/*

 * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>

 * Copyright (c) 2024, Jamie Mansfield <jmansfield@cadixdev.org>

 *

 * SPDX-License-Identifier: BSD-2-Clause

 */

#include <LibURL/URL.h>

#include <LibWeb/DOM/Document.h>

#include <LibWeb/DOMURL/DOMURL.h>

#include <LibWeb/Fetch/Infrastructure/HTTP/Requests.h>

#include <LibWeb/Fetch/Infrastructure/URL.h>

#include <LibWeb/HTML/Window.h>

#include <LibWeb/ReferrerPolicy/AbstractOperations.h>

#include <LibWeb/ReferrerPolicy/ReferrerPolicy.h>

#include <LibWeb/SecureContexts/AbstractOperations.h>

namespace Web::ReferrerPolicy {

// https://w3c.github.io/webappsec-referrer-policy/#parse-referrer-policy-from-header

ReferrerPolicy parse_a_referrer_policy_from_a_referrer_policy_header(Fetch::Infrastructure::Response const& response)

{

    // 1. Let policy-tokens be the result of extracting header list values given `Referrer-Policy` and response’s header list.

    auto policy_tokens_or_failure = Fetch::Infrastructure::extract_header_list_values("Referrer-Policy"sv.bytes(), response.header_list());

    auto policy_tokens = policy_tokens_or_failure.has<Vector<ByteBuffer>>() ? policy_tokens_or_failure.get<Vector<ByteBuffer>>() : Vector<ByteBuffer> {};

    // 2. Let policy be the empty string.

    auto policy = ReferrerPolicy::EmptyString;

    // 3. For each token in policy-tokens, if token is a referrer policy and token is not the empty string, then set policy to token.

    for (auto token : policy_tokens) {

        auto referrer_policy = from_string(token);

        if (referrer_policy.has_value() && referrer_policy.value() != ReferrerPolicy::EmptyString)

            policy = referrer_policy.release_value();

    }

    // 4. Return policy.

    return policy;

}

// https://w3c.github.io/webappsec-referrer-policy/#set-requests-referrer-policy-on-redirect

void set_request_referrer_policy_on_redirect(Fetch::Infrastructure::Request& request, Fetch::Infrastructure::Response const& response)

{

    // 1. Let policy be the result of executing § 8.1 Parse a referrer policy from a Referrer-Policy header on

    //    actualResponse.

    auto policy = parse_a_referrer_policy_from_a_referrer_policy_header(response);

    // 2. If policy is not the empty string, then set request’s referrer policy to policy.

    if (policy != ReferrerPolicy::EmptyString)

        request.set_referrer_policy(policy);

}

// https://w3c.github.io/webappsec-referrer-policy/#determine-requests-referrer

Optional<URL::URL> determine_requests_referrer(Fetch::Infrastructure::Request const& request)

{

    // 1. Let policy be request’s referrer policy.

    auto const& policy = request.referrer_policy();

    // 2. Let environment be request’s client.

    auto environment = request.client();

    // 3. Switch on request’s referrer:

    auto referrer_source = request.referrer().visit(

        // "client"

        [&](Fetch::Infrastructure::Request::Referrer referrer) -> Optional<URL::URL> {

            // Note: If request’s referrer is "no-referrer", Fetch will not call into this algorithm.

            VERIFY(referrer == Fetch::Infrastructure::Request::Referrer::Client);

            // FIXME: Add a const global_object() getter to ESO

            auto& global_object = const_cast<HTML::EnvironmentSettingsObject&>(*environment).global_object();

            // 1. If environment’s global object is a Window object, then

            if (is<HTML::Window>(global_object)) {

                // 1. Let document be the associated Document of environment’s global object.

                auto const& document = static_cast<HTML::Window const&>(global_object).associated_document();

                // 2. If document’s origin is an opaque origin, return no referrer.

                if (document.origin().is_opaque())

                    return {};

                // FIXME: 3. While document is an iframe srcdoc document, let document be document’s browsing context’s

                //           browsing context container’s node document.

                // 4. Let referrerSource be document’s URL.

                return document.url();

            }

            // 2. Otherwise, let referrerSource be environment’s creation URL.

            else {

                return environment->creation_url;

            }

        },

        // a URL

        [&](URL::URL const& url) -> Optional<URL::URL> {

            // Let referrerSource be request’s referrer.

            return url;

        });

    // NOTE: This only happens in step 1.2. of the "client" case above.

    if (!referrer_source.has_value())

        return {};

    // 4. Let request’s referrerURL be the result of stripping referrerSource for use as a referrer.

    auto referrer_url = strip_url_for_use_as_referrer(referrer_source);

    // 5. Let referrerOrigin be the result of stripping referrerSource for use as a referrer, with the origin-only flag

    //    set to true.

    auto referrer_origin = strip_url_for_use_as_referrer(referrer_source, OriginOnly::Yes);

    // 6. If the result of serializing referrerURL is a string whose length is greater than 4096, set referrerURL to

    //    referrerOrigin.

    if (referrer_url.has_value() && referrer_url.value().serialize().length() > 4096)

        referrer_url = referrer_origin;

    // 7. The user agent MAY alter referrerURL or referrerOrigin at this point to enforce arbitrary policy

    //    considerations in the interests of minimizing data leakage. For example, the user agent could strip the URL

    //    down to an origin, modify its host, replace it with an empty string, etc.

