=== Introduction === 

This is an implementation of a technical challenge for lendico. 
Both the mandatory part ( creating a payment plan for a loan ) and the optional part ( exposing this functionality as a web service ) 
are implemented.

The mandatory part uses only JavaSE and its standard classes, such as ArrayList. 
The optional part uses SpringBoot.

To make life easier for those who will be checking my solution - I've made a brief video overview. 
You can view it here - https://www.youtube.com/watch?v=eFPJymoWjBw&feature=youtu.be

Please note that this is a PRIVATE video and only people with the URL can view it. 
The only two places where this URL is posted - is in this README and in an e-mail to Lendico recruiter.

Therefore, there is no risk that the text of the assignment will be "leaked". 
Once I get feedback for the assignment, naturally, I will remove the video from Youtube, as I understand 
how important it is for companies to keep their test assignments private. 


Here is the TABLE OF CONTENTS for this file

1. How to install the application 
2. How to run the application 
3. Discussion of application architecture for the mandatory part ( creating a payment plan for a loan ) 
4. Discussion of the application architecture for the optional part ( creating a web service ) 
5. Discussion of testing 


=== 1. How to install the application ===

1. Clone the application from its GitHub repository - https://github.com/klezovics/payment-plan-generator
2. Import it into your IDE 
3. Right click on the project -> Select 'Maven' -> Select 'Update Project' 
4. Right click on the project -> Select 'Run As' -> Select 'Maven Install' 

=== 2. How to run the application ==== 

== 2.1 Running the mandatory part ==

1. Go to the package 'com.klezovich.payment_plan_generator'
2. Open the 'DesktopApp.java' class in your IDE 
3. Run it as a Java application, like you would run any Java class with a main method 
4. The command line will prompt you for input. An example of an input is given  
5. Provide the input 
6. The output will be printed to the command line 
7. A file with the output will also be printed to the 'output' directory, which is a top level directory. 
   This means that this directory is located in the same directory as the 'pom.xml' file 
8. A path to this file will also be printed to the command line 

Here are the command line input and output after a single execution ... 
The 'Program Output >>' and 'User Input>>' tokens in the code below are NOT part of the 
actual user input or output, but are my comments just to make clear what is the input and what is the output  

Program Output>> Please provide the following input parameters separated by a space
Program Output>> Loan amount (integer), nominal rate as percentage (double), duration (in months), start date (YYYY-MM-DD) 
Program Output>> Sample input:'5000 5.0 24 2017-12-29'
User Input >> 5000 5.0 24 2017-12-29 


Program Output>> The payment plan for these parameters is:

Program Output>> PaymentDate,PaymentAmount,Principal,Interest,initialOutstandingPrincipal,remainingOutstandingPrincipal
Program Output>> 2018-01-29,219.36,198.52,20.83,5000.00,4801.48
Program Output>> 2018-02-28,219.36,199.35,20.01,4801.48,4602.13
Program Output>> 2018-03-29,219.36,200.18,19.18,4602.13,4401.94
Program Output>> 2018-04-29,219.36,201.02,18.34,4401.94,4200.93
Program Output>> 2018-05-29,219.36,201.85,17.50,4200.93,3999.08
Program Output>> 2018-06-29,219.36,202.69,16.66,3999.08,3796.38
Program Output>> 2018-07-29,219.36,203.54,15.82,3796.38,3592.84
Program Output>> 2018-08-29,219.36,204.39,14.97,3592.84,3388.46
Program Output>> 2018-09-29,219.36,205.24,14.12,3388.46,3183.22
Program Output>> 2018-10-29,219.36,206.09,13.26,3183.22,2977.12
Program Output>> 2018-11-29,219.36,206.95,12.40,2977.12,2770.17
Program Output>> 2018-12-29,219.36,207.81,11.54,2770.17,2562.36
Program Output>> 2019-01-29,219.36,208.68,10.68,2562.36,2353.68
Program Output>> 2019-02-28,219.36,209.55,9.81,2353.68,2144.13
Program Output>> 2019-03-29,219.36,210.42,8.93,2144.13,1933.70
Program Output>> 2019-04-29,219.36,211.30,8.06,1933.70,1722.40
Program Output>> 2019-05-29,219.36,212.18,7.18,1722.40,1510.22
Program Output>> 2019-06-29,219.36,213.06,6.29,1510.22,1297.16
Program Output>> 2019-07-29,219.36,213.95,5.40,1297.16,1083.21
Program Output>> 2019-08-29,219.36,214.84,4.51,1083.21,868.36
Program Output>> 2019-09-29,219.36,215.74,3.62,868.36,652.62
Program Output>> 2019-10-29,219.36,216.64,2.72,652.62,435.99
Program Output>> 2019-11-29,219.36,217.54,1.82,435.99,218.45
Program Output>> 2019-12-29,219.36,218.45,0.91,218.45,0.00

