Regular Expressions Basics

// Creating regex patterns
// Method 1: Literal notation (most common)
let pattern1 = /hello/;

// Method 2: Constructor
let pattern2 = new RegExp('hello');

// Both create the same pattern
console.log(pattern1);  // /hello/
console.log(pattern2);  // /hello/

// Use literal for static patterns
let emailPattern = /^[\w-\.]+@[\w-]+\.[a-z]{2,}$/;

// Use constructor for dynamic patterns
let searchTerm = 'world';
let dynamicPattern = new RegExp(searchTerm);  // Pattern based on variable

// test() returns true/false
let pattern = /hello/;

console.log(pattern.test('hello world'));  // true
console.log(pattern.test('Hello world'));  // false (case-sensitive)
console.log(pattern.test('hi there'));     // false

// Practical: Validate format
let hasNumber = /\d/;  // \d matches any digit
console.log(hasNumber.test('abc123'));  // true
console.log(hasNumber.test('abc'));     // false

// Check if string contains only letters
let onlyLetters = /^[a-zA-Z]+$/;
console.log(onlyLetters.test('hello'));    // true
console.log(onlyLetters.test('hello123')); // false

// Validate email (basic)
let emailPattern = /@/;
console.log(emailPattern.test('user@example.com'));  // true
console.log(emailPattern.test('invalid'));           // false

// match() returns array of matches or null
let text = 'The phone numbers are 123-456-7890 and 987-654-3210';

// Without 'g' flag - returns first match with details
let pattern1 = /\d{3}-\d{3}-\d{4}/;
let result1 = text.match(pattern1);
console.log(result1);
// ['123-456-7890', index: 22, input: '...', groups: undefined]
console.log(result1[0]);  // '123-456-7890'

// With 'g' flag - returns all matches
let pattern2 = /\d{3}-\d{3}-\d{4}/g;
let result2 = text.match(pattern2);
console.log(result2);
// ['123-456-7890', '987-654-3210']

// No match returns null
let noMatch = text.match(/xyz/);
console.log(noMatch);  // null

// Extract words
let sentence = 'Hello world, how are you?';
let words = sentence.match(/\w+/g);
console.log(words);
// ['Hello', 'world', 'how', 'are', 'you']

// Extract numbers
let numbers = 'I have 5 apples and 10 oranges'.match(/\d+/g);
console.log(numbers);  // ['5', '10']

// replace() replaces matched text
let text = 'Hello world, hello everyone';

// Replace first match
let result1 = text.replace(/hello/i, 'Hi');
console.log(result1);  // "Hi world, hello everyone"

// Replace all matches (use 'g' flag)
let result2 = text.replace(/hello/gi, 'Hi');
console.log(result2);  // "Hi world, Hi everyone"

// Replace with function
let numbers = 'I have 5 apples and 10 oranges';
let doubled = numbers.replace(/\d+/g, (match) => {
  return match * 2;
});
console.log(doubled);  // "I have 10 apples and 20 oranges"

// Censor words
let message = 'This is bad and terrible';
let censored = message.replace(/bad|terrible/gi, '***');
console.log(censored);  // "This is *** and ***"

// Format phone number
let phone = '1234567890';
let formatted = phone.replace(/(\d{3})(\d{3})(\d{4})/, '($1) $2-$3');
console.log(formatted);  // "(123) 456-7890"

// split() with regex
let text = 'apple,banana;orange|grape';

// Split by multiple delimiters
let fruits = text.split(/[,;|]/);
console.log(fruits);
// ['apple', 'banana', 'orange', 'grape']

// Split by whitespace (including multiple spaces)
let sentence = 'Hello    world     how   are you';
let words = sentence.split(/\s+/);
console.log(words);
// ['Hello', 'world', 'how', 'are', 'you']

// Split but keep delimiter
let text2 = 'Hello. How are you? I am fine!';
let sentences = text2.split(/([.?!])/);
console.log(sentences);
// ['Hello', '.', ' How are you', '?', ' I am fine', '!', '']

// Exact match
/hello/.test('hello');       // true
/hello/.test('Hello');       // false (case-sensitive)
/hello/.test('hello world'); // true (contains 'hello')

// Multiple characters
/cat/.test('I have a cat');  // true
/dog/.test('I have a cat');  // false

// [abc] - matches any single character in brackets
/[aeiou]/.test('hello');  // true (matches 'e' and 'o')
/[0-9]/.test('abc');      // false
/[0-9]/.test('abc3');     // true

// [^abc] - matches any character NOT in brackets
/[^0-9]/.test('123');   // false (all are digits)
/[^0-9]/.test('abc');   // true

// Ranges
/[a-z]/.test('Hello');    // true (matches lowercase letters)
/[A-Z]/.test('hello');    // false
/[a-zA-Z]/.test('Hello'); // true (matches any letter)
/[0-9]/.test('5');        // true (matches any digit)

// \d - digit (0-9)
/\d/.test('abc123');  // true

// \D - NOT digit
/\D/.test('123');     // false
/\D/.test('abc');     // true

// \w - word character (letter, digit, underscore)
/\w/.test('hello');   // true
/\w/.test('_test');   // true
/\w/.test('@');       // false

