/*
 * $Id$
 */

package edu.jas.application;


import edu.jas.kern.PrettyPrint;
import edu.jas.poly.GenPolynomial;
import edu.jas.poly.PolyUtil;
import edu.jas.structure.GcdRingElem;


/**
 * Residue ring element based on GenPolynomial with RingElem interface. Objects
 * of this class are (nearly) immutable.
 * @author Heinz Kredel
 */
public class Residue<C extends GcdRingElem<C>> implements GcdRingElem<Residue<C>> {


    /**
     * Residue class factory data structure.
     */
    public final ResidueRing<C> ring;


    /**
     * Value part of the element data structure.
     */
    public final GenPolynomial<C> val;


    /**
     * Flag to remember if this residue element is a unit. -1 is unknown, 1 is
     * unit, 0 not a unit.
     */
    protected int isunit = -1; // initially unknown


    /**
     * The constructor creates a Residue object from a ring factory.
     * @param r residue ring factory.
     */
    public Residue(ResidueRing<C> r) {
        this(r, r.ring.getZERO(), 0);
    }


    /**
     * The constructor creates a Residue object from a ring factory and a
     * polynomial.
     * @param r residue ring factory.
     * @param a polynomial.
     */
    public Residue(ResidueRing<C> r, GenPolynomial<C> a) {
        this(r, a, -1);
    }


    /**
     * The constructor creates a Residue object from a ring factory, a
     * polynomial and an indicator if a is a unit.
     * @param r residue ring factory.
     * @param a polynomial.
     * @param u isunit indicator, -1, 0, 1.
     */
    public Residue(ResidueRing<C> r, GenPolynomial<C> a, int u) {
        ring = r;
        val = ring.ideal.normalform(a); //.monic() no go
        if (u == 0 || u == 1) {
            isunit = u;
            return;
        }
        if (val.isZERO()) {
            isunit = 0;
            return;
        }
        if (ring.isField()) {
            isunit = 1;
            return;
        }
        if (val.isUnit()) {
            isunit = 1;
            //} else { // not possible
            //isunit = 0;
        }
        isunit = -1;
    }


    /**
     * Get the corresponding element factory.
     * @return factory for this Element.
     * @see edu.jas.structure.Element#factory()
     */
    public ResidueRing<C> factory() {
        return ring;
    }


    /**
     * Clone this.
     * @see java.lang.Object#clone()
     */
    @Override
    public Residue<C> copy() {
        return new Residue<C>(ring, val, isunit);
    }


    /**
     * Is Residue zero.
     * @return If this is 0 then true is returned, else false.
     * @see edu.jas.structure.RingElem#isZERO()
     */
    public boolean isZERO() {
        return val.isZERO();
    }


    /**
     * Is Residue one.
     * @return If this is 1 then true is returned, else false.
     * @see edu.jas.structure.RingElem#isONE()
     */
    public boolean isONE() {
        return val.isONE();
    }


    /**
     * Is Residue unit.
     * @return If this is a unit then true is returned, else false.
     * @see edu.jas.structure.RingElem#isUnit()
     */
    public boolean isUnit() {
        if (isunit > 0) {
            return true;
        }
        if (isunit == 0) {
            return false;
        }
        // not jet known
        boolean u = ring.ideal.isUnit(val);
        if (u) {
            isunit = 1;
        } else {
            isunit = 0;
        }
        return (u);
    }


    /**
     * Is Residue a constant.
     * @return true if this.val is a constant polynomial, else false.
     */
    public boolean isConstant() {
        return val.isConstant();
    }


    /**
     * Get the String representation as RingElem.
     * @see java.lang.Object#toString()
     */
    @Override
    public String toString() {
        if (PrettyPrint.isTrue()) {
            return val.toString(ring.ring.getVars());
        }
        return "Residue[ " + val.toString() + " mod " + ring.toString() + " ]";
    }


    /**
     * Get a scripting compatible string representation.
     * @return script compatible representation for this Element.
     * @see edu.jas.structure.Element#toScript()
     */
    @Override
    public String toScript() {
        // Python case
        return val.toScript();
        //         return "PolyResidue( " + val.toScript() 
        //                         + ", " + ring.toScript() + " )";
    }


    /**
     * Get a scripting compatible string representation of the factory.
     * @return script compatible representation for this ElemFactory.
     * @see edu.jas.structure.Element#toScriptFactory()
     */
    @Override
    public String toScriptFactory() {
        // Python case
        return factory().toScript();
    }


