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src/app.js

@@ -1 +1,41 @@
 'use strict';
+
+const { generateNumber } = require('./generateNumber');
+const { calculateBullsAndCows } = require('./calculateBullsAndCows');
+const { terminal } = require('./userInterface');
+const { validateInput } = require('./validateInput');
+const {
+  QUESTION,
+  WINNER_MESSAGE,
+  INVALID_INPUT_MESSAGE,
+} = require('./constants');
+
+const generatedNumber = generateNumber();
+
+function askQuestion() {
+  terminal.question(QUESTION, (userNumber) => {
+    const isInputValid = validateInput(userNumber);
+
+    if (!isInputValid) {
+      terminal.write(INVALID_INPUT_MESSAGE);
+      askQuestion();
+
+      return;
+    }
+
+    if (+userNumber === generatedNumber) {
+      terminal.write(WINNER_MESSAGE);
+      terminal.close();
+
+      return;
+    }
+
+    const { bulls, cows } = calculateBullsAndCows(userNumber, generatedNumber);
+    const WRONG_GUESS_MESSAGE = `Bulls: ${bulls}, Cows: ${cows}\n`;
+
+    terminal.write(WRONG_GUESS_MESSAGE);
+    askQuestion();
+  });
+}
+
+askQuestion();

src/calculateBullsAndCows.js

@@ -0,0 +1,22 @@
+'use strict';
+
+const { DEFAULT_ANSWER_VALUE } = require('./constants');
+
+function calculateBullsAndCows(userNumber, generatedNumber) {
+  const userNumberSplited = userNumber.split('');
+  const generatedStringNumber = String(generatedNumber);
+
+  return userNumberSplited.reduce((acc, number, index) => {
+    if (number === generatedStringNumber[index]) {
+      acc.bulls++;
+    } else if (generatedStringNumber.includes(number)) {
+      acc.cows++;
+    }
+
+    return acc;
+  }, { ...DEFAULT_ANSWER_VALUE });
+}
+
+module.exports = {
+  calculateBullsAndCows,
+};

src/constants.js

@@ -0,0 +1,20 @@
+'use strict';
+
+const DEFAULT_ANSWER_VALUE = {
+  bulls: 0,
+  cows: 0,
+};
+
+const QUESTION = 'Please enter your 4-digit guess: ';
+const INVALID_INPUT_MESSAGE = 'Expecting a number of 4 different digits\n';
+const WINNER_MESSAGE = "Congratulations! You've guessed the number!";
+
+const EXPECTED_NUMBER_LENGTH = 4;
+
+module.exports = {
+  DEFAULT_ANSWER_VALUE,
+  QUESTION,
+  INVALID_INPUT_MESSAGE,
+  WINNER_MESSAGE,
+  EXPECTED_NUMBER_LENGTH,
+};

src/generateNumber.js

@@ -0,0 +1,26 @@
+'use strict';
+
+const { EXPECTED_NUMBER_LENGTH } = require('./constants');
+
+function generateNumber() {
+  const digitsToInsert = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
+  const distinctDigits = [];
+
+  while (distinctDigits.length < EXPECTED_NUMBER_LENGTH) {
+    const randomIndex = Math.floor(Math.random() * digitsToInsert.length);
+
+    if (!distinctDigits.length && digitsToInsert[randomIndex] === 0) {
+      continue;
+    }
+
+    const digitToInsert = digitsToInsert.splice(randomIndex, 1);
+
+    distinctDigits.push(digitToInsert);
+  }
+
+  return +distinctDigits.join('');
+}
+
+module.exports = {
+  generateNumber,
+};

src/userInterface.js

@@ -0,0 +1,12 @@
+'use strict';
+
+const readline = require('readline');
+
+const terminal = readline.createInterface({
+  input: process.stdin,
+  output: process.stdout,
+});
+
+module.exports = {
+  terminal,
+};

src/validateInput.js

@@ -0,0 +1,16 @@
+'use strict';
+
+const { EXPECTED_NUMBER_LENGTH } = require('./constants');
+
+function validateInput(input) {
+  const inputSplited = input.split('');
+  const inputSet = new Set(inputSplited);
+  const hasValidLength = inputSplited.length === EXPECTED_NUMBER_LENGTH;
+  const hasDistinctDigits = inputSplited.length === inputSet.size;
+
+  return hasValidLength && hasDistinctDigits;
+};
+
+module.exports = {
+  validateInput,
+};