Function get_change_at_sequence

atomic-repository/src/history/operations.rs:134–180

Get a specific change by sequence number. # Arguments `txn` - Read transaction `view` - View to query `sequence` - Sequence number to retrieve # Returns The history entry at the given sequence, or an error if out of range.

(
    txn: &T,
    view: &ViewState,
    sequence: u64,
)

///
/// The history entry at the given sequence, or an error if out of range.
pub fn get_change_at_sequence<T: ViewTxnT>(
    txn: &T,
    view: &ViewState,
    sequence: u64,
) -> HistoryResult<HistoryEntry> {
    if sequence >= view.change_count {
        return Err(HistoryError::SequenceOutOfRange {
            sequence,
            max: view.change_count.saturating_sub(1),
        });
    }

    let node_id = txn
        .get_change_at_seq(view, sequence)
        .map_err(|e| HistoryError::Database(e.to_string()))?
        .ok_or_else(|| HistoryError::SequenceOutOfRange {
            sequence,
            max: view.change_count.saturating_sub(1),
        })?;

    let hash = txn
        .get_external(node_id)
        .map_err(|e| HistoryError::Database(e.to_string()))?
        .ok_or_else(|| HistoryError::ChangeNotFound {
            hash: format!("{:?}", node_id),
        })?;

    // Get the Merkle state - we need to iterate to find it
    // This is a bit inefficient but maintains correctness
    let iter = txn
        .iter_changes(view, sequence)
        .map_err(|e| HistoryError::Database(e.to_string()))?;

    for result in iter {
        match result {
            Ok((seq, id, merkle)) if seq == sequence && id == node_id => {
                return Ok(HistoryEntry::new(sequence, node_id, hash, merkle));
            }
            Ok((seq, _, _)) if seq > sequence => break,
            Err(e) => return Err(HistoryError::Database(e.to_string())),
            _ => continue,
        }
    }

    // Fallback with zero merkle if we couldn't find it
    Ok(HistoryEntry::new(sequence, node_id, hash, Merkle::ZERO))
}

/// Find the sequence number for a change by its hash.
///