    /**
     * Residue comparison.
     * @param b Residue.
     * @return sign(this-b), 0 means that this and b are equivalent in this
     *         residue class ring.
     */
    @Override
    public int compareTo(Residue<C> b) {
        GenPolynomial<C> v = b.val;
        if (!ring.equals(b.ring)) {
            v = ring.ideal.normalform(v);
        }
        return val.compareTo(v);
    }


    /**
     * Comparison with any other object.
     * @see java.lang.Object#equals(java.lang.Object)
     * @return true means that this and b are equivalent in this residue class
     *         ring.
     */
    @Override
    @SuppressWarnings("unchecked")
    public boolean equals(Object b) {
        if (!(b instanceof Residue)) {
            return false;
        }
        Residue<C> a = null;
        try {
            a = (Residue<C>) b;
        } catch (ClassCastException e) {
        }
        if (a == null) {
            return false;
        }
        return compareTo(a) == 0;
    }


    /**
     * Hash code for this residue.
     * @see java.lang.Object#hashCode()
     */
    @Override
    public int hashCode() {
        int h;
        h = ring.hashCode();
        h = 37 * h + val.hashCode();
        return h;
    }


    /**
     * Residue absolute value.
     * @return the absolute value of this.
     * @see edu.jas.structure.RingElem#abs()
     */
    public Residue<C> abs() {
        return new Residue<C>(ring, val.abs(), isunit);
    }


    /**
     * Residue summation.
     * @param S Residue.
     * @return this+S.
     */
    public Residue<C> sum(Residue<C> S) {
        return new Residue<C>(ring, val.sum(S.val));
    }


    /**
     * Residue negate.
     * @return -this.
     * @see edu.jas.structure.RingElem#negate()
     */
    public Residue<C> negate() {
        return new Residue<C>(ring, val.negate(), isunit);
    }


    /**
     * Residue signum.
     * @see edu.jas.structure.RingElem#signum()
     * @return signum(this).
     */
    public int signum() {
        return val.signum();
    }


    /**
     * Residue subtraction.
     * @param S Residue.
     * @return this-S.
     */
    public Residue<C> subtract(Residue<C> S) {
        return new Residue<C>(ring, val.subtract(S.val));
    }


    /**
     * Residue division.
     * @param S Residue.
     * @return this/S.
     */
    public Residue<C> divide(Residue<C> S) {
        if (ring.isField()) {
            return multiply(S.inverse());
        }
        GenPolynomial<C> x = PolyUtil.<C> basePseudoDivide(val, S.val);
        return new Residue<C>(ring, x);
    }


    /**
     * Residue inverse.
     * @see edu.jas.structure.RingElem#inverse()
     * @return S with S = 1/this if defined.
     */
    public Residue<C> inverse() {
        GenPolynomial<C> x = ring.ideal.inverse(val);
        return new Residue<C>(ring, x, 1);
    }


    /**
     * Residue remainder.
     * @param S Residue.
     * @return this - (this/S)*S.
     */
    public Residue<C> remainder(Residue<C> S) {
        //GenPolynomial<C> x = val.remainder( S.val );
        GenPolynomial<C> x = PolyUtil.<C> baseSparsePseudoRemainder(val, S.val);
        return new Residue<C>(ring, x);
    }


    /**
     * Residue multiplication.
     * @param S Residue.
     * @return this*S.
     */
    public Residue<C> multiply(Residue<C> S) {
        GenPolynomial<C> x = val.multiply(S.val);
        int i = -1;
        if (isunit == 1 && S.isunit == 1) {
            i = 1;
        } else if (isunit == 0 || S.isunit == 0) {
            i = 0;
        }
        return new Residue<C>(ring, x, i);
    }


    /**
     * Residue monic.
     * @return this with monic value part.
     */
    public Residue<C> monic() {
        return new Residue<C>(ring, val.monic(), isunit);
    }


    /**
     * Greatest common divisor.
     * @param b other element.
     * @return gcd(this,b).
     */
    public Residue<C> gcd(Residue<C> b) {
        GenPolynomial<C> x = ring.engine.gcd(val, b.val);
        int i = -1; // gcd might become a unit
        if (x.isONE()) {
            i = 1;
            //} else {
            //System.out.println("Residue gcd = " + x);
        }
        if (isunit == 1 && b.isunit == 1) {
            i = 1;
        }
        return new Residue<C>(ring, x, i);
    }


    /**
     * Extended greatest common divisor. <b>Note: </b>Not implemented, throws
     * UnsupportedOperationException.
     * @param b other element.
     * @return [ gcd(this,b), c1, c2 ] with c1*this + c2*b = gcd(this,b).
     */
    public Residue<C>[] egcd(Residue<C> b) {
        throw new UnsupportedOperationException("egcd not implemented");
    }
}
