/*
 * Units of Measurement Reference Implementation
 * Copyright (c) 2005-2021, 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.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.HashMap;
import java.util.Map;

import javax.measure.Dimension;
import javax.measure.IncommensurableException;
import javax.measure.Prefix;
import javax.measure.Quantity;
import javax.measure.UnconvertibleException;
import javax.measure.Unit;
import javax.measure.UnitConverter;
import javax.measure.format.MeasurementParseException;
import javax.measure.quantity.Dimensionless;

import tech.units.indriya.format.LocalUnitFormat;
import tech.units.indriya.format.SimpleUnitFormat;
import tech.units.indriya.function.AbstractConverter;
import tech.units.indriya.function.AddConverter;
import tech.units.indriya.function.Calculus;
import tech.units.indriya.function.MultiplyConverter;
import tech.units.indriya.function.RationalNumber;
import tech.units.indriya.internal.function.Calculator;
import tech.units.indriya.spi.DimensionalModel;
import tech.units.indriya.unit.AlternateUnit;
import tech.units.indriya.unit.AnnotatedUnit;
import tech.units.indriya.unit.ProductUnit;
import tech.units.indriya.unit.TransformedUnit;
import tech.units.indriya.unit.UnitDimension;
import tech.units.indriya.unit.Units;
import tech.uom.lib.common.function.Nameable;
import tech.uom.lib.common.function.PrefixOperator;
import tech.uom.lib.common.function.SymbolSupplier;

/**
 * <p>
 * The class represents units founded on the seven <b>SI</b> base units for
 * seven base quantities assumed to be mutually independent.
 * </p>
 *
 * <p>
 * For all physics units, unit conversions are symmetrical:
 * <code>u1.getConverterTo(u2).equals(u2.getConverterTo(u1).inverse())</code>.
 * Non-physical units (e.g. currency units) for which conversion is not
 * symmetrical should have their own separate class hierarchy and are considered
 * distinct (e.g. financial units), although they can always be combined with
 * physics units (e.g. "€/Kg", "$/h").
 * </p>
 *
 * @see <a href=
 *      "http://en.wikipedia.org/wiki/International_System_of_Units">Wikipedia:
 *      International System of Units</a>
 * @author <a href="mailto:jean-marie@dautelle.com">Jean-Marie Dautelle</a>
 * @author <a href="mailto:werner@units.tech">Werner Keil</a>
 * @version 3.2, April 16, 2021
 * @since 1.0
 */
public abstract class AbstractUnit<Q extends Quantity<Q>>
                implements Unit<Q>, Comparable<Unit<Q>>, PrefixOperator<Q>, Nameable, Serializable, SymbolSupplier {

        /**
         * 
         */
        private static final long serialVersionUID = -4344589505537030204L;

        /**
         * Holds the dimensionless unit <code>ONE</code>.
         * 
         * @see <a href=
         *      "https://en.wikipedia.org/wiki/Natural_units#Choosing_constants_to_normalize">
         *      Wikipedia: Natural Units - Choosing constants to normalize</a>
         * @see <a href= "http://www.av8n.com/physics/dimensionless-units.htm">Units of
         *      Dimension One</a>
         */
        public static final Unit<Dimensionless> ONE = new ProductUnit<>();

        /**
         * Holds the name.
         */
        protected String name;

        /**
         * Holds the symbol.
         */
        private String symbol;

        /**
         * Holds the unique symbols collection (base units or alternate units).
         */
        protected static final transient Map<String, Unit<?>> SYMBOL_TO_UNIT = new HashMap<>();

        /**
         * Default constructor.
         */
        protected AbstractUnit() {
        }

        /**
         * Constructor setting a symbol.
         * 
         * @param symbol the unit symbol.
         */
        protected AbstractUnit(String symbol) {
                this.symbol = symbol;
        }

        protected Type getActualType() {
                ParameterizedType parameterizedType = (ParameterizedType) getClass().getGenericSuperclass();
                return parameterizedType.getActualTypeArguments()[0].getClass().getGenericInterfaces()[0];
        }

