/*
 * $Id: GroebnerBaseSeqPairParallel.java 5956 2018-10-29 21:58:01Z kredel $
 */

package edu.jas.gb;


import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.ListIterator;
import java.util.concurrent.Semaphore;
import java.util.concurrent.Executors;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.LogManager; 

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


/**
 * Groebner Base parallel algorithm. Makes some effort to produce the same
 * sequence of critical pairs as in the sequential version. However already
 * reduced pairs are not rereduced if new polynomials appear. Implements a
 * shared memory parallel version of Groebner bases. Slaves maintain pairlist.
 * @param <C> coefficient type
 * @author Heinz Kredel
 */

public class GroebnerBaseSeqPairParallel<C extends RingElem<C>> extends GroebnerBaseAbstract<C> {


    private static final Logger logger = LogManager.getLogger(GroebnerBaseSeqPairParallel.class);


    /**
     * Number of threads to use.
     */
    protected final int threads;


    /**
     * Pool of threads to use.
     */
    protected transient final ExecutorService pool;


    /**
     * Constructor.
     */
    public GroebnerBaseSeqPairParallel() {
        this(2);
    }


    /**
     * Constructor.
     * @param threads number of threads to use.
     */
    public GroebnerBaseSeqPairParallel(int threads) {
        this(threads, Executors.newFixedThreadPool(threads));
    }


    /**
     * Constructor.
     * @param threads number of threads to use.
     * @param pool ExecutorService to use.
     */
    public GroebnerBaseSeqPairParallel(int threads, ExecutorService pool) {
        this(threads, pool, new ReductionPar<C>());
    }


    /**
     * Constructor.
     * @param threads number of threads to use.
     * @param red parallelism aware reduction engine
     */
    public GroebnerBaseSeqPairParallel(int threads, Reduction<C> red) {
        this(threads, Executors.newFixedThreadPool(threads), red);
    }


    /**
     * Constructor.
     * @param threads number of threads to use.
     * @param pool ExecutorService to use.
     * @param red parallelism aware reduction engine
     */
    public GroebnerBaseSeqPairParallel(int threads, ExecutorService pool, Reduction<C> red) {
        super(red);
        if (!(red instanceof ReductionPar)) {
            logger.warn("parallel GB should use parallel aware reduction");
        }
        if (threads < 1) {
            threads = 1;
        }
        this.threads = threads;
        this.pool = pool;
    }


    /**
     * Cleanup and terminate ExecutorService.
     */
    @Override
    public void terminate() {
        if (pool == null) {
            return;
        }
        pool.shutdown();
        try {
            while (!pool.isTerminated()) {
                //logger.info("await");
                boolean rest = pool.awaitTermination(1000L, TimeUnit.MILLISECONDS);
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        logger.info(pool.toString());
    }


    /**
     * Cancel ExecutorService.
     */
    @Override
    public int cancel() {
        if (pool == null) {
            return 0;
        }
        int s = pool.shutdownNow().size();
        logger.info(pool.toString());
        return s;
    }


    /**
     * Parallel Groebner base using sequential pair order class. Slaves maintain
     * pairlist.
     * @param modv number of module variables.
     * @param F polynomial list.
     * @return GB(F) a Groebner base of F.
     */
    public List<GenPolynomial<C>> GB(int modv, List<GenPolynomial<C>> F) {
        GenPolynomial<C> p;
        List<GenPolynomial<C>> G = new ArrayList<GenPolynomial<C>>();
        CriticalPairList<C> pairlist = null;
        int l = F.size();
        ListIterator<GenPolynomial<C>> it = F.listIterator();
        while (it.hasNext()) {
            p = it.next();
            if (p.length() > 0) {
                p = p.monic();
                if (p.isONE()) {
                    G.clear();
                    G.add(p);
                    return G; // since no threads activated jet
                }
                G.add(p);
                if (pairlist == null) {
                    pairlist = new CriticalPairList<C>(modv, p.ring);
                    if (!p.ring.coFac.isField()) {
                        throw new IllegalArgumentException("coefficients not from a field");
                    }
                }
                // putOne not required
                pairlist.put(p);
            } else {
                l--;
            }
        }
        if (l <= 1) {
            return G; // since no threads activated jet
        }

