regexp

import "regexp"

// Compile regex
re := regexp.MustCompile(`\d+`)

// Find first match
match := re.FindString("Age: 25 years") // "25"

// Check if matches
matched := re.MatchString("123") // true

// Find all matches
matches := re.FindAllString("1 2 3", -1) // ["1", "2", "3"]

// Compile (returns error)
re, err := regexp.Compile(`[a-z]+`)
if err != nil {
    log.Fatal(err)
}

// MustCompile (panics on error)
re := regexp.MustCompile(`[a-z]+`)

// Case-insensitive
re := regexp.MustCompile(`(?i)hello`)

re := regexp.MustCompile(`go+`)

// Match string
matched := re.MatchString("goooo") // true

// Match bytes
matched = re.Match([]byte("goo")) // true

// Find first match
s := re.FindString("golang go goo") // "go"

// Find with index
loc := re.FindStringIndex("golang") // [0, 2]

re := regexp.MustCompile(`\d+`)
text := "Age: 25, Height: 180"

// Find first
first := re.FindString(text) // "25"

// Find all (n = -1 for all matches)
all := re.FindAllString(text, -1) // ["25", "180"]

// Find with limit
some := re.FindAllString(text, 1) // ["25"]

// Find with indices
indices := re.FindAllStringIndex(text, -1)
// [[5, 7], [18, 21]]

re := regexp.MustCompile(`(\w+)@(\w+\.\w+)`)
email := "[email protected]"

// Find submatches
matches := re.FindStringSubmatch(email)
// ["[email protected]", "user", "example.com"]

if len(matches) > 0 {
    full := matches[0]  // Full match
    user := matches[1]  // First group
    domain := matches[2] // Second group
}

// Find all submatches
allMatches := re.FindAllStringSubmatch("[email protected], [email protected]", -1)

re := regexp.MustCompile(`\d+`)

// Replace all
result := re.ReplaceAllString("Age: 25", "XX")
// "Age: XX"

// Replace with function
result = re.ReplaceAllStringFunc("1 2 3", func(s string) string {
    n, _ := strconv.Atoi(s)
    return strconv.Itoa(n * 2)
})
// "2 4 6"

// Replace with captured groups
re = regexp.MustCompile(`(\w+)@(\w+)`)
result = re.ReplaceAllString("user@example", "$1 at $2")
// "user at example"

re := regexp.MustCompile(`\s+`)
parts := re.Split("one  two   three", -1)
// ["one", "two", "three"]

// Split with limit
parts = re.Split("a b c d", 2)
// ["a", "b c d"]

re := regexp.MustCompile(`(?P<user>\w+)@(?P<domain>\w+\.\w+)`)
email := "[email protected]"

match := re.FindStringSubmatch(email)
if match != nil {
    names := re.SubexpNames()
    result := make(map[string]string)
    
    for i, name := range names {
        if i != 0 && name != "" {
            result[name] = match[i]
        }
    }
    
    fmt.Println(result["user"])   // "alice"
    fmt.Println(result["domain"]) // "example.com"
}

func isValidEmail(email string) bool {
    re := regexp.MustCompile(`^[a-zA-Z0-9._%+\-]+@[a-zA-Z0-9.\-]+\.[a-zA-Z]{2,}$`)
    return re.MatchString(email)
}

func extractURLs(text string) []string {
    re := regexp.MustCompile(`https?://[^\s]+`)
    return re.FindAllString(text, -1)
}

func formatPhoneNumber(phone string) string {
    re := regexp.MustCompile(`(\d{3})(\d{3})(\d{4})`)
    return re.ReplaceAllString(phone, "($1) $2-$3")
}

// "5551234567" -> "(555) 123-4567"

func validatePassword(password string) bool {
    // At least 8 chars, 1 uppercase, 1 lowercase, 1 digit
    checks := []*regexp.Regexp{
        regexp.MustCompile(`.{8,}`),
        regexp.MustCompile(`[A-Z]`),
        regexp.MustCompile(`[a-z]`),
        regexp.MustCompile(`\d`),
    }
    
    for _, re := range checks {
        if !re.MatchString(password) {
            return false
        }
    }
    
    return true
}

func extractHashtags(text string) []string {
    re := regexp.MustCompile(`#\w+`)
    return re.FindAllString(text, -1)
}

func stripHTML(html string) string {
    re := regexp.MustCompile(`<[^>]*>`)
    return re.ReplaceAllString(html, "")
}

func parseLogLine(line string) map[string]string {
    re := regexp.MustCompile(
        `(?P<timestamp>\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2}) ` +
        `\[(?P<level>\w+)\] ` +
        `(?P<message>.*)`)
    
    match := re.FindStringSubmatch(line)
    if match == nil {
        return nil
    }
    
    result := make(map[string]string)
    for i, name := range re.SubexpNames() {
        if i != 0 && name != "" {
            result[name] = match[i]
        }
    }
    
    return result
}

var patterns = map[string]string{
    "email":    `^[a-zA-Z0-9._%+\-]+@[a-zA-Z0-9.\-]+\.[a-zA-Z]{2,}$`,
    "url":      `https?://[^\s]+`,
    "ip":       `\b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b`,
    "phone":    `\(?\d{3}\)?[\s.-]?\d{3}[\s.-]?\d{4}`,
    "date":     `\d{4}-\d{2}-\d{2}`,
    "time":     `\d{2}:\d{2}(:\d{2})?`,
    "hex":      `#?[0-9A-Fa-f]{6}`,
    "uuid":     `[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}`,
    "username": `^[a-zA-Z0-9_]{3,16}$`,
}

.       any character
[abc]   a, b, or c
[^abc]  not a, b, or c
[a-z]   a through z
\d      digit
\D      non-digit
\w      word character
\W      non-word character
\s      whitespace
\S      non-whitespace

*       0 or more
+       1 or more
?       0 or 1
{n}     exactly n
{n,}    n or more
{n,m}   between n and m

^       start of string
$       end of string
\b      word boundary
\B      not word boundary

(...)      capturing group
(?:...)    non-capturing group
(?P<name>...) named group