        /**
         * Indicates if this unit belongs to the set of coherent SI units (unscaled SI
         * units).
         * 
         * The base and coherent derived units of the SI form a coherent set, designated
         * the set of coherent SI units. The word coherent is used here in the following
         * sense: when coherent units are used, equations between the numerical values
         * of quantities take exactly the same form as the equations between the
         * quantities themselves. Thus if only units from a coherent set are used,
         * conversion factors between units are never required.
         * 
         * @return <code>equals(toSystemUnit())</code>
         */
        public boolean isSystemUnit() {
                Unit<Q> sys = this.toSystemUnit();
                return this == sys || this.equals(sys);
        }
        
        /**
         * Returns the converter from this unit to its unscaled {@link #toSystemUnit
         * System Unit} unit.
         *
         * @return <code>getConverterTo(this.toSystemUnit())</code>
         * @see #toSystemUnit
         */
        public abstract UnitConverter getSystemConverter();
        
        /**
         * Returns the unscaled {@link SI} unit from which this unit is derived.
         * 
         * The SI unit can be be used to identify a quantity given the unit. For
         * example:<code> static boolean isAngularVelocity(AbstractUnit<?> unit) {
         * return unit.toSystemUnit().equals(RADIAN.divide(SECOND)); } assert(REVOLUTION.divide(MINUTE).isAngularVelocity()); // Returns true. </code>
         *
         * @return the unscaled metric unit from which this unit is derived.
         */
        protected abstract Unit<Q> toSystemUnit();

        /**
         * Annotates the specified unit. Annotation does not change the unit semantic.
         * Annotations are often written between curly braces behind units. For
         * example:<br>
         * <code> Unit<Volume> PERCENT_VOL = ((AbstractUnit)Units.PERCENT).annotate("vol"); // "%{vol}" Unit<Mass> KG_TOTAL =
         * ((AbstractUnit)Units.KILOGRAM).annotate("total"); // "kg{total}" Unit<Dimensionless> RED_BLOOD_CELLS = ((AbstractUnit)Units.ONE).annotate("RBC"); // "{RBC}" </code>
         *
         * Note: Annotation of system units are not considered themselves as system
         * units.
         *
         * @param annotation the unit annotation.
         * @return the annotated unit.
         */
    public final Unit<Q> annotate(String annotation) {
      return new AnnotatedUnit<>(this, annotation);
    }

        /**
         * Returns the abstract unit represented by the specified characters as per
         * default format.
         *
         * Locale-sensitive unit parsing could be handled using {@link LocalUnitFormat}
         * in subclasses of AbstractUnit.
         *
         * <p>
         * Note: The standard format supports dimensionless
         * units.<code> AbstractUnit<Dimensionless> PERCENT =
         * AbstractUnit.parse("100").inverse().asType(Dimensionless.class); </code>
         * </p>
         *
         * @param charSequence the character sequence to parse.
         * @return <code>SimpleUnitFormat.getInstance().parse(csq)</code>
         * @throws MeasurementParseException if the specified character sequence cannot
         *                                   be correctly parsed (e.g. not UCUM
         *                                   compliant).
         */
        public static Unit<?> parse(CharSequence charSequence) {
                return SimpleUnitFormat.getInstance().parse(charSequence);
        }

        /**
         * Returns the standard representation of this physics unit. The string produced
         * for a given unit is always the same; it is not affected by the locale. It can
         * be used as a canonical string representation for exchanging units, or as a
         * key for a Hashtable, etc.
         *
         * Locale-sensitive unit parsing could be handled using {@link LocalUnitFormat}
         * in subclasses of AbstractUnit.
         *
         * @return <code>SimpleUnitFormat.getInstance().format(this)</code>
         */
        @Override
        public String toString() {
                return SimpleUnitFormat.getInstance().format(this);
        }

