/*
 * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
 * Copyright (c) 2023, Aliaksandr Kalenik <kalenik.aliaksandr@gmail.com>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <LibWeb/Crypto/Crypto.h>
#include <LibWeb/DOM/Document.h>
#include <LibWeb/DOM/DocumentLoading.h>
#include <LibWeb/Fetch/Fetching/Fetching.h>
#include <LibWeb/Fetch/Infrastructure/FetchAlgorithms.h>
#include <LibWeb/Fetch/Infrastructure/FetchController.h>
#include <LibWeb/Fetch/Infrastructure/URL.h>
#include <LibWeb/HTML/BrowsingContext.h>
#include <LibWeb/HTML/DocumentState.h>
#include <LibWeb/HTML/Navigable.h>
#include <LibWeb/HTML/NavigationParams.h>
#include <LibWeb/HTML/SessionHistoryEntry.h>
#include <LibWeb/HTML/TraversableNavigable.h>
#include <LibWeb/Platform/EventLoopPlugin.h>

namespace Web::HTML {

static HashTable<Navigable*>& all_navigables()
{
    static HashTable<Navigable*> set;
    return set;
}

Navigable::Navigable()
{
    all_navigables().set(this);
}

Navigable::~Navigable()
{
    all_navigables().remove(this);
}

void Navigable::visit_edges(Cell::Visitor& visitor)
{
    Base::visit_edges(visitor);
    visitor.visit(m_parent);
    visitor.visit(m_current_session_history_entry);
    visitor.visit(m_active_session_history_entry);
    visitor.visit(m_container);
}

JS::GCPtr<Navigable> Navigable::navigable_with_active_document(JS::NonnullGCPtr<DOM::Document> document)
{
    for (auto* navigable : all_navigables()) {
        if (navigable->active_document() == document)
            return navigable;
    }
    return nullptr;
}

// https://html.spec.whatwg.org/multipage/document-sequences.html#initialize-the-navigable
ErrorOr<void> Navigable::initialize_navigable(JS::NonnullGCPtr<DocumentState> document_state, JS::GCPtr<Navigable> parent)
{
    static int next_id = 0;
    m_id = TRY(String::number(next_id++));

    // 1. Let entry be a new session history entry, with
    JS::NonnullGCPtr<SessionHistoryEntry> entry = *heap().allocate_without_realm<SessionHistoryEntry>();

    // URL: document's URL
    entry->url = document_state->document()->url();

    // document state: documentState
    entry->document_state = document_state;

    // 2. Set navigable's current session history entry to entry.
    m_current_session_history_entry = entry;

    // 3. Set navigable's active session history entry to entry.
    m_active_session_history_entry = entry;

    // 4. Set navigable's parent to parent.
    m_parent = parent;

    return {};
}

// https://html.spec.whatwg.org/multipage/browsing-the-web.html#getting-the-target-history-entry
JS::GCPtr<SessionHistoryEntry> Navigable::get_the_target_history_entry(int target_step) const
{
    // 1. Let entries be the result of getting session history entries for navigable.
    auto& entries = get_session_history_entries();

    // 2. Return the item in entries that has the greatest step less than or equal to step.
    JS::GCPtr<SessionHistoryEntry> result = nullptr;
    for (auto& entry : entries) {
        auto entry_step = entry->step.get<int>();
        if (entry_step <= target_step) {
            if (!result || result->step.get<int>() < entry_step) {
                result = entry;
            }
        }
    }

    return result;
}

// https://html.spec.whatwg.org/multipage/document-sequences.html#nav-document
JS::GCPtr<DOM::Document> Navigable::active_document()
{
    // A navigable's active document is its active session history entry's document.
    return m_active_session_history_entry->document_state->document();
}

// https://html.spec.whatwg.org/multipage/document-sequences.html#nav-bc
JS::GCPtr<BrowsingContext> Navigable::active_browsing_context()
{
    // A navigable's active browsing context is its active document's browsing context.
    // If this navigable is a traversable navigable, then its active browsing context will be a top-level browsing context.
    if (auto document = active_document())
        return document->browsing_context();
    return nullptr;
}

// https://html.spec.whatwg.org/multipage/document-sequences.html#nav-wp
JS::GCPtr<HTML::WindowProxy> Navigable::active_window_proxy()
{
    // A navigable's active WindowProxy is its active browsing context's associated WindowProxy.
    if (auto browsing_context = active_browsing_context())
        return browsing_context->window_proxy();
    return nullptr;
}

// https://html.spec.whatwg.org/multipage/document-sequences.html#nav-window
JS::GCPtr<HTML::Window> Navigable::active_window()
{
    // A navigable's active window is its active WindowProxy's [[Window]].
    if (auto window_proxy = active_window_proxy())
        return window_proxy->window();
    return nullptr;
}

