public class GridWorld implements RLWorld {

    // Actions.
    final int N = 0;
    final int E = 1;
    final int S = 2; 
    final int W = 3;

    // dimension: { x, y, actions }
    final int[] dimSize = { 10, 10, 4 };

    public int[] getDimension() {
	
	return dimSize;
    }
    
    public int[] getNextState( int[] state, int action ) {
		
	int[] newstate = new int[state.length] ;
	System.arraycopy( state, 0, newstate, 0, state.length); 

	// N-W corner in coordinates 0,0
	if( action == N )
	    newstate[1]--;
	else if( action == E )
	    newstate[0]++;
	else if( action == S )
	    newstate[1]++;
	else if( action == W )
	    newstate[0]--;
	return newstate;
    }    

    public boolean validAction( int[] state, int action ) {
	
	// West border
	if( state[0] == 0 && action == W )
		return false;
	// East border
	else if( state[0] == 9 && action == E )
	    return false;
	// North border
	else if( state[1] == 0 && action == N )
	    return false;
	// South border
	else if( state[1] == 9 && action == S )
	    return false;
	else return true;
    }

    public boolean endState( int[] state ) {
	
	// Absorbing state in north-east corner.
	if( state[0] == 5 && state[1] == 5 ) {  
	    return true;
	}
	else return false;
    }

    public double getReward( int[] state, int action ) {
	
	// Square in the west of the goal state. 
	if( state[0] == 4 && state[1] == 5 ) {
		if ( action == E )
		    return 1;
		else return 0;
	}
	// Square in the south of the goal state. 
	if( state[0] == 6 && state[1] == 5 ) {
	    if ( action == W )
		return 1;
	    else return 0;
	}
	// Square in the south of the goal state. 
	if( state[0] == 5 && state[1] == 4 ) {
	    if ( action == S )
		return 1;
	    else return 0;
	}
	// Square in the south of the goal state. 
	if( state[0] == 5 && state[1] == 6 ) {
	    if ( action == N )
		return 1;
	    else return 0;
	}
	else return 0;
    }
    
    public void resetState( int[] state ) {
	
	// reposition to 0,0
	for( int j = 0 ; j < 2 ; j++ )
		state[j] = (int) ( Math.random() * dimSize[j] );
    }
    
    public double getInitValues() {
	return 0;
    }

}