// \W - NOT word character
/\W/.test('hello');   // false
/\W/.test('@');       // true

// \s - whitespace (space, tab, newline)
/\s/.test('hello world');  // true
/\s/.test('hello');        // false

// \S - NOT whitespace
/\S/.test(' ');       // false
/\S/.test('a');       // true

// . - any character except newline
/./.test('a');         // true
/./.test('5');         // true
/./.test('@');         // true

// + - one or more
/\d+/.test('123');     // true
/\d+/.test('abc');     // false
'abc123'.match(/\d+/); // ['123']

// * - zero or more
/\d*/.test('abc');     // true (zero digits is OK)
/\d*/.test('123');     // true

// ? - zero or one (optional)
/colou?r/.test('color');   // true
/colou?r/.test('colour');  // true

// {n} - exactly n times
/\d{3}/.test('12');    // false
/\d{3}/.test('123');   // true
/\d{3}/.test('1234');  // true (has at least 3)

// {n,} - n or more times
/\d{3,}/.test('12');     // false
/\d{3,}/.test('123');    // true
/\d{3,}/.test('12345');  // true

// {n,m} - between n and m times
/\d{2,4}/.test('1');      // false
/\d{2,4}/.test('12');     // true
/\d{2,4}/.test('123');    // true
/\d{2,4}/.test('1234');   // true
/\d{2,4}/.test('12345');  // true (has at least 2)

// ^ - start of string
/^hello/.test('hello world');  // true
/^hello/.test('say hello');    // false

// $ - end of string
/world$/.test('hello world');  // true
/world$/.test('world hello');  // false

// ^...$ - exact match (start to end)
/^hello$/.test('hello');        // true
/^hello$/.test('hello world');  // false
/^hello$/.test('say hello');    // false

// Practical: Validate exact format
let zipCode = /^\d{5}$/;
console.log(zipCode.test('12345'));   // true
console.log(zipCode.test('1234'));    // false
console.log(zipCode.test('123456'));  // false

// i - case-insensitive
/hello/i.test('HELLO');    // true
/hello/i.test('Hello');    // true

// g - global (find all matches)
'hello hello'.match(/hello/);   // ['hello'] (first only)
'hello hello'.match(/hello/g);  // ['hello', 'hello'] (all)

// m - multiline (^ and $ match line breaks)
let text = `line1
line2
line3`;

/^line2/.test(text);   // false (^ only matches start of string)
/^line2/m.test(text);  // true (^ matches start of any line)

// Combine flags
/hello/gi.test('HELLO');  // true (case-insensitive + global)

// s - dotAll (. matches newlines)
/.+/.test('a\nb');    // false (. doesn't match \n)
/.+/s.test('a\nb');   // true (. matches everything)

// u - unicode
/\u{1F600}/u.test('😀');  // true (emoji support)

// Simple email validation
let emailPattern = /^[\w.-]+@[\w.-]+\.[a-z]{2,}$/i;

console.log(emailPattern.test('user@example.com'));     // true
console.log(emailPattern.test('user.name@test.co.uk')); // true
console.log(emailPattern.test('invalid@'));             // false
console.log(emailPattern.test('@example.com'));         // false

// More comprehensive (still not perfect for all cases)
let betterEmail = /^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/;

function validateEmail(email) {
  return betterEmail.test(email);
}

console.log(validateEmail('test@gmail.com'));      // true
console.log(validateEmail('test+tag@domain.co')); // true
console.log(validateEmail('invalid.email'));      // false

// US phone number formats
let phone1 = /^\d{10}$/;                    // 1234567890
let phone2 = /^\d{3}-\d{3}-\d{4}$/;       // 123-456-7890
let phone3 = /^\(\d{3}\) \d{3}-\d{4}$/; // (123) 456-7890

console.log(phone1.test('1234567890'));      // true
console.log(phone2.test('123-456-7890'));    // true
console.log(phone3.test('(123) 456-7890'));  // true

// Flexible phone validator (multiple formats)
let flexiblePhone = /^(\d{10}|\d{3}-\d{3}-\d{4}|\(\d{3}\) \d{3}-\d{4})$/;

function validatePhone(phone) {
  return flexiblePhone.test(phone);
}

console.log(validatePhone('1234567890'));      // true
console.log(validatePhone('123-456-7890'));    // true
console.log(validatePhone('(123) 456-7890'));  // true
console.log(validatePhone('12345'));           // false

// Basic URL validation
let urlPattern = /^https?:\/\/[\w.-]+\.[a-z]{2,}(:[0-9]+)?(\/.*)?$/i;

console.log(urlPattern.test('http://example.com'));          // true
console.log(urlPattern.test('https://www.google.com'));      // true
console.log(urlPattern.test('https://site.com:8080/path')); // true
console.log(urlPattern.test('not-a-url'));                   // false

function validateURL(url) {
  return urlPattern.test(url);
}

console.log(validateURL('https://falytom.com.ng'));  // true
console.log(validateURL('ftp://example.com'));       // false (not http/https)