// https://html.spec.whatwg.org/multipage/document-sequences.html#nav-target
String Navigable::target_name() const
{
    // FIXME: A navigable's target name is its active session history entry's document state's navigable target name.
    dbgln("FIXME: Implement Navigable::target_name()");
    return {};
}

// https://html.spec.whatwg.org/multipage/document-sequences.html#nav-container
JS::GCPtr<NavigableContainer> Navigable::container() const
{
    // The container of a navigable navigable is the navigable container whose nested navigable is navigable, or null if there is no such element.
    return m_container;
}

void Navigable::set_container(JS::GCPtr<NavigableContainer> container)
{
    m_container = container;
}

// https://html.spec.whatwg.org/multipage/document-sequences.html#nav-traversable
JS::GCPtr<TraversableNavigable> Navigable::traversable_navigable() const
{
    // 1. Let navigable be inputNavigable.
    auto navigable = const_cast<Navigable*>(this);

    // 2. While navigable is not a traversable navigable, set navigable to navigable's parent.
    while (navigable && !is<TraversableNavigable>(*navigable))
        navigable = navigable->parent();

    // 3. Return navigable.
    return static_cast<TraversableNavigable*>(navigable);
}

// https://html.spec.whatwg.org/multipage/document-sequences.html#nav-top
JS::GCPtr<TraversableNavigable> Navigable::top_level_traversable()
{
    // 1. Let navigable be inputNavigable.
    auto navigable = this;

    // 2. While navigable's parent is not null, set navigable to navigable's parent.
    while (navigable->parent())
        navigable = navigable->parent();

    // 3. Return navigable.
    return verify_cast<TraversableNavigable>(navigable);
}

// https://html.spec.whatwg.org/multipage/browsing-the-web.html#getting-session-history-entries
Vector<JS::NonnullGCPtr<SessionHistoryEntry>>& Navigable::get_session_history_entries() const
{
    // 1. Let traversable be navigable's traversable navigable.
    auto traversable = traversable_navigable();

    // FIXME 2. Assert: this is running within traversable's session history traversal queue.

    // 3. If navigable is traversable, return traversable's session history entries.
    if (this == traversable)
        return traversable->session_history_entries();

    // 4. Let docStates be an empty ordered set of document states.
    Vector<JS::GCPtr<DocumentState>> doc_states;

    // 5. For each entry of traversable's session history entries, append entry's document state to docStates.
    for (auto& entry : traversable->session_history_entries())
        doc_states.append(entry->document_state);

    // 6. For each docState of docStates:
    while (!doc_states.is_empty()) {
        auto doc_state = doc_states.take_first();

        // 1. For each nestedHistory of docState's nested histories:
        for (auto& nested_history : doc_state->nested_histories()) {
            // 1. If nestedHistory's id equals navigable's id, return nestedHistory's entries.
            if (nested_history.id == id())
                return nested_history.entries;

            // 2. For each entry of nestedHistory's entries, append entry's document state to docStates.
            for (auto& entry : nested_history.entries)
                doc_states.append(entry->document_state);
        }
    }

    VERIFY_NOT_REACHED();
}

// https://html.spec.whatwg.org/multipage/browsing-the-web.html#create-navigation-params-from-a-srcdoc-resource
static WebIDL::ExceptionOr<NavigationParams> create_navigation_params_from_a_srcdoc_resource(JS::GCPtr<SessionHistoryEntry> entry, JS::GCPtr<Navigable> navigable, SourceSnapshotParams const&, Optional<String> navigation_id)
{
    auto& vm = navigable->vm();
    auto& realm = navigable->active_window()->realm();

    // 1. Let documentResource be entry's document state's resource.
    auto document_resource = entry->document_state->resource();
    VERIFY(document_resource.has<String>());

    // 2. Let response be a new response with
    //    URL: about:srcdoc
    //    header list: (`Content-Type`, `text/html`)
    //    body: the UTF-8 encoding of documentResource, as a body
    auto response = Fetch::Infrastructure::Response::create(vm);
    response->url_list().append(AK::URL("about:srcdoc"));
    auto header = TRY_OR_THROW_OOM(vm, Fetch::Infrastructure::Header::from_string_pair("Content-Type"sv, "text/html"sv));
    TRY_OR_THROW_OOM(vm, response->header_list()->append(move(header)));
    response->set_body(TRY(Fetch::Infrastructure::byte_sequence_as_body(realm, document_resource.get<String>().bytes())));

    // FIXME: 3. Let responseOrigin be the result of determining the origin given response's URL, targetSnapshotParams's sandboxing flags, null, and entry's document state's origin.

    // 4. Let coop be a new cross-origin opener policy.
    CrossOriginOpenerPolicy coop;

    // 5. Let coopEnforcementResult be a new cross-origin opener policy enforcement result with
    //    url: response's URL
    //    FIXME: origin: responseOrigin
    //    cross-origin opener policy: coop
    CrossOriginOpenerPolicyEnforcementResult coop_enforcement_result {
        .url = *response->url(),
        .origin = Origin {},
        .cross_origin_opener_policy = coop
    };

    // FIXME: 6. Let policyContainer be the result of determining navigation params policy container given response's URL, entry's document state's history policy container, null, navigable's container document's policy container, and null.

