ニコニコ動画のコメントを正規表現でNGするスクリプト

nicovideo_regexp_comment_ng.js

// ==UserScript==
// @name         nicovideo_regexp_comment_ng
// @version      0.1
// @description  ニコニコ動画のコメントを正規表現でNGするスクリプト。EscキーでNGパターンを変更して保存できます。
// @match        https://www.nicovideo.jp/watch/*
// ==/UserScript==

(function() {
    'use strict';

    const storageKey = 'regexp_comment_ng';
    const patDefault = 'NG|厨|信者|批判|文句|民度|名人|幼稚|小学生|キッズ|ガキ|ゆとり';

    let image_to_is_safe;
    let patCurrent = null;
    let regexp;
    const updatePat = (pat) => {
        if (pat !== patCurrent) {
            try {
                regexp = new RegExp(pat, 'i');
                patCurrent = pat;
                image_to_is_safe = new WeakMap();
                localStorage.setItem(storageKey, pat);
                console.log('NGパターンが更新された');
            } catch(e) {
                return false;
            }
        }
        return true;
    };
    updatePat(localStorage.getItem(storageKey) ?? patDefault);

    document.addEventListener('keyup', e => {
        if (e.code === 'Escape') {
            let pat = localStorage.getItem(storageKey);
            while (true) {
                pat = prompt('NGパターン設定', pat);
                if (!pat || updatePat(pat)) {
                    break;
                }
            }
        }
    });

    // createElementで生成されたcanvasのfillTextを監視
    const canvas_to_text = new WeakMap();
    const createElement = document.createElement;
    document.createElement = function(tagName, ...args) {
        const elem = createElement.call(this, tagName, ...args);
        if (tagName === 'canvas') {
            const ctx = elem.getContext('2d');
            const fillText = ctx.fillText;
            ctx.fillText = function(text, ...args) {
                canvas_to_text.set(elem, text);
                return fillText.call(this, text, ...args);
            };
        }
        return elem;
    };
    // コメント描画canvasのdrawImageを監視
    const modifyCommentCanvas = () => {
        const commentCanvas = document.querySelector('.CommentRenderer > canvas');
        if (!commentCanvas) {
            setTimeout(modifyCommentCanvas, 100);
            return;
        }
        const commentCtx = commentCanvas.getContext('2d');
        const drawImage = commentCtx.drawImage;
        commentCtx.drawImage = function(image, ...args) {
            let is_safe = image_to_is_safe.get(image);
            if (is_safe === undefined) {
                const text = canvas_to_text.get(image);
                if (text === undefined) {
                    is_safe = true;
                } else {
                    const m = text.match(regexp);
                    if (m) {
                        console.log('NG', m[0]);
                        is_safe = false;
                    } else {
                        is_safe = true;
                    }
                }
                image_to_is_safe.set(image, is_safe);
            }
            if (is_safe) {
                drawImage.call(this, image, ...args);
            }
        };
        console.log('コメント描画のCanvasを書き換えた');
    };
    modifyCommentCanvas();
})();