# Cargo.toml
[dependencies]
regex = "1.10"

use regex::Regex;
 
fn main() {
    // Basic pattern matching
    let pattern = Regex::new(r"\d{3}-\d{3}-\d{4}").unwrap();
    let text = "Call me at 555-123-4567 or 800-999-0000";
    
    // Check if pattern exists
    if pattern.is_match(text) {
        println!("Found a phone number!");
    }
 
    // Find all matches
    for match_obj in pattern.find_iter(text) {
        println!("Phone: {}", match_obj.as_str());
    }
 
    // Capture groups
    let email_pattern = Regex::new(r"(\w+)@(\w+)\.(\w+)").unwrap();
    let email = "user@example.com";
    
    if let Some(captures) = email_pattern.captures(email) {
        println!("Full match: {}", &captures[0]);      // user@example.com
        println!("Username: {}", &captures[1]);        // user
        println!("Domain: {}", &captures[2]);          // example
        println!("TLD: {}", &captures[3]);             // com
    }
 
    // Named capture groups
    let named_pattern = Regex::new(r"(?P<year>\d{4})-(?P<month>\d{2})-(?P<day>\d{2})").unwrap();
    let date = "2024-03-15";
    
    if let Some(caps) = named_pattern.captures(date) {
        println!("Year: {}", &caps["year"]);
        println!("Month: {}", &caps["month"]);
        println!("Day: {}", &caps["day"]);
    }
 
    // Replace matches
    let censored = pattern.replace_all(text, "XXX-XXX-XXXX");
    println!("Censored: {}", censored);
 
    // Replace with captures
    let swap_pattern = Regex::new(r"(\w+)\s+(\w+)").unwrap();
    let swapped = swap_pattern.replace("hello world", "$2 $1");
    println!("Swapped: {}", swapped); // world hello
 
    // Split text by pattern
    let split_pattern = Regex::new(r"\s+").unwrap();
    let parts: Vec<&str> = split_pattern.split("one   two\tthree\nfour").collect();
    println!("Parts: {:?}", parts); // ["one", "two", "three", "four"]
}

use regex::Regex;
 
struct LogEntry {
    timestamp: String,
    level: String,
    message: String,
}
 
fn parse_log(line: &str) -> Option<LogEntry> {
    // Pattern: 2024-03-15 10:30:45 [INFO] Application started
    let pattern = Regex::new(
        r"(?P<timestamp>\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2})\s+\[(?P<level>\w+)\]\s+(?P<message>.+)"
    ).ok()?;
 
    pattern.captures(line).map(|caps| LogEntry {
        timestamp: caps["timestamp"].to_string(),
        level: caps["level"].to_string(),
        message: caps["message"].to_string(),
    })
}
 
fn main() {
    let log_lines = vec![
        "2024-03-15 10:30:45 [INFO] Application started",
        "2024-03-15 10:30:46 [WARN] Configuration file not found",
        "2024-03-15 10:30:47 [ERROR] Connection refused",
        "Invalid log line",
    ];
 
    for line in log_lines {
        if let Some(entry) = parse_log(line) {
            println!("[{}] {}: {}", entry.level, entry.timestamp, entry.message);
        }
    }
}