package org.bouncycastle.math.ec;

import java.math.BigInteger;

Class representing a simple version of a big decimal. A
SimpleBigDecimal is basically a BigInteger with a few digits on the right of the decimal point. The number of (binary) digits on the right of the decimal point is called the scale of the SimpleBigDecimal. Unlike in BigDecimal, the scale is not adjusted automatically, but must be set manually. All SimpleBigDecimals
taking part in the same arithmetic operation must have equal scale. The
result of a multiplication of two SimpleBigDecimals returns a
SimpleBigDecimal with double scale.
/**
 * Class representing a simple version of a big decimal. A
 * <code>SimpleBigDecimal</code> is basically a
 * {@link java.math.BigInteger BigInteger} with a few digits on the right of
 * the decimal point. The number of (binary) digits on the right of the decimal
 * point is called the <code>scale</code> of the <code>SimpleBigDecimal</code>.
 * Unlike in {@link java.math.BigDecimal BigDecimal}, the scale is not adjusted
 * automatically, but must be set manually. All <code>SimpleBigDecimal</code>s
 * taking part in the same arithmetic operation must have equal scale. The
 * result of a multiplication of two <code>SimpleBigDecimal</code>s returns a
 * <code>SimpleBigDecimal</code> with double scale.
 */
class SimpleBigDecimal
    //extends Number   // not in J2ME - add compatibility class?
{
    private static final long serialVersionUID = 1L;

    private final BigInteger bigInt;
    private final int scale;

    
Returns a SimpleBigDecimal representing the same numerical
value as value.
Params:
value – The value of the SimpleBigDecimal to be
created.
scale – The scale of the SimpleBigDecimal to be
created.
Returns:
The such created SimpleBigDecimal./**
     * Returns a <code>SimpleBigDecimal</code> representing the same numerical
     * value as <code>value</code>.
     * @param value The value of the <code>SimpleBigDecimal</code> to be
     * created. 
     * @param scale The scale of the <code>SimpleBigDecimal</code> to be
     * created. 
     * @return The such created <code>SimpleBigDecimal</code>.
     */
    public static SimpleBigDecimal getInstance(BigInteger value, int scale)
    {
        return new SimpleBigDecimal(value.shiftLeft(scale), scale);
    }

    
Constructor for SimpleBigDecimal. The value of the
constructed SimpleBigDecimal equals bigInt / 
2scale.
Params:
bigInt – The bigInt value parameter.
scale – The scale of the constructed SimpleBigDecimal./**
     * Constructor for <code>SimpleBigDecimal</code>. The value of the
     * constructed <code>SimpleBigDecimal</code> equals <code>bigInt / 
     * 2<sup>scale</sup></code>.
     * @param bigInt The <code>bigInt</code> value parameter.
     * @param scale The scale of the constructed <code>SimpleBigDecimal</code>.
     */
    public SimpleBigDecimal(BigInteger bigInt, int scale)
    {
        if (scale < 0)
        {
            throw new IllegalArgumentException("scale may not be negative");
        }

        this.bigInt = bigInt;
        this.scale = scale;
    }

    private void checkScale(SimpleBigDecimal b)
    {
        if (scale != b.scale)
        {
            throw new IllegalArgumentException("Only SimpleBigDecimal of " +
                "same scale allowed in arithmetic operations");
        }
    }

    public SimpleBigDecimal adjustScale(int newScale)
    {
        if (newScale < 0)
        {
            throw new IllegalArgumentException("scale may not be negative");
        }

        if (newScale == scale)
        {
            return this;
        }

        return new SimpleBigDecimal(bigInt.shiftLeft(newScale - scale),
                newScale);
    }

    public SimpleBigDecimal add(SimpleBigDecimal b)
    {
        checkScale(b);
        return new SimpleBigDecimal(bigInt.add(b.bigInt), scale);
    }

    public SimpleBigDecimal add(BigInteger b)
    {
        return new SimpleBigDecimal(bigInt.add(b.shiftLeft(scale)), scale);
    }

