>
#include <LibWeb/WebIDL/DOMException.h>
#include <LibWeb/WebIDL/ExceptionOr.h>

namespace Web::HTML {

HTMLElement::HTMLElement(DOM::Document& document, DOM::QualifiedName qualified_name)
    : Element(document, move(qualified_name))
{
    set_prototype(&window().cached_web_prototype("HTMLElement"));
}

HTMLElement::~HTMLElement() = default;

void HTMLElement::initialize(JS::Realm& realm)
{
    Base::initialize(realm);
    m_dataset = DOMStringMap::create(*this);
}

void HTMLElement::visit_edges(Cell::Visitor& visitor)
{
    Base::visit_edges(visitor);
    visitor.visit(m_dataset.ptr());
}

HTMLElement::ContentEditableState HTMLElement::content_editable_state() const
{
    auto contenteditable = attribute(HTML::AttributeNames::contenteditable);
    // "true", an empty string or a missing value map to the "true" state.
    if ((!contenteditable.is_null() && contenteditable.is_empty()) || contenteditable.equals_ignoring_case("true"sv))
        return ContentEditableState::True;
    // "false" maps to the "false" state.
    if (contenteditable.equals_ignoring_case("false"sv))
        return ContentEditableState::False;
    // Having no such attribute or an invalid value maps to the "inherit" state.
    return ContentEditableState::Inherit;
}

bool HTMLElement::is_editable() const
{
    switch (content_editable_state()) {
    case ContentEditableState::True:
        return true;
    case ContentEditableState::False:
        return false;
    case ContentEditableState::Inherit:
        return parent() && parent()->is_editable();
    default:
        VERIFY_NOT_REACHED();
    }
}

String HTMLElement::content_editable() const
{
    switch (content_editable_state()) {
    case ContentEditableState::True:
        return "true";
    case ContentEditableState::False:
        return "false";
    case ContentEditableState::Inherit:
        return "inherit";
    default:
        VERIFY_NOT_REACHED();
    }
}

// https://html.spec.whatwg.org/multipage/interaction.html#contenteditable
WebIDL::ExceptionOr<void> HTMLElement::set_content_editable(String const& content_editable)
{
    if (content_editable.equals_ignoring_case("inherit"sv)) {
        remove_attribute(HTML::AttributeNames::contenteditable);
        return {};
    }
    if (content_editable.equals_ignoring_case("true"sv)) {
        set_attribute(HTML::AttributeNames::contenteditable, "true");
        return {};
    }
    if (content_editable.equals_ignoring_case("false"sv)) {
        set_attribute(HTML::AttributeNames::contenteditable, "false");
        return {};
    }
    return WebIDL::SyntaxError::create(global_object(), "Invalid contentEditable value, must be 'true', 'false', or 'inherit'");
}

void HTMLElement::set_inner_text(StringView text)
{
    remove_all_children();
    append_child(document().create_text_node(text));

    set_needs_style_update(true);
}

String HTMLElement::inner_text()
{
    StringBuilder builder;

    // innerText for element being rendered takes visibility into account, so force a layout and then walk the layout tree.
    document().update_layout();
    if (!layout_node())
        return text_content();

    Function<void(Layout::Node const&)> recurse = [&](auto& node) {
        for (auto* child = node.first_child(); child; child = child->next_sibling()) {
            if (is<Layout::TextNode>(child))
                builder.append(verify_cast<Layout::TextNode>(*child).text_for_rendering());
            if (is<Layout::BreakNode>(child))
                builder.append('\n');
            recurse(*child);
        }
    };
    recurse(*layout_node());

    return builder.to_string();
}

// // https://drafts.csswg.org/cssom-view/#dom-htmlelement-offsettop
int HTMLElement::offset_top() const
{
    // NOTE: Ensure that layout is up-to-date before looking at metrics.
    const_cast<DOM::Document&>(document()).update_layout();

    if (is<HTML::HTMLBodyElement>(this) || !layout_node() || !parent_element() || !parent_element()->layout_node())
        return 0;
    auto position = layout_node()->box_type_agnostic_position();
    auto parent_position = parent_element()->layout_node()->box_type_agnostic_position();
    return position.y() - parent_position.y();
}

