Pricing Engine - GoLang

Application in goLang to work in a simple pricing engine considering various factors from the customer who is trying to rent a vehicle from a rental service provider.

Requirements

The requirement of this application is to bring up a go based REST API which will determine the rental cost of a car bases on the attributes of the customer who is purchasing it. You can go through the detailed requirements Here. The essential attributes that play key aspects in the pricing calculation are as follows:

• Rent Duration
• Age of the customer
• Insurance Group
• Validity of the licence held by the customer

The Pricing formula

Total Rental Cost = BaseFare based on the Duration * Factor based on Age * Factor based on the Insurance Group * Factor based on Licence Validity

Understanding the existing setup

The current application is built on top on an existing code as per the Requirements. The setup typically had a layered data flow among the components as follows:

• The main.go file which typically invokes the service built on top of the RPC/Middleware libraries.
• The service that serves various REST end point for the application and passing on the data to RPC layer.
• The RPC which typically takes care of doing the conversion from HTTP middleware understandable data to the Application understandable data.
• Then the RPC passes the application understandable data to the App component which has all the business logics of computing the pricing and serving the required data.

The Approach in solving the problem

• Single responsibility Principle : Proper structuring of business logics to serve finer and granular purposes will help in greater lengths, hence I have split the data processing accordingly such that components like ConfigFetcher, FactorMapper and RPC have unique responsibilities that are really granular and the handing down of data to other actors also became really smooth and testable.
• Generalisations and Specialisations : Bringing in StrategyChain and Strategy method reference was really fun. It totally minimised the boiler plate code by embracing the code reuse and carving out the skeleton that a lot of repeated code to repeatedly apply the subsequent pricing were really brought down to 3 lines as shown under Chain of Commandssection below.
• Configurable and plugin code: Decoupling the configuration from the implementation along with an auto expiring cache like approach is taken in this application considering the fact that fare prices or decision factors in most of the pricing related businesses tend to change often than we usually think.
• Strategy Pattern :

	var thirdStrategy = func( resp *pricingengine.PricingItem) (*pricingengine.PricingItem, error) {
		log.Println("Processing LicenceValidityFactor Stragegy")
		return strategies.ApplySubsecuentFactorsToPricing(request, resp, licence_factor_range, nil) // final call so no next strategy
	}

	var secondStrategy = func( resp *pricingengine.PricingItem) (*pricingengine.PricingItem, error) {
		log.Println("Got Previous Strategy in InsuranceGroupFactor Stragegy data here::", resp)
		return strategies.ApplySubsecuentFactorsToPricing(request, resp, insurance_factor_range, thirdStrategy)
	}

	var firstStrategy = func( resp *pricingengine.PricingItem) (*pricingengine.PricingItem, error) {
		log.Println("Got Previous Strategy in DriverAgeFactor Stragegy data here::", resp)
		return strategies.ApplySubsecuentFactorsToPricing(request, resp, driver_factor_range, secondStrategy)
	}

• Chain of command pattern : One more interesting approach I chose to minimise the lines of code in implementation is to simplify the way the incremental factors are applied on the base price. This model is completely dependant on the configurable model and is totally extendable with really less implementation code. All credits goes to the method references/Function as a data type approach supported by Go which helped a long way. The actual implementation of the Chain is completely upto the invoker, however, the chain will continue as long as there is a chain connected to the current one. Code snippet below:

if fn != nil {
  log.Println("Found a chain function, Passing on the result for further computation")
  return fn(&result)
}

