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 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *  3. Neither the name of the copyright holder nor the
 *     names of its contributors may be used to endorse or promote products
 *     derived from this software without specific prior written permission.
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/**
 * @file
 *   This file includes definitions for Verhoeff checksum calculation and validation.
 */

#ifndef OT_CORE_UTILS_VERHOEFF_CHECKSUM_HPP_
#define OT_CORE_UTILS_VERHOEFF_CHECKSUM_HPP_

#include "openthread-core-config.h"

#if OPENTHREAD_CONFIG_VERHOEFF_CHECKSUM_ENABLE

#include <openthread/verhoeff_checksum.h>

#include "common/error.hpp"

namespace ot {
namespace Utils {

class VerhoeffChecksum
{
public:
    /**
     * Specifies the maximum length of decimal string input.
     */
    static constexpr uint16_t kMaxStringLength = OT_VERHOEFF_CHECKSUM_MAX_STRING_LENGTH;

    /**
     * Calculates the Verhoeff checksum for a given decimal string.
     *
     *
     * @param[in] a DecimalString  The string containing decimal digits.
     * @param[out] aChecksum       Reference to a `char` to return the calculated checksum.
     *
     * @retval kErrorNone          Successfully calculated the checksum, @p aChecksum is updated.
     * @retval kErrorInvalidArgs   The @p aDecimalString is not valid, i.e. it either contains chars other than
     *                             ['0'-'9'], or is longer than `kMaxStringLength`.
     */
    static Error Calculate(const char *aDecimalString, char &aChecksum);

    /**
     * Validates the Verhoeff checksum for a given decimal string.
     *
     * @param[in] aDecimalString   The string containing decimal digits (last char is treated as checksum).
     *
     * @retval kErrorNone            Successfully validated the checksum in @p aDecimalString.
     * @retval kErrorFailed          Checksum is not valid.
     * @retval kErrorInvalidArgs     The @p aDecimalString is not valid, i.e. it either contains chars other than
     *                               ['0'-'9'], or is longer than `kMaxStringLength`.
     */
    static Error Validate(const char *aDecimalString);

    VerhoeffChecksum(void) = delete;

private:
    static Error   ComputeCode(const char *aDecimalString, uint8_t &aCode, bool aValidate);
    static uint8_t Lookup(uint8_t aIndex, const uint8_t aCompressedArray[]);
    static uint8_t Multiply(uint8_t aFirst, uint8_t aSecond);
    static uint8_t Permute(uint8_t aPosition, uint8_t aValue);
    static uint8_t InverseOf(uint8_t aValue);
};

} // namespace Utils
} // namespace ot

#endif // OPENTHREAD_CONFIG_VERHOEFF_CHECKSUM_ENABLE

#endif // OT_CORE_UTILS_VERHOEFF_CHECKSUM_HPP_
