VinSpee/rereplace

import fs from 'fs-jetpack';
const createRegexFromString = (str) => {
    const regParts = str.match(/^\/(.*?)\/([gim]*)$/);
    let regexp;
    if (regParts) {
        regexp = new RegExp(regParts[1], regParts[2]);
    } else {
        regexp = new RegExp(str);
    }
    return regexp;
};

const getFile = file => {
    if (fs.exists(file) !== 'file') {
        throw new Error(`Output file doesn't exist`);
    }
    return fs.read(file);
};

const getModifiedOutput = (pattern, modifier, output) => {
    const tokenToReplace = pattern.exec(output)[1];
    if (!tokenToReplace) {
        throw new Error('The pattern was not found in the file.');
    }
    return output.replace(tokenToReplace, modifier);
};

const rereplace = (input = [], flags) => {
    let inFile;
    let outFile;
    if (!input || input.length !== 3) {
        return '';
    }
    try {
        inFile = getFile(input[1]);
        outFile = getFile(input[2]);
    } catch (e) {
        return e;
    }

    const params = {
        pattern: createRegexFromString(input[0]),
        input: inFile,
        output: outFile,
    };

    let modifiedOutput;
    try {
        modifiedOutput = getModifiedOutput(params.pattern, params.input, params.output);
    } catch (e) {
        throw e;
    }
    fs.write(input[2], modifiedOutput, { atomic: true });
    if (flags && flags.silent) {
        console.log(`injected ${input[1]} to ${input[2]}`);
    }
    return modifiedOutput;
};

export default rereplace;