# TransferMoneyContext.java

    /*
     * Copyright (c) 2010, Rickard Öberg. All Rights Reserved.
     *
     * Licensed under the Apache License, Version 2.0 (the "License");
     * you may not use this file except in compliance with the License.
     * You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     *
     */

    package org.qi4j.dci.moneytransfer.context;

    import org.qi4j.api.injection.scope.This;
    import org.qi4j.api.mixin.Mixins;
    import org.qi4j.dci.moneytransfer.domain.data.BalanceData;

    /**
     * Context for transfer of money between two accounts. Roles are defined within the context,
     * and only the role maps know about them outside of this context.
     */
    public class TransferMoneyContext
    {
        // Object->Role mappings
        public SourceAccountRole sourceAccount;
        public DestinationAccountRole destinationAccount;

        // Context setup
        // Objects are specified using their data interface, and then cast to the role interfaces
        public TransferMoneyContext bind( BalanceData source, BalanceData destination )
        {
            this.sourceAccount = (SourceAccountRole) source;
            this.destinationAccount = (DestinationAccountRole) destination;
            return this;
        }

        // Interactions
        public Integer availableFunds()
        {
            return sourceAccount.availableFunds();
        }

        public void transfer( int amount )
            throws IllegalArgumentException
        {
            sourceAccount.transfer( amount, destinationAccount );
        }

        // More interactions could go here...

        // Roles defined by this context, with default implementations
        @Mixins( SourceAccountRole.Mixin.class )
        public interface SourceAccountRole
        {
            // Role Methods
            public void transfer( int amount, DestinationAccountRole destinationAccount )
                throws IllegalArgumentException;

            Integer availableFunds();

            // Default implementation

            class Mixin
                implements SourceAccountRole
            {
                @This
                BalanceData data;

                public Integer availableFunds()
                {
                    // Could be balance, or balance - non-confirmed transfers, or somesuch
                    return data.getBalance();
                }

                public void transfer( int amount, DestinationAccountRole destinationAccount )
                    throws IllegalArgumentException
                {
                    // Validate command
                    if( !( data.getBalance() >= amount ) )
                    {
                        throw new IllegalArgumentException( "Not enough available funds" );
                    }

                    // Command is ok - create events in the data
                    data.decreasedBalance( amount );

                    // Look up the destination account from the current transfer context
                    destinationAccount.deposit( amount );
                }
            }
        }

        @Mixins( DestinationAccountRole.Mixin.class )
        public interface DestinationAccountRole
        {
            public void deposit( int amount );

            class Mixin
                implements DestinationAccountRole
            {
                @This
                BalanceData data;

                public void deposit( int amount )
                {
                    data.increasedBalance( amount );
                }
            }
        }
    }