    public SimpleBigDecimal negate()
    {
        return new SimpleBigDecimal(bigInt.negate(), scale);
    }

    public SimpleBigDecimal subtract(SimpleBigDecimal b)
    {
        return add(b.negate());
    }

    public SimpleBigDecimal subtract(BigInteger b)
    {
        return new SimpleBigDecimal(bigInt.subtract(b.shiftLeft(scale)),
                scale);
    }

    public SimpleBigDecimal multiply(SimpleBigDecimal b)
    {
        checkScale(b);
        return new SimpleBigDecimal(bigInt.multiply(b.bigInt), scale + scale);
    }

    public SimpleBigDecimal multiply(BigInteger b)
    {
        return new SimpleBigDecimal(bigInt.multiply(b), scale);
    }

    public SimpleBigDecimal divide(SimpleBigDecimal b)
    {
        checkScale(b);
        BigInteger dividend = bigInt.shiftLeft(scale);
        return new SimpleBigDecimal(dividend.divide(b.bigInt), scale);
    }

    public SimpleBigDecimal divide(BigInteger b)
    {
        return new SimpleBigDecimal(bigInt.divide(b), scale);
    }

    public SimpleBigDecimal shiftLeft(int n)
    {
        return new SimpleBigDecimal(bigInt.shiftLeft(n), scale);
    }

    public int compareTo(SimpleBigDecimal val)
    {
        checkScale(val);
        return bigInt.compareTo(val.bigInt);
    }

    public int compareTo(BigInteger val)
    {
        return bigInt.compareTo(val.shiftLeft(scale));
    }

    public BigInteger floor()
    {
        return bigInt.shiftRight(scale);
    }

    public BigInteger round()
    {
        SimpleBigDecimal oneHalf = new SimpleBigDecimal(ECConstants.ONE, 1);
        return add(oneHalf.adjustScale(scale)).floor();
    }

    public int intValue()
    {
        return floor().intValue();
    }
    
    public long longValue()
    {
        return floor().longValue();
    }
          /* NON-J2ME compliant.
    public double doubleValue()
    {
        return Double.valueOf(toString()).doubleValue();
    }

    public float floatValue()
    {
        return Float.valueOf(toString()).floatValue();
    }
       */
    public int getScale()
    {
        return scale;
    }

    public String toString()
    {
        if (scale == 0)
        {
            return bigInt.toString();
        }

        BigInteger floorBigInt = floor();
        
        BigInteger fract = bigInt.subtract(floorBigInt.shiftLeft(scale));
        if (bigInt.signum() == -1)
        {
            fract = ECConstants.ONE.shiftLeft(scale).subtract(fract);
        }

        if ((floorBigInt.signum() == -1) && (!(fract.equals(ECConstants.ZERO))))
        {
            floorBigInt = floorBigInt.add(ECConstants.ONE);
        }
        String leftOfPoint = floorBigInt.toString();

        char[] fractCharArr = new char[scale];
        String fractStr = fract.toString(2);
        int fractLen = fractStr.length();
        int zeroes = scale - fractLen;
        for (int i = 0; i < zeroes; i++)
        {
            fractCharArr[i] = '0';
        }
        for (int j = 0; j < fractLen; j++)
        {
            fractCharArr[zeroes + j] = fractStr.charAt(j);
        }
        String rightOfPoint = new String(fractCharArr);

        StringBuffer sb = new StringBuffer(leftOfPoint);
        sb.append(".");
        sb.append(rightOfPoint);

        return sb.toString();
    }

    public boolean equals(Object o)
    {
        if (this == o)
        {
            return true;
        }

        if (!(o instanceof SimpleBigDecimal))
        {
            return false;
        }

        SimpleBigDecimal other = (SimpleBigDecimal)o;
        return ((bigInt.equals(other.bigInt)) && (scale == other.scale));
    }

    public int hashCode()
    {
        return bigInt.hashCode() ^ scale;
    }

}