Shallow snapshot exported at frontiers with an odd number of heads (≥3) cannot be imported into an empty document #1095

use loro::{ExportMode, LoroDoc};

fn merged(peers: u64) -> LoroDoc {
    let doc = LoroDoc::new();
    doc.set_peer_id(1).unwrap();
    doc.get_text("text").insert(0, "a").unwrap();
    doc.commit();
    for p in 2..=peers {
        let other = LoroDoc::new();
        other.set_peer_id(p).unwrap();
        other.get_text("text").insert(0, "b").unwrap();
        other.commit();
        doc.import(&other.export(ExportMode::all_updates()).unwrap())
            .unwrap();
    }
    doc
}

fn empty_doc() -> LoroDoc {
    let doc = LoroDoc::new();
    doc.set_peer_id(100).unwrap();
    doc
}

fn doc_with_one_commit() -> LoroDoc {
    let doc = empty_doc();
    doc.get_text("other").insert(0, "z").unwrap();
    doc.commit();
    doc
}

fn import_into(doc: LoroDoc, bytes: &[u8]) -> String {
    match doc.import(bytes) {
        Ok(_) => format!("Ok({:?})", doc.get_text("text").to_string()),
        Err(e) => format!("Err({e:?})"),
    }
}

fn main() {
    for peers in 1..=7 {
        let doc = merged(peers);
        let frontiers = doc.oplog_frontiers();
        let shallow = doc
            .export(ExportMode::shallow_snapshot(&frontiers))
            .unwrap();
        let state_only = doc
            .export(ExportMode::state_only(Some(&frontiers)))
            .unwrap();
        println!(
            "{} heads (source doc {:?}): shallow into empty doc {}, shallow into doc with one commit {}, state_only into empty doc {}",
            frontiers.len(),
            doc.get_text("text").to_string(),
            import_into(empty_doc(), &shallow),
            import_into(doc_with_one_commit(), &shallow),
            import_into(empty_doc(), &state_only),
        );
    }
}