/*
 * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <LibWeb/DOM/Document.h>
#include <LibWeb/HTML/FormAssociatedElement.h>
#include <LibWeb/HTML/HTMLButtonElement.h>
#include <LibWeb/HTML/HTMLFieldSetElement.h>
#include <LibWeb/HTML/HTMLFormElement.h>
#include <LibWeb/HTML/HTMLInputElement.h>
#include <LibWeb/HTML/HTMLLegendElement.h>
#include <LibWeb/HTML/HTMLSelectElement.h>
#include <LibWeb/HTML/HTMLTextAreaElement.h>
#include <LibWeb/HTML/Parser/HTMLParser.h>

namespace Web::HTML {

void FormAssociatedElement::set_form(HTMLFormElement* form)
{
    if (m_form)
        m_form->remove_associated_element({}, form_associated_element_to_html_element());
    m_form = form;
    if (m_form)
        m_form->add_associated_element({}, form_associated_element_to_html_element());
}

bool FormAssociatedElement::enabled() const
{
    // https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#concept-fe-disabled
    auto const& html_element = form_associated_element_to_html_element();

    // A form control is disabled if any of the following conditions are met:
    // 1. The element is a button, input, select, textarea, or form-associated custom element, and the disabled attribute is specified on this element (regardless of its value).
    // FIXME: This doesn't check for form-associated custom elements.
    if ((is<HTMLButtonElement>(html_element) || is<HTMLInputElement>(html_element) || is<HTMLSelectElement>(html_element) || is<HTMLTextAreaElement>(html_element)) && html_element.has_attribute(HTML::AttributeNames::disabled))
        return false;

    // 2. The element is a descendant of a fieldset element whose disabled attribute is specified, and is not a descendant of that fieldset element's first legend element child, if any.
    for (auto* fieldset_ancestor = html_element.first_ancestor_of_type<HTMLFieldSetElement>(); fieldset_ancestor; fieldset_ancestor = fieldset_ancestor->first_ancestor_of_type<HTMLFieldSetElement>()) {
        if (fieldset_ancestor->has_attribute(HTML::AttributeNames::disabled)) {
            auto* first_legend_element_child = fieldset_ancestor->first_child_of_type<HTMLLegendElement>();
            if (!first_legend_element_child || !html_element.is_descendant_of(*first_legend_element_child))
                return false;
        }
    }

    return true;
}

void FormAssociatedElement::set_parser_inserted(Badge<HTMLParser>)
{
    m_parser_inserted = true;
}

// https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#association-of-controls-and-forms:nodes-are-inserted
void FormAssociatedElement::form_node_was_inserted()
{
    // 1. If the form-associated element's parser inserted flag is set, then return.
    if (m_parser_inserted)
        return;

    // 2. Reset the form owner of the form-associated element.
    reset_form_owner();
}

// https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#association-of-controls-and-forms:nodes-are-removed
void FormAssociatedElement::form_node_was_removed()
{
    // 1. If the form-associated element has a form owner and the form-associated element and its form owner are no longer in the same tree, then reset the form owner of the form-associated element.
    if (m_form && &form_associated_element_to_html_element().root() != &m_form->root())
        reset_form_owner();
}

// https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#association-of-controls-and-forms:category-listed-3
void FormAssociatedElement::form_node_attribute_changed(FlyString const& name, Optional<String> const& value)
{
    // When a listed form-associated element's form attribute is set, changed, or removed, then the user agent must
    // reset the form owner of that element.
    if (name == HTML::AttributeNames::form) {
        auto& html_element = form_associated_element_to_html_element();

        if (value.has_value())
            html_element.document().add_form_associated_element_with_form_attribute(*this);
        else
            html_element.document().remove_form_associated_element_with_form_attribute(*this);

        reset_form_owner();
    }
}

// https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#association-of-controls-and-forms:category-listed-4
void FormAssociatedElement::element_id_changed(Badge<DOM::Document>)
{
    // When a listed form-associated element has a form attribute and the ID of any of the elements in the tree changes,
    // then the user agent must reset the form owner of that form-associated element.
    VERIFY(form_associated_element_to_html_element().has_attribute(HTML::AttributeNames::form));
    reset_form_owner();
}

// https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#association-of-controls-and-forms:category-listed-5
void FormAssociatedElement::element_with_id_was_added_or_removed(Badge<DOM::Document>)
{
    // When a listed form-associated element has a form attribute and an element with an ID is inserted into or removed
    // from the Document, then the user agent must reset the form owner of that form-associated element.
    VERIFY(form_associated_element_to_html_element().has_attribute(HTML::AttributeNames::form));
    reset_form_owner();
}