    // 8. Execute the statements corresponding to the value of policy:

    // Note: If request’s referrer policy is the empty string, Fetch will not call into this algorithm.

    VERIFY(policy != ReferrerPolicy::EmptyString);

    switch (policy) {

    // "no-referrer"

    case ReferrerPolicy::NoReferrer:

        // Return no referrer

        return {};

    // "origin"

    case ReferrerPolicy::Origin:

        // Return referrerOrigin

        return referrer_origin;

    // "unsafe-url"

    case ReferrerPolicy::UnsafeURL:

        // Return referrerURL.

        return referrer_url;

    // "strict-origin"

    case ReferrerPolicy::StrictOrigin:

        // 1. If referrerURL is a potentially trustworthy URL and request’s current URL is not a potentially

        //    trustworthy URL, then return no referrer.

        if (referrer_url.has_value()

            && SecureContexts::is_url_potentially_trustworthy(*referrer_url) == SecureContexts::Trustworthiness::PotentiallyTrustworthy

            && SecureContexts::is_url_potentially_trustworthy(request.current_url()) == SecureContexts::Trustworthiness::NotTrustworthy) {

            return {};

        }

        // 2. Return referrerOrigin.

        return referrer_origin;

    // "strict-origin-when-cross-origin"

    case ReferrerPolicy::StrictOriginWhenCrossOrigin:

        // 1. If the origin of referrerURL and the origin of request’s current URL are the same, then return

        //    referrerURL.

        if (referrer_url.has_value() && referrer_url->origin().is_same_origin(request.current_url().origin()))

            return referrer_url;

        // 2. If referrerURL is a potentially trustworthy URL and request’s current URL is not a potentially

        //    trustworthy URL, then return no referrer.

        if (referrer_url.has_value()

            && SecureContexts::is_url_potentially_trustworthy(*referrer_url) == SecureContexts::Trustworthiness::PotentiallyTrustworthy

            && SecureContexts::is_url_potentially_trustworthy(request.current_url()) == SecureContexts::Trustworthiness::NotTrustworthy) {

            return {};

        }

        // 3. Return referrerOrigin.

        return referrer_origin;

    // "same-origin"

    case ReferrerPolicy::SameOrigin:

        // 1. If the origin of referrerURL and the origin of request’s current URL are the same, then return

        //    referrerURL.

        if (referrer_url.has_value()

            && referrer_url->origin().is_same_origin(request.current_url().origin())) {

            return referrer_url;

        }

        // 2. Return no referrer.

        return {};

    // "origin-when-cross-origin"

    case ReferrerPolicy::OriginWhenCrossOrigin:

        // 1. If the origin of referrerURL and the origin of request’s current URL are the same, then return

        //    referrerURL.

        if (referrer_url.has_value()

            && referrer_url->origin().is_same_origin(request.current_url().origin())) {

            return referrer_url;

        }

        // 2. Return referrerOrigin.

        return referrer_origin;

    // "no-referrer-when-downgrade"

    case ReferrerPolicy::NoReferrerWhenDowngrade:

        // 1. If referrerURL is a potentially trustworthy URL and request’s current URL is not a potentially

        //    trustworthy URL, then return no referrer.

        if (referrer_url.has_value()

            && SecureContexts::is_url_potentially_trustworthy(*referrer_url) == SecureContexts::Trustworthiness::PotentiallyTrustworthy

            && SecureContexts::is_url_potentially_trustworthy(request.current_url()) == SecureContexts::Trustworthiness::NotTrustworthy) {

            return {};

        }

        // 2. Return referrerURL.

        return referrer_url;

    default:

        VERIFY_NOT_REACHED();

    }

}

// https://w3c.github.io/webappsec-referrer-policy/#strip-url

Optional<URL::URL> strip_url_for_use_as_referrer(Optional<URL::URL> url, OriginOnly origin_only)

{

    // 1. If url is null, return no referrer.

    if (!url.has_value())

        return {};

    // 2. If url’s scheme is a local scheme, then return no referrer.

    if (Fetch::Infrastructure::LOCAL_SCHEMES.span().contains_slow(url->scheme()))

        return {};

    // 3. Set url’s username to the empty string.

    url->set_username(""sv);

    // 4. Set url’s password to the empty string.

    url->set_password(""sv);

    // 5. Set url’s fragment to null.

    url->set_fragment({});

    // 6. If the origin-only flag is true, then:

    if (origin_only == OriginOnly::Yes) {

        // 1. Set url’s path to « the empty string ».

        url->set_paths({ ""sv });

        // 2. Set url’s query to null.

        url->set_query({});

    }

    // 7. Return url.

    return url;

}

}