/**
 * @module memory/database
 * @description Thread-safe SQLite database manager for the SAP MCP agent memory subsystem.
 *
 * Uses better-sqlite3 (synchronous, native, FTS5-enabled) with WAL mode for
 * concurrent read access. The database is a singleton — one connection per process.
 *
 * Design principles:
 * - Synchronous I/O: better-sqlite3 is synchronous, no async overhead, no callback hell.
 * - WAL mode: readers don't block writers, crash-safe via WAL journal.
 * - Prepared statements: cached for performance, reused across calls.
 * - FTS5: inverted full-text index for relevance-ranked retrieval.
 * - Schema versioning: idempotent migrations on init.
 * - Graceful degradation: if the DB can't be opened, tools return empty results.
 */
import type { Database as DatabaseType, Statement } from 'better-sqlite3';
import type { MemoryConfig } from './types.js';
/**
 * @name DEFAULT_CONFIG
 * @description Default memory configuration. The DB is stored in
 * ~/.config/mcp-sap/memory/ which is the standard SAP MCP config directory.
 */
export declare const DEFAULT_CONFIG: MemoryConfig;
/**
 * @name MemoryDatabase
 * @description Thread-safe singleton managing the SQLite connection for agent memory.
 *
 * The class lazily initializes the database on first access and caches prepared
 * statements for performance. All methods are synchronous (better-sqlite3 is
 * synchronous by design). The database runs in WAL mode for concurrent reads.
 *
 * If the database cannot be opened (e.g. disk full, permissions), the instance
 * enters a degraded mode where all queries return empty results instead of
 * crashing the MCP server.
 */
export declare class MemoryDatabase {
    private db;
    private readonly config;
    private degraded;
    private initialized;
    private statements;
    constructor(config?: Partial<MemoryConfig>);
    /**
     * @name init
     * @description Initializes the database connection, creates the schema, and
     * enables WAL mode. Called lazily on first query.
     */
    init(): void;
    /**
     * @name getDb
     * @description Returns the underlying Database instance. Throws if degraded.
     * @internal
     */
    getDb(): DatabaseType;
    /**
     * @name isDegraded
     * @description Returns true if the database is in degraded mode (init failed).
     */
    isDegraded(): boolean;
    /**
     * @name getStatement
     * @description Returns a cached prepared statement by key.
     * @internal
     */
    getStatement(key: string): Statement | undefined;
    /**
     * @name close
     * @description Closes the database connection gracefully.
     */
    close(): void;
    /**
     * @name getDbSize
     * @description Returns the database file size in bytes.
     */
    getDbSize(): number;
    /**
     * @name runMigrations
     * @description Runs idempotent schema migrations. Each migration checks if
     * the current schema version is below the target and applies changes.
     * @internal
     */
    private runMigrations;
    /**
     * @name migrateToV1
     * @description Creates the initial schema: tool_calls, agent_memory,
     * stream_buffers, and their FTS5 indexes.
     * @internal
     */
    private migrateToV1;
    /**
     * @name prepareStatements
     * @description Pre-compiles and caches frequently used SQL statements.
     * @internal
     */
    private prepareStatements;
}
/**
 * @name memoryDatabase
 * @description Singleton instance of the memory database.
 * Lazily initialized on first access. Shared across all memory tools.
 */
export declare const memoryDatabase: MemoryDatabase;
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