// https://drafts.csswg.org/cssom-view/#dom-htmlelement-offsetleft
int HTMLElement::offset_left() const
{
    // NOTE: Ensure that layout is up-to-date before looking at metrics.
    const_cast<DOM::Document&>(document()).update_layout();

    if (is<HTML::HTMLBodyElement>(this) || !layout_node() || !parent_element() || !parent_element()->layout_node())
        return 0;
    auto position = layout_node()->box_type_agnostic_position();
    auto parent_position = parent_element()->layout_node()->box_type_agnostic_position();
    return position.x() - parent_position.x();
}

// https://drafts.csswg.org/cssom-view/#dom-htmlelement-offsetwidth
int HTMLElement::offset_width() const
{
    // NOTE: Ensure that layout is up-to-date before looking at metrics.
    const_cast<DOM::Document&>(document()).update_layout();

    // 1. If the element does not have any associated CSS layout box return zero and terminate this algorithm.
    if (!paint_box())
        return 0;

    // 2. Return the width of the axis-aligned bounding box of the border boxes of all fragments generated by the element’s principal box,
    //    ignoring any transforms that apply to the element and its ancestors.
    // FIXME: Account for inline boxes.
    return paint_box()->border_box_width();
}

// https://drafts.csswg.org/cssom-view/#dom-htmlelement-offsetheight
int HTMLElement::offset_height() const
{
    // NOTE: Ensure that layout is up-to-date before looking at metrics.
    const_cast<DOM::Document&>(document()).update_layout();

    // 1. If the element does not have any associated CSS layout box return zero and terminate this algorithm.
    if (!paint_box())
        return 0;

    // 2. Return the height of the axis-aligned bounding box of the border boxes of all fragments generated by the element’s principal box,
    //    ignoring any transforms that apply to the element and its ancestors.
    // FIXME: Account for inline boxes.
    return paint_box()->border_box_height();
}

// https://html.spec.whatwg.org/multipage/links.html#cannot-navigate
bool HTMLElement::cannot_navigate() const
{
    // An element element cannot navigate if one of the following is true:

    // - element's node document is not fully active
    if (!document().is_fully_active())
        return true;

    // - element is not an a element and is not connected.
    return !is<HTML::HTMLAnchorElement>(this) && !is_connected();
}

void HTMLElement::parse_attribute(FlyString const& name, String const& value)
{
    Element::parse_attribute(name, value);

    // 1. If namespace is not null, or localName is not the name of an event handler content attribute on element, then return.
    // FIXME: Add the namespace part once we support attribute namespaces.
#undef __ENUMERATE
#define __ENUMERATE(attribute_name, event_name)                     \
    if (name == HTML::AttributeNames::attribute_name) {             \
        element_event_handler_attribute_changed(event_name, value); \
    }
    ENUMERATE_GLOBAL_EVENT_HANDLERS(__ENUMERATE)
#undef __ENUMERATE
}

// https://html.spec.whatwg.org/multipage/interaction.html#focus-update-steps
static void run_focus_update_steps(Vector<JS::Handle<DOM::Node>> old_chain, Vector<JS::Handle<DOM::Node>> new_chain, DOM::Node& new_focus_target)
{
    // 1. If the last entry in old chain and the last entry in new chain are the same,
    //    pop the last entry from old chain and the last entry from new chain and redo this step.
    while (!old_chain.is_empty()
        && !new_chain.is_empty()
        && &old_chain.last() == &new_chain.last()) {
        (void)old_chain.take_last();
        (void)new_chain.take_last();
    }

    // 2. For each entry entry in old chain, in order, run these substeps:
    for (auto& entry : old_chain) {
        // FIXME: 1. If entry is an input element, and the change event applies to the element,
        //           and the element does not have a defined activation behavior,
        //           and the user has changed the element's value or its list of selected files
        //           while the control was focused without committing that change
        //           (such that it is different to what it was when the control was first focused),
        //           then fire an event named change at the element,
        //           with the bubbles attribute initialized to true.

        JS::GCPtr<DOM::EventTarget> blur_event_target;
        if (is<DOM::Element>(*entry)) {
            // 2. If entry is an element, let blur event target be entry.
            blur_event_target = entry.ptr();
        } else if (is<DOM::Document>(*entry)) {
            // If entry is a Document object, let blur event target be that Document object's relevant global object.
            blur_event_target = &static_cast<DOM::Document&>(*entry).window();
        }

        // 3. If entry is the last entry in old chain, and entry is an Element,
        //    and the last entry in new chain is also an Element,
        //    then let related blur target be the last entry in new chain.
        //    Otherwise, let related blur target be null.
        JS::GCPtr<DOM::EventTarget> related_blur_target;
        if (!old_chain.is_empty()
            && &entry == &old_chain.last()
            && is<DOM::Element>(*entry)
            && !new_chain.is_empty()
            && is<DOM::Element>(*new_chain.last())) {
            related_blur_target = new_chain.last().ptr();
        }