    // 7. Return a new navigation params, with
    //    id: navigationId
    //    request: null
    //    response: response
    //    FIXME: origin: responseOrigin
    //    FIXME: policy container: policyContainer
    //    FIXME: final sandboxing flag set: targetSnapshotParams's sandboxing flags
    //    cross-origin opener policy: coop
    //    COOP enforcement result: coopEnforcementResult
    //    reserved environment: null
    //    navigable: navigable
    //    FIXME: navigation timing type: navTimingType
    //    fetch controller: null
    //    commit early hints: null
    HTML::NavigationParams navigation_params {
        .id = navigation_id,
        .request = {},
        .response = *response,
        .origin = Origin {},
        .policy_container = PolicyContainer {},
        .final_sandboxing_flag_set = SandboxingFlagSet {},
        .cross_origin_opener_policy = move(coop),
        .coop_enforcement_result = move(coop_enforcement_result),
        .reserved_environment = {},
        .browsing_context = navigable->active_browsing_context(),
        .navigable = navigable,
    };

    return { navigation_params };
}

// https://html.spec.whatwg.org/multipage/browsing-the-web.html#create-navigation-params-by-fetching
static WebIDL::ExceptionOr<Optional<NavigationParams>> create_navigation_params_by_fetching(JS::GCPtr<SessionHistoryEntry> entry, JS::GCPtr<Navigable> navigable, SourceSnapshotParams const& source_snapshot_params, Optional<String> navigation_id)
{
    auto& vm = navigable->vm();
    auto& realm = navigable->active_window()->realm();

    // FIXME: 1. Assert: this is running in parallel.

    // 2. Let documentResource be entry's document state's resource.
    auto document_resource = entry->document_state->resource();

    // 3. Let request be a new request, with
    //    url: entry's URL
    //    client: sourceSnapshotParams's fetch client
    //    destination: "document"
    //    credentials mode: "include"
    //    use-URL-credentials flag: set
    //    redirect mode: "manual"
    //    replaces client id: navigable's active document's relevant settings object's id
    //    mode: "navigate"
    //    referrer: entry's document state's request referrer
    //    FIXME: referrer policy: entry's document state's request referrer policy
    auto request = Fetch::Infrastructure::Request::create(vm);
    request->set_url(entry->url);
    request->set_client(source_snapshot_params.fetch_client);
    request->set_destination(Fetch::Infrastructure::Request::Destination::Document);
    request->set_credentials_mode(Fetch::Infrastructure::Request::CredentialsMode::Include);
    request->set_use_url_credentials(true);
    request->set_redirect_mode(Fetch::Infrastructure::Request::RedirectMode::Manual);
    auto replaces_client_id = TRY_OR_THROW_OOM(vm, String::from_deprecated_string(navigable->active_document()->relevant_settings_object().id));
    request->set_replaces_client_id(replaces_client_id);
    request->set_mode(Fetch::Infrastructure::Request::Mode::Navigate);
    request->set_referrer(entry->document_state->request_referrer());

    // 4. If documentResource is a POST resource, then:
    if (document_resource.has<POSTResource>()) {
        // 1. Set request's method to `POST`.
        request->set_method(TRY_OR_THROW_OOM(vm, ByteBuffer::copy("post"sv.bytes())));

        // 2. Set request's body to documentResource's request body.
        request->set_body(document_resource.get<POSTResource>().request_body.value());

        // 3. Set `Content-Type` to documentResource's request content-type in request's header list.
        auto request_content_type = document_resource.get<POSTResource>().request_content_type;
        auto request_content_type_string = [request_content_type]() {
            switch (request_content_type) {
            case POSTResource::RequestContentType::ApplicationXWWWFormUrlencoded:
                return "application/x-www-form-urlencoded"sv;
            case POSTResource::RequestContentType::MultipartFormData:
                return "multipart/form-data"sv;
            case POSTResource::RequestContentType::TextPlain:
                return "text/plain"sv;
            default:
                VERIFY_NOT_REACHED();
            }
        }();
        auto header = TRY_OR_THROW_OOM(vm, Fetch::Infrastructure::Header::from_string_pair("Content-Type"sv, request_content_type_string));
        TRY_OR_THROW_OOM(vm, request->header_list()->append(move(header)));
    }

    // 5. If entry's document state's reload pending is true, then set request's reload-navigation flag.
    if (entry->document_state->reload_pending())
        request->set_reload_navigation(true);

    // 6. Otherwise, if entry's document state's ever populated is true, then set request's history-navigation flag.
    if (entry->document_state->ever_populated())
        request->set_history_navigation(true);

    // 9. Let response be null.
    JS::GCPtr<Fetch::Infrastructure::Response> response = nullptr;

    // 10. Let responseOrigin be null.
    Optional<HTML::Origin> response_origin;

    // 11. Let fetchController be null.
    JS::GCPtr<Fetch::Infrastructure::FetchController> fetch_controller = nullptr;

    // 13. Let finalSandboxFlags be an empty sandboxing flag set.
    SandboxingFlagSet final_sandbox_flags;

    // 16. Let locationURL be null.
    ErrorOr<Optional<AK::URL>> location_url { OptionalNone {} };

    // 17. Let currentURL be request's current URL.
    AK::URL current_url = request->current_url();

    // FIXME: 18. Let commitEarlyHints be null.

