Prompt for y/N Without readline Cruft

// Split the prompt into two pieces. The pure half ('did the user type yes?')
// is testable; the IO half (read a line from stdin) is the thin wrapper that
// changes between Node, browser, and a test harness.

// Pure: takes the raw answer string, returns boolean per the default-no rule.
function interpretAnswer(rawAnswer, defaultAnswer) {
    const trimmed = String(rawAnswer || '').trim().toLowerCase();
    if (trimmed === '') return defaultAnswer;
    return trimmed === 'y' || trimmed === 'yes';
}

// The hint is what tells the user the default. Capital N is the convention
// every git/cargo/kubectl prompt uses; veteran terminal users read it as
// 'press Enter for no'.
function promptHint(defaultAnswer) {
    return defaultAnswer ? '[Y/n]' : '[y/N]';
}

// Tests of the pure layer; in a real codebase these go in a Jest file.
const cases = [
    ['',     false, false],
    ['',     true,  true ],
    ['y',    false, true ],
    ['Yes',  false, true ],
    ['n',    true,  false],
    ['lol',  true,  false],
    ['  Y ', false, true ],
];
for (const [input, def, expected] of cases) {
    const got = interpretAnswer(input, def);
    const marker = got === expected ? 'ok ' : 'FAIL';
    console.log(`${marker} interpretAnswer(${JSON.stringify(input)}, default=${def}) = ${got}`);
}
console.log('hint default=false:', promptHint(false));
console.log('hint default=true :', promptHint(true));

// In a Node script you compose the pure parser with readline. The wrapper is
// twelve lines; everything that matters is in the pure layer above.
//
// The code in this accordion is the SHAPE you would copy into a Node script.
// In this snippet we run it against a fake stdin to keep the demo runnable
// in any sandbox.

function interpretAnswer(rawAnswer, defaultAnswer) {
    const trimmed = String(rawAnswer || '').trim().toLowerCase();
    if (trimmed === '') return defaultAnswer;
    return trimmed === 'y' || trimmed === 'yes';
}

// In a real Node script:
//   const readline = require('readline');
//   function confirm(question, { default: defaultAnswer = false } = {}) {
//       const hint = defaultAnswer ? '[Y/n]' : '[y/N]';
//       const rl = readline.createInterface({ input: process.stdin, output: process.stdout });
//       return new Promise((resolve) => {
//           rl.question(`${question} ${hint} `, (answer) => {
//               rl.close();
//               resolve(interpretAnswer(answer, defaultAnswer));
//           });
//       });
//   }
//   const ok = await confirm('Deploy to production?');
//
// For a runnable demo we substitute readline with an injected line-getter:
function makeConfirm(readLine) {
    return async function confirm(question, { default: defaultAnswer = false } = {}) {
        const hint = defaultAnswer ? '[Y/n]' : '[y/N]';
        const answer = await readLine(`${question} ${hint} `);
        return interpretAnswer(answer, defaultAnswer);
    };
}

// Fake stdin: every readLine() call returns the next item from a queued list.
const inputs = ['y', '', 'NO'];
const readLine = (prompt) => {
    const next = inputs.shift();
    console.log(prompt + JSON.stringify(next));
    return Promise.resolve(next);
};

const confirm = makeConfirm(readLine);
(async () => {
    console.log('=> deploy:', await confirm('Deploy to production?'));
    console.log('=> migrate:', await confirm('Run migration?', { default: true }));
    console.log('=> drop   :', await confirm('Drop database?'));
})();