import type { Invoice, InvoiceListInput, Client } from '../models/invoice.js';
/** JSON file-based storage with AsyncLock for concurrent write protection. Supports optional custom data directory for test isolation. */
export declare class Storage {
    private readonly dataDir;
    private readonly invoicesPath;
    private readonly clientsPath;
    private readonly counterPath;
    private readonly lock;
    private initialized;
    constructor(dataDir?: string);
    private init;
    private read;
    private write;
    nextInvoiceNumber(): Promise<string>;
    getAllInvoices(): Promise<Invoice[]>;
    getInvoiceById(id: string): Promise<Invoice | null>;
    addInvoice(invoice: Invoice): Promise<Invoice>;
    updateInvoice(id: string, updates: Partial<Invoice>): Promise<Invoice | null>;
    searchInvoices(filters: InvoiceListInput): Promise<{
        invoices: Invoice[];
        total: number;
    }>;
    getAllClients(): Promise<Client[]>;
    getClientById(id: string): Promise<Client | null>;
    getClientByEmail(email: string): Promise<Client | null>;
    addClient(client: Client): Promise<Client>;
    updateClient(id: string, updates: Partial<Client>): Promise<Client | null>;
}
/** Default global storage instance using process.cwd()/data directory. */
export declare const storage: Storage;