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/*
  Combinatorics Library 3
  Copyright 2009-2016 Dmytro Paukov [email protected]
 */
package org.paukov.combinatorics3;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

class IntegerPartitionIterator implements Iterator> {

  private final InternalVector mVector;
  private final InternalVector zVector;
  private List currentPartition = null;
  private long currentIndex = 0;
  private int stopIndex = 1; //it should be 0 to stop the iteration


  IntegerPartitionIterator(IntegerPartitionGenerator generator) {
    int partitionValue = generator.value;

    if (partitionValue > 0) {
      currentIndex = 0;
      mVector = new InternalVector(partitionValue, 0, 0, partitionValue);
      zVector = new InternalVector(partitionValue, 0, partitionValue + 1, 1);
    } else {
      stopIndex = 0;
      mVector = new InternalVector(1, 0, 0, 0);
      zVector = new InternalVector(1, 0, 0, 0);
    }
  }

  private static List createCurrentPartition(int k, InternalVector mVector,
      InternalVector zVector) {
    List list = new ArrayList<>();
    for (int index = 1; index <= k; index++) {
      for (int j = 0; j < mVector.get(index); j++) {
        list.add(zVector.get(index));
      }
    }
    return list;
  }

  @Override
  public boolean hasNext() {
    return stopIndex != 0;
  }


  @Override
  public List next() {
    currentIndex++;
    currentPartition = createCurrentPartition(stopIndex, mVector, zVector);

    int sum = mVector.get(stopIndex) * zVector.get(stopIndex);

    if (mVector.get(stopIndex) == 1) {
      stopIndex--;
      sum += mVector.get(stopIndex) * zVector.get(stopIndex);
    }

    if (zVector.get(stopIndex - 1) == zVector.get(stopIndex) + 1) {
      stopIndex--;
      mVector.set(stopIndex, mVector.get(stopIndex) + 1);
    } else {
      zVector.set(stopIndex, zVector.get(stopIndex) + 1);
      mVector.set(stopIndex, 1);
    }
    if (sum > zVector.get(stopIndex)) {
      zVector.set(stopIndex + 1, 1);
      mVector.set(stopIndex + 1, sum - zVector.get(stopIndex));
      stopIndex++;
    }

    return currentPartition;
  }

  @Override
  public void remove() {
    throw new UnsupportedOperationException();
  }

  @Override
  public String toString() {
    return "IntegerPartitionIterator=[#" + currentIndex + ", " + currentPartition + "]";
  }

  private static class InternalVector {

    final int[] internalVector;

    InternalVector(int size, int value0, int value1, int value2) {
      internalVector = new int[size + 2];
      internalVector[0] = value0;
      internalVector[1] = value1;
      internalVector[2] = value2;
    }

    int get(int index) {
      return internalVector[index + 1];
    }

    void set(int index, int value) {
      internalVector[index + 1] = value;
    }
  }
}