// AP(r) Computer Science Marine Biology Simulation:
// The Environment interface is copyright(c) 2002 College Entrance
// Examination Board (www.collegeboard.com).
//
// This class is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation.
//
// This class is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

import java.util.ArrayList;

/**
 *  AP&reg; Computer Science Marine Biology Simulation:<br>
 *  <code>Environment</code> provides an interface for a two-dimensional,
 *  grid-like environment containing locatable objects.  For example,
 *  it could be an environment of fish for a marine biology simulation.
 *
 *  <p>
 *  The <code>Environment</code> interface is
 *  copyright&copy; 2002 College Entrance Examination Board
 *  (www.collegeboard.com).
 *
 *  @author Alyce Brady
 *  @author APCS Development Committee
 *  @version 1 July 2002
 *  @see Direction
 *  @see Locatable
 *  @see Location
 **/

public interface Environment
{
  // accessor methods for determining environment dimensions

    /** Returns number of rows in this environment.
     *  @return   the number of rows, or -1 if the environment is unbounded
     **/
    int numRows();

    /** Returns number of columns in this environment.
     *  @return   the number of columns, or -1 if the environment is unbounded
     **/
    int numCols();


  // accessor methods for navigating around this environment

    /** Verifies whether a location is valid in this environment.
     *  @param  loc    location to check
     *  @return <code>true</code> if <code>loc</code> is valid;
     *          <code>false</code> otherwise
     **/
    boolean isValid(Location loc);

    /** Returns the number of sides around each cell.
     *  @return    the number of cell sides in this environment
     **/
    int numCellSides();

    /** Returns the number of adjacent neighbors around each cell.
     *  @return    the number of adjacent neighbors
     **/
    int numAdjacentNeighbors();

    /** Generates a random direction.  The direction returned by
     *  <code>randomDirection</code> reflects the direction from
     *  a cell in the environment to one of its adjacent neighbors.
     *  @return a direction
     **/
    Direction randomDirection();

    /** Returns the direction from one location to another.
     *  @param  fromLoc       starting location for search
     *  @param  toLoc         destination location
     *  @return direction from <code>fromLoc</code> to <code>toLoc</code>
     **/
    Direction getDirection(Location fromLoc, Location toLoc);

    /** Returns the adjacent neighbor (whether valid or invalid) of a location
     *  in the specified direction.
     *  @param  fromLoc       starting location for search
     *  @param  compassDir    direction in which to look for adjacent neighbor
     *  @return neighbor of <code>fromLoc</code> in given direction
     **/
    Location getNeighbor(Location fromLoc, Direction compassDir);

    /** Returns the adjacent neighbors of a specified location.
     *  Only neighbors that are valid locations in the environment will be
     *  included.
     *  @param  ofLoc       location whose neighbors to get
     *  @return a list of locations that are neighbors of <code>ofLoc</code>
     **/
    ArrayList neighborsOf(Location ofLoc);


  // accessor methods that deal with objects in this environment

    /** Returns the number of objects in this environment.
     *  @return   the number of objects
     **/
    int numObjects();

    /** Returns all the objects in this environment.
     *  @return    an array of all the environment objects
     **/
    Locatable[] allObjects();

    /** Determines whether a specific location in this environment is
     *  empty.
     *  @param loc  the location to test
     *  @return     <code>true</code> if <code>loc</code> is a
     *              valid location in the context of this environment
     *              and is empty; <code>false</code> otherwise
     **/
    boolean isEmpty(Location loc);

    /** Returns the object at a specific location in this environment.
     *  @param loc    the location in which to look
     *  @return       the object at location <code>loc</code>;
     *                <code>null</code> if <code>loc</code> is not
     *                in the environment or is empty
     **/
    Locatable objectAt(Location loc);


  // modifier methods

    /** Adds a new object to this environment at the location it specifies.
     *  (Precondition: <code>obj.location()</code> is a valid empty location.)
     *  @param obj the new object to be added
     *  @throws    IllegalArgumentException if the precondition is not met
     **/
    void add(Locatable obj);

    /** Removes the object from this environment.
     *  (Precondition: <code>obj</code> is in this environment.)
     *  @param obj     the object to be removed
     *  @throws    IllegalArgumentException if the precondition is not met
     **/
    void remove(Locatable obj);

    /** Updates this environment to reflect the fact that an object moved.
     *  (Precondition: <code>obj.location()</code> is a valid location
     *  and there is no other object there.
     *  Postcondition: <code>obj</code> is at the appropriate location
     *  (<code>obj.location()</code>), and either <code>oldLoc</code> is 
     *  equal to <code>obj.location()</code> (there was no movement) or
     *  <code>oldLoc</code> is empty.)
     *  @param obj       the object that moved
     *  @param oldLoc    the previous location of <code>obj</code>
     *  @throws    IllegalArgumentException if the precondition is not met
     **/
    void recordMove(Locatable obj, Location oldLoc);

}