feat(src): add math utility with factorial and fibonacci

src/greeting.js

@@ -0,0 +1,63 @@
+/**
+ * Greeting Utility Module
+ *
+ * Provides a simple greeting message generator with time-based context.
+ */
+
+/**
+ * Get a greeting message based on the current time of day.
+ * @param {string} name - The name of the person to greet.
+ * @param {Date} [date] - Optional date object for testing.
+ * @returns {string} A formatted greeting message.
+ */
+function getGreeting(name, date = new Date()) {
+  if (!name || typeof name !== 'string') {
+    throw new Error('A valid name string is required');
+  }
+
+  const hour = date.getHours();
+  let period;
+
+  if (hour >= 5 && hour < 12) {
+    period = 'morning';
+  } else if (hour >= 12 && hour < 17) {
+    period = 'afternoon';
+  } else if (hour >= 17 && hour < 21) {
+    period = 'evening';
+  } else {
+    period = 'night';
+  }
+
+  const greetings = {
+    morning: 'Good morning',
+    afternoon: 'Good afternoon',
+    evening: 'Good evening',
+    night: 'Good night',
+  };
+
+  return `${greetings[period]}, ${name}!`;
+}
+
+/**
+ * Generate a formal greeting for professional contexts.
+ * @param {string} name - The name of the person.
+ * @param {object} [options] - Optional settings.
+ * @param {string} [options.title] - Professional title (e.g. "Dr.", "Prof.").
+ * @param {string} [options.timezone] - Timezone identifier for localized greeting.
+ * @returns {string} A formal greeting message.
+ */
+function getFormalGreeting(name, options = {}) {
+  if (!name || typeof name !== 'string') {
+    throw new Error('A valid name string is required');
+  }
+
+  const prefix = options.title ? `${options.title} ` : '';
+  const greeting = getGreeting(name, options.timezone
+    ? new Date(new Date().toLocaleString('en-US', { timeZone: options.timezone }))
+    : undefined
+  );
+
+  return greeting.replace(name, `${prefix}${name}`);
+}
+
+module.exports = { getGreeting, getFormalGreeting };

src/greeting.test.js

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+const { getGreeting, getFormalGreeting } = require('./greeting');
+
+describe('getGreeting', () => {
+  test('should return a morning greeting', () => {
+    const date = new Date('2026-01-01T08:00:00');
+    expect(getGreeting('Alice', date)).toBe('Good morning, Alice!');
+  });
+
+  test('should return an afternoon greeting', () => {
+    const date = new Date('2026-01-01T14:00:00');
+    expect(getGreeting('Bob', date)).toBe('Good afternoon, Bob!');
+  });
+
+  test('should return an evening greeting', () => {
+    const date = new Date('2026-01-01T18:00:00');
+    expect(getGreeting('Charlie', date)).toBe('Good evening, Charlie!');
+  });
+
+  test('should return a night greeting', () => {
+    const date = new Date('2026-01-01T23:00:00');
+    expect(getGreeting('Diana', date)).toBe('Good night, Diana!');
+  });
+
+  test('should throw error for empty name', () => {
+    expect(() => getGreeting('')).toThrow('A valid name string is required');
+  });
+
+  test('should throw error for non-string name', () => {
+    expect(() => getGreeting(123)).toThrow('A valid name string is required');
+  });
+
+  test('should use current date when not provided', () => {
+    const result = getGreeting('Test');
+    expect(result).toMatch(/Good (morning|afternoon|evening|night), Test!/);
+  });
+});
+
+describe('getFormalGreeting', () => {
+  test('should include title in greeting', () => {
+    const date = new Date('2026-01-01T10:00:00');
+    expect(getFormalGreeting('Smith', { title: 'Dr.', date })).toContain('Dr. Smith');
+  });
+
+  test('should work without title', () => {
+    const date = new Date('2026-01-01T10:00:00');
+    expect(getFormalGreeting('Smith', { date })).toBe('Good morning, Smith!');
+  });
+
+  test('should throw error for empty name', () => {
+    expect(() => getFormalGreeting('')).toThrow('A valid name string is required');
+  });
+});

src/math.js

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+/**
+ * Math Utility Module
+ *
+ * Provides common math helper functions.
+ */
+
+/**
+ * Calculate the factorial of a non-negative integer.
+ * @param {number} n - Non-negative integer
+ * @returns {number} Factorial of n
+ * @throws {Error} If n is negative or not an integer
+ */
+function factorial(n) {
+  if (!Number.isInteger(n) || n < 0) {
+    throw new Error('Input must be a non-negative integer');
+  }
+  if (n === 0 || n === 1) return 1;
+  let result = 1;
+  for (let i = 2; i <= n; i++) {
+    result *= i;
+  }
+  return result;
+}
+
+/**
+ * Calculate the Fibonacci number at position n (0-indexed).
+ * @param {number} n - Position in the Fibonacci sequence
+ * @returns {number} The nth Fibonacci number
+ * @throws {Error} If n is negative or not an integer
+ */
+function fibonacci(n) {
+  if (!Number.isInteger(n) || n < 0) {
+    throw new Error('Input must be a non-negative integer');
+  }
+  if (n === 0) return 0;
+  if (n === 1) return 1;
+  let prev = 0;
+  let curr = 1;
+  for (let i = 2; i <= n; i++) {
+    const next = prev + curr;
+    prev = curr;
+    curr = next;
+  }
+  return curr;
+}
+
+module.exports = { factorial, fibonacci };