/*
 * $Id$
 */

package edu.jas.gb;


import java.util.List;
import java.util.Map;

import edu.jas.poly.ExpVector;
import edu.jas.poly.GenPolynomial;
import edu.jas.structure.RingElem;


/**
 * Polynomial Reduction sequential use algorithm. Implements normalform.
 * @param  coefficient type
 * @author Heinz Kredel
 */

public class ReductionSeq> // should be FieldElem>
                extends ReductionAbstract {


    //private static final Logger logger = Logger.getLogger(ReductionSeq.class);


    /**
     * Constructor.
     */
    public ReductionSeq() {
    }


    /**
     * Normalform.
     * @param Ap polynomial.
     * @param Pp polynomial list.
     * @return nf(Ap) with respect to Pp.
     */
    @SuppressWarnings("unchecked")
    public GenPolynomial normalform(List> Pp, GenPolynomial Ap) {
        if (Pp == null || Pp.isEmpty()) {
            return Ap;
        }
        if (Ap == null || Ap.isZERO()) {
            return Ap;
        }
        if (!Ap.ring.coFac.isField()) {
            throw new IllegalArgumentException("coefficients not from a field");
        }
        Map.Entry m;
        int l;
        GenPolynomial[] P;
        synchronized (Pp) {
            l = Pp.size();
            P = new GenPolynomial[l];
            //P = Pp.toArray();
            for (int i = 0; i < Pp.size(); i++) {
                P[i] = Pp.get(i);
            }
        }
        ExpVector[] htl = new ExpVector[l];
        Object[] lbc = new Object[l]; // want C[]
        GenPolynomial[] p = new GenPolynomial[l];
        int i;
        int j = 0;
        for (i = 0; i < l; i++) {
            p[i] = P[i];
            m = p[i].leadingMonomial();
            if (m != null) {
                p[j] = p[i];
                htl[j] = m.getKey();
                lbc[j] = m.getValue();
                j++;
            }
        }
        l = j;
        ExpVector e;
        C a;
        boolean mt = false;
        GenPolynomial R = Ap.ring.getZERO().copy();

        //GenPolynomial T = null;
        //GenPolynomial Q = null;
        GenPolynomial S = Ap.copy();
        while (S.length() > 0) {
            m = S.leadingMonomial();
            e = m.getKey();
            a = m.getValue();
            for (i = 0; i < l; i++) {
                mt = e.multipleOf(htl[i]);
                if (mt)
                    break;
            }
            if (!mt) {
                //logger.debug("irred");
                //R = R.sum( a, e );
                //S = S.subtract( a, e ); 
                R.doPutToMap(e, a);
                S.doRemoveFromMap(e, a);
                // System.out.println(" S = " + S);
            } else {
                e = e.subtract(htl[i]);
                //logger.info("red div = " + e);
                a = a.divide((C) lbc[i]);
                //Q = p[i].multiply( a, e );
                //S = S.subtract( Q );
                S = S.subtractMultiple(a, e, p[i]);
            }
        }
        return R;
    }


    /**
     * Normalform with recording.
     * @param row recording matrix, is modified.
     * @param Pp a polynomial list for reduction.
     * @param Ap a polynomial.
     * @return nf(Pp,Ap), the normal form of Ap wrt. Pp.
     */
    @SuppressWarnings("unchecked")
    public GenPolynomial normalform(List> row, List> Pp,
                    GenPolynomial Ap) {
        if (Pp == null || Pp.isEmpty()) {
            return Ap;
        }
        if (Ap == null || Ap.isZERO()) {
            return Ap;
        }
        if (!Ap.ring.coFac.isField()) {
            throw new IllegalArgumentException("coefficients not from a field");
        }
        int l = Pp.size();
        GenPolynomial[] P = new GenPolynomial[l];
        synchronized (Pp) {
            //P = Pp.toArray();
            for (int i = 0; i < Pp.size(); i++) {
                P[i] = Pp.get(i);
            }
        }
        ExpVector[] htl = new ExpVector[l];
        Object[] lbc = new Object[l]; // want C[]
        GenPolynomial[] p = new GenPolynomial[l];
        Map.Entry m;
        int j = 0;
        int i;
        for (i = 0; i < l; i++) {
            p[i] = P[i];
            m = p[i].leadingMonomial();
            if (m != null) {
                p[j] = p[i];
                htl[j] = m.getKey();
                lbc[j] = m.getValue();
                j++;
            }
        }
        l = j;
        ExpVector e;
        C a;
        boolean mt = false;
        GenPolynomial zero = Ap.ring.getZERO();
        GenPolynomial R = Ap.ring.getZERO().copy();

        GenPolynomial fac = null;
        // GenPolynomial T = null;
        //GenPolynomial Q = null;
        GenPolynomial S = Ap.copy();
        while (S.length() > 0) {
            m = S.leadingMonomial();
            e = m.getKey();
            a = m.getValue();
            for (i = 0; i < l; i++) {
                mt = e.multipleOf(htl[i]);
                if (mt)
                    break;
            }
            if (!mt) {
                //logger.debug("irred");
                //R = R.sum( a, e );
                //S = S.subtract( a, e ); 
                R.doPutToMap(e, a);
                S.doRemoveFromMap(e, a);
                // System.out.println(" S = " + S);
                //throw new RuntimeException("Syzygy no GB");
            } else {
                e = e.subtract(htl[i]);
                //logger.info("red div = " + e);
                C c = (C) lbc[i];
                a = a.divide(c);
                //Q = p[i].multiply( a, e );
                //S = S.subtract( Q );
                S = S.subtractMultiple(a, e, p[i]);
                fac = row.get(i);
                if (fac == null) {
                    fac = zero.sum(a, e);
                } else {
                    fac = fac.sum(a, e);
                }
                row.set(i, fac);
            }
        }
        return R;
    }

}