/*******************************************************************************

    uBlock Origin - a comprehensive, efficient content blocker
    Copyright (C) 2021-present Raymond Hill

    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.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see {http://www.gnu.org/licenses/}.

    Home: https://github.com/gorhill/uBlock
*/

import { StaticExtFilteringHostnameDB } from './static-ext-filtering-db.js';
import { entityFromHostname } from './uri-utils.js';
import logger from './logger.js';
import { sessionFirewall } from './filtering-engines.js';
import µb from './background.js';

/******************************************************************************/

const duplicates = new Set();
const filterDB = new StaticExtFilteringHostnameDB();

let acceptedCount = 0;
let discardedCount = 0;

const headerIndexFromName = function(name, headers, start = 0) {
    for ( let i = start; i < headers.length; i++ ) {
        if ( headers[i].name.toLowerCase() !== name ) { continue; }
        return i;
    }
    return -1;
};

const logOne = function(isException, token, fctxt) {
    fctxt.duplicate()
        .setRealm('extended')
        .setType('header')
        .setFilter({
            modifier: true,
            result: isException ? 2 : 1,
            source: 'extended',
            raw: `${(isException ? '#@#' : '##')}^responseheader(${token})`,
        })
        .toLogger();
};

const httpheaderFilteringEngine = {
    get acceptedCount() {
        return acceptedCount;
    },
    get discardedCount() {
        return discardedCount;
    }
};

httpheaderFilteringEngine.reset = function() {
    filterDB.clear();
    duplicates.clear();
    acceptedCount = 0;
    discardedCount = 0;
};

httpheaderFilteringEngine.freeze = function() {
    duplicates.clear();
    filterDB.collectGarbage();
};

httpheaderFilteringEngine.compile = function(parser, writer) {
    writer.select('HTTPHEADER_FILTERS');

    const isException = parser.isException();
    const headerName = parser.getResponseheaderName();

    // Tokenless is meaningful only for exception filters.
    if ( headerName === '' && isException === false ) { return; }

    // Only exception filters are allowed to be global.
    if ( parser.hasOptions() === false ) {
        if ( isException ) {
            writer.push([ 64, '', 1, headerName ]);
        }
        return;
    }

    // https://github.com/gorhill/uBlock/issues/3375
    //   Ignore instances of exception filter with negated hostnames,
    //   because there is no way to create an exception to an exception.

    for ( const { hn, not, bad } of parser.getExtFilterDomainIterator() ) {
        if ( bad ) { continue; }
        const prefix = ((isException ? 1 : 0) ^ (not ? 1 : 0)) ? '-' : '+';
        writer.push([ 64, hn, `${prefix}${headerName}` ]);
    }
};

// 01234567890123456789
// responseheader(name)
//                ^   ^
//               15  -1

httpheaderFilteringEngine.fromCompiledContent = function(reader) {
    reader.select('HTTPHEADER_FILTERS');

    while ( reader.next() ) {
        acceptedCount += 1;
        const fingerprint = reader.fingerprint();
        if ( duplicates.has(fingerprint) ) {
            discardedCount += 1;
            continue;
        }
        duplicates.add(fingerprint);
        const args = reader.args();
        filterDB.store(args[1], args[2]);
    }
};

httpheaderFilteringEngine.apply = function(fctxt, headers) {
    if ( filterDB.size === 0 ) { return; }

    const hostname = fctxt.getHostname();
    if ( hostname === '' ) { return; }

    const all = new Set();
    filterDB.retrieveSpecifics(all, hostname);
    const entity = entityFromHostname(hostname, fctxt.getDomain());
    filterDB.retrieveSpecifics(all, entity);
    filterDB.retrieveSpecificsByRegex(all, hostname, fctxt.url);
    filterDB.retrieveGenerics(all);
    if ( all.size === 0 ) { return; }

    // https://github.com/gorhill/uBlock/issues/2835
    //   Do not filter response headers if the site is under an `allow` rule.
    if ( µb.userSettings.advancedUserEnabled ) {
        if ( sessionFirewall.evaluateCellZY(hostname, hostname, '*') === 2 ) { return; }
    }

    // Split filters in different groups
    const filters = new Set();
    const exceptions = new Set();
    for ( const s of all ) {
        const selector = s.slice(1);
        if ( s.charCodeAt(0) === 0x2D /* - */ ) {
            exceptions.add(selector);
        } else {
            filters.add(selector);
        }
    }

    const hasGlobalException = exceptions.has('');

    let modified = false;
    let i = 0;

    for ( const name of filters ) {
        const isExcepted = hasGlobalException || exceptions.has(name);
        if ( isExcepted ) {
            if ( logger.enabled ) {
                logOne(true, hasGlobalException ? '' : name, fctxt);
            }
            continue;
        }
        i = 0;
        for (;;) {
            i = headerIndexFromName(name, headers, i);
            if ( i === -1 ) { break; }
            headers.splice(i, 1);
            if ( logger.enabled ) {
                logOne(false, name, fctxt);
            }
            modified = true;
        }
    }

    return modified;
};

httpheaderFilteringEngine.toSelfie = function() {
    return filterDB.toSelfie();
};

httpheaderFilteringEngine.fromSelfie = function(selfie) {
    filterDB.fromSelfie(selfie);
};

/******************************************************************************/

export default httpheaderFilteringEngine;

/******************************************************************************/