// Password requirements:
// - At least 8 characters
// - Contains uppercase
// - Contains lowercase
// - Contains digit
// - Contains special character

function validatePassword(password) {
  let minLength = /.{8,}/;
  let hasUpper = /[A-Z]/;
  let hasLower = /[a-z]/;
  let hasDigit = /\d/;
  let hasSpecial = /[!@#$%^&*(),.?":{}|<>]/;
  
  return (
    minLength.test(password) &&
    hasUpper.test(password) &&
    hasLower.test(password) &&
    hasDigit.test(password) &&
    hasSpecial.test(password)
  );
}

console.log(validatePassword('Pass123!'));      // true
console.log(validatePassword('weakpass'));      // false
console.log(validatePassword('NoDigit!'));      // false

// All-in-one pattern (more complex)
let strongPassword = /^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[@$!%*?&])[A-Za-z\d@$!%*?&]{8,}$/;

console.log(strongPassword.test('Pass123!'));  // true
console.log(strongPassword.test('weak'));      // false

// MM/DD/YYYY
let usDate = /^\d{2}\/\d{2}\/\d{4}$/;
console.log(usDate.test('12/31/2024'));  // true
console.log(usDate.test('2024-12-31'));  // false

// YYYY-MM-DD (ISO format)
let isoDate = /^\d{4}-\d{2}-\d{2}$/;
console.log(isoDate.test('2024-12-31'));  // true
console.log(isoDate.test('12/31/2024'));  // false

// Flexible date validator
function validateDate(date) {
  let us = /^(0?[1-9]|1[0-2])\/(0?[1-9]|[12][0-9]|3[01])\/\d{4}$/;
  let iso = /^\d{4}-(0?[1-9]|1[0-2])-(0?[1-9]|[12][0-9]|3[01])$/;
  
  return us.test(date) || iso.test(date);
}

console.log(validateDate('12/31/2024'));  // true
console.log(validateDate('2024-12-31'));  // true
console.log(validateDate('invalid'));     // false

// Complete form validator
class FormValidator {
  static patterns = {
    email: /^[\w.-]+@[\w.-]+\.[a-z]{2,}$/i,
    phone: /^\d{10}$/,
    zipCode: /^\d{5}(-\d{4})?$/,
    username: /^[a-zA-Z0-9_]{3,20}$/,
    url: /^https?:\/\/[\w.-]+\.[a-z]{2,}/i
  };
  
  static validate(field, value) {
    let pattern = this.patterns[field];
    
    if (!pattern) {
      return { valid: false, error: 'Unknown field type' };
    }
    
    let valid = pattern.test(value);
    
    return {
      valid,
      error: valid ? null : `Invalid ${field} format`
    };
  }
  
  static validateForm(data) {
    let errors = {};
    
    for (let field in data) {
      let result = this.validate(field, data[field]);
      if (!result.valid) {
        errors[field] = result.error;
      }
    }
    
    return {
      valid: Object.keys(errors).length === 0,
      errors
    };
  }
}

// Usage
let formData = {
  email: 'user@example.com',
  phone: '1234567890',
  zipCode: '12345',
  username: 'john_doe'
};

let result = FormValidator.validateForm(formData);

if (result.valid) {
  console.log('Form is valid!');
} else {
  console.log('Errors:', result.errors);
}

// Extract and process data from text
class TextProcessor {
  // Extract all emails
  static extractEmails(text) {
    let pattern = /[\w.-]+@[\w.-]+\.[a-z]{2,}/gi;
    return text.match(pattern) || [];
  }
  
  // Extract all phone numbers
  static extractPhones(text) {
    let pattern = /\d{3}-\d{3}-\d{4}|\(\d{3}\) \d{3}-\d{4}|\d{10}/g;
    return text.match(pattern) || [];
  }
  
  // Extract URLs
  static extractURLs(text) {
    let pattern = /https?:\/\/[\w.-]+\.[a-z]{2,}[^\s]*/gi;
    return text.match(pattern) || [];
  }
  
  // Redact emails
  static redactEmails(text) {
    return text.replace(/[\w.-]+@[\w.-]+\.[a-z]{2,}/gi, '[EMAIL REDACTED]');
  }
  
  // Highlight mentions
  static highlightMentions(text) {
    return text.replace(/@(\w+)/g, '<strong>@$1</strong>');
  }
  
  // Remove extra whitespace
  static normalizeWhitespace(text) {
    return text.replace(/\s+/g, ' ').trim();
  }
}

// Usage
let text = `
  Contact us at support@example.com or sales@company.com
  Call 123-456-7890 or (987) 654-3210
  Visit https://example.com for more info
  Hey @john and @jane, check this out!
`;

console.log('Emails:', TextProcessor.extractEmails(text));
console.log('Phones:', TextProcessor.extractPhones(text));
console.log('URLs:', TextProcessor.extractURLs(text));
console.log('Redacted:', TextProcessor.redactEmails(text));