• Functional Decomposition : As a bi-product of applying the Single responsibility Principle, Functionally decomposing the data flow became really easy considering the fact that each actor has a defined, highly cohesive data flow within itself and low coupling with other actors in the ecosystem.
• Non-TDD/Implementation first : I am a hard core follower of TDD principles while developing any of the application or business logics. However, due to the lack of experience in go programming language I was not able to follow TDD approach 100%. During the initial spike/experimental faces I just started with the implementation and then jumped in to the respective unit test/functional test later.
• Test Pyramid: I have followed test pyramid starting from UnitTests --> FunctionalTest --> IntegrationTest for this project such that all the scenarios are covered.
• Integration testing with httptest
• Unit test with testing framework
• Dedicated logging: Logging is one of the crucially best practices among all programming languages. I have used a simplistic logging approach with GoLang's logging package.
• The request response structures: As part of the design it was pointed out to be extra cautious on designing the Request/Response object. Below is the way the GeneratePricing Request and Response object fields are classified.

type GeneratePricingRequest struct {
  DateOfBirth string `json:"date_of_birth"`
  InsuranceGroup int `json:"insurance_group"`
  LicenseHeldSince string `json:"license_held_since"`
}

type GeneratePricingResponse struct {
	Input GeneratePricingRequest `json:"input"`
  IsEligible bool `json:"is-eligible"`
  Message string `json:"message"`
  PricingList []PricingItem `json:"pricing"`
}

type PricingItem struct {
	Premium float64 `json:"premium"`
  Currency string  `json:"currency"`
  FareGroup string `json:"fare_group"`
}

The Flow

Architecture:

The Endpoints

Generate Pricing for a customer

Request

POST /generate_pricing HTTP/1.1
Host: localhost:3000
Content-Type: application/json

{
    "date_of_birth": "1970-12-04",
    "insurance_group": 12,
    "license_held_since": "1988-08-01"
}

Request format:

date_of_birth – Date of Birth of the customer who is trying to rent the vehicle insurance_group – the insurance group to which the customer belongs to license_held_since – The date of acquiring of the Driver's licence by the existing customer

Response

Returns: Empty body with one of the following:

200 – in case of success

HTTP/1.1 200 OK
Content-Type: application/json
{
  "input": {
          "date_of_birth": "1970-12-04",
          "insurance_group": 12,
          "license_held_since": "1988-08-01"
      },
      "is-eligible": true,
      "message": "Success",
      "pricing": [
          {
              "premium": 278.28254999999996,
              "currency": "£",
              "fare_group": "0.5 hours, Driver Age >26, Insurance Group:9-16, Licence Validity:6"
          },
          {....},
          {....},
          .....
      ]
}

Get current pricing configuration ranges

Request

GET /generate_pricing HTTP/1.1
Host: localhost:3000

Response

Returns: The computed statistics for all the posted transaction or empty if there are no transactions present.

HTTP/1.1 200
Content-Type: application/json;charset=UTF-8
{
  "base-rate": [
        {
            "Start": 0,
            "End": 1800,
            "IsEligible": true,
            "Value": 273,
            "Label": "0.5 hours"
        },
        {....}
        ....
        ],
    "driver-age-factor": [
        {
            "Start": 0,
            "End": 16,
            "IsEligible": false,
            "Value": 0,
            "Label": "Driver Age:0-16"
        },
        {...}
        ....
      ],
      "insurance-group-factor": [
          {
              "Start": 1,
              "End": 8,
              "IsEligible": true,
              "Value": 1,
              "Label": "Insurance Group:1-8"
          },
          {...}
          ....
      ],
      "licence-validity-factor": [
        {
            "Start": 0,
            "End": 1,
            "IsEligible": true,
            "Value": 1.1,
            "Label": "Licence Validity:0-1"
        },
        {...}
        ....
      ]
    }

