source: node_modules/prismjs/plugins/diff-highlight/prism-diff-highlight.js@ d24f17c

(function () {

        if (typeof Prism === 'undefined') {
                return;
        }


        var LANGUAGE_REGEX = /^diff-([\w-]+)/i;
        var HTML_TAG = /<\/?(?!\d)[^\s>\/=$<%]+(?:\s(?:\s*[^\s>\/=]+(?:\s*=\s*(?:"[^"]*"|'[^']*'|[^\s'">=]+(?=[\s>]))|(?=[\s/>])))+)?\s*\/?>/g;
        //this will match a line plus the line break while ignoring the line breaks HTML tags may contain.
        var HTML_LINE = RegExp(/(?:__|[^\r\n<])*(?:\r\n?|\n|(?:__|[^\r\n<])(?![^\r\n]))/.source.replace(/__/g, function () { return HTML_TAG.source; }), 'gi');

        var warningLogged = false;

        Prism.hooks.add('before-sanity-check', function (env) {
                var lang = env.language;
                if (LANGUAGE_REGEX.test(lang) && !env.grammar) {
                        env.grammar = Prism.languages[lang] = Prism.languages.diff;
                }
        });
        Prism.hooks.add('before-tokenize', function (env) {
                if (!warningLogged && !Prism.languages.diff && !Prism.plugins.autoloader) {
                        warningLogged = true;
                        console.warn("Prism's Diff Highlight plugin requires the Diff language definition (prism-diff.js)." +
                                "Make sure the language definition is loaded or use Prism's Autoloader plugin.");
                }

                var lang = env.language;
                if (LANGUAGE_REGEX.test(lang) && !Prism.languages[lang]) {
                        Prism.languages[lang] = Prism.languages.diff;
                }
        });

        Prism.hooks.add('wrap', function (env) {
                var diffLanguage; var diffGrammar;

                if (env.language !== 'diff') {
                        var langMatch = LANGUAGE_REGEX.exec(env.language);
                        if (!langMatch) {
                                return; // not a language specific diff
                        }

                        diffLanguage = langMatch[1];
                        diffGrammar = Prism.languages[diffLanguage];
                }

                var PREFIXES = Prism.languages.diff && Prism.languages.diff.PREFIXES;

                // one of the diff tokens without any nested tokens
                if (PREFIXES && env.type in PREFIXES) {
                        /** @type {string} */
                        var content = env.content.replace(HTML_TAG, ''); // remove all HTML tags

                        /** @type {string} */
                        var decoded = content.replace(/&lt;/g, '<').replace(/&amp;/g, '&');

                        // remove any one-character prefix
                        var code = decoded.replace(/(^|[\r\n])./g, '$1');

                        // highlight, if possible
                        var highlighted;
                        if (diffGrammar) {
                                highlighted = Prism.highlight(code, diffGrammar, diffLanguage);
                        } else {
                                highlighted = Prism.util.encode(code);
                        }

                        // get the HTML source of the prefix token
                        var prefixToken = new Prism.Token('prefix', PREFIXES[env.type], [/\w+/.exec(env.type)[0]]);
                        var prefix = Prism.Token.stringify(prefixToken, env.language);

                        // add prefix
                        var lines = []; var m;
                        HTML_LINE.lastIndex = 0;
                        while ((m = HTML_LINE.exec(highlighted))) {
                                lines.push(prefix + m[0]);
                        }
                        if (/(?:^|[\r\n]).$/.test(decoded)) {
                                // because both "+a\n+" and "+a\n" will map to "a\n" after the line prefixes are removed
                                lines.push(prefix);
                        }
                        env.content = lines.join('');

                        if (diffGrammar) {
                                env.classes.push('language-' + diffLanguage);
                        }
                }
        });

}());