/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2015-2023 decimal4j (tools4j), Marco Terzer
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
package org.decimal4j.arithmetic;

import java.math.BigDecimal;
import java.math.BigInteger;
import java.math.RoundingMode;

import org.decimal4j.scale.ScaleMetrics;
import org.decimal4j.scale.Scales;

/**
 * Contains methods to convert from and to {@link BigDecimal}.
 */
final class BigDecimalConversion {

        /**
         * Converts the specified big decimal value to a long value applying the
         * given rounding mode. An exception is thrown if the value exceeds the
         * valid long range.
         * 
         * @param roundingMode
         *            the rounding mode to apply if necessary
         * @param value
         *            the big decimal value to convert
         * @return <code>round(value)</code>
         * @throws IllegalArgumentException
         *             if the value is outside of the valid long range
         * @throws ArithmeticException
         *             if {@code roundingMode==UNNECESSARY} and rounding is
         *             necessary
         */
        public static final long bigDecimalToLong(RoundingMode roundingMode, BigDecimal value) {
                // TODO any chance to make this garbage free?
                // Difficult as we cannot look inside the BigDecimal value
                final BigInteger scaled = value//
                                .setScale(0, roundingMode)//
                                .toBigInteger();
                if (scaled.bitLength() <= 63) {
                        return scaled.longValue();
                }
                throw new IllegalArgumentException("Overflow: cannot convert " + value + " to long");
        }

        /**
         * Converts the specified big decimal value to an unscaled decimal applying
         * the given rounding mode if necessary. An exception is thrown if the value
         * exceeds the valid Decimal range.
         * 
         * @param scaleMetrics
         *            the scale metrics of the result value
         * @param roundingMode
         *            the rounding mode to apply if necessary
         * @param value
         *            the big decimal value to convert
         * @return <code>round(value)</code>
         * @throws IllegalArgumentException
         *             if the value is outside of the valid Decimal range
         * @throws ArithmeticException
         *             if {@code roundingMode==UNNECESSARY} and rounding is
         *             necessary
         */
        public static final long bigDecimalToUnscaled(ScaleMetrics scaleMetrics, RoundingMode roundingMode, BigDecimal value) {
                // TODO any chance to make this garbage free?
                // Difficult as we cannot look inside the BigDecimal value
                final BigInteger scaled = value//
                                .multiply(scaleMetrics.getScaleFactorAsBigDecimal())//
                                .setScale(0, roundingMode)//
                                .toBigInteger();
                if (scaled.bitLength() <= 63) {
                        return scaled.longValue();
                }
                throw new IllegalArgumentException(
                                "Overflow: cannot convert " + value + " to Decimal with scale " + scaleMetrics.getScale());
        }

        /**
         * Converts the given unscaled decimal value to a {@link BigDecimal} of the
         * same scale as the given decimal value.
         * 
         * @param scaleMetrics
         *            the scale metrics associated with the unscaled value
         * @param uDecimal
         *            the unscaled decimal value to convert
         * @return a big decimal with the scale from scale metrics
         */
        public static final BigDecimal unscaledToBigDecimal(ScaleMetrics scaleMetrics, long uDecimal) {
                return BigDecimal.valueOf(uDecimal, scaleMetrics.getScale());
        }

        /**
         * Converts the given unscaled decimal value to a {@link BigDecimal} of the
         * specified {@code targetScale} rounding the value if necessary.
         * 
         * @param scaleMetrics
         *            the scale metrics associated with the unscaled value
         * @param roundingMode
         *            the rounding mode to use if rounding is necessary
         * @param uDecimal
         *            the unscaled decimal value to convert
         * @param targetScale
         *            the scale of the result value
         * @return a big decimal with the specified {@code targetScale}
         * @throws ArithmeticException
         *             if {@code roundingMode==UNNECESSARY} and rounding is
         *             necessary
         */
        public static final BigDecimal unscaledToBigDecimal(ScaleMetrics scaleMetrics, RoundingMode roundingMode, long uDecimal, int targetScale) {
                final int sourceScale = scaleMetrics.getScale();
                if (targetScale == sourceScale) {
                        return unscaledToBigDecimal(scaleMetrics, uDecimal);
                }
                if (targetScale < sourceScale) {
                        final int diff = sourceScale - targetScale;
                        if (diff <= 18) {
                                final ScaleMetrics diffMetrics = Scales.getScaleMetrics(diff);
                                final long rescaled = diffMetrics.getArithmetic(roundingMode).divideByPowerOf10(uDecimal, diff);
                                return BigDecimal.valueOf(rescaled, targetScale);
                        }
                } else {
                        // does it fit in a long?
                        final int diff = targetScale - sourceScale;
                        if (diff <= 18) {
                                final ScaleMetrics diffMetrics = Scales.getScaleMetrics(diff);
                                if (diffMetrics.isValidIntegerValue(uDecimal)) {
                                        final long rescaled = diffMetrics.multiplyByScaleFactor(uDecimal);
                                        return BigDecimal.valueOf(rescaled, targetScale);
                                }
                        }
                }
                // let the big decimal deal with such large numbers then
                return BigDecimal.valueOf(uDecimal, sourceScale).setScale(targetScale, roundingMode);
        }

        // no instances
        private BigDecimalConversion() {
                super();
        }
}