    // 19. While true:
    while (true) {
        // FIXME: 1. If request's reserved client is not null and currentURL's origin is not the same as request's reserved client's creation URL's origin, then:
        // FIXME: 2. If request's reserved client is null, then:
        // FIXME: 3. If the result of should navigation request of type be blocked by Content Security Policy? given request and cspNavigationType is "Blocked", then set response to a network error and break. [CSP]

        // 4. Set response to null.
        response = nullptr;

        // 5. If fetchController is null, then set fetchController to the result of fetching request,
        //    with processEarlyHintsResponse set to processEarlyHintsResponseas defined below, processResponse
        //    set to processResponse as defined below, and useParallelQueue set to true.
        if (!fetch_controller) {
            // FIXME: Let processEarlyHintsResponse be the following algorithm given a response earlyResponse:

            // Let processResponse be the following algorithm given a response fetchedResponse:
            auto process_response = [&response](JS::NonnullGCPtr<Fetch::Infrastructure::Response> fetch_response) {
                // 1. Set response to fetchedResponse.
                response = fetch_response;
            };

            fetch_controller = TRY(Fetch::Fetching::fetch(
                realm,
                request,
                Fetch::Infrastructure::FetchAlgorithms::create(vm,
                    {
                        .process_request_body_chunk_length = {},
                        .process_request_end_of_body = {},
                        .process_early_hints_response = {},
                        .process_response = move(process_response),
                        .process_response_end_of_body = {},
                        .process_response_consume_body = {},
                    }),
                Fetch::Fetching::UseParallelQueue::Yes));
        }
        // 6. Otherwise, process the next manual redirect for fetchController.
        else {
            fetch_controller->process_next_manual_redirect();
        }

        // 7. Wait until either response is non-null, or navigable's ongoing navigation changes to no longer equal navigationId.
        Platform::EventLoopPlugin::the().spin_until([&]() {
            if (response != nullptr)
                return true;

            if (navigation_id.has_value() && (!navigable->ongoing_navigation().has<String>() || navigable->ongoing_navigation().get<String>() != *navigation_id))
                return true;

            return false;
        });
        // If the latter condition occurs, then abort fetchController, and return. Otherwise, proceed onward.
        if (navigation_id.has_value() && (!navigable->ongoing_navigation().has<String>() || navigable->ongoing_navigation().get<String>() != *navigation_id)) {
            fetch_controller->abort(realm, {});
            return OptionalNone {};
        }

        // 8. If request's body is null, then set entry's document state's resource to null.
        if (!request->body().has<Empty>()) {
            entry->document_state->set_resource(Empty {});
        }

        // 11. Set responseOrigin to the result of determining the origin given response's URL, finalSandboxFlags,
        //     entry's document state's initiator origin, and null.
        response_origin = determine_the_origin(*response->url(), final_sandbox_flags, entry->document_state->initiator_origin(), {});

        // 14. Set locationURL to response's location URL given currentURL's fragment.
        auto const& fragment = current_url.fragment();
        auto fragment_string = fragment.is_null() ? Optional<String> {} : TRY_OR_THROW_OOM(vm, String::from_deprecated_string(fragment));
        auto location_url = response->location_url(fragment_string);

        VERIFY(!location_url.is_error());

        // 15. If locationURL is failure or null, then break.
        if (location_url.is_error() || !location_url.value().has_value()) {
            break;
        }

        // 16. Assert: locationURL is a URL.
        VERIFY(location_url.value()->is_valid());

        // FIXME: 17. Set entry's serialized state to StructuredSerializeForStorage(null).

        // 18. Let oldDocState be entry's document state.
        auto old_doc_state = entry->document_state;

        // 19. Set entry's document state to a new document state, with
        // history policy container: a clone of the oldDocState's history policy container if it is non-null; null otherwise
        // request referrer: oldDocState's request referrer
        // request referrer policy: oldDocState's request referrer policy
        // origin: oldDocState's origin
        // resource: oldDocState's resource
        // ever populated: oldDocState's ever populated
        // navigable target name: oldDocState's navigable target name
        entry->document_state = navigable->heap().allocate_without_realm<DocumentState>();
        entry->document_state->set_history_policy_container(old_doc_state->history_policy_container());
        entry->document_state->set_request_referrer(old_doc_state->request_referrer());
        entry->document_state->set_request_referrer_policy(old_doc_state->request_referrer_policy());
        entry->document_state->set_origin(old_doc_state->origin());
        entry->document_state->set_resource(old_doc_state->resource());
        entry->document_state->set_ever_populated(old_doc_state->ever_populated());
        entry->document_state->set_navigable_target_name(old_doc_state->navigable_target_name());

