/**
 * This file is part of Haketilo.
 *
 * Function: Modify HTTP traffic usng webRequest API.
 *
 * Copyright (C) 2021 Wojtek Kosior <koszko@koszko.org>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * As additional permission under GNU GPL version 3 section 7, you
 * may distribute forms of that code without the copy of the GNU
 * GPL normally required by section 4, provided you include this
 * license notice and, in case of non-source distribution, a URL
 * through which recipients can access the Corresponding Source.
 * If you modify file(s) with this exception, you may extend this
 * exception to your version of the file(s), but you are not
 * obligated to do so. If you do not wish to do so, delete this
 * exception statement from your version.
 *
 * As a special exception to the GPL, any HTML file which merely
 * makes function calls to this code, and for that purpose
 * includes it by reference shall be deemed a separate work for
 * copyright law purposes. If you modify this code, you may extend
 * this exception to your version of the code, but you are not
 * obligated to do so. If you do not wish to do so, delete this
 * exception statement from your version.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 *
 * I, Wojtek Kosior, thereby promise not to sue for violation of this file's
 * license. Although I request that you do not make use of this code in a
 * proprietary program, I am not going to enforce this in court.
 */

#IMPORT common/indexeddb.js        AS haketilodb
#IF MOZILLA
#IMPORT background/stream_filter.js
#ENDIF

#FROM common/browser.js IMPORT browser
#FROM common/misc.js    IMPORT is_privileged_url, csp_header_regex
#FROM common/policy.js  IMPORT decide_policy

#FROM background/patterns_query_manager.js IMPORT tree, default_allow

let secret;

function on_headers_received(details)
{
    const url = details.url;
    if (is_privileged_url(details.url))
	return;

    let headers = details.responseHeaders;

    const policy =
	  decide_policy(tree, details.url, !!default_allow.value, secret);
    if (policy.allow)
	return;

    if (policy.payload)
	headers = headers.filter(h => !csp_header_regex.test(h.name));

    headers.push({name: "Content-Security-Policy", value: policy.csp});

#IF MOZILLA
    let skip = false;
    for (const header of headers) {
	if (header.name.toLowerCase().trim() !== "content-disposition")
	    continue;

	if (/^\s*attachment\s*(;.*)$/i.test(header.value)) {
		skip = true;
	} else {
	    skip = false;
	    break;
	}
    }
    skip = skip || (details.statusCode >= 300 && details.statusCode < 400);

    if (!skip)
	headers = stream_filter.apply(details, headers, policy);
#ENDIF

    return {responseHeaders: headers};
}

#IF CHROMIUM && MV2
const request_url_regex = /^[^?]*\?url=(.*)$/;
const redirect_url_template = browser.runtime.getURL("dummy") + "?settings=";

function on_before_request(details)
{
    /*
     * Content script will make a synchronous XmlHttpRequest to extension's
     * `dummy` file to query settings for given URL. We smuggle that
     * information in query parameter of the URL we redirect to.
     * A risk of fingerprinting arises if a page with script execution allowed
     * guesses the dummy file URL and makes an AJAX call to it. It is currently
     * a problem in ManifestV2 Chromium-family port of Haketilo because Chromium
     * uses predictable URLs for web-accessible resources. We plan to fix it in
     * the future ManifestV3 port.
     */
    if (details.type !== "xmlhttprequest")
	return {cancel: true};

    if (details.url.startsWith(redirect_url_template))
	return;

#IF DEBUG
    console.debug(`Haketilo: Settings queried using XHR for '${details.url}'.`);
#ENDIF

    /*
     * request_url should be of the following format:
     *     <url_for_extension's_dummy_file>?url=<valid_urlencoded_url>
     */
    const match = request_url_regex.exec(details.url);
    if (match) {
	const queried_url = decodeURIComponent(match[1]);

	if (details.initiator && !queried_url.startsWith(details.initiator)) {
	    console.warn(`Haketilo: Blocked suspicious query of '${url}' by '${details.initiator}'. This might be the result of page fingerprinting the browser.`);
	    return {cancel: true};
	}

	const policy = decide_policy(tree, queried_url, default_allow, secret);
	if (!policy.error) {
	    const encoded_policy = encodeURIComponent(JSON.stringify(policy));
	    return {redirectUrl: redirect_url_template + encoded_policy};
	}
    }

    console.warn(`Haketilo: Bad request! Expected ${browser.runtime.getURL("dummy")}?url=<valid_urlencoded_url>. Got ${details.url}. This might be the result of page fingerprinting the browser.`);

    return {cancel: true};
}

const all_types = [
    "main_frame", "sub_frame", "stylesheet", "script", "image", "font",
    "object", "xmlhttprequest", "ping", "csp_report", "media", "websocket",
    "other", "main_frame", "sub_frame"
];
#ENDIF

async function start(secret_)
{
    secret = secret_;

#IF CHROMIUM
    const extra_opts = ["blocking", "extraHeaders"];
#ELSE
    const extra_opts = ["blocking"];
#ENDIF

    browser.webRequest.onHeadersReceived.addListener(
	on_headers_received,
	{urls: ["<all_urls>"], types: ["main_frame", "sub_frame"]},
	extra_opts.concat("responseHeaders")
    );

#IF CHROMIUM && MV2
    browser.webRequest.onBeforeRequest.addListener(
	on_before_request,
	{urls: [browser.runtime.getURL("dummy") + "*"], types: all_types},
	extra_opts
    );
#ENDIF
}
#EXPORT start