CellWorld.java

package aima.core.environment.cellworld;

import java.util.HashMap;
import java.util.LinkedHashSet;
import java.util.Map;
import java.util.Set;

/**
 * Artificial Intelligence A Modern Approach (3rd Edition): page 645.<br>
 * <br>
 * 
 * A representation for the environment depicted in figure 17.1.<br>
 * <br>
 * <b>Note:<b> the x and y coordinates are always positive integers starting at
 * 1.<br>
 * <b>Note:<b> If looking at a rectangle - the coordinate (x=1, y=1) will be the
 * bottom left hand corner.<br>
 * 
 * 
 * @param <C>
 *            the type of content for the Cells in the world.
 * 
 * @author Ciaran O'Reilly
 * @author Ravi Mohan
 */
public class CellWorld<C> {
	private Set<Cell<C>> cells = new LinkedHashSet<Cell<C>>();
	private Map<Integer, Map<Integer, Cell<C>>> cellLookup = new HashMap<Integer, Map<Integer, Cell<C>>>();

	/**
	 * Construct a Cell World with size xDimension * y Dimension cells, all with
	 * their values set to a default content value.
	 * 
	 * @param xDimension
	 *            the size of the x dimension.
	 * @param yDimension
	 *            the size of the y dimension.
	 * 
	 * @param defaultCellContent
	 *            the default content to assign to each cell created.
	 */
	public CellWorld(int xDimension, int yDimension, C defaultCellContent) {
		for (int x = 1; x <= xDimension; x++) {
			Map<Integer, Cell<C>> xCol = new HashMap<Integer, Cell<C>>();
			for (int y = 1; y <= yDimension; y++) {
				Cell<C> c = new Cell<C>(x, y, defaultCellContent);
				cells.add(c);
				xCol.put(y, c);
			}
			cellLookup.put(x, xCol);
		}
	}

	/**
	 * 
	 * @return all the cells in this world.
	 */
	public Set<Cell<C>> getCells() {
		return cells;
	}

	/**
	 * Determine what cell would be moved into if the specified action is
	 * performed in the specified cell. Normally, this will be the cell adjacent
	 * in the appropriate direction. However, if there is no cell in the
	 * adjacent direction of the action then the outcome of the action is to
	 * stay in the same cell as the action was performed in.
	 * 
	 * @param s
	 *            the cell location from which the action is to be performed.
	 * @param a
	 *            the action to perform (Up, Down, Left, or Right).
	 * @return the Cell an agent would end up in if they performed the specified
	 *         action from the specified cell location.
	 */
	public Cell<C> result(Cell<C> s, CellWorldAction a) {
		Cell<C> sDelta = getCellAt(a.getXResult(s.getX()), a.getYResult(s
				.getY()));
		if (null == sDelta) {
			// Default to no effect
			// (i.e. bumps back in place as no adjoining cell).
			sDelta = s;
		}

		return sDelta;
	}

	/**
	 * Remove the cell at the specified location from this Cell World. This
	 * allows you to introduce barriers into different location.
	 * 
	 * @param x
	 *            the x dimension of the cell to be removed.
	 * @param y
	 *            the y dimension of the cell to be removed.
	 */
	public void removeCell(int x, int y) {
		Map<Integer, Cell<C>> xCol = cellLookup.get(x);
		if (null != xCol) {
			cells.remove(xCol.remove(y));
		}
	}

	/**
	 * Get the cell at the specified x and y locations.
	 * 
	 * @param x
	 *            the x dimension of the cell to be retrieved.
	 * @param y
	 *            the y dimension of the cell to be retrieved.
	 * @return the cell at the specified x,y location, null if no cell exists at
	 *         this location.
	 */
	public Cell<C> getCellAt(int x, int y) {
		Cell<C> c = null;
		Map<Integer, Cell<C>> xCol = cellLookup.get(x);
		if (null != xCol) {
			c = xCol.get(y);
		}

		return c;
	}
}