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/*
 * Copyright (c) 1998-2007, Peter T Mount

 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 
 *   Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 *   Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 *
 *   Neither the name of the retep.org.uk nor the names of its contributors
 *   may be used to endorse or promote products derived from this software
 *   without specific prior written permission.
 *
 * 
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER
 * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package uk.org.retep.util.state;

import java.util.HashMap;
import java.util.Map;

/**
 * A state engine used to validate a state change between one state and another
 * usually Enum's.
 *
 * @author peter
 */
public class StateEngine
{
    private Map          validStateMap;
    private Map>   sequenceMap;
    private String              stateName;
    
    /** Creates a new instance of StateEngine */
    public StateEngine()
    {
        validStateMap = new HashMap();
        sequenceMap = new HashMap>();
    }
    
    private String getStateName()
    {
        return stateName == null ? "Unknown" : stateName;
    }
    
    public void setStateChange( T state, T... validStates )
    {
        validStateMap.put( state, validStates );
        
        // Lazy initialise stateName t the first state set, as we cannot find the
        // class name from the generics
        if( stateName==null )
        {
            stateName = state.getClass().getSimpleName();
        }
    }
    
    public T getNextState( T state )
    throws UnknownStateException
    {
        T[] validStateChanges = getValidStates( state );
        if( validStateChanges.length==0 )
        {
            return null;
        }
        return validStateChanges[0];
    }
    
    public void setStateSequence( T from, T to, T... sequence )
    throws UnknownStateException
    {
        // Assert that from, to an the contents of sequence have all been defined
        assertState( from );
        assertState( to );
        for( T t: sequence )
        {
            assertState( t );
        }
        
        Map map = sequenceMap.get( from );
        if( map==null )
        {
            map = new HashMap();
            sequenceMap.put( from, map );
        }
        map.put( to, sequence );
    }
    
    public T[] getStateChangeSequence( T from, T to )
    throws
            UnknownStateException,
            InvalidStateChangeException
    {
        assertState( from );
        assertState( to );
        
        T[] sequence = null;
        
        Map map = sequenceMap.get( from );
        if( map==null )
        {
            throw new InvalidStateChangeException( from, to );
        }
        
        sequence = map.get( to );
        if( sequence==null )
        {
            throw new InvalidStateChangeException( from, to );
        }
        return sequence;
    }
    
    public T[] getValidStates( T state )
    throws UnknownStateException
    {
        T[] validStates = validStateMap.get( state );
        
        // Throw IllegalStateException if the state is unknown
        if( validStates==null )
        {
            throw new UnknownStateException( state );
        }
        
        return validStates;
    }
    
    
    /**
     * Is it possible to change this state into the required state?
     * @param newState DependencyState required
     * @return true if it's valid, false if not
     */
    public boolean isStateChangeValid( final T oldState, final T newState )
    throws UnknownStateException
    {
        if( oldState==null )
        {
            throw new NullPointerException( "Provided old state is null" );
        }
        
        if( newState==null )
        {
            throw new NullPointerException( "Provided new state is null" );
        }
        
        for( T state: getValidStates( oldState ) )
        {
            if( newState.equals( state ) )
            {
                return true;
            }
        }
        
        return false;
    }
    
    /**
     * Is it possible to change this state into the required state?
     * This will simply return if it is valid or throw InvalidStateChangeException
     * if the state is invalid.
     * @param newState DependencyState required
     * @throws InvalidStateChangeException if the state change is invalid
     */
    public void assertStateChange( final T oldState, final T newState )
    throws
            InvalidStateChangeException,
            UnknownStateException
    {
        if( !isStateChangeValid( oldState, newState ) )
        {
            throw new InvalidStateChangeException( oldState, newState );
        }
    }
    
    public void assertState( final T state )
    throws UnknownStateException
    {
        if( !validStateMap.containsKey( state ) )
        {
            throw new UnknownStateException( state );
        }
    }
    
}