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

    uBlock Origin - a comprehensive, efficient content blocker
    Copyright (C) 2019-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

    The scriptlets below are meant to be injected only into a
    web page context.
*/

import { registerScriptlet } from './base.js';
import { safeSelf } from './safe-self.js';

/* eslint no-prototype-builtins: 0 */

/**
 * @helperScriptlet run-at.fn
 * 
 * @description
 * Execute a function at a specific page-load milestone.
 * 
 * @param fn
 * The function to call.
 * 
 * @param when
 * An identifier which tells when the function should be executed.
 * See <https://developer.mozilla.org/en-US/docs/Web/API/Document/readyState>.
 * 
 * @example
 * `runAt(( ) => { start(); }, 'interactive')`
 * 
 * */

export function runAt(fn, when) {
    const intFromReadyState = state => {
        const targets = {
            'loading': 1, 'asap': 1,
            'interactive': 2, 'end': 2, '2': 2,
            'complete': 3, 'idle': 3, '3': 3,
        };
        const tokens = Array.isArray(state) ? state : [ state ];
        for ( const token of tokens ) {
            const prop = `${token}`;
            if ( targets.hasOwnProperty(prop) === false ) { continue; }
            return targets[prop];
        }
        return 0;
    };
    const runAt = intFromReadyState(when);
    if ( intFromReadyState(document.readyState) >= runAt ) {
        fn(); return;
    }
    const onStateChange = ( ) => {
        if ( intFromReadyState(document.readyState) < runAt ) { return; }
        fn();
        safe.removeEventListener.apply(document, args);
    };
    const safe = safeSelf();
    const args = [ 'readystatechange', onStateChange, { capture: true } ];
    safe.addEventListener.apply(document, args);
}
registerScriptlet(runAt, {
    name: 'run-at.fn',
    dependencies: [
        safeSelf,
    ],
});

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

function runAtHtmlElementFn(fn) {
    if ( document.documentElement ) {
        fn();
        return;
    }
    const observer = new MutationObserver(( ) => {
        observer.disconnect();
        fn();
    });
    observer.observe(document, { childList: true });
}
registerScriptlet(runAtHtmlElementFn, {
    name: 'run-at-html-element.fn',
});