use actix_web::{HttpRequest, http::header::HeaderName};
use uuid::Uuid;

pub const REQUEST_ID_HEADER: &str = "x-request-id";

pub fn from_request(request: &HttpRequest) -> String {
    request
        .headers()
        .get(HeaderName::from_static(REQUEST_ID_HEADER))
        .and_then(|value| value.to_str().ok())
        .map(str::trim)
        .filter(|value| is_valid(value))
        .map(str::to_owned)
        .unwrap_or_else(|| Uuid::new_v4().to_string())
}

fn is_valid(value: &str) -> bool {
    !value.is_empty()
        && value.len() <= 128
        && value
            .chars()
            .all(|character| character.is_ascii_alphanumeric() || "-_:.".contains(character))
}

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

    #[test]
    fn rejects_header_injection() {
        assert!(!is_valid("abc\nerror"));
        assert!(is_valid("req-123"));
    }
}