/*
 * 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;

import java.io.Serializable;
import java.math.BigDecimal;
import java.math.BigInteger;
import java.math.MathContext;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.Objects;
import java.util.stream.Collectors;

import javax.measure.UnitConverter;

import tech.units.indriya.function.Calculus;
import tech.units.indriya.function.PowersOfIntConverter;
import tech.units.indriya.function.UnitComparator;
import tech.units.indriya.internal.simplify.Simplifier;
import tech.units.indriya.unit.Prefix;

/**
 * <p>
 * The base class for our {@link UnitConverter} implementations.
 * </p>
 *
 * @author <a href="mailto:jean-marie@dautelle.com">Jean-Marie Dautelle</a>
 * @author <a href="mailto:units@catmedia.us">Werner Keil</a>
 * @author Andi Huber
 * @version 1.6, April 26, 2018
 * @since 1.0
 */
public abstract class AbstractConverter
                implements UnitConverter, Serializable, Comparable<UnitConverter> {

        /**
        *
        */
        private static final long serialVersionUID = 5790242858468427131L;

        /**
         * Holds identity converter.
         */
        // [ahuber] potentially misused: checking whether a UnitConverter is an identity operator
        // should be done with unitConverter.isIdentity() rather then unitConverter == AbstractConverter.IDENTITY
        public static final AbstractConverter IDENTITY = new Identity();

        /**
         * memoization for getConversionSteps
         */
        protected List<? extends UnitConverter> conversionSteps; 

        /**
         * DefaultQuantityFactory constructor.
         */
        protected AbstractConverter() {
        }

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

        @Override
        public abstract boolean equals(Object cvtr);

        @Override
        public abstract int hashCode();
        
        // -- TO-STRING - CONTRACT AND INTERFACE IMPLEMENTATION (FINAL)
        
        /**
         * Non-API
         * <p>
         * Returns a String describing the transformation that is represented by this converter. 
         * Contributes to converter's {@code toString} method. If null or empty
         * {@code toString} output becomes simplified.
         * </p>
         * @return 
         */
        protected abstract String transformationLiteral();
        
        @Override
        public final String toString() {
                String converterName = getClass().getSimpleName();
                // omit trailing 'Converter'
                if(converterName.endsWith("Converter")) {
                        converterName = converterName.substring(0, converterName.length()-"Converter".length());
                }
                if(isIdentity()) {
                        return String.format("%s(IDENTITY)", converterName);
                }
                final String transformationLiteral = transformationLiteral();
                if(transformationLiteral==null || transformationLiteral.length()==0) {
                        return String.format("%s", converterName);
                }
                return String.format("%s(%s)", converterName, transformationLiteral);
        }

        // -- INVERSION - CONTRACT AND INTERFACE IMPLEMENTATION (FINAL)
        
        /**
         * Non-API
         * <p>
         * Returns an AbstractConverter that represents the inverse transformation of this converter,
         * for cases where the transformation is not the identity transformation.
         * </p>  
         * @return 
         */
        protected abstract AbstractConverter inverseWhenNotIdentity();
        
        @Override
        public final AbstractConverter inverse() {
                if(isIdentity()) {
                        return this;
                }
                return inverseWhenNotIdentity();
        }
        
        // -- COMPOSITION CONTRACTS (TO BE IMPLEMENTED BY SUB-CLASSES)

        /**
         * Non-API
         * Guard for {@link #simpleCompose(AbstractConverter)}
         * @param that
         * @return whether or not a 'simple' composition of transformations is possible
         */
        protected abstract boolean isSimpleCompositionWith(AbstractConverter that);
        
        /**
         * Non-API
         * Guarded by {@link #isSimpleCompositionWith(AbstractConverter)}
         * @param that
         * @return a new AbstractConverter that adds no additional conversion step
         */
        protected AbstractConverter simpleCompose(AbstractConverter that) {
                throw new IllegalStateException(
                                String.format("Concrete UnitConverter '%s' does not implement simpleCompose(...).", this)); 
        }
        
        // -- COMPOSITION INTERFACE IMPLEMENTATION (FINAL)
        
