/**
 * Search result containing document index and relevance score
 */
interface SearchResult {
    /** Index of the matched document */
    index: number;
    /** BM25 relevance score */
    score: number;
}
/**
 * Options for configuring the BM25 algorithm
 */
interface BM25Options {
    /** Term frequency saturation parameter (default: 1.5) */
    k1?: number;
    /** Length normalization factor (default: 0.75) */
    b?: number;
    /** Minimum token length to consider (default: 2) */
    minLength?: number;
    /** Set of stop words to filter out */
    stopWords?: Set<string>;
    /** Enable word stemming (default: false) */
    stemming?: boolean;
    /** Custom word stemming function */
    stemWords?: (word: string) => string;
}
/**
 * Field boost factors to control importance of different fields
 */
interface FieldBoosts {
    /** Field name to boost factor mapping */
    [field: string]: number;
}
/**
 * Document structure where each field contains text content
 */
interface Document {
    /** Field name to text content mapping */
    [field: string]: string;
}

/**
 * Implementation of the Okapi BM25 ranking algorithm with field boosting support
 */
declare class BM25 {
    private readonly termFrequencySaturation;
    private readonly lengthNormalizationFactor;
    private readonly tokenizer;
    private documentLengths;
    private averageDocLength;
    private readonly termToIndex;
    private documentFrequency;
    private readonly termFrequencies;
    private readonly fieldBoosts;
    private readonly workerOptions;
    private documents;
    /**
     * Creates a new BM25 search instance
     * @param docs - Optional array of documents to index
     * @param options - BM25 algorithm options and field boost settings
     */
    constructor(docs?: Document[], options?: BM25Options & {
        fieldBoosts?: FieldBoosts;
    });
    private processDocuments;
    /**
     * Adds multiple documents to the index using parallel processing
     * @param docs - Array of documents to add
     */
    addDocumentsParallel(docs: Document[]): Promise<void>;
    private updateDocumentFrequency;
    private recalculateAverageLength;
    /**
     * Searches the indexed documents using BM25 ranking
     * @param query - Search query text
     * @param limit - Maximum number of results to return
     * @returns Array of search results sorted by relevance score
     */
    search(query: string, topK?: number): SearchResult[];
    searchPhrase(phrase: string, topK?: number): SearchResult[];
    private calculatePhraseScore;
    /**
     * Adds a new document to the index
     * @param doc - Document to add
     */
    addDocument(doc: Document): Promise<void>;
    private calculateIDF;
    private getTermFrequency;
    private getDocument;
    clearDocuments(): void;
    getDocumentCount(): number;
    addDocuments(docs: Document[]): Promise<void>;
}

export { BM25 };