        // 20. If locationURL's scheme is not an HTTP(S) scheme, then:
        if (!Fetch::Infrastructure::is_http_or_https_scheme(location_url.value()->scheme())) {
            // 1. Set entry's document state's resource to null.
            entry->document_state->set_resource(Empty {});

            // 2. Break.
            break;
        }

        // 21. Set currentURL to locationURL.
        current_url = location_url.value().value();

        // 22. Set entry's URL to currentURL.
        entry->url = current_url;
    }

    // FIXME: 20. If locationURL is a URL whose scheme is not a fetch scheme, then return a new non-fetch scheme navigation params, with
    //            initiator origin request's current URL's origin
    if (!location_url.is_error() && location_url.value().has_value() && !Fetch::Infrastructure::is_fetch_scheme(location_url.value().value().scheme())) {
        TODO();
    }

    // 21. If any of the following are true:
    //       - response is a network error;
    //       - locationURL is failure; or
    //       - locationURL is a URL whose scheme is a fetch scheme
    //     then return null.
    if (response->is_network_error() || location_url.is_error() || (location_url.value().has_value() && Fetch::Infrastructure::is_fetch_scheme(location_url.value().value().scheme()))) {
        return OptionalNone {};
    }

    // 22. Assert: locationURL is null and response is not a network error.
    VERIFY(!location_url.value().has_value());
    VERIFY(!response->is_network_error());

    // FIXME: 23. Let resultPolicyContainer be the result of determining navigation params policy container given response's
    //        URL, entry's document state's history policy container, sourceSnapshotParams's source policy container,
    //        null, and responsePolicyContainer.

    // 25. Return a new navigation params, with
    //     id: navigationId
    //     request: request
    //     response: response
    //     origin: responseOrigin
    //     FIXME: policy container: resultPolicyContainer
    //     FIXME: final sandboxing flag set: finalSandboxFlags
    //     FIXME: cross-origin opener policy: responseCOOP
    //     FIXME: COOP enforcement result: coopEnforcementResult
    //     FIXME: reserved environment: request's reserved client
    //     navigable: navigable
    //     FIXME: navigation timing type: navTimingType
    //     fetch controller: fetchController
    //     FIXME: commit early hints: commitEarlyHints
    HTML::NavigationParams navigation_params {
        .id = navigation_id,
        .request = request,
        .response = *response,
        .origin = *response_origin,
        .policy_container = PolicyContainer {},
        .final_sandboxing_flag_set = SandboxingFlagSet {},
        .cross_origin_opener_policy = CrossOriginOpenerPolicy {},
        .coop_enforcement_result = CrossOriginOpenerPolicyEnforcementResult {},
        .reserved_environment = {},
        .browsing_context = navigable->active_browsing_context(),
        .navigable = navigable,
        .fetch_controller = fetch_controller,
    };

    return { navigation_params };
}

// https://html.spec.whatwg.org/multipage/browsing-the-web.html#attempt-to-populate-the-history-entry's-document
WebIDL::ExceptionOr<void> Navigable::populate_session_history_entry_document(JS::GCPtr<SessionHistoryEntry> entry, Optional<NavigationParams> navigation_params, Optional<String> navigation_id, SourceSnapshotParams const& source_snapshot_params, Function<void()> completion_steps)
{
    // FIXME: 1. Assert: this is running in parallel.

    // 2. Assert: if navigationParams is non-null, then navigationParams's response is non-null.
    if (navigation_params.has_value())
        VERIFY(navigation_params->response);

    // 3. Let currentBrowsingContext be navigable's active browsing context.
    [[maybe_unused]] auto current_browsing_context = active_browsing_context();

    // 4. Let documentResource be entry's document state's resource.
    auto document_resource = entry->document_state->resource();

    // 5. If navigationParams is null, then:
    if (!navigation_params.has_value()) {
        // 1. If documentResource is a string, then set navigationParams to the result
        //    of creating navigation params from a srcdoc resource given entry, navigable,
        //    targetSnapshotParams, navigationId, and navTimingType.
        if (document_resource.has<String>()) {
            navigation_params = create_navigation_params_from_a_srcdoc_resource(entry, this, source_snapshot_params, navigation_id).release_value_but_fixme_should_propagate_errors();
        }
        // 2. Otherwise, if both of the following are true:
        //    - entry's URL's scheme is a fetch scheme; and
        //    - documentResource is null, FIXME: or allowPOST is true and documentResource's request body is not failure
        else if (Fetch::Infrastructure::is_fetch_scheme(entry->url.scheme()) && document_resource.has<Empty>()) {
            navigation_params = create_navigation_params_by_fetching(entry, this, source_snapshot_params, navigation_id).release_value_but_fixme_should_propagate_errors();
        }
        // FIXME: 3. Otherwise, if entry's URL's scheme is not a fetch scheme, then set navigationParams to a new non-fetch scheme navigation params, with
        //    initiator origin: entry's document state's initiator origin
        else {
            TODO();
        }
    }

