package jalview.datamodel;

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

/**
 * A local iterator which reverse iterates over hidden column regions in a
 * range. Intended for use ONLY within the HiddenColumns class, because it works
 * directly with the hiddenColumns collection without locking (callers should
 * lock hiddenColumns).
 */
public class ReverseRegionsIterator implements Iterator<int[]>
{
  // start position to iterate to
  private int start;

  // end position to iterate from
  private int end;

  // current index in hiddenColumns
  private int currentPosition = 0;

  // current column in hiddenColumns
  private int[] nextRegion = null;

  private final List<int[]> hiddenColumns;

  // Constructor with bounds
  ReverseRegionsIterator(int lowerBound, int upperBound,
          List<int[]> hiddenCols)
  {
    hiddenColumns = hiddenCols;
    start = lowerBound;
    end = upperBound;

    if (hiddenColumns != null)
    {
      // iterate until a region overlaps with [start,end]
      currentPosition = hiddenColumns.size() - 1;
      while (currentPosition >= 0
              && hiddenColumns.get(currentPosition)[1] > end)
      {
        currentPosition--;
      }
      if (currentPosition >= 0)
      {
        nextRegion = hiddenColumns.get(currentPosition);
      }
    }
  }

  @Override
  public boolean hasNext()
  {
    return (hiddenColumns != null) && (nextRegion != null)
            && (nextRegion[1] >= start);
  }

  @Override
  public int[] next()
  {
    int[] region = nextRegion;
    currentPosition--;
    if (currentPosition >= 0)
    {
      nextRegion = hiddenColumns.get(currentPosition);
    }
    else
    {
      nextRegion = null;
    }
    return region;
  }

}