        @Override
        public final UnitConverter concatenate(UnitConverter converter) {
                Objects.requireNonNull(converter, "Can not concatenate null.");
                if(converter instanceof AbstractConverter) {
                        // let Simplifier decide
                        AbstractConverter other = (AbstractConverter) converter;
                        return Simplifier.compose(this, other, 
                                        AbstractConverter::isSimpleCompositionWith, 
                                        AbstractConverter::simpleCompose);
                }
                // converter is not known to this implementation ...
                if(converter.isIdentity()) {
                        return this;
                }
                if(this.isIdentity()) {
                        return converter;
                }
                throw new IllegalArgumentException(
                                "Concatenate is currently only supported for sub-classes of AbstractConverter"); 
                //[ahuber] we don't know how to simplify into a 'normal-form' with 'foreign' converters
                //return new Pair(this, converter);
        }

        @Override
        public final List<? extends UnitConverter> getConversionSteps() {
                if(conversionSteps != null) {
                        return conversionSteps;  
                }
                if(this instanceof Pair) {
                        return conversionSteps = ((Pair)this).createConversionSteps();
                }
                return conversionSteps = Collections.singletonList(this);
        }
        
        // -- CONVERSION CONTRACTS (TO BE IMPLEMENTED BY SUB-CLASSES)
        
        /**
         * Non-API
         * @param value
         * @return transformed value 
         */
        protected abstract double convertWhenNotIdentity(double value);

        /**
         * Non-API
         * @param value
         * @param ctx
         * @return transformed value (most likely a BigInteger or BigDecimal)
         */
        protected Number convertWhenNotIdentity(BigInteger value, MathContext ctx) {
                return convertWhenNotIdentity(new BigDecimal(value), ctx);
        }
        
        /**
         * Non-API
         * @param value
         * @param ctx
         * @return transformed value
         */
        protected abstract BigDecimal convertWhenNotIdentity(BigDecimal value, MathContext ctx);

        // -- CONVERSION INTERFACE IMPLEMENTATION (FINAL)
        
        @Override
        public final double convert(double value) {
                if(isIdentity()) {
                        return value;
                }
                return convertWhenNotIdentity(value);
        }
        
        /**
         * @throws IllegalArgumentException
         *             if the value is </code>null</code>.
         */
        @Override
        public final Number convert(Number value) {
                if(isIdentity()) {
                        return value;
                }
                if (value == null) {
                        throw new IllegalArgumentException("Value cannot be null");
                }
                if (value instanceof BigDecimal) {
                        return convertWhenNotIdentity((BigDecimal) value, Calculus.MATH_CONTEXT);
                }
                if (value instanceof BigInteger) {
                        return convertWhenNotIdentity((BigInteger) value, Calculus.MATH_CONTEXT);
                }
                return convertWhenNotIdentity(value.doubleValue());
        }
        
        // -- DEFAULT IMPLEMENTATION OF IDENTITY

        /**
         * This class represents the identity converter (singleton).
         */
        private static final class Identity extends AbstractConverter {

                /**
                 * 
                 */
                private static final long serialVersionUID = -4460463244427587361L;

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

                @Override
                public double convertWhenNotIdentity(double value) {
                        throw new IllegalStateException("code was reached, that is expected unreachable");
                }

                @Override
                public Number convertWhenNotIdentity(BigInteger value, MathContext ctx) {
                        throw new IllegalStateException("code was reached, that is expected unreachable");
                }
                
                @Override
                public BigDecimal convertWhenNotIdentity(BigDecimal value, MathContext ctx) {
                        throw new IllegalStateException("code was reached, that is expected unreachable");
                }

                @Override
                public boolean equals(Object cvtr) {
                        return (cvtr instanceof Identity); 
                }

                @Override
                public int hashCode() {
                        return 0;
                }

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

                @Override
                public int compareTo(UnitConverter o) {
                        if (o instanceof Identity) {
                                return 0;
                        }
                        return -1;
                }

                @Override
                protected boolean isSimpleCompositionWith(AbstractConverter that) {
                        throw new IllegalStateException("code was reached, that is expected unreachable");
                }
                
                @Override
                protected AbstractConverter simpleCompose(AbstractConverter that) {
                        throw new IllegalStateException("code was reached, that is expected unreachable");
                }

                @Override
                protected AbstractConverter inverseWhenNotIdentity() {
                        throw new IllegalStateException("code was reached, that is expected unreachable");
                }
                
                @Override
                protected String transformationLiteral() {
                        return null;
                }
                
        }
        
        // -- BINARY TREE (PAIR)

        /**
         * This class represents converters made up of two or more separate converters
         * (in matrix notation <code>[pair] = [left] x [right]</code>).
         */
        public static final class Pair extends AbstractConverter implements Serializable {

                /**
                 * 
                 */
                private static final long serialVersionUID = -123063827821728331L;