    // 6. Queue a global task on the navigation and traversal task source, given navigable's active window, to run these steps:
    queue_global_task(Task::Source::NavigationAndTraversal, *active_window(), [this, entry, navigation_params, navigation_id, completion_steps = move(completion_steps)] {
        // 1. If navigable's ongoing navigation no longer equals navigationId, then run completionSteps and return.
        if (navigation_id.has_value() && (!ongoing_navigation().has<String>() || ongoing_navigation().get<String>() != *navigation_id)) {
            completion_steps();
            return;
        }

        // 2. Let failure be false.
        auto failure = false;

        // FIXME: 3. If navigationParams is a non-fetch scheme navigation params, then set entry's document state's document to the result of running attempt to create a non-fetch
        //    scheme document given entry's URL, navigable, targetSnapshotParams's sandboxing flags, navigationId, navTimingType, sourceSnapshotParams's has transient
        //    activation, and navigationParams's initiator origin.

        // 4. Otherwise, if navigationParams is null, then set failure to true.
        if (!navigation_params.has_value()) {
            failure = true;
        }

        // FIXME: 5. Otherwise, if the result of should navigation response to navigation request of type in target be blocked by Content Security Policy? given navigationParams's request,
        //    navigationParams's response, navigationParams's policy container's CSP list, cspNavigationType, and navigable is "Blocked", then set failure to true.

        // FIXME: 6. Otherwise, if navigationParams's reserved environment is non-null and the result of checking a navigation response's adherence to its embedder policy given
        //    navigationParams's response, navigable, and navigationParams's policy container's embedder policy is false, then set failure to true.

        // 8. If failure is true, then:
        if (failure) {
            // 1. Set entry's document state's document to the result of creating a document for inline content that doesn't have a DOM, given navigable, null, and navTimingType.
            //    The inline content should indicate to the user the sort of error that occurred.
            // FIXME: Use SourceGenerator to produce error page from file:///res/html/error.html
            //        and display actual error from fetch response.
            auto error_html = String::formatted("<h1>Failed to load {}</h1>"sv, entry->url).release_value_but_fixme_should_propagate_errors();
            entry->document_state->set_document(create_document_for_inline_content(this, navigation_id, error_html));

            // 2. Set entry's document state's document's salvageable to false.
            entry->document_state->document()->set_salvageable(false);

            // FIXME: 3. If navigationParams is not null, then:
            if (navigation_params.has_value()) {
                TODO();
            }
        }
        // FIXME: 9. Otherwise, if navigationParams's response's status is 204 or 205, then:
        else if (navigation_params->response->status() == 204 || navigation_params->response->status() == 205) {
            // 1. Run completionSteps.
            completion_steps();

            // 2. Return.
            return;
        }
        // FIXME: 10. Otherwise, if navigationParams's response has a `Content-Disposition`
        //            header specifying the attachment disposition type, then:
        // 11. Otherwise:
        else {
            // 1. Let document be the result of loading a document given navigationParams, sourceSnapshotParams,
            //    and entry's document state's initiator origin.
            auto document = load_document(navigation_params);

            // 2. If document is null, then run completionSteps and return.
            if (!document) {
                VERIFY_NOT_REACHED();

                completion_steps();
                return;
            }

            // 3. Set entry's document state's document to document.
            entry->document_state->set_document(document.ptr());

            // 4. Set entry's document state's origin to document's origin.
            entry->document_state->set_origin(document->origin());
        }

        // FIXME: 12. If entry's document state's request referrer is "client", then set it to request's referrer.

        // 13. If entry's document state's document is not null, then set entry's document state's ever populated to true.
        if (entry->document_state->document()) {
            entry->document_state->set_ever_populated(true);
        }

        // 14. Run completionSteps.
        completion_steps();
    });

    return {};
}

// To navigate a navigable navigable to a URL url using a Document sourceDocument,
// with an optional POST resource, string, or null documentResource (default null),
// an optional response-or-null response (default null), an optional boolean exceptionsEnabled (default false),
// an optional history handling behavior historyHandling (default "push"),
// an optional string cspNavigationType (default "other"),
// and an optional referrer policy referrerPolicy (default the empty string):

