/**
 * Write a description of class Life here.
 * 
 * @author (your name) 
 * @version (a version number or a date)
 */
public class Life
{
    private boolean[][] map, nextMap;
    private int width, height;
    
    public Life(boolean[][] initial)
    {
        map = initial; // we assume that initial is non-empty and rectangular
        width = map.length;
        height = map[0].length; 
        nextMap = new boolean[width][height];
    }
    
    public Life(int width, int height, double probability)
    {
        map = new boolean[width][height];
        this.width  = width;
        this.height = height;
        initializeMap(probability);
        nextMap = new boolean[width][height];
    }
    
    public Life()
    {
        this(128, 128, 0.1);
    }
    
    private void initializeMap(double probability)
    {
        for (int i = 0; i < width; i++)
            for (int j = 0; j < height; j++)
                map[i][j] = Math.random() < probability;
    }
    
    public boolean[][] getMap()
    {
        return map;
    }
    
    public void nextGeneration()
    {
        for (int i = 0; i < width; i++)
            for (int j = 0; j < height; j++)
                 switch (numNeighbours(i, j))
                 {
                   case 2:  nextMap[i][j] = map[i][j]; break;
                   case 3:  nextMap[i][j] = true;      break;
                   default: nextMap[i][j] = false;
                 } 
        boolean[][] swap = map;
        map = nextMap; 
        nextMap = swap;
    }
    
    private int numNeighbours(int i, int j)
    {
        int n = 0;
        int ip = (i + 1)          % width;
        int im = (i - 1 + width)  % width;
        int jp = (j + 1)          % height;
        int jm = (j - 1 + height) % height;
        if (map[im][jm]) n++;
        if (map[im][j])  n++;
        if (map[im][jp]) n++;
        if (map[i] [jm]) n++;
        if (map[i] [jp]) n++;
        if (map[ip][jm]) n++;
        if (map[ip][j])  n++;
        if (map[ip][jp]) n++;
        return n;
    }

}