/**
 * Constant value stored when a captcha is successfully verified
 */
declare const ON_VERIFY_CAPTCHA_VALUE = "verified";
/**
 * Configuration options for creating a new captcha
 * @interface CreateCaptchaProps
 */
interface CreateCaptchaProps {
    /** Optional custom image buffer to use as the captcha background */
    image?: Buffer;
    /** Optional custom captcha ID (if not provided, a UUID will be generated) */
    captchaId?: string;
    /** Fallback local image path if remote image fetching fails */
    fallbackImgPath?: string;
    /**
     * Function to store the captcha ID and its solution value
     * @param id - The captcha ID
     * @param value - The correct slider position value
     */
    storeCaptchaId: (id: string, value: string) => Promise<void>;
}
/**
 * Return type for captcha creation
 * @interface CaptchaData
 */
interface CaptchaData {
    /** Base64 encoded puzzle piece image */
    puzzle: string;
    /** Base64 encoded background image with puzzle piece removed */
    background: string;
    /** Unique captcha identifier */
    id: string;
}
/**
 * Return type for captcha verification
 * @interface VerificationResult
 */
interface VerificationResult {
    /** Whether the verification was successful */
    success: boolean;
    /** Reason for failure (if success is false) */
    reason?: string;
}
/**
 * Props for verifying a captcha
 * @interface VerifyCaptchaProps
 */
interface VerifyCaptchaProps {
    /** The unique captcha identifier */
    captchaId: string;
    /** The user's slider position as a string */
    value: string;
    /** Function to retrieve the stored correct position */
    getCaptchaValue: (id: string) => Promise<string | null>;
    /** Function to mark captcha as verified */
    changeCaptchaIdOnSuccess: (id: string, value: string) => Promise<void>;
    /** Optional tolerance value for correct positioning (default: 10px) */
    tolerance?: number;
}
/**
 * Creates a new sliding puzzle captcha with a randomly positioned puzzle piece.
 *
 * This function generates a captcha by:
 * 1. Selecting a random horizontal position for the puzzle piece (55-249px)
 * 2. Extracting a 50x50px puzzle piece from that position
 * 3. Creating a background image with the puzzle piece area blacked out
 * 4. Storing the correct position in your database/storage system
 *
 * @example
 * ```typescript
 * const captcha = await createCaptcha({
 *   fallbackImgPath: './assets/fallback.jpg',
 *   storeCaptchaId: async (id, value) => {
 *     // Store in your database/redis/etc.
 *     await redis.setex(id, value, 60 * 10); // Store in Redis with 10 minute TTL;
 *   }
 * });
 *
 * // return captcha data to client refreshCaptcha function
 * ```
 *
 * @param props - Configuration options for captcha creation
 * @returns Promise resolving to captcha data with base64 encoded images and ID
 * @throws {Error} When image processing fails or storage function throws
 *
 */
declare const createCaptcha: ({ image, captchaId, fallbackImgPath, storeCaptchaId, }: CreateCaptchaProps) => Promise<CaptchaData>;
/**
 * Fetches a random image for use as a captcha background.
 *
 * This function attempts to fetch a random image from Picsum Photos API.
 * If the API request fails, it falls back to a local image file if provided.
 * Note: It is recommended to give a fallback image path to ensure captcha
 *
 * @example
 * ```typescript
 * // Fetch random image from API
 * const imageBuffer = await getCaptchaImage();
 *
 * // With fallback image
 * const imageBuffer = await getCaptchaImage('./assets/fallback.jpg');
 * ```
 *
 * @param fallbackImgPath - Optional path to a local fallback image
 * @returns Promise resolving to image buffer or null if all methods fail
 * @throws {Error} When both API fetch and fallback image reading fail
 *
 * @since 1.0.0
 */
declare const getCaptchaImage: (fallbackImgPath?: string) => Promise<ArrayBuffer | Buffer | null>;
/**
 * Verifies a user's captcha solution by comparing their slider position with the stored correct position.
 *
 * This function:
 * 1. Retrieves the stored correct position for the given captcha ID
 * 2. Compares the user's answer with the correct position (allowing 10px tolerance)
 * 3. Marks the captcha as verified if correct
 * 4. Returns the verification result
 *
 * @example
 * ```typescript
 * const result = await verifyCaptcha({
 *   captchaId: 'captcha-id-123',
 *   value: '185', // User's slider position
 *   getCaptchaValue: async (id) => ...,
 *   changeCaptchaIdOnSuccess: async (id, value) => ...,
 *   tolerance: 12 // Optional, defaults to 10px
 * });
 *
 * if (result.success) {
 *   console.log('Captcha verified successfully!');
 * } else {
 *   console.log('Verification failed:', result.reason);
 * }
 * ```
 *
 * @param props - Configuration object containing all verification parameters
 * @returns Promise resolving to verification result
 *
 * @since 1.0.0
 */
declare const verifyCaptcha: (props: VerifyCaptchaProps) => Promise<VerificationResult>;
/**
 * Checks if a captcha has been successfully verified by examining its stored value.
 *
 * This utility function helps determine if a captcha ID corresponds to a
 * successfully completed captcha challenge by comparing it against the verification constant.
 *
 * @example
 * ```
 * const isVerified = await hasCaptchaBeenVerified({
 *   captchaId: 'captcha-123',
 *   getCaptchaValue: async (id) => ....
 * });
 *
 * if (isVerified) {
 *   console.log('This captcha was successfully completed');
 * }
 * ```
 *
 * @param props - Configuration object for captcha verification
 * @param props.captchaId - The unique identifier for the captcha to verify
 * @param props.getCaptchaValue - Function that retrieves captcha value from database/redis/etc
 * @returns Promise resolving to true if the captcha has been verified
 */
interface HasCaptchaBeenVerifiedProps {
    captchaId: string;
    getCaptchaValue: (captchaId: string) => Promise<string | null | undefined>;
}
declare const hasCaptchaBeenVerified: (props: HasCaptchaBeenVerifiedProps) => Promise<boolean>;

export { type CaptchaData, type CreateCaptchaProps, ON_VERIFY_CAPTCHA_VALUE, type VerificationResult, type VerifyCaptchaProps, createCaptcha, getCaptchaImage, hasCaptchaBeenVerified, verifyCaptcha };