const fs = require('fs');
const path = require('path');

function replaceOption(string, key, value) {
    const re = new RegExp(`\\$\{${key}\}`, 'g');
    return string.replace(re, value);
}

function cleanUnsetVars(string) {
    const re = new RegExp('\\$\{[a-zA-Z-_]+\}', 'g');
    return string.replace(re, '');
}

module.exports.get = (templateName, options, callback) => {
    const filename = path.join(__dirname, 'templates', templateName + '.template');

    fs.readFile(filename, 'utf-8', (err, template) => {
        if (err) {
            callback(err);
            return;
        }
        const replaced = Object.keys(options).reduce((memo, key) => {
            return replaceOption(memo, key, options[key]);
        }, template);

        const result = cleanUnsetVars(replaced);

        callback(null, result);
    });
};