        Terminator fin = new Terminator(threads);
        ReducerSeqPair<C> R;
        for (int i = 0; i < threads; i++) {
            R = new ReducerSeqPair<C>(fin, G, pairlist);
            pool.execute(R);
        }
        fin.waitDone();
        if (Thread.currentThread().isInterrupted()) {
            throw new RuntimeException("interrupt before minimalGB");
        }
        logger.debug("#parallel list = " + G.size());
        G = minimalGB(G);
        // not in this context // pool.terminate();
        logger.info("" + pairlist);
        return G;
    }


    /**
     * Minimal ordered groebner basis, parallel.
     * @param Fp a Groebner base.
     * @return minimalGB(F) a minimal Groebner base of Fp.
     */
    @Override
    public List<GenPolynomial<C>> minimalGB(List<GenPolynomial<C>> Fp) {
        GenPolynomial<C> a;
        ArrayList<GenPolynomial<C>> G;
        G = new ArrayList<GenPolynomial<C>>(Fp.size());
        ListIterator<GenPolynomial<C>> it = Fp.listIterator();
        while (it.hasNext()) {
            a = it.next();
            if (a.length() != 0) { // always true
                // already monic  a = a.monic();
                G.add(a);
            }
        }
        if (G.size() <= 1) {
            return G;
        }

        ExpVector e;
        ExpVector f;
        GenPolynomial<C> p;
        ArrayList<GenPolynomial<C>> F;
        F = new ArrayList<GenPolynomial<C>>(G.size());
        boolean mt;
        while (G.size() > 0) {
            a = G.remove(0);
            e = a.leadingExpVector();

            it = G.listIterator();
            mt = false;
            while (it.hasNext() && !mt) {
                p = it.next();
                f = p.leadingExpVector();
                mt = e.multipleOf(f);
            }
            it = F.listIterator();
            while (it.hasNext() && !mt) {
                p = it.next();
                f = p.leadingExpVector();
                mt = e.multipleOf(f);
            }
            if (!mt) {
                F.add(a); // no thread at this point
            } else {
                // System.out.println("dropped " + a.length());
            }
        }
        G = F;
        if (G.size() <= 1) {
            return G;
        }
        Collections.reverse(G); // important for lex GB

        @SuppressWarnings("unchecked")
        MiReducerSeqPair<C>[] mirs = (MiReducerSeqPair<C>[]) new MiReducerSeqPair[G.size()];
        int i = 0;
        F = new ArrayList<GenPolynomial<C>>(G.size());
        while (G.size() > 0) {
            a = G.remove(0);
            // System.out.println("doing " + a.length());
            List<GenPolynomial<C>> R = new ArrayList<GenPolynomial<C>>(G.size() + F.size());
            R.addAll(G);
            R.addAll(F);
            mirs[i] = new MiReducerSeqPair<C>(R, a);
            pool.execute(mirs[i]);
            i++;
            F.add(a);
        }
        G = F;
        F = new ArrayList<GenPolynomial<C>>(G.size());
        for (i = 0; i < mirs.length; i++) {
            a = mirs[i].getNF();
            F.add(a);
        }
        return F;
    }

}


/**
 * Reducing worker threads.
 */
class ReducerSeqPair<C extends RingElem<C>> implements Runnable {


    private final List<GenPolynomial<C>> G;


    private final CriticalPairList<C> pairlist;


    private final Terminator fin;


    private final ReductionPar<C> red;


    private static final Logger logger = LogManager.getLogger(ReducerSeqPair.class);


    ReducerSeqPair(Terminator fin, List<GenPolynomial<C>> G, CriticalPairList<C> L) {
        this.fin = fin;
        this.G = G;
        pairlist = L;
        red = new ReductionPar<C>();
    }


