Apex Plug-In for Force.com Cloud Flow Designer Workbook

gistfile1.txt

global class MortgageCalculator implements Process.Plugin
{
    global Process.PluginResult invoke(Process.PluginRequest request)
    {
        Double amount = (Double)request.inputParameters.get('Amount');
        Double term = (Double)request.inputParameters.get('Term');
        // Magic here
        Double cMonthlyPayment;
        cMonthlyPayment=2750;
        Map<String, Object> result = new Map<String, Object>();
        result.put('MonthlyPayment', cMonthlyPayment);
        return new Process.PluginResult(result);
    }
    global Process.PluginDescribeResult describe()
    {
        Process.PluginDescribeResult result = new Process.PluginDescribeResult();
        result.description='This plug-in generates a monthly payment quote given the term and amount.';
        result.tag='Mortgage Quote';
        result.inputParameters = new List<Process.PluginDescribeResult.InputParameter> {
            new Process.PluginDescribeResult.InputParameter('Amount',
                Process.PluginDescribeResult.ParameterType.DOUBLE, true),
            new Process.PluginDescribeResult.InputParameter('Term',
                Process.PluginDescribeResult.ParameterType.DOUBLE, true)
        };
        result.outputParameters = new List<Process.PluginDescribeResult.OutputParameter> {
            new Process.PluginDescribeResult.OutputParameter('MonthlyPayment',
                Process.PluginDescribeResult.ParameterType.DOUBLE)
        };
        return result;
    }
    public static testmethod void testAll() 
    {
        MortgageCalculator plugin = new MortgageCalculator();
        Map<String,Object> inputParams = new Map<String,Object>();
        Double amount = 100000;
        Double term = 25;
        inputParams.put('Amount', amount);
        inputParams.put('Term', term);
        Process.PluginRequest request = new Process.PluginRequest(inputParams);
        Process.PluginResult aresult = Plugin.invoke(request);
        Double monthlyAmount = (Double) aresult.outputParameters.get('MonthlyPayment');
        System.assertEquals(monthlyAmount,2750);
        Process.PluginDescribeResult describe = plugin.describe();
        System.assertEquals(describe.InputParameters.size(), 2);
        System.assertEquals(describe.InputParameters[0].name, 'Amount');
        System.assertEquals(describe.InputParameters[1].name, 'Term');
        System.assertEquals(describe.OutputParameters.size(), 1);
        System.assertEquals(describe.OutputParameters[0].name, 'MonthlyPayment');
    }
}

Tutorial #3 of the Cloud Flow Designer workbook (see http://wiki.developerforce.com/) uses this Apex class as a plug-in for a flow.

There's no magic here :)
It's returning the same Monthly Payment whatever the term and amout...

If you add a third input parameter called 'interest' then the following will work to change the amount in the appropriate way (monthly payments increase as interest rate increases and term decreases but total payment decreases as term decreases) albeit not fully mathematically correctly.
Double monthlyPayment;
monthlyPayment=amount_(1+interest/100_term/12)/term;
You will need to make a few other changes as needed to account for the new input parameter and to change the output to the new calculated variable.

See https://gist.github.com/2422564 for the latest gist that supports the workbook. Thanks Chris!