        // ///////////////////////////////////////////////////////
        // Implements javax.measure.Unit<Q> interface //
        // ///////////////////////////////////////////////////////

        /**
         * Returns the system unit (unscaled SI unit) from which this unit is derived.
         * They can be be used to identify a quantity given the unit. For example:<br>
         * <code> static boolean isAngularVelocity(AbstractUnit<?> unit) {<br>&nbsp;&nbsp;return unit.getSystemUnit().equals(RADIAN.divide(SECOND));<br>}
         * <br>assert(REVOLUTION.divide(MINUTE).isAngularVelocity()); // Returns true. </code>
         *
         * @return the unscaled metric unit from which this unit is derived.
         */
        @Override
        public final Unit<Q> getSystemUnit() {
                return toSystemUnit();
        }

        /**
         * Indicates if this unit is compatible with the unit specified. To be
         * compatible both units must be physics units having the same fundamental
         * dimension.
         *
         * @param that the other unit.
         * @return <code>true</code> if this unit and that unit have the same
         *         fundamental dimension according to the current dimensional model;
         *         <code>false</code> otherwise.
         */
        @Override
        public final boolean isCompatible(Unit<?> that) {
                return internalIsCompatible(that, true);
        }

        /**
         * Casts this unit to a parameterized unit of specified nature or throw a
         * ClassCastException if the dimension of the specified quantity and this unit's
         * dimension do not match (regardless whether or not the dimensions are
         * independent or not).
         *
         * @param type the quantity class identifying the nature of the unit.
         * @throws ClassCastException if the dimension of this unit is different from
         *                            the SI dimension of the specified type.
         * @see Units#getUnit(Class)
         */
        @SuppressWarnings("unchecked")
        @Override
        public final <T extends Quantity<T>> Unit<T> asType(Class<T> type) {
                Dimension typeDimension = UnitDimension.of(type);
                if (typeDimension != null && !typeDimension.equals(this.getDimension()))
                        throw new ClassCastException("The unit: " + this + " is not compatible with quantities of type " + type);
                return (Unit<T>) this;
        }

        @Override
        public abstract Map<? extends Unit<?>, Integer> getBaseUnits();

        @Override
        public abstract Dimension getDimension();

        protected void setName(String name) {
                this.name = name;
        }

        public String getName() {
                return name;
        }

        public String getSymbol() {
                return symbol;
        }

        protected void setSymbol(String s) {
                this.symbol = s;
        }

        @Override
        public final UnitConverter getConverterTo(Unit<Q> that) throws UnconvertibleException {
                return internalGetConverterTo(that, true);
        }

        @SuppressWarnings("rawtypes")
        @Override
        public final UnitConverter getConverterToAny(Unit<?> that) throws IncommensurableException, UnconvertibleException {
                if (!isCompatible(that))
                        throw new IncommensurableException(this + " is not compatible with " + that);
                AbstractUnit thatAbstr = (AbstractUnit) that; // Since both units are
                // compatible they must both be abstract units.
                final DimensionalModel model = DimensionalModel.current();
                Unit thisSystemUnit = this.getSystemUnit();
                UnitConverter thisToDimension = model.getDimensionalTransform(thisSystemUnit.getDimension())
                                .concatenate(this.getSystemConverter());
                Unit thatSystemUnit = thatAbstr.getSystemUnit();
                UnitConverter thatToDimension = model.getDimensionalTransform(thatSystemUnit.getDimension())
                                .concatenate(thatAbstr.getSystemConverter());
                return thatToDimension.inverse().concatenate(thisToDimension);
        }

        @Override
        public final Unit<Q> alternate(String newSymbol) {
                return new AlternateUnit<>(this, newSymbol);
        }

