nodedb-fts 0.0.5

Shared full-text search engine for NodeDB — inverted index, BM25 scoring, analyzers, fuzzy matching
Documentation 
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use crate::posting::Posting;

/// Storage backend abstraction for the full-text search engine.
///
/// Origin implements this with redb (persistent). Lite implements with
/// in-memory HashMap. All scoring, BMW, compression, and analysis logic
/// works identically over any backend.
///
/// Write methods take `&self` (not `&mut self`) because:
/// - Redb provides transactional isolation internally — concurrent writes
///   are safe through redb's MVCC.
/// - MemoryBackend uses interior mutability (`RefCell`) to match the same
///   trait signature, keeping the trait uniform.
pub trait FtsBackend {
    /// Error type for backend operations.
    type Error: std::fmt::Display;

    /// Read the posting list for a term in a collection.
    fn read_postings(&self, collection: &str, term: &str) -> Result<Vec<Posting>, Self::Error>;

    /// Write/replace the posting list for a term in a collection.
    fn write_postings(
        &self,
        collection: &str,
        term: &str,
        postings: &[Posting],
    ) -> Result<(), Self::Error>;

    /// Remove a term's posting list entirely.
    fn remove_postings(&self, collection: &str, term: &str) -> Result<(), Self::Error>;

    /// Read the document length (token count) for a document.
    fn read_doc_length(&self, collection: &str, doc_id: &str) -> Result<Option<u32>, Self::Error>;

    /// Write/replace the document length for a document.
    fn write_doc_length(
        &self,
        collection: &str,
        doc_id: &str,
        length: u32,
    ) -> Result<(), Self::Error>;

    /// Remove a document's length entry.
    fn remove_doc_length(&self, collection: &str, doc_id: &str) -> Result<(), Self::Error>;

    /// Get all term keys for a collection (for fuzzy matching).
    /// Returns terms without the collection prefix.
    fn collection_terms(&self, collection: &str) -> Result<Vec<String>, Self::Error>;

    /// Get total document count and sum of all document lengths for a collection.
    /// Returns `(doc_count, total_token_sum)`.
    ///
    /// Implementations should maintain these incrementally for O(1) lookup.
    fn collection_stats(&self, collection: &str) -> Result<(u32, u64), Self::Error>;

    /// Increment collection stats after indexing a document.
    /// `doc_len` is the number of tokens in the newly indexed document.
    fn increment_stats(&self, collection: &str, doc_len: u32) -> Result<(), Self::Error>;

    /// Decrement collection stats after removing a document.
    /// `doc_len` is the token count of the removed document.
    fn decrement_stats(&self, collection: &str, doc_len: u32) -> Result<(), Self::Error>;

    /// Read a metadata blob by key (e.g., "docmap:{collection}", "fieldnorms:{collection}").
    fn read_meta(&self, key: &str) -> Result<Option<Vec<u8>>, Self::Error>;

    /// Write a metadata blob by key.
    fn write_meta(&self, key: &str, value: &[u8]) -> Result<(), Self::Error>;

    /// Write a segment blob. Key format: "{collection}:seg:{segment_id}".
    fn write_segment(&self, key: &str, data: &[u8]) -> Result<(), Self::Error>;

    /// Read a segment blob. Returns None if not found.
    fn read_segment(&self, key: &str) -> Result<Option<Vec<u8>>, Self::Error>;

    /// List all segment keys for a collection (prefix "{collection}:seg:").
    fn list_segments(&self, collection: &str) -> Result<Vec<String>, Self::Error>;

    /// Remove a segment blob.
    fn remove_segment(&self, key: &str) -> Result<(), Self::Error>;

    /// Remove all entries for a collection prefix. Returns count of removed entries.
    fn purge_collection(&self, collection: &str) -> Result<usize, Self::Error>;
}