// https://html.spec.whatwg.org/multipage/browsing-the-web.html#navigate
WebIDL::ExceptionOr<void> Navigable::navigate(
    AK::URL const& url,
    JS::NonnullGCPtr<DOM::Document> source_document,
    Variant<Empty, String, POSTResource> document_resource,
    JS::GCPtr<Fetch::Infrastructure::Response> response,
    bool exceptions_enabled,
    HistoryHandlingBehavior history_handling,
    CSPNavigationType csp_navigation_type,
    ReferrerPolicy::ReferrerPolicy referrer_policy)
{
    // 1. Let sourceSnapshotParams be the result of snapshotting source snapshot params given sourceDocument.
    auto source_snapshot_params = SourceSnapshotParams {
        .has_transient_activation = false,
        .sandboxing_flags = source_document->active_sandboxing_flag_set(),
        .allows_downloading = true,
        .fetch_client = source_document->relevant_settings_object(),
        .source_policy_container = source_document->policy_container()
    };

    // 2. Let initiatorOriginSnapshot be sourceDocument's origin.
    auto initiator_origin_snapshot = source_document->origin();

    // FIXME: 3. If sourceDocument's node navigable is not allowed by sandboxing to navigate navigable given and sourceSnapshotParams, then:
    if constexpr (false) {
        // 1. If exceptionsEnabled is true, then throw a "SecurityError" DOMException.
        if (exceptions_enabled) {
            return WebIDL::SecurityError::create(*vm().current_realm(), "Source document's node navigable is not allowed to navigate"sv);
        }

        // 2 Return.
        return {};
    }

    // 4. Let navigationId be the result of generating a random UUID.
    String navigation_id = TRY_OR_THROW_OOM(vm(), Crypto::generate_random_uuid());

    // FIXME: 5. If the surrounding agent is equal to navigable's active document's relevant agent, then continue these steps.
    //           Otherwise, queue a global task on the navigation and traversal task source given navigable's active window to continue these steps.

    // FIXME: 6. If navigable's active document's unload counter is greater than 0,
    //           then invoke WebDriver BiDi navigation failed with a WebDriver BiDi navigation status whose id is navigationId,
    //           status is "canceled", and url is url, and return.

    // 7. If any of the following are true:
    //    - url equals navigable's active document's URL;
    //    - url's scheme is "javascript"; or
    //    - navigable's active document's is initial about:blank is true
    if (url.equals(active_document()->url())
        || url.scheme() == "javascript"sv
        || active_document()->is_initial_about_blank()) {
        // then set historyHandling to "replace".
        history_handling = HistoryHandlingBehavior::Replace;
    }

    // 8. If all of the following are true:
    //    - documentResource is null;
    //    - response is null;
    //    - url equals navigable's active session history entry's URL with exclude fragments set to true; and
    //    - url's fragment is non-null
    if (document_resource.has<Empty>()
        && !response
        && url.equals(active_session_history_entry()->url, AK::URL::ExcludeFragment::Yes)
        && !url.fragment().is_null()) {
        // 1. Navigate to a fragment given navigable, url, historyHandling, and navigationId.
        TRY(navigate_to_a_fragment(url, history_handling, navigation_id));

        // 2. Return.
        return {};
    }

    // 9. If navigable's parent is non-null, then set navigable's is delaying load events to true.
    if (parent() != nullptr) {
        set_delaying_load_events(true);
    }

    // 10. Let targetBrowsingContext be navigable's active browsing context.
    [[maybe_unused]] auto target_browsing_context = active_browsing_context();

    // FIXME: 11. Let targetSnapshotParams be the result of snapshotting target snapshot params given navigable.

    // FIXME: 12. Invoke WebDriver BiDi navigation started with targetBrowsingContext, and a new WebDriver BiDi navigation status whose id is navigationId, url is url, and status is "pending".

    // 13. If navigable's ongoing navigation is "traversal", then:
    if (ongoing_navigation().has<Traversal>()) {
        // FIXME: 1. Invoke WebDriver BiDi navigation failed with targetBrowsingContext and a new WebDriver BiDi navigation status whose id is navigationId, status is "canceled", and url is url.

        // 2. Return.
        return {};
    }

    // 14. Set navigable's ongoing navigation to navigationId.
    m_ongoing_navigation = navigation_id;

    // 15. If url's scheme is "javascript", then:
    if (url.scheme() == "javascript"sv) {
        // 1. Queue a global task on the navigation and traversal task source given navigable's active window to navigate to a javascript: URL given navigable, url, historyHandling, initiatorOriginSnapshot, and cspNavigationType.
        queue_global_task(Task::Source::NavigationAndTraversal, *active_window(), [this, url, history_handling, initiator_origin_snapshot, csp_navigation_type] {
            (void)navigate_to_a_javascript_url(url, history_handling, initiator_origin_snapshot, csp_navigation_type);
        });

        // 2. Return.
        return {};
    }

    // 16. In parallel, run these steps:
    Platform::EventLoopPlugin::the().deferred_invoke([this, source_snapshot_params = move(source_snapshot_params), document_resource, url, navigation_id, referrer_policy, initiator_origin_snapshot, response, history_handling] {
        // FIXME: 1. Let unloadPromptCanceled be the result of checking if unloading is user-canceled for navigable's active document's inclusive descendant navigables.

