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package org.xrpl.xrpl4j.codec.binary.math;

/*-
 * ========================LICENSE_START=================================
 * xrpl4j :: binary-codec
 * %%
 * Copyright (C) 2020 - 2022 XRPL Foundation and its contributors
 * %%
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 * =========================LICENSE_END==================================
 */

import com.google.common.base.Strings;

import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.Objects;

/**
 * Utility functions for XRPL-related math operations.
 */
public class MathUtils {

  /**
   * Get the exponent value for {@code value}.
   *
   * @param value A {@link BigDecimal} to obtain the exponent from.
   *
   * @return An int representing the exponent value of {@code value}.
   */
  public static int getExponent(BigDecimal value) {
    return value.precision() - value.scale() - 1;
  }

  /**
   * XRPL amounts are right-padded with 0s, so both 1, 10, 100 are converted to 10000000000000000, which, when combined
   * with the exponent field can be used to reconstruct the actual decimal value. The resulting value will have {@code
   * expectedDigits}. Examples:
   * 
   *   {@code toPaddedBigInteger(1, 4)} yields 1000
   *   {@code toPaddedBigInteger(1.23, 4)} yields 1230
   *   {@code toPaddedBigInteger(0.1234, 4)} yields 1234
   *   {@code toPaddedBigInteger(0.1234, 3)} throws an IllegalArgumentException as the numberToPad cannot fit in
   *   3 digits.
   * 
   *
   * @param numberToPad    A {@link BigDecimal} to pad.
   * @param expectedDigits An int representing the total number of digits that {@code numberToPad} is expected to have.
   *
   * @return A {@link BigInteger} that is correctly padded.
   * @throws IllegalArgumentException if {@code numberToPad} does not have a total digit count equal to {@code
   *                                  expectedDigits}.
   */
  public static BigInteger toPaddedBigInteger(final BigDecimal numberToPad, int expectedDigits) {
    Objects.requireNonNull(numberToPad);

    String unscaled = numberToPad.abs().stripTrailingZeros().unscaledValue().toString();
    if (unscaled.length() > expectedDigits) {
      throw new IllegalArgumentException(numberToPad + " has more than " + expectedDigits + " digits");
    }
    return new BigInteger(Strings.padEnd(unscaled, expectedDigits, '0'));
  }

}