import { Canvas } from "skia-canvas";
/**
 * Configuration interface for Canvas Pool settings.
 */
export interface CanvasPoolConfig {
    /** Maximum number of canvas instances to keep in the pool */
    maxPoolSize?: number;
    /** Initial number of canvas instances to create */
    initialPoolSize?: number;
    /** Enable debug logging for pool operations */
    debug?: boolean;
}
/**
 * Metrics interface for Canvas Pool performance monitoring.
 */
export interface CanvasPoolMetrics {
    /** Current number of available canvas instances in pool */
    available: number;
    /** Current number of canvas instances in use */
    inUse: number;
    /** Total number of canvas instances created */
    totalCreated: number;
    /** Total number of acquire operations */
    totalAcquires: number;
    /** Total number of release operations */
    totalReleases: number;
    /** Number of times pool was exhausted and new canvas was created */
    poolMisses: number;
    /** Number of canvas instances evicted due to pool size limits */
    evictions: number;
}
/**
 * Canvas Pool implementation for reusing skia-canvas Canvas instances.
 *
 * This pool manages reusable Canvas instances to reduce memory allocation overhead
 * and improve performance in CAPTCHA generation. Uses LRU eviction strategy when
 * the pool reaches capacity.
 *
 * @example Basic usage
 * ```typescript
 * const pool = new CanvasPool({ maxPoolSize: 10 });
 *
 * const canvas = pool.acquire(300, 100);
 * // Use canvas for drawing operations
 * pool.release(canvas);
 * ```
 *
 * @example With custom configuration
 * ```typescript
 * const pool = new CanvasPool({
 *   maxPoolSize: 20,
 *   initialPoolSize: 5,
 *   debug: true
 * });
 * ```
 */
export declare class CanvasPool {
    private pool;
    private readonly maxPoolSize;
    private readonly debug;
    private metrics;
    /**
     * Creates a new Canvas Pool instance.
     *
     * @param config - Pool configuration options
     */
    constructor(config?: CanvasPoolConfig);
    /**
     * Pre-creates canvas instances for the pool.
     *
     * @param count - Number of canvas instances to create
     */
    private preCreateCanvases;
    /**
     * Creates a new Canvas instance with error handling.
     *
     * @param width - Canvas width in pixels
     * @param height - Canvas height in pixels
     * @returns New Canvas instance
     */
    private createCanvas;
    /**
     * Resets canvas state to prepare it for reuse.
     *
     * @param canvas - Canvas to reset
     * @param width - Target width
     * @param height - Target height
     */
    private resetCanvas;
    /**
     * Acquires a canvas from the pool or creates a new one.
     *
     * @param width - Required canvas width in pixels
     * @param height - Required canvas height in pixels
     * @returns Canvas instance ready for use
     *
     * @example
     * ```typescript
     * const canvas = pool.acquire(400, 150);
     * const ctx = canvas.getContext('2d');
     * // Draw on canvas...
     * pool.release(canvas);
     * ```
     */
    acquire(width: number, height: number): Canvas;
    /**
     * Releases a canvas back to the pool for reuse.
     *
     * @param canvas - Canvas to release
     *
     * @example
     * ```typescript
     * const canvas = pool.acquire(300, 100);
     * // Use canvas...
     * pool.release(canvas);
     * ```
     */
    release(canvas: Canvas): void;
    /**
     * Performs LRU eviction if the pool exceeds capacity.
     */
    private evictIfNeeded;
    /**
     * Clears all available canvases from the pool.
     * In-use canvases are not affected.
     */
    clear(): void;
    /**
     * Disposes of all canvases and clears the pool completely.
     * This should be called when shutting down the application.
     */
    dispose(): void;
    /**
     * Gets current pool metrics for monitoring and debugging.
     *
     * @returns Current pool metrics including usage statistics
     *
     * @example
     * ```typescript
     * const metrics = pool.getMetrics();
     * console.log(`Pool usage: ${metrics.inUse}/${metrics.available + metrics.inUse}`);
     * console.log(`Cache hit rate: ${(metrics.totalAcquires - metrics.poolMisses) / metrics.totalAcquires * 100}%`);
     * ```
     */
    getMetrics(): CanvasPoolMetrics;
}