    /**
     * to string
     */
    @Override
    public String toString() {
        return "ReducerSeqPair";
    }


    public void run() {
        CriticalPair<C> pair;
        GenPolynomial<C> S;
        GenPolynomial<C> H;
        boolean set = false;
        int reduction = 0;
        int sleeps = 0;
        while (pairlist.hasNext() || fin.hasJobs()) {
            while (!pairlist.hasNext()) {
                pairlist.update();
                // wait
                fin.beIdle();
                set = true;
                try {
                    sleeps++;
                    if (sleeps % 10 == 0) {
                        logger.info(" reducer is sleeping");
                    } else {
                        logger.debug("r");
                    }
                    Thread.sleep(100);
                } catch (InterruptedException e) {
                    fin.allIdle();
                    logger.info("shutdown " + fin + " after: " + e);
                    //throw new RuntimeException("interrupt 1 in pairlist.hasNext loop");
                    break;
                }
                if (Thread.currentThread().isInterrupted()) {
                    fin.allIdle();
                    logger.info("shutdown after .isInterrupted(): " + fin);
                    //throw new RuntimeException("interrupt 2 in pairlist.hasNext loop");
                    break;
                }
                if (!fin.hasJobs()) {
                    break;
                }
            }
            if (!pairlist.hasNext() && !fin.hasJobs()) {
                break;
            }
            if (set) {
                fin.notIdle();
                set = false;
            }
            pair = pairlist.getNext();
            if (Thread.currentThread().isInterrupted()) {
                throw new RuntimeException("interrupt after getNext");
            }
            if (pair == null) {
                pairlist.update();
                continue;
            }
            if (logger.isDebugEnabled()) {
                logger.debug("pi = " + pair.pi);
                logger.debug("pj = " + pair.pj);
            }
            S = red.SPolynomial(pair.pi, pair.pj);
            if (S.isZERO()) {
                pairlist.record(pair, S);
                continue;
            }
            if (logger.isDebugEnabled()) {
                logger.debug("ht(S) = " + S.leadingExpVector());
            }
            H = red.normalform(G, S); //mod
            reduction++;
            if (H.isZERO()) {
                pairlist.record(pair, H);
                continue;
            }
            if (logger.isDebugEnabled()) {
                logger.debug("ht(H) = " + H.leadingExpVector());
            }
            H = H.monic();
            // System.out.println("H   = " + H);
            if (H.isONE()) {
                // pairlist.update( pair, H );
                pairlist.putOne(); // not really required
                synchronized (G) {
                    G.clear();
                    G.add(H);
                }
                fin.allIdle();
                return;
            }
            if (logger.isDebugEnabled()) {
                logger.debug("H = " + H);
            }
            synchronized (G) {
                G.add(H);
            }
            pairlist.update(pair, H);
            //pairlist.record( pair, H );
            //pairlist.update();
        }
        logger.info("terminated, done " + reduction + " reductions");
    }
}


/**
 * Reducing worker threads for minimal GB.
 */
class MiReducerSeqPair<C extends RingElem<C>> implements Runnable {


    private final List<GenPolynomial<C>> G;


    private GenPolynomial<C> H;


    private final ReductionPar<C> red;


    private final Semaphore done = new Semaphore(0);


    private static final Logger logger = LogManager.getLogger(MiReducerSeqPair.class);


    MiReducerSeqPair(List<GenPolynomial<C>> G, GenPolynomial<C> p) {
        this.G = G;
        H = p;
        red = new ReductionPar<C>();
    }


    /**
     * to string
     */
    @Override
    public String toString() {
        return "MiReducerSeqpair";
    }


    /**
     * getNF. Blocks until the normal form is computed.
     * @return the computed normal form.
     */
    public GenPolynomial<C> getNF() {
        try {
            done.acquire(); //done.P();
        } catch (InterruptedException e) {
            throw new RuntimeException("interrupt in getNF");
        }
        return H;
    }


    public void run() {
        if (logger.isDebugEnabled()) {
            logger.debug("ht(H) = " + H.leadingExpVector());
        }
        try {
            H = red.normalform(G, H); //mod
            done.release(); //done.V();
        } catch (RuntimeException e) {
            Thread.currentThread().interrupt();
            //throw new RuntimeException("interrupt in getNF");
        }
        if (logger.isDebugEnabled()) {
            logger.debug("ht(H) = " + H.leadingExpVector());
        }
        // H = H.monic();
    }

}