/**
 * This file is part of Haketilo.
 *
 * Function: Determining what to do on a given web page.
 *
 * Copyright (C) 2021 Wojtek Kosior
 *
 * 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/patterns_query_tree.js AS pqt

#FROM common/sha256.js IMPORT sha256

/*
 * CSP rule that either blocks all scripts or only allows scripts with specified
 * nonce attached.
 */
function make_csp(nonce)
{
    const rule = nonce ? `nonce-${nonce}` : "none";
    const csp_dict = {"prefetch-src": "none", "script-src-attr": "none"};
    Object.assign(csp_dict, {"script-src": rule, "script-src-elem": rule});
    return Object.entries(csp_dict).map(([a, b]) => `${a} '${b}';`).join(" ");
}

function decide_policy(patterns_tree, url, default_allow, secret)
{
    const policy = {allow: default_allow};

    try {
	var payloads = pqt.search(patterns_tree, url).next().value;
    } catch (e) {
	console.error("Haketilo:", e);
	policy.allow = false;
	policy.error = {haketilo_error_type: "deciding_policy"};
    }

    if (payloads !== undefined) {
	/*
	 * mapping will be either the actual mapping identifier or "~allow" if
	 * we matched a simple script block/allow rule.
	 */
	policy.mapping = Object.keys(payloads).sort()[0];
	const payload = payloads[policy.mapping];
	if (policy.mapping === "~allow") {
	    /* Convert 0/1 back to false/true. */
	    policy.allow = !!payload;
	} else /* if (payload.identifier) */ {
	    policy.allow = false;
	    policy.payload = payload;
	    /*
	     * Hash a secret and other values into a string that's unpredictable
	     * to someone who does not know these values. What we produce here
	     * is not a true "nonce" because it might get produced multiple
	     * times given the same url and mapping choice. Nevertheless, this
	     * is reasonably good given the limitations WebExtension APIs and
	     * environments give us. If we were using a true nonce, we'd have no
	     * reliable way of passing it to our content scripts.
	     */
	    const nonce_source = [
		policy.mapping,
		policy.payload.identifier,
		url,
		secret
	    ];
	    policy.nonce = sha256(nonce_source.join(":"));
	}
    }

    if (!policy.allow)
	policy.csp = make_csp(policy.nonce);

    return policy;
}
#EXPORT decide_policy

#EXPORT  () => ({allow: false, csp: make_csp()})  AS fallback_policy