/*
 * 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/HTTP/Responses.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 = response.header_list()->extract_header_list_values("Referrer-Policy"sv);

    // 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.
    if (auto const* policy_tokens = policy_tokens_or_failure.get_pointer<Vector<ByteString>>()) {
        for (auto const& 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()) {
        auto serialized_referrer_url = referrer_url.value().serialize();
        if (serialized_referrer_url.bytes().size() > 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;
}

}