        @Override
        public final Unit<Q> transform(UnitConverter operation) {
                Unit<Q> systemUnit = this.getSystemUnit();
                UnitConverter cvtr;
                if (this.isSystemUnit()) {
                        cvtr = this.getSystemConverter().concatenate(operation);
                } else {
                        cvtr = operation;
                }
                return cvtr.isIdentity() ? systemUnit : new TransformedUnit<>(null, this, systemUnit, cvtr);
        }

        @Override
        public final Unit<Q> shift(Number offset) {
                if (Calculus.currentNumberSystem().isZero(offset))
                        return this;
                return transform(new AddConverter(offset));
        }

        @Override
        public final Unit<Q> multiply(Number factor) {
                if (Calculus.currentNumberSystem().isOne(factor))
                        return this;
                return transform(MultiplyConverter.of(factor));
        }

        @Override
        public Unit<Q> shift(double offset) {
                return shift(RationalNumber.of(offset));
        }

        @Override
        public Unit<Q> multiply(double multiplier) {
                return multiply(RationalNumber.of(multiplier));
        }

        @Override
        public Unit<Q> divide(double divisor) {
                return divide(RationalNumber.of(divisor));
        }
        
        /**
         * Internal helper for isCompatible
         */
        private final boolean internalIsCompatible(Unit<?> that, boolean checkEquals) {
                if (checkEquals) {
                        if (this == that || this.equals(that))
                                return true;
                } else {
                        if (this == that)
                                return true;
                }
                if (!(that instanceof Unit))
                        return false;
                Dimension thisDimension = this.getDimension();
                Dimension thatDimension = that.getDimension();
                if (thisDimension.equals(thatDimension))
                        return true;
                DimensionalModel model = DimensionalModel.current(); // Use
                // dimensional
                // analysis
                // model.
                return model.getFundamentalDimension(thisDimension).equals(model.getFundamentalDimension(thatDimension));
        }

        protected final UnitConverter internalGetConverterTo(Unit<Q> that, boolean useEquals)
                        throws UnconvertibleException {
                if (useEquals) {
                        if (this == that || this.equals(that))
                                return AbstractConverter.IDENTITY;
                } else {
                        if (this == that)
                                return AbstractConverter.IDENTITY;
                }
                Unit<Q> thisSystemUnit = this.getSystemUnit();
                Unit<Q> thatSystemUnit = that.getSystemUnit();
                if (!thisSystemUnit.equals(thatSystemUnit))
                        try {
                                return getConverterToAny(that);
                        } catch (IncommensurableException e) {
                                throw new UnconvertibleException(e);
                        }
                UnitConverter thisToSI = this.getSystemConverter();
                UnitConverter thatToSI = that.getConverterTo(thatSystemUnit);
                return thatToSI.inverse().concatenate(thisToSI);
        }

        /**
         * Returns the product of this physical unit with the one specified.
         *
         * @param that the physical unit multiplicand.
         * @return <code>this * that</code>
         */
        public final Unit<?> multiply(Unit<?> that) {
                if (this.equals(ONE))
                        return that;
                if (that.equals(ONE))
                        return this;
                return ProductUnit.ofProduct(this, that);
        }

        /**
         * Returns the inverse of this physical unit.
         *
         * @return <code>1 / this</code>
         */
        @Override
        public final Unit<?> inverse() {
                if (this.equals(ONE))
                        return this;
                return ProductUnit.ofQuotient(ONE, this);
        }

        /**
         * Returns the result of dividing this unit by the specified divisor. If the
         * factor is an integer value, the division is exact. For example:
         * 
         * <pre>
         * <code>
         *    QUART = GALLON_LIQUID_US.divide(4); // Exact definition.
         * </code>
         * </pre>
         * 
         * @param divisor the divisor value.
         * @return this unit divided by the specified divisor.
         */
        @Override
        public final Unit<Q> divide(Number divisor) {
            if (Calculus.currentNumberSystem().isOne(divisor))
                        return this;
            Number factor = Calculator.of(divisor).reciprocal().peek(); 
                return transform(MultiplyConverter.of(factor));
        }