                /**
                 * Holds the first converter.
                 */
                private final UnitConverter left;

                /**
                 * Holds the second converter.
                 */
                private final UnitConverter right;

                /**
                 * Creates a pair converter resulting from the combined transformation of the
                 * specified converters.
                 *
                 * @param left
                 *            the left converter, not <code>null</code>.
                 * @param right
                 *            the right converter.
                 * @throws IllegalArgumentException
                 *             if either the left or right converter are </code> null</code>
                 */
                public Pair(UnitConverter left, UnitConverter right) {
                        if (left != null && right != null) {
                                this.left = left;
                                this.right = right;
                        } else {
                                throw new IllegalArgumentException("Converters cannot be null");
                        }
                }

                @Override
                public boolean isLinear() {
                        return left.isLinear() && right.isLinear();
                }

                @Override
                public boolean isIdentity() {
                        return false;
                }

                /*
                 * Non-API
                 */
                protected List<? extends UnitConverter> createConversionSteps(){
                        List<? extends UnitConverter> leftCompound = left.getConversionSteps();
                        List<? extends UnitConverter> rightCompound = right.getConversionSteps();
                        final List<UnitConverter> steps = new ArrayList<>(leftCompound.size() + rightCompound.size());
                        steps.addAll(leftCompound);
                        steps.addAll(rightCompound);
                        return steps;
                }

                @Override
                public Pair inverseWhenNotIdentity() {
                        return new Pair(right.inverse(), left.inverse());
                }

                @Override
                public double convertWhenNotIdentity(double value) {
                        return left.convert(right.convert(value));
                }
                
                @Override
                public Number convertWhenNotIdentity(BigInteger value, MathContext ctx) {
                        if (right instanceof AbstractConverter) {
                                //TODO [ahuber] assumes left is always instanceof AbstractConverter, why?
                                final AbstractConverter _left = (AbstractConverter) left;
                                final AbstractConverter _right = (AbstractConverter) right;
                                
                                final Number rightValue = _right.convertWhenNotIdentity(value, ctx);
                                if(rightValue instanceof BigDecimal) {
                                        return _left.convertWhenNotIdentity((BigDecimal) rightValue, ctx);
                                }
                                if(rightValue instanceof BigInteger) {
                                        return _left.convertWhenNotIdentity((BigInteger) rightValue, ctx);
                                }
                                return _left.convertWhenNotIdentity(Calculus.toBigDecimal(rightValue), ctx);
                        }
                        return convertWhenNotIdentity(new BigDecimal(value), ctx);
                }

                @Override
                public BigDecimal convertWhenNotIdentity(BigDecimal value, MathContext ctx) {
                        if (right instanceof AbstractConverter) {
                                //TODO [ahuber] assumes left is always instanceof AbstractConverter, why?
                                final AbstractConverter _left = (AbstractConverter) left;
                                final AbstractConverter _right = (AbstractConverter) right;
                                return _left.convertWhenNotIdentity(_right.convertWhenNotIdentity(value, ctx), ctx);
                        }
                        return Calculus.toBigDecimal(left.convert(right.convert(value)));
                }
                
                @Override
                public boolean equals(Object obj) {
                        if (this == obj) {
                                return true;
                        }
                        if (obj instanceof Pair) {
                                Pair that = (Pair) obj;
                                return Objects.equals(left, that.left) && Objects.equals(right, that.right);
                        }
                        return false;
                }

                @Override
                public int hashCode() {
                        return Objects.hash(left, right);
                }

                public UnitConverter getLeft() {
                        return left;
                }

                public UnitConverter getRight() {
                        return right;
                }

                @SuppressWarnings("unchecked")
                @Override
                public int compareTo(UnitConverter obj) {
                        if (this == obj) {
                                return 0;
                        }
                        if (obj instanceof Pair) {
                                Pair that = (Pair) obj;
                                @SuppressWarnings("rawtypes")
                                Comparator c = new UnitComparator<>();
                                return Objects.compare(left, that.left, c) + Objects.compare(right, that.right, c);
                        }
                        return -1;
                }
                
                @Override
                protected String transformationLiteral() {
                        return String.format("%s",
                                getConversionSteps().stream()
                                .map(UnitConverter::toString)
                                .collect(Collectors.joining(" ○ ")) );
                }
                

                @Override
                protected boolean isSimpleCompositionWith(AbstractConverter that) {
                        return false;
                }
                
        }


}