/*
 * $Id: ReductionSeq.java 3288 2010-08-25 21:46:14Z kredel $
 */

package edu.jas.gb;

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

//import org.apache.log4j.Logger;

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

import edu.jas.structure.RingElem;


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

public class ReductionSeq<C extends RingElem<C>> // should be FieldElem<C>>
             extends ReductionAbstract<C> {

    //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<C> normalform(List<GenPolynomial<C>> Pp, 
                                       GenPolynomial<C> 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<ExpVector,C> m;
        int l;
        GenPolynomial<C>[] 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<C>[] 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<C> R = Ap.ring.getZERO();

        //GenPolynomial<C> T = null;
        GenPolynomial<C> Q = null;
        GenPolynomial<C> S = Ap;
        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");
                 //T = new OrderedMapPolynomial( a, e );
                 R = R.sum( a, e );
                 S = S.subtract( a, e ); 
                 // 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 );
              }
        }
        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<C> 
        normalform(List<GenPolynomial<C>> row,
                   List<GenPolynomial<C>> Pp, 
                   GenPolynomial<C> 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<C>[] 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<C>[] p = new GenPolynomial[ l ];
        Map.Entry<ExpVector,C> 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<C> zero = Ap.ring.getZERO();
        GenPolynomial<C> R = Ap.ring.getZERO();

        GenPolynomial<C> fac = null;
        // GenPolynomial<C> T = null;
        GenPolynomial<C> Q = null;
        GenPolynomial<C> S = Ap;
        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 ); 
                // 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 );
                fac = row.get(i);
                if ( fac == null ) {
                    fac = zero.sum( a, e );
                } else {
                    fac = fac.sum( a, e );
                }
                row.set(i,fac);
            }
        }
        return R;
    }

}
