Solution

src/app.js

@@ -1,3 +1,43 @@
+/* eslint-disable no-console */
 'use strict';
 
-// Write your code here
+const readline = require('readline');
+const { generateRandomNumber } = require('./modules/generateRandomNumber');
+const { getBullsAndCows } = require('./modules/getBullsAndCows');
+const { checkIsValidUserInput } = require('./modules/checkIsValidUserInput');
+
+const terminal = readline.createInterface({
+  input: process.stdin,
+  output: process.stdout,
+});
+
+const generatedDigits = generateRandomNumber();
+let firstQuestion = false;
+
+function askUser() {
+  terminal.question(
+    `${firstQuestion ? `Try again ` : `I've chosen a number of 4 different digits. Try to guess it: `}`,
+    (digits) => {
+      if (!checkIsValidUserInput(digits)) {
+        return false;
+      }
+
+      firstQuestion = true;
+
+      const { bulls, cows } = getBullsAndCows(digits, generatedDigits);
+
+      console.log(
+        `Your result: ${bulls > 0 ? `${bulls > 1 ? `${bulls} bulls` : `${bulls} bull`}` : ''}${bulls > 0 && cows > 0 ? ` and ` : ``}${cows > 0 ? `${cows > 1 ? `${cows} cows` : `${cows} cow`}` : ''}`,
+      );
+
+      if (bulls === 4) {
+        console.log('Congratulations. You guessed it.');
+        terminal.close();
+      } else {
+        askUser();
+      }
+    },
+  );
+}
+
+askUser();

src/modules/checkIsValidUserInput.js

@@ -9,7 +9,29 @@
  * @return {boolean} - True if the user input is valid, false otherwise
  */
 function checkIsValidUserInput(userInput) {
-  /* Write your code here */
+  if (isNaN(userInput)) {
+    return false;
+  }
+
+  if (userInput < 1000 || userInput > 9999) {
+    return false;
+  }
+
+  const userInputString = userInput.toString();
+
+  for (let i = 0; i < userInputString.length; i++) {
+    for (let j = i + 1; j < userInputString.length; j++) {
+      if (userInputString[i] === userInputString[j]) {
+        return false;
+      }
+    }
+  }
+
+  if (userInputString[0] === '0') {
+    return false;
+  }
+
+  return true;
 }
 
 module.exports = {

src/modules/generateRandomNumber.js

@@ -7,7 +7,21 @@
  * @return {number} A random 4-digit number
  */
 function generateRandomNumber() {
-  /* Write your code here */
+  const digits = [];
+
+  while (digits.length < 4) {
+    const digit = Math.floor(Math.random() * 10);
+
+    if (digits.length === 0 && digit === 0) {
+      continue;
+    }
+
+    if (!digits.includes(digit)) {
+      digits.push(digit);
+    }
+  }
+
+  return Number(digits.join(''));
 }
 
 module.exports = {

src/modules/getBullsAndCows.js

@@ -1,3 +1,4 @@
+/* eslint-disable no-console */
 'use strict';
 
 /**
@@ -13,7 +14,23 @@
  * Example: { bulls: 1, cows: 2 }
  */
 function getBullsAndCows(userInput, numberToGuess) {
-  /* Write your code here */
+  let bulls = 0;
+  let cows = 0;
+
+  const userInputString = userInput.toString();
+  const numberToGuessString = numberToGuess.toString();
+
+  for (let i = 0; i < userInputString.length; i++) {
+    const digit = userInputString[i];
+
+    if (digit === numberToGuessString[i]) {
+      bulls++;
+    } else if (numberToGuessString.includes(digit)) {
+      cows++;
+    }
+  }
+
+  return { bulls, cows };
 }
 
 module.exports = {