        /**
         * Returns the quotient of this unit with the one specified.
         *
         * @param that the unit divisor.
         * @return <code>this.multiply(that.inverse())</code>
         */
        @Override
        public final Unit<?> divide(Unit<?> that) {
                return this.multiply(that.inverse());
        }

        /**
         * Returns a unit equals to the given root of this unit.
         *
         * @param n the root's order.
         * @return the result of taking the given root of this unit.
         * @throws ArithmeticException if <code>n == 0</code> or if this operation would
         *                             result in an unit with a fractional exponent.
         */
        @Override
        public final Unit<?> root(int n) {
                if (n > 0)
                        return ProductUnit.ofRoot(this, n);
                else if (n == 0)
                        throw new ArithmeticException("Root's order of zero");
                else
                        // n < 0
                        return ONE.divide(this.root(-n));
        }

        /**
         * Returns a unit equals to this unit raised to an exponent.
         *
         * @param n the exponent.
         * @return the result of raising this unit to the exponent.
         */
        @Override
        public Unit<?> pow(int n) {
                if (n > 0)
                        return this.multiply(this.pow(n - 1));
                else if (n == 0)
                        return ONE;
                else
                        // n < 0
                        return ONE.divide(this.pow(-n));
        }

        @Override
        public Unit<Q> prefix(Prefix prefix) {
                return this.transform(MultiplyConverter.ofPrefix(prefix));
        }
        
        /**
         * Compares this unit to the specified unit. The default implementation compares
         * the name and symbol of both this unit and the specified unit, giving
         * precedence to the symbol.
         *
         * @return a negative integer, zero, or a positive integer as this unit is less
         *         than, equal to, or greater than the specified unit.
         */
        @Override
        public int compareTo(Unit<Q> that) {
                int symbolComparison = compareToWithPossibleNullValues(getSymbol(), that.getSymbol());
                if (symbolComparison == 0) {
                        return compareToWithPossibleNullValues(name, that.getName());
                } else {
                        return symbolComparison;
                }
        }

        private int compareToWithPossibleNullValues(String a, String b) {
                if (a == null) {
                        return (b == null) ? 0 : -1;
                } else {
                        return (b == null) ? 1 : a.compareTo(b);
                }
        }

        @Override
        public boolean isEquivalentTo(Unit<Q> that) {
                return this.getConverterTo(that).isIdentity();
        }

        // //////////////////////////////////////////////////////////////
        // Ensures that sub-classes implement the hashCode method.
        // //////////////////////////////////////////////////////////////

        @Override
        public abstract boolean equals(Object obj);

        @Override
        public abstract int hashCode();

        /**
         * Utility class for number comparison and equality
         */
        protected static final class Equalizer {
                /**
                 * Indicates if this unit is considered equals to the specified object. order).
                 *
                 * @param obj the object to compare for equality.
                 * @return <code>true</code> if <code>this</code> and <code>obj</code> are
                 *         considered equal; <code>false</code>otherwise.
                 */
                public static boolean areEqual(@SuppressWarnings("rawtypes") Unit u1,
                                @SuppressWarnings("rawtypes") Unit u2) {
                        /*
                         * if (u1 != null && u2 != null) { if (u1.getName() != null && u1.getSymbol() !=
                         * null) { return u1.getName().equals(u2.getName()) &&
                         * u1.getSymbol().equals(u2.getSymbol()) && u1.internalIsCompatible(u2, false);
                         * } else if (u1.getSymbol() != null) { return
                         * u1.getSymbol().equals(u2.getSymbol()) && u1.internalIsCompatible(u2, false);
                         * } else { return u1.toString().equals(u2.toString()) &&
                         * u1.internalIsCompatible(u2, false); } } else {
                         */
                        if (u1 != null && u1.equals(u2))
                                return true;
                        return false;
                }
        }
}