use std::any::type_name;

pub fn topic_for_type<T>(prefix: &str) -> String {
    let raw = type_name::<T>();
    format!("{prefix}.{}", sanitize_topic_component(raw))
}

pub fn sanitize_topic_component(raw: &str) -> String {
    let mut out = String::with_capacity(raw.len());
    let mut last_was_underscore = false;
    for ch in raw.chars() {
        let allowed = ch.is_ascii_alphanumeric() || ch == '.' || ch == '-';
        if allowed {
            out.push(ch);
            last_was_underscore = false;
        } else if !last_was_underscore {
            out.push('_');
            last_was_underscore = true;
        }
    }
    let trimmed = out.trim_matches('_').to_string();
    if trimmed.is_empty() {
        "unknown".to_string()
    } else {
        trimmed
    }
}

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

    #[test]
    fn strips_module_path() {
        let t = topic_for_type::<crate_test_marker::Inner>("svc");
        assert!(t.starts_with("svc."));
        assert!(!t.contains("::"));
        assert!(!t.contains('<'));
    }

    #[test]
    fn replaces_special_chars() {
        let s = sanitize_topic_component("a::b<c>d");
        assert_eq!(s, "a_b_c_d");
    }

    #[test]
    fn collapses_replacements() {
        let s = sanitize_topic_component("a:::b");
        assert_eq!(s, "a_b");
    }

    #[test]
    fn empty_fallback() {
        let s = sanitize_topic_component("<<<>>>");
        assert_eq!(s, "unknown");
    }

    mod crate_test_marker {
        pub struct Inner;
    }
}