/*
 * JScience - Java(TM) Tools and Libraries for the Advancement of Sciences.
 * Copyright (C) 2006 - JScience (http://jscience.org/)
 * All rights reserved.
 * 
 * Permission to use, copy, modify, and distribute this software is
 * freely granted, provided that this notice is preserved.
 */
package javax.measure.converter;

/**
 * 
 This class represents a logarithmic converter. Such converter 
 *     is typically used to create logarithmic unit. For example:[code]
 *     Unit BEL = Unit.ONE.transform(new LogConverter(10).inverse());
 *     [/code]
 *     
 * 
 Instances of this class are immutable.
 *
 * @author  Jean-Marie Dautelle
 * @version 3.1, April 22, 2006
 */
public final class LogConverter extends UnitConverter {

    /**
     * Holds the logarithmic base.
     */
    private final double _base;

    /**
     * Holds the natural logarithm of the base.
     */
    private final double _logBase;

    /**
     * Holds the inverse of the natural logarithm of the base.
     */
    private final double _invLogBase;

    /**
     * Holds the inverse of this converter.
     */
    private final Inverse _inverse = new Inverse();

    /**
     * Creates a logarithmic converter having the specified base.
     * 
     * @param  base the logarithmic base (e.g. Math.E for
     *         the Natural Logarithm).
     */
    public LogConverter(double base) {
        _base = base;
        _logBase = Math.log(base);
        _invLogBase = 1.0 / _logBase;
    }

    /**
     * Returns the logarithmic base of this converter.
     *
     * @return the logarithmic base (e.g. Math.E for
     *         the Natural Logarithm).
     */
    public double getBase() {
        return _base;
    }

    @Override
    public UnitConverter inverse() {
        return _inverse;
    }

    @Override
    public double convert(double amount) {
        return _invLogBase * Math.log(amount);
    }

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

    /**
     * This inner class represents the inverse of the logarithmic converter
     * (exponentiation converter).
     */
    private class Inverse extends UnitConverter {


        @Override
        public UnitConverter inverse() {
            return LogConverter.this;
        }

        @Override
        public double convert(double amount) {
            return Math.exp(_logBase * amount);
        }

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

        private static final long serialVersionUID = 1L;
    }

    private static final long serialVersionUID = 1L;
}