// https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#reset-the-form-owner
void FormAssociatedElement::reset_form_owner()
{
    auto& html_element = form_associated_element_to_html_element();

    // 1. Unset element's parser inserted flag.
    m_parser_inserted = false;

    // 2. If all of the following conditions are true
    //    - element's form owner is not null
    //    - element is not listed or its form content attribute is not present
    //    - element's form owner is its nearest form element ancestor after the change to the ancestor chain
    //    then do nothing, and return.
    if (m_form
        && (!is_listed() || !html_element.has_attribute(HTML::AttributeNames::form))
        && html_element.first_ancestor_of_type<HTMLFormElement>() == m_form.ptr()) {
        return;
    }

    // 3. Set element's form owner to null.
    set_form(nullptr);

    // 4. If element is listed, has a form content attribute, and is connected, then:
    if (is_listed() && html_element.has_attribute(HTML::AttributeNames::form) && html_element.is_connected()) {
        // 1. If the first element in element's tree, in tree order, to have an ID that is identical to element's form content attribute's value, is a form element, then associate the element with that form element.
        auto form_value = html_element.attribute(HTML::AttributeNames::form);
        html_element.root().for_each_in_inclusive_subtree_of_type<HTMLFormElement>([this, &form_value](HTMLFormElement& form_element) {
            if (form_element.id() == form_value) {
                set_form(&form_element);
                return TraversalDecision::Break;
            }

            return TraversalDecision::Continue;
        });
    }

    // 5. Otherwise, if element has an ancestor form element, then associate element with the nearest such ancestor form element.
    else {
        auto* form_ancestor = html_element.first_ancestor_of_type<HTMLFormElement>();
        if (form_ancestor)
            set_form(form_ancestor);
    }
}

// https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#dom-textarea/input-selectionstart
WebIDL::UnsignedLong FormAssociatedElement::selection_start() const
{
    // 1. If this element is an input element, and selectionStart does not apply to this element, return null.
    // NOTE: This is done by HTMLInputElement before calling this function

    // 2. If there is no selection, return the code unit offset within the relevant value to the character that
    //    immediately follows the text entry cursor.
    if (auto cursor = form_associated_element_to_html_element().document().cursor_position())
        return cursor->offset();

    // FIXME: 3. Return the code unit offset within the relevant value to the character that immediately follows the start of
    //           the selection.
    return 0;
}

// https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#textFieldSelection:dom-textarea/input-selectionstart-2
WebIDL::ExceptionOr<void> FormAssociatedElement::set_selection_start(Optional<WebIDL::UnsignedLong> const&)
{
    // 1. If this element is an input element, and selectionStart does not apply to this element, throw an
    //    "InvalidStateError" DOMException.
    // NOTE: This is done by HTMLInputElement before calling this function

    // FIXME: 2. Let end be the value of this element's selectionEnd attribute.
    // FIXME: 3. If end is less than the given value, set end to the given value.
    // FIXME: 4. Set the selection range with the given value, end, and the value of this element's selectionDirection attribute.
    return {};
}

// https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#dom-textarea/input-selectionend
WebIDL::UnsignedLong FormAssociatedElement::selection_end() const
{
    // 1. If this element is an input element, and selectionEnd does not apply to this element, return null.
    // NOTE: This is done by HTMLInputElement before calling this function

    // 2. If there is no selection, return the code unit offset within the relevant value to the character that
    //    immediately follows the text entry cursor.
    if (auto cursor = form_associated_element_to_html_element().document().cursor_position())
        return cursor->offset();

    // FIXME: 3. Return the code unit offset within the relevant value to the character that immediately follows the end of
    //           the selection.
    return 0;
}

// https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#textFieldSelection:dom-textarea/input-selectionend-3
WebIDL::ExceptionOr<void> FormAssociatedElement::set_selection_end(Optional<WebIDL::UnsignedLong> const&)
{
    // 1. If this element is an input element, and selectionEnd does not apply to this element, throw an
    //    "InvalidStateError" DOMException.
    // NOTE: This is done by HTMLInputElement before calling this function

    // FIXME: 2. Set the selection range with the value of this element's selectionStart attribute, the given value, and the
    //           value of this element's selectionDirection attribute.
    return {};
}

}