//! DNS-safe encoding for publication AT-URIs.
//!
//! Custom domains use self-describing CNAME records pointing to
//! `nb-{encoded-did}-{rkey}.weaver.sh`. This module handles
//! encoding and decoding the subdomain portion.

use jacquard::IntoStatic;
use jacquard::types::string::{Did, Tid};

const PREFIX: &str = "nb-";

/// Encode a Publication AT-URI into a DNS-safe subdomain.
///
/// Encoding rules:
/// - DID `:` separators become `-`
/// - `did:web` dots become `_` (underscores are invalid in domain names, so unambiguous)
/// - rkey is appended as last segment (TIDs never contain hyphens)
///
/// Examples:
/// - `did:plc:z72i7hdynmk6r22` + `3jui7kd2y2e2b` → `nb-plc-z72i7hdynmk6r22-3jui7kd2y2e2b`
/// - `did:web:example.com` + `3jui7kd2y2e2b` → `nb-web-example_com-3jui7kd2y2e2b`
pub fn encode_publication_subdomain(did: &Did, rkey: &Tid) -> String {
    let did_str = did.as_str();

    // did:plc:abc123 -> plc-abc123
    // did:web:example.com -> web-example_com
    let encoded_did = did_str
        .strip_prefix("did:")
        .expect("valid DID")
        .replace(':', "-")
        .replace('.', "_");

    format!("{}{}-{}", PREFIX, encoded_did, rkey.as_str())
}

/// Decode a publication subdomain back to DID and rkey.
///
/// Parsing strategy: work from both ends since rkeys (TIDs) never contain hyphens.
pub fn decode_publication_subdomain(subdomain: &str) -> Option<(Did<'static>, Tid)> {
    let inner = subdomain.strip_prefix(PREFIX)?;

    // Split at the LAST hyphen - rkey is on the right (TIDs have no hyphens)
    let (did_part, rkey_str) = inner.rsplit_once('-')?;

    // Parse rkey as TID
    let rkey = Tid::from(rkey_str.to_owned());

    // Reconstruct DID from encoded form
    // plc-abc123 -> did:plc:abc123
    // web-example_com -> did:web:example.com
    let (method, identifier) = did_part.split_once('-')?;
    let decoded_identifier = identifier.replace('_', ".");
    let did_str = format!("did:{}:{}", method, decoded_identifier);
    let did = Did::new(&did_str).ok()?;

    Some((did.into_static(), rkey))
}

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

    #[test]
    fn roundtrip_did_plc() {
        let did = Did::new("did:plc:z72i7hdynmk6r22").unwrap();
        let rkey = Tid::from("3jui7kd2y2e2b".to_owned());

        let encoded = encode_publication_subdomain(&did, &rkey);
        assert_eq!(encoded, "nb-plc-z72i7hdynmk6r22-3jui7kd2y2e2b");

        let (decoded_did, decoded_rkey) = decode_publication_subdomain(&encoded).unwrap();
        assert_eq!(decoded_did, did.into_static());
        assert_eq!(decoded_rkey, rkey);
    }

    #[test]
    fn roundtrip_did_web() {
        let did = Did::new("did:web:example.com").unwrap();
        let rkey = Tid::from("3jui7kd2y2e2b".to_owned());

        let encoded = encode_publication_subdomain(&did, &rkey);
        assert_eq!(encoded, "nb-web-example_com-3jui7kd2y2e2b");

        let (decoded_did, decoded_rkey) = decode_publication_subdomain(&encoded).unwrap();
        assert_eq!(decoded_did, did.into_static());
        assert_eq!(decoded_rkey, rkey);
    }

    #[test]
    fn roundtrip_did_web_with_hyphens() {
        let did = Did::new("did:web:my-cool-site.example.com").unwrap();
        let rkey = Tid::from("3jui7kd2y2e2b".to_owned());

        let encoded = encode_publication_subdomain(&did, &rkey);
        assert_eq!(encoded, "nb-web-my-cool-site_example_com-3jui7kd2y2e2b");

        let (decoded_did, decoded_rkey) = decode_publication_subdomain(&encoded).unwrap();
        assert_eq!(decoded_did, did.into_static());
        assert_eq!(decoded_rkey, rkey);
    }

    #[test]
    fn decode_invalid_prefix() {
        assert!(decode_publication_subdomain("foo-plc-abc123-rkey").is_none());
    }

    #[test]
    fn decode_missing_method() {
        assert!(decode_publication_subdomain("nb-abc123").is_none());
    }
}