ST regex engine POC.

ST-regex.js

// Goal: Provide regex replacement with any regex string
// Advantages:
//  - Lots of flexibility. Any regex string can be used
//  - Strings with the same delimiter can be used
// Disadvantages:
//  - Requires the user to know how regex works
//  - More complicated UI
//  - Can become confusing, fast.

// matchRegexString - Can be anything. In this case it checks for if the string is surrounded by braces and grabs with braces.
// endingChar - Can be anything. In this case it checks for if the string is surrounded by braces and grabs w/o braces.
// exampleString - The example string that's passed to the parser
// charName - The character's name. Ideally, this will be dynamic
const matchRegexString = "/\`([^`]*)`/g";
const exampleString = "`She looks very pretty today` Hey! how are you doing? `This is a pen`";
const replaceString = "`{{char}}'s thoughts: {{match}}`"
const charName = "Manami";

// From: https://github.com/IonicaBizau/regex-parser.js/blob/master/lib/index.js
function regexFromString(input) {
    // Parse input
    var m = input.match(/(\/?)(.+)\1([a-z]*)/i);

    // Invalid flags
    if (m[3] && !/^(?!.*?(.).*?\1)[gmixXsuUAJ]+$/.test(m[3])) {
        return RegExp(input);
    }

    // Create the regular expression
    return new RegExp(m[2], m[3]);
}

function parseString(matchRegexString, replaceString, exampleString) {
    const matchRegex = regexFromString(matchRegexString);

    let newString = exampleString;
    while ((match = matchRegex.exec(exampleString)) !== null) {
        const fencedMatch = match[0];
        const capturedMatch = match[1];

        // TODO: Use substrings for replacement. But not necessary at this time.
        // A substring is from match.index to match.index + match[0].length or fencedMatch.length
        const subReplaceString = substituteParams(replaceString, { regexMatch: capturedMatch, charName });
        newString = newString.replace(fencedMatch, subReplaceString);

        if (!matchRegex.flags.includes('g')) {
            break;            
        }
    }

    console.log(newString);
}

// Substitutes parameters 
function substituteParams(rawString, { regexMatch, charName }) {
    return rawString.replace("{{match}}", regexMatch).replace("{{char}}", charName);
}

parseString(matchRegexString, replaceString, exampleString);