/*
 * Units of Measurement Reference Implementation
 * Copyright (c) 2005-2018, Jean-Marie Dautelle, Werner Keil, Otavio Santana.
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright 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 JSR-385, Indriya nor the names of their contributors may be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
 * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package tech.units.indriya.function;

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

import javax.measure.UnitConverter;

import tech.units.indriya.AbstractConverter;
import tech.units.indriya.unit.Prefix;

/**
 * UnitConverter for numbers in base^exponent representation.
 * @author Andi Huber
 * @author Werner Keil
 * @version 1.1, April 24, 2018
 * @since 2.0
 */
public final class PowersOfIntConverter extends AbstractConverter {
        private static final long serialVersionUID = 3546932001671571300L;

        private final int base;
        private final int exponent;
        private final int hashCode;
        private final double doubleFactor; // for double calculus only

        /**
         * Creates a converter with the specified Prefix.
         * 
         * @param prefix
         *            the prefix for the factor.
         */
        public static PowersOfIntConverter of(Prefix prefix) {
                return new PowersOfIntConverter(prefix.getBase(), prefix.getExponent());
        }

        /**
         * Creates a converter with a factor represented by specified base^exponent.
         * 
         * @param base
         * @param exponent
         * @return
         */
        public static PowersOfIntConverter of(int base, int exponent) {
                return new PowersOfIntConverter(base, exponent);
        }

        protected PowersOfIntConverter(int base, int exponent) {
                if(base == 0) {
                        throw new IllegalArgumentException("base cannot be zero (because 0^0 is undefined)");
                }
                this.base = base;
                this.exponent = exponent;
                this.doubleFactor = Math.pow(base, exponent);
                this.hashCode = Objects.hash(base, exponent);
        }

        public int getBase() {
                return base;
        }

        public int getExponent() {
                return exponent;
        }

        @Override
        public boolean isIdentity() {
                if( base == 1 ) {
                        return true; // 1^x = 1
                }
                return exponent == 0; // x^0 = 1, for any x!=0
                // [ahuber] 0^0 is undefined, but we guard against base==0 in the constructor,
                // and there is no composition, that changes the base
        }

        @Override
        public boolean isLinear() {
                return true;
        }

        @Override
        protected boolean isSimpleCompositionWith(AbstractConverter that) {
                if (that instanceof PowersOfIntConverter) {
                        return ((PowersOfIntConverter) that).base == this.base;
                }
                return that instanceof RationalConverter;
        }

        @Override
        protected AbstractConverter simpleCompose(AbstractConverter that) {
                if (that instanceof PowersOfIntConverter) {
                        PowersOfIntConverter other = (PowersOfIntConverter) that;
                        if(this.base == other.base) { // always true due to guard above
                                return composeSameBaseNonIdentity(other);
                        } 
                }
                if (that instanceof RationalConverter) {
                        return (AbstractConverter) toRationalConverter().concatenate((RationalConverter) that);
                }
                throw new IllegalStateException(String.format(
                                "%s.simpleCompose() not handled for converter %s", 
                                this, that));
        }

        @Override
        public AbstractConverter inverseWhenNotIdentity() {
                return new PowersOfIntConverter(base, -exponent);
        }

        @Override
        protected Number convertWhenNotIdentity(BigInteger value, MathContext ctx) {
                //[ahuber] exact number representation of factor 
                final BigInteger bintFactor = BigInteger.valueOf(base).pow(Math.abs(exponent));

                if(exponent>0) {
                        return bintFactor.multiply(value);
                }

                //[ahuber] we try to return an exact BigInteger if possible
                final BigInteger[] divideAndRemainder = value.divideAndRemainder(bintFactor);
                final BigInteger divisionResult = divideAndRemainder[0]; 
                final BigInteger divisionRemainder = divideAndRemainder[1];

                if(BigInteger.ZERO.compareTo(divisionRemainder) == 0) {
                        return divisionResult;
                }

                //[ahuber] fallback to BigDecimal, thats where we are loosing 'exactness'
                final BigDecimal bdecFactor = new BigDecimal(bintFactor);
                final BigDecimal bdecValue = new BigDecimal(value);

                return bdecValue.divide(bdecFactor, Calculus.MATH_CONTEXT);
        }

        @Override
        public BigDecimal convertWhenNotIdentity(BigDecimal value, MathContext ctx) throws ArithmeticException {

                //[ahuber] thats where we are loosing 'exactness'
                final BigDecimal bdecFactor = new BigDecimal(BigInteger.valueOf(base).pow(Math.abs(exponent)));
                final BigDecimal bdecValue = (BigDecimal) value;
                
                return exponent>0 
                                ? bdecValue.multiply(bdecFactor, ctx)
                                                : bdecValue.divide(bdecFactor, ctx);
        }

        @Override
        public double convertWhenNotIdentity(double value) {
                //[ahuber] multiplication is probably non-critical regarding preservation of precision
                return value * doubleFactor;
        }

        @Override
        public boolean equals(Object obj) {
                if (this == obj) {
                        return true;
                }
                if (obj instanceof UnitConverter) {
                        UnitConverter other = (UnitConverter) obj;
                        if(this.isIdentity() && other.isIdentity()) {
                                return true;
                        }
                }
                if (obj instanceof PowersOfIntConverter) {
                        PowersOfIntConverter other = (PowersOfIntConverter) obj;
                        return this.base == other.base && this.exponent == other.exponent;
                }
                return false;
        }

        @Override
        public final String transformationLiteral() {
                if(base<0) {
                        return String.format("x -> x * (%s)^%s", base, exponent);
                }
                return String.format("x -> x * %s^%s", base, exponent);
        }

        @Override
        public int compareTo(UnitConverter o) {
                if (this == o) {
                        return 0;
                }
                if(this.isIdentity() && o.isIdentity()) {
                        return 0;
                }
                if (o instanceof PowersOfIntConverter) {
                        PowersOfIntConverter other = (PowersOfIntConverter) o;
                        int c = Integer.compare(base, other.base);
                        if(c!=0) {
                                return c;
                        }
                        return Integer.compare(exponent, other.exponent);
                }
                return this.getClass().getName().compareTo(o.getClass().getName());
        }

        @Override
        public int hashCode() {
                return hashCode;
        }

        // -- HELPER

        private PowersOfIntConverter composeSameBaseNonIdentity(PowersOfIntConverter other) {
                // no check for identity required
                return new PowersOfIntConverter(this.base, this.exponent + other.exponent);
        }

        public RationalConverter toRationalConverter() {
                return exponent>0
                                ? new RationalConverter(BigInteger.valueOf(base).pow(exponent), BigInteger.ONE)
                                                : new RationalConverter(BigInteger.ONE, BigInteger.valueOf(base).pow(-exponent));
        }
}