package rac;

/**
 * This class represents a generalized Restriced Access Container ("RACont").
 * Objects can be stored and retrieved from the internal coubly-linked circular
 * list by  using the algorithms defined by an externally installable policy
 * object.
 * @author S. Wong
 */
public class RACont  {
    /**
    * The externally installable policy that determines the store and retrieve
    * behavior of the RACont.
    */
    private ARACPolicy aRACPolicy;

    /**
    * The RACStopNode that is the head and tail of the contained data list.
    */
    private RACStopNode stopNode = new RACStopNode();

    /**
    * Initializes this RACont to a given ARACPolicy. Note that ARACPolicy.init()
    * is not called as it is not needed on an empty data list.
    * @param aRACPolicy The ARACPolicy to be installed.
    */
    public RACont(ARACPolicy aRACPolicy) {
        this.aRACPolicy = aRACPolicy;
    }


    /**
    * Stores the supplied data object in the RACont using the installed
    * ARACPolicy.
    * @param data The data to be stored.
    */
    public void store(Object data) {
        aRACPolicy.store(data,stopNode);
    }

    /**
    * Retrieves the data element specified by the installed  ARACPolicy.
    * @return The retrieved data element.
    */
    public Object retrieve() {
        return aRACPolicy.retrieve(stopNode);
    }


    /**
    * Installs the supplied ARACPolicy as the active store/retrieve policy.
    * ARACPolicy.init() will be called to prepare the internal data list.
    * @param aPolicy The policy to install.
    */
    public void installPolicy(ARACPolicy aPolicy) {
        aRACPolicy = aPolicy;
        aRACPolicy.init(stopNode);
    }


    /**
    * Accessor method for the active ARACPolicy.
    * @return The installed ARACPolicy.
    */
    public ARACPolicy getRACPolicy() {
        return(aRACPolicy);
    }

    /**
    * Creates a String representation of the internal list with line feeds
    * between each data element.
    * @return The String representation of the RAC.
    */
    public String toString() {
        return (String)stopNode.getNext().execute(ToString.Singleton, null);
    }

    /**
    * Clears all data from the internal data list.
    */
    public void clear() {
        stopNode = new RACStopNode();
    }

    /**
    * Test if the internal data list is empty.
    * @return true if empty, false if not.
    */
    public boolean isEmpty() {
        return (stopNode.getNext()== stopNode);
    }
}