/**
 * This file is part of Haketilo.
 *
 * Function: Injecting policy to page by modifying HTTP headers.
 *
 * Copyright (C) 2021, Wojtek Kosior
 * Copyright (C) 2021, jahoti
 *
 * 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 this code in a
 * proprietary program, I am not going to enforce this in court.
 */

/*
 * IMPORTS_START
 * IMPORT sign_data
 * IMPORT extract_signed
 * IMPORT make_csp_rule
 * IMPORT csp_header_regex
 * IMPORTS_END
 */

function inject_csp_headers(headers, policy)
{
    let csp_headers;
    let old_signature;
    let haketilo_header;

    for (const header of headers.filter(h => h.name === "x-haketilo")) {
	/* x-haketilo header has format: <signature>_0_<data> */
	const match = /^([^_]+)_(0_.*)$/.exec(header.value);
	if (!match)
	    continue;

	const result = extract_signed(...match.slice(1, 3));
	if (result.fail)
	    continue;

	/* This should succeed - it's our self-produced valid JSON. */
	const old_data = JSON.parse(decodeURIComponent(result.data));

	/* Confirmed- it's the originals, smuggled in! */
	csp_headers = old_data.csp_headers;
	old_signature = old_data.policy_sig;

	haketilo_header = header;
	break;
    }

    if (policy.has_payload) {
	csp_headers = [];
	const non_csp_headers = [];
	const header_list =
	      h => csp_header_regex.test(h) ? csp_headers : non_csp_headers;
	headers.forEach(h => header_list(h.name).push(h));
	headers = non_csp_headers;
    } else {
	headers.push(...csp_headers || []);
    }

    if (!haketilo_header) {
	haketilo_header = {name: "x-haketilo"};
	headers.push(haketilo_header);
    }

    if (old_signature)
	headers = headers.filter(h => h.value.search(old_signature) === -1);

    const policy_str = encodeURIComponent(JSON.stringify(policy));
    const signed_policy = sign_data(policy_str, new Date().getTime());
    const later_30sec = new Date(new Date().getTime() + 30000).toGMTString();
    headers.push({
	name: "Set-Cookie",
	value: `haketilo-${signed_policy.join("=")}; Expires=${later_30sec};`
    });

    /*
     * Smuggle in the signature and the original CSP headers for future use.
     * These are signed with a time of 0, as it's not clear there is a limit on
     * how long Firefox might retain headers in the cache.
     */
    let haketilo_data = {csp_headers, policy_sig: signed_policy[0]};
    haketilo_data = encodeURIComponent(JSON.stringify(haketilo_data));
    haketilo_header.value = sign_data(haketilo_data, 0).join("_");

    if (!policy.allow) {
	headers.push({
	    name: "content-security-policy",
	    value: make_csp_rule(policy)
	});
    }

    return headers;
}

/*
 * EXPORTS_START
 * EXPORT inject_csp_headers
 * EXPORTS_END
 */