        // 4. If blur event target is not null, fire a focus event named blur at blur event target,
        //    with related blur target as the related target.
        if (blur_event_target) {
            // FIXME: Implement the "fire a focus event" spec operation.
            auto blur_event = UIEvents::FocusEvent::create(blur_event_target->global_object(), HTML::EventNames::blur);
            blur_event->set_related_target(related_blur_target);
            blur_event_target->dispatch_event(*blur_event);
        }
    }

    // FIXME: 3. Apply any relevant platform-specific conventions for focusing new focus target.
    //           (For example, some platforms select the contents of a text control when that control is focused.)
    (void)new_focus_target;

    // 4. For each entry entry in new chain, in reverse order, run these substeps:
    for (auto& entry : new_chain.in_reverse()) {
        // 1. If entry is a focusable area: designate entry as the focused area of the document.
        // FIXME: This isn't entirely right.
        if (is<DOM::Element>(*entry))
            entry->document().set_focused_element(&static_cast<DOM::Element&>(*entry));

        JS::GCPtr<DOM::EventTarget> focus_event_target;
        if (is<DOM::Element>(*entry)) {
            // 2. If entry is an element, let focus event target be entry.
            focus_event_target = entry.ptr();
        } else if (is<DOM::Document>(*entry)) {
            // If entry is a Document object, let focus event target be that Document object's relevant global object.
            focus_event_target = &static_cast<DOM::Document&>(*entry).window();
        }

        // 3. If entry is the last entry in new chain, and entry is an Element,
        //    and the last entry in old chain is also an Element,
        //    then let related focus target be the last entry in old chain.
        //    Otherwise, let related focus target be null.
        JS::GCPtr<DOM::EventTarget> related_focus_target;
        if (!new_chain.is_empty()
            && &entry == &new_chain.last()
            && is<DOM::Element>(*entry)
            && !old_chain.is_empty()
            && is<DOM::Element>(*old_chain.last())) {
            related_focus_target = old_chain.last().ptr();
        }

        // 4. If focus event target is not null, fire a focus event named focus at focus event target,
        //    with related focus target as the related target.
        if (focus_event_target) {
            // FIXME: Implement the "fire a focus event" spec operation.
            auto focus_event = UIEvents::FocusEvent::create(focus_event_target->global_object(), HTML::EventNames::focus);
            focus_event->set_related_target(related_focus_target);
            focus_event_target->dispatch_event(*focus_event);
        }
    }
}
// https://html.spec.whatwg.org/multipage/interaction.html#focus-chain
static Vector<JS::Handle<DOM::Node>> focus_chain(DOM::Node* subject)
{
    // FIXME: Move this somewhere more spec-friendly.
    if (!subject)
        return {};

    // 1. Let output be an empty list.
    Vector<JS::Handle<DOM::Node>> output;

    // 2. Let currentObject be subject.
    auto* current_object = subject;

    // 3. While true:
    while (true) {
        // 1. Append currentObject to output.
        output.append(JS::make_handle(*current_object));

        // FIXME: 2. If currentObject is an area element's shape, then append that area element to output.

        // FIXME:    Otherwise, if currentObject's DOM anchor is an element that is not currentObject itself, then append currentObject's DOM anchor to output.

        // FIXME: Everything below needs work. The conditions are not entirely right.
        if (!is<DOM::Document>(*current_object)) {
            // 3. If currentObject is a focusable area, then set currentObject to currentObject's DOM anchor's node document.
            current_object = &current_object->document();
        } else if (is<DOM::Document>(*current_object)
            && static_cast<DOM::Document&>(*current_object).browsing_context()
            && !static_cast<DOM::Document&>(*current_object).browsing_context()->is_top_level()) {
            // Otherwise, if currentObject is a Document whose browsing context is a child browsing context,
            // then set currentObject to currentObject's browsing context's container.
            current_object = static_cast<DOM::Document&>(*current_object).browsing_context()->container();
        } else {
            break;
        }
    }

    // 4. Return output.
    return output;
}

// https://html.spec.whatwg.org/multipage/interaction.html#focusing-steps
// FIXME: This should accept more types.
static void run_focusing_steps(DOM::Node* new_focus_target, DOM::Node* fallback_target = nullptr, [[maybe_unused]] Optional<String> focus_trigger = {})
{
    // FIXME: 1. If new focus target is not a focusable area, then set new focus target
    //           to the result of getting the focusable area for new focus target,
    //           given focus trigger if it was passed.