Program Output>> Output saved to file:C:\Users\klezo\Desktop\import\output\PaymentPlan_5000_0.05_24_2017-12-29

Each payment plan file name has the following structure PaymentPlan_(loan Amount)_(nominalRate)_(duration)_(startDate)
 
== 2.2 Running the optional part ==

1. Go to the package 'com.klezovich.payment_plan_generator' 
2. Right click on the 'PaymentPlanGeneratorApplication' 
3. Select 'Run As' -> 'Spring Boot App' 
4. This will start the server 
5. You can now send POST request to http://localhost:8080/generate-plan
6. This can be done by using for example the 'Postman' Chrome extension 
7. From within this 'Postman' Chrome extension you will also be able to view the results in JSON format 

=== 3. Discussion of the application architecture for the mandatory part === 

The main class for this is the DesktopApp.java class ( 'com.klezovich.payment_plan_generator' package). 
This class start the application, gets the input from the user and then uses certain domain classes 
to achieve this objective. 

The key domain classes are the following (all are resident in the 'com.klezovich.payment_plan_generator.domain' package) :
1. LoanData - stores the four parameters which define a loan 
2. PaymentPlan - stores the payment plan information 
3. PaymentPlan.MonthlyPaymentDetail - stores the information for the monthly payment detail 
4. PaymentPlanGenerator -> takes a LoanData object as input and produces a PaymentPlan object if you call the relevant method. 

The 'PaymentPlan' classes implements the formula for loan calculation from here (http://financeformulas.net/Annuity_Payment_Formula.html)
and contains internally a list of PaymentPlan.MonthlyPayment detail objects. 

To print a 'PaymentPlan' object to a CSV format the 'PaymentPlanPrinter' class is used from the 'com.klezovich.payment_plan_generator.util' package.

=== 4. Discussion of the application architecture for the optional part === 

In order to implement the optional part - SpringBoot is used. 
The key class is 'ServiceController' ('com.klezovich.payment_plan_generator.controller' package )
It has a single method, which processes POST requests. 

POST request parameters are obtained as input arguments to this method. They are stored in a LoanData object.
Then a PaymentPlanGenerator is used. 

Then a PaymentPlanJsonCoverter object is used to convert the PaymentPlan object into a 
a list of MonthlyPaymentDetailJson. This is done to match the output (field names and their type ) to the requirements 
in the PDF of this task. 

You cannot just send a PaymentPlan object, because it stores data (such as interest for each month) as doubles, but the 
requirements for the optional part, for example, require that the JSON response contain doubles rounded to the second 
digit after the comma. 


=== 5. Discussion of testing === 

To run test for this project you need to do the following:  

1. Go to /src/test/java 
2. Open the com.klezovich.payment_plan_generator package there 
3. It will contain a class called 'PaymentPlanGeneratorApplicationTests.java'
4. Right click on it ->  Run As -> 'JUnit Test'
5. This will run the tests

Here's how testing works ... 

1. A set of input parameters is given 
2. A file from the 'src/test/resources/test_payment_plans' directory is loaded.
This is a CSV file, which contains payment plan data. This file is 
constructed NOT by the application. It contains premade test data, which is known to be correct. 
A 'PaymentPlan' object is contructed out of this CSV file. 

3. A payment plan is contstucted by using the 'PaymentPlanGeneator' class 
4. The two payment plans are compared by using the overriden .equals() method