use crate::errors::{SpaceError, SpaceResult};

const MIN_EMAIL_LEN: usize = 3;
const MAX_EMAIL_LEN: usize = 254;

pub fn validate_email(raw: &str) -> SpaceResult<String> {
    let email = raw.trim().to_lowercase();
    if email.len() < MIN_EMAIL_LEN || email.len() > MAX_EMAIL_LEN {
        return Err(SpaceError::InvalidEmail);
    }
    if email.chars().any(char::is_whitespace) {
        return Err(SpaceError::InvalidEmail);
    }
    let mut parts = email.split('@');
    let (Some(local), Some(domain), None) = (parts.next(), parts.next(), parts.next()) else {
        return Err(SpaceError::InvalidEmail);
    };
    if !valid_local_part(local) || !valid_domain(domain) {
        return Err(SpaceError::InvalidEmail);
    }
    Ok(email)
}

fn valid_local_part(local: &str) -> bool {
    const MAX_LOCAL_LEN: usize = 64;
    if local.is_empty() || local.len() > MAX_LOCAL_LEN {
        return false;
    }
    if local.starts_with('.') || local.ends_with('.') || local.contains("..") {
        return false;
    }
    local.chars().all(|c| {
        c.is_ascii_alphanumeric()
            || matches!(
                c,
                '.' | '!'
                    | '#'
                    | '$'
                    | '%'
                    | '&'
                    | '\''
                    | '*'
                    | '+'
                    | '-'
                    | '/'
                    | '='
                    | '?'
                    | '^'
                    | '_'
                    | '`'
                    | '{'
                    | '|'
                    | '}'
                    | '~'
            )
    })
}

fn valid_domain(domain: &str) -> bool {
    const MAX_LABEL_LEN: usize = 63;
    let labels: Vec<&str> = domain.split('.').collect();
    if labels.len() < 2 {
        return false;
    }
    for label in &labels {
        if label.is_empty() || label.len() > MAX_LABEL_LEN {
            return false;
        }
        if label.starts_with('-') || label.ends_with('-') {
            return false;
        }
        if !label.chars().all(|c| c.is_ascii_alphanumeric() || c == '-') {
            return false;
        }
    }
    let Some(tld) = labels.last() else {
        return false;
    };
    tld.len() >= 2 && tld.chars().all(|c| c.is_ascii_alphabetic())
}