    // 2. If new focus target is null, then:
    if (!new_focus_target) {
        // 1. If no fallback target was specified, then return.
        if (!fallback_target)
            return;

        // 2. Otherwise, set new focus target to the fallback target.
        new_focus_target = fallback_target;
    }

    // 3. If new focus target is a browsing context container with non-null nested browsing context,
    //    then set new focus target to the nested browsing context's active document.
    if (is<BrowsingContextContainer>(*new_focus_target)) {
        auto& browsing_context_container = static_cast<BrowsingContextContainer&>(*new_focus_target);
        if (auto* nested_browsing_context = browsing_context_container.nested_browsing_context())
            new_focus_target = nested_browsing_context->active_document();
    }

    // FIXME: 4. If new focus target is a focusable area and its DOM anchor is inert, then return.

    // 5. If new focus target is the currently focused area of a top-level browsing context, then return.
    if (!new_focus_target->document().browsing_context())
        return;
    auto& top_level_browsing_context = new_focus_target->document().browsing_context()->top_level_browsing_context();
    if (new_focus_target == top_level_browsing_context.currently_focused_area().ptr())
        return;

    // 6. Let old chain be the current focus chain of the top-level browsing context in which
    //    new focus target finds itself.
    auto old_chain = focus_chain(top_level_browsing_context.currently_focused_area());

    // 7. Let new chain be the focus chain of new focus target.
    auto new_chain = focus_chain(new_focus_target);

    // 8. Run the focus update steps with old chain, new chain, and new focus target respectively.
    run_focus_update_steps(old_chain, new_chain, *new_focus_target);
}

// https://html.spec.whatwg.org/multipage/interaction.html#dom-focus
void HTMLElement::focus()
{
    // 1. If the element is marked as locked for focus, then return.
    if (m_locked_for_focus)
        return;

    // 2. Mark the element as locked for focus.
    m_locked_for_focus = true;

    // 3. Run the focusing steps for the element.
    run_focusing_steps(this);

    // FIXME: 4. If the value of the preventScroll dictionary member of options is false,
    //           then scroll the element into view with scroll behavior "auto",
    //           block flow direction position set to an implementation-defined value,
    //           and inline base direction position set to an implementation-defined value.

    // 5. Unmark the element as locked for focus.
    m_locked_for_focus = false;
}

// https://html.spec.whatwg.org/multipage/webappapis.html#fire-a-synthetic-pointer-event
bool HTMLElement::fire_a_synthetic_pointer_event(FlyString const& type, DOM::Element& target, bool not_trusted)
{
    // 1. Let event be the result of creating an event using PointerEvent.
    // 2. Initialize event's type attribute to e.
    // FIXME: Actually create a PointerEvent!
    auto event = UIEvents::MouseEvent::create(document().window(), type);

    // 3. Initialize event's bubbles and cancelable attributes to true.
    event->set_bubbles(true);
    event->set_cancelable(true);

    // 4. Set event's composed flag.
    event->set_composed(true);

    // 5. If the not trusted flag is set, initialize event's isTrusted attribute to false.
    if (not_trusted) {
        event->set_is_trusted(false);
    }

    // FIXME: 6. Initialize event's ctrlKey, shiftKey, altKey, and metaKey attributes according to the current state
    //           of the key input device, if any (false for any keys that are not available).

    // FIXME: 7. Initialize event's view attribute to target's node document's Window object, if any, and null otherwise.

    // FIXME: 8. event's getModifierState() method is to return values appropriately describing the current state of the key input device.

    // 9. Return the result of dispatching event at target.
    return target.dispatch_event(*event);
}

// https://html.spec.whatwg.org/multipage/interaction.html#dom-click
void HTMLElement::click()
{
    // FIXME: 1. If this element is a form control that is disabled, then return.

    // 2. If this element's click in progress flag is set, then return.
    if (m_click_in_progress)
        return;

    // 3. Set this element's click in progress flag.
    m_click_in_progress = true;

    // FIXME: 4. Fire a synthetic pointer event named click at this element, with the not trusted flag set.
    fire_a_synthetic_pointer_event(HTML::EventNames::click, *this, true);

    // 5. Unset this element's click in progress flag.
    m_click_in_progress = false;
}

}