//! Handle validation. Handles look like email local-parts: short,
//! lowercase, restricted charset, must not collide with reserved names.

use crate::error::ApiError;

/// Names we never let users register (system / role / well-known).
/// Conservative starter list; operators can extend.
const RESERVED: &[&str] = &[
    "admin", "administrator", "root", "system", "api", "internal",
    "kez", "support", "help", "abuse", "postmaster", "noreply",
    "no-reply", "mailer-daemon", "webmaster", "hostmaster",
    "www", "ftp", "mail", "smtp", "imap", "pop3",
    "everyone", "all", "anyone", "nobody",
];

pub fn validate_handle(handle: &str) -> Result<(), ApiError> {
    if handle.len() < 3 {
        return Err(ApiError::BadRequest("handle must be at least 3 chars".into()));
    }
    if handle.len() > 32 {
        return Err(ApiError::BadRequest("handle must be at most 32 chars".into()));
    }
    let bytes = handle.as_bytes();
    let first = bytes[0];
    if !(first.is_ascii_lowercase() || first.is_ascii_digit()) {
        return Err(ApiError::BadRequest(
            "handle must start with a lowercase letter or digit".into(),
        ));
    }
    for &b in bytes {
        let ok = b.is_ascii_lowercase()
            || b.is_ascii_digit()
            || b == b'-'
            || b == b'_';
        if !ok {
            return Err(ApiError::BadRequest(format!(
                "handle contains invalid character: {:?}",
                b as char
            )));
        }
    }
    if RESERVED.contains(&handle) {
        return Err(ApiError::Forbidden(format!("handle is reserved: {handle}")));
    }
    Ok(())
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn accepts_normal_handles() {
        for h in &["tudisco", "chris", "alice", "user_123", "ab-cd", "a1b2c3"] {
            assert!(validate_handle(h).is_ok(), "expected ok: {h}");
        }
    }

    #[test]
    fn rejects_short_or_long() {
        assert!(validate_handle("ab").is_err());
        assert!(validate_handle(&"a".repeat(33)).is_err());
    }

    #[test]
    fn rejects_invalid_chars() {
        for h in &["Tudisco", "ali.ce", "user@name", "name space", "emo😀"] {
            assert!(validate_handle(h).is_err(), "expected err: {h}");
        }
    }

    #[test]
    fn rejects_bad_first_char() {
        for h in &["-name", "_name"] {
            assert!(validate_handle(h).is_err(), "expected err: {h}");
        }
    }

    #[test]
    fn rejects_reserved() {
        for h in &["admin", "root", "kez", "noreply"] {
            assert!(matches!(validate_handle(h), Err(ApiError::Forbidden(_))));
        }
    }
}