Function is_valid_username 

pub fn is_valid_username(username: &str) -> bool

Validate username (alphanumeric, underscore, hyphen, 3-20 chars).

Examples

use chie_shared::is_valid_username;

// Valid usernames
assert!(is_valid_username("alice"));
assert!(is_valid_username("bob_123"));
assert!(is_valid_username("user-name"));
assert!(is_valid_username("test_user_2024"));

// Invalid usernames
assert!(!is_valid_username("ab")); // Too short
assert!(!is_valid_username("a".repeat(21).as_str())); // Too long
assert!(!is_valid_username("user@name")); // Invalid character
assert!(!is_valid_username("user name")); // Spaces not allowed