/**
 * Snapshot Manager Implementation
 * Handles RAM tier persistence and recovery through snapshots
 * Requirements: 11.2, 11.3, 11.4
 */
import { StorageTier } from '../storage/StorageTier.js';
import { TierManager } from '../tier/TierManager.js';
/**
 * Entry in a RAM snapshot containing key data and metadata
 */
export interface SnapshotEntry {
    /** The cache key */
    key: string;
    /** The value as base64-encoded string (for JSON serialization) */
    value: string;
    /** Unix timestamp (ms) when this key expires, null if no expiration */
    expiresAt: number | null;
    /** Access count for the key */
    accessCount: number;
    /** Unix timestamp (ms) of last access */
    lastAccess: number;
    /** Unix timestamp (ms) when this key was created */
    createdAt: number;
    /** Size of the value in bytes */
    sizeBytes: number;
}
/**
 * RAM tier snapshot for persistence
 * Requirement 11.3: Support configurable persistence intervals for RAM_Tier snapshots
 */
export interface RamSnapshot {
    /** Snapshot format version for compatibility */
    version: number;
    /** Unix timestamp (ms) when snapshot was created */
    timestamp: number;
    /** Array of snapshot entries containing key-value pairs with metadata */
    entries: SnapshotEntry[];
    /** SHA-256 checksum of the entries for integrity validation */
    checksum: string;
}
/**
 * SnapshotManager handles RAM tier persistence and recovery.
 *
 * Requirements:
 * - 11.2: Restore the tier index from persistent storage on startup
 * - 11.3: Support configurable persistence intervals for RAM_Tier snapshots
 * - 11.4: Recover from the last snapshot and SSD_Tier state on unexpected shutdown
 */
export declare class SnapshotManager {
    /**
     * Create a snapshot of the RAM tier.
     * Captures all key-value pairs with their metadata for persistence.
     *
     * @param ramTier - The RAM tier storage to snapshot
     * @param tierManager - The tier manager for accessing key metadata
     * @returns A RamSnapshot containing all RAM tier data
     */
    createSnapshot(ramTier: StorageTier, tierManager: TierManager): Promise<RamSnapshot>;
    /**
     * Save a snapshot to a file.
     * Creates the directory if it doesn't exist.
     *
     * @param snapshot - The snapshot to save
     * @param path - The file path to save to
     */
    saveSnapshot(snapshot: RamSnapshot, snapshotPath: string): Promise<void>;
    /**
     * Load a snapshot from a file.
     * Returns null if the file doesn't exist or is invalid.
     *
     * @param path - The file path to load from
     * @returns The loaded snapshot, or null if not found/invalid
     */
    loadSnapshot(path: string): Promise<RamSnapshot | null>;
    /**
     * Validate a snapshot's checksum.
     *
     * @param snapshot - The snapshot to validate
     * @returns true if the checksum is valid, false otherwise
     */
    validateSnapshot(snapshot: RamSnapshot): boolean;
    /**
     * Restore RAM tier from a snapshot.
     * Loads all entries from the snapshot into the RAM tier and registers them in the tier manager.
     *
     * Requirement 11.2: Restore the tier index from persistent storage on startup
     * Requirement 11.4: Recover from the last snapshot and SSD_Tier state
     *
     * @param snapshot - The snapshot to restore from
     * @param ramTier - The RAM tier storage to restore to
     * @param tierManager - The tier manager to register keys with
     */
    restoreFromSnapshot(snapshot: RamSnapshot, ramTier: StorageTier, tierManager: TierManager): Promise<void>;
    /**
     * Calculate SHA-256 checksum of snapshot entries.
     *
     * @param entries - The entries to calculate checksum for
     * @returns The hex-encoded SHA-256 checksum
     */
    private calculateChecksum;
    /**
     * Delete a snapshot file.
     *
     * @param path - The file path to delete
     * @returns true if deleted, false if file didn't exist
     */
    deleteSnapshot(path: string): Promise<boolean>;
    /**
     * Check if a snapshot file exists.
     *
     * @param path - The file path to check
     * @returns true if the file exists, false otherwise
     */
    snapshotExists(path: string): Promise<boolean>;
}
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