        // FIXME: 2. If unloadPromptCanceled is true, or navigable's ongoing navigation is no longer navigationId, then:

        // 3. Queue a global task on the navigation and traversal task source given navigable's active window to abort navigable's active document.
        queue_global_task(Task::Source::NavigationAndTraversal, *active_window(), [this] {
            VERIFY(active_document());
            active_document()->abort();
        });

        // 4. Let documentState be a new document state with
        //    request referrer policy: referrerPolicy
        //    initiator origin: initiatorOriginSnapshot
        //    resource: documentResource
        //    navigable target name: navigable's target name
        JS::NonnullGCPtr<DocumentState> document_state = *heap().allocate_without_realm<DocumentState>();
        document_state->set_request_referrer_policy(referrer_policy);
        document_state->set_resource(document_resource);
        document_state->set_initiator_origin(initiator_origin_snapshot);
        document_state->set_navigable_target_name(target_name());

        // 5. If url is about:blank, then set documentState's origin to documentState's initiator origin.
        if (url == "about:blank"sv) {
            document_state->set_origin(document_state->initiator_origin());
        }

        // 6. Otherwise, if url is about:srcdoc, then set documentState's origin to navigable's parent's active document's origin.
        else if (url == "about:srcdoc"sv) {
            document_state->set_origin(parent()->active_document()->origin());
        }

        // 7. Let historyEntry be a new session history entry, with its URL set to url and its document state set to documentState.
        JS::NonnullGCPtr<SessionHistoryEntry> history_entry = *heap().allocate_without_realm<SessionHistoryEntry>();
        history_entry->url = url;
        history_entry->document_state = document_state;

        // 8. Let navigationParams be null.
        Optional<NavigationParams> navigation_params;

        // FIXME: 9. If response is non-null:
        if (response) {
        }

        // 10. Attempt to populate the history entry's document
        //     for historyEntry, given navigable, "navigate", sourceSnapshotParams,
        //     targetSnapshotParams, navigationId, navigationParams, cspNavigationType, with allowPOST
        //     set to true and completionSteps set to the following step:
        populate_session_history_entry_document(history_entry, navigation_params, navigation_id, source_snapshot_params, [this, history_entry, history_handling] {
            // https://html.spec.whatwg.org/multipage/browsing-the-web.html#finalize-a-cross-document-navigation

            // 1. FIXME: Assert: this is running on navigable's traversable navigable's session history traversal queue.

            // 2. Set navigable's is delaying load events to false.
            set_delaying_load_events(false);

            // 3. If historyEntry's document is null, then return.
            if (!history_entry->document_state->document())
                return;

            // 4. FIXME: If all of the following are true:
            //    - navigable's parent is null;
            //    - historyEntry's document's browsing context is not an auxiliary browsing context whose opener browsing context is non-null; and
            //    - historyEntry's document's origin is not navigable's active document's origin
            //    then set historyEntry's document state's navigable target name to the empty string.

            // 5. Let entryToReplace be navigable's active session history entry if historyHandling is "replace", otherwise null.
            auto entry_to_replace = history_handling == HistoryHandlingBehavior::Replace ? active_session_history_entry() : nullptr;

            // 6. Let traversable be navigable's traversable navigable.
            auto traversable = traversable_navigable();

            // 7. Let targetStep be null.
            int target_step;

            // 8. Let targetEntries be the result of getting session history entries for navigable.
            auto& target_entries = get_session_history_entries();

            // 9. If entryToReplace is null, then:
            if (entry_to_replace == nullptr) {
                // FIXME: 1. Clear the forward session history of traversable.

                // 2. Set targetStep to traversable's current session history step + 1.
                target_step = traversable->current_session_history_step() + 1;

                // 3. Set historyEntry's step to targetStep.
                history_entry->step = target_step;

                // 4. Append historyEntry to targetEntries.
                target_entries.append(move(history_entry));
            } else {
                // 1. Replace entryToReplace with historyEntry in targetEntries.
                *(target_entries.find(*entry_to_replace)) = history_entry;

                // 2. Set historyEntry's step to entryToReplace's step.
                history_entry->step = entry_to_replace->step;

                // 3. Set targetStep to traversable's current session history step.
                target_step = traversable->current_session_history_step();
            }

            // FIXME: 10. Apply the history step targetStep to traversable.
        }).release_value_but_fixme_should_propagate_errors();
    });

    return {};
}

WebIDL::ExceptionOr<void> Navigable::navigate_to_a_fragment(AK::URL const&, HistoryHandlingBehavior, String navigation_id)
{
    (void)navigation_id;
    TODO();
}

WebIDL::ExceptionOr<void> Navigable::navigate_to_a_javascript_url(AK::URL const&, HistoryHandlingBehavior, Origin const& initiator_origin, CSPNavigationType csp_navigation_type)
{
    (void)initiator_origin;
    (void)csp_navigation_type;
    TODO();
}

}