Test coverage data

Following is the entire test coverage data for the project

go test ./test/... -p 1 -v
=== RUN   TestMain
--- PASS: TestMain (0.00s)
PASS
ok      pricingengine/test  0.359s
=== RUN   TestPriceGenerationAppWithActualConfigs
=== RUN   TestPriceGenerationAppWithActualConfigs/TestPriceGenerationAppToGetValidGeneratedPriceList-FailureScenario-1
=== RUN   TestPriceGenerationAppWithActualConfigs/TestPriceGenerationAppToGetValidGeneratedPriceList-FailureScenario-2
=== RUN   TestPriceGenerationAppWithActualConfigs/TestPriceGenerationAppToGetValidGeneratedPriceList-FailureScenario-3
=== RUN   TestPriceGenerationAppWithActualConfigs/TestPriceGenerationAppToGetValidGeneratedPriceList-FailureScenario-4
=== RUN   TestPriceGenerationAppWithActualConfigs/TestPriceGenerationAppToGetValidGeneratedPriceList-FailureScenario-5
=== RUN   TestPriceGenerationAppWithActualConfigs/TestPriceGenerationAppToGetValidGeneratedPriceList-SuccessScenario-1
=== RUN   TestPriceGenerationAppWithActualConfigs/TestPriceGenerationAppToGetValidGeneratedPriceList-SuccessScenario-2
--- PASS: TestPriceGenerationAppWithActualConfigs (0.02s)
   --- PASS: TestPriceGenerationAppWithActualConfigs/TestPriceGenerationAppToGetValidGeneratedPriceList-FailureScenario-1 (0.02s)
   --- PASS: TestPriceGenerationAppWithActualConfigs/TestPriceGenerationAppToGetValidGeneratedPriceList-FailureScenario-2 (0.00s)
   --- PASS: TestPriceGenerationAppWithActualConfigs/TestPriceGenerationAppToGetValidGeneratedPriceList-FailureScenario-3 (0.00s)
   --- PASS: TestPriceGenerationAppWithActualConfigs/TestPriceGenerationAppToGetValidGeneratedPriceList-FailureScenario-4 (0.00s)
   --- PASS: TestPriceGenerationAppWithActualConfigs/TestPriceGenerationAppToGetValidGeneratedPriceList-FailureScenario-5 (0.00s)
   --- PASS: TestPriceGenerationAppWithActualConfigs/TestPriceGenerationAppToGetValidGeneratedPriceList-SuccessScenario-1 (0.00s)
   --- PASS: TestPriceGenerationAppWithActualConfigs/TestPriceGenerationAppToGetValidGeneratedPriceList-SuccessScenario-2 (0.00s)
PASS
ok      pricingengine/test/app  0.414s
=== RUN   TestConfigCacheScenarios
=== RUN   TestConfigCacheScenarios/TestConfigCacheInitOnExistingCache
=== RUN   TestConfigCacheScenarios/TestConfigCacheInitWithNoCacheRefreshButNoTTL
=== RUN   TestConfigCacheScenarios/TestConfigCacheInitWithCacheRefreshFlag
=== RUN   TestConfigCacheScenarios/TestConfigCacheInitWithCacheRefreshAfterTimeout
--- PASS: TestConfigCacheScenarios (0.02s)
   --- PASS: TestConfigCacheScenarios/TestConfigCacheInitOnExistingCache (0.02s)
   --- PASS: TestConfigCacheScenarios/TestConfigCacheInitWithNoCacheRefreshButNoTTL (0.00s)
   --- PASS: TestConfigCacheScenarios/TestConfigCacheInitWithCacheRefreshFlag (0.00s)
   --- PASS: TestConfigCacheScenarios/TestConfigCacheInitWithCacheRefreshAfterTimeout (0.00s)
=== RUN   TestConfigFetch
=== RUN   TestConfigFetch/TestConfigFetchSuccess
=== RUN   TestConfigFetch/TestConfigFetchFileNotFoundError
--- PASS: TestConfigFetch (0.00s)
   --- PASS: TestConfigFetch/TestConfigFetchSuccess (0.00s)
   --- PASS: TestConfigFetch/TestConfigFetchFileNotFoundError (0.00s)
PASS
ok      pricingengine/test/config   0.389s
=== RUN   TestServiceEndpointsIntegrationTestWithActualConfigs
=== RUN   TestServiceEndpointsIntegrationTestWithActualConfigs/TestRESTAPIEndpointToGetValidGeneratedPriceList-FailureScenario-1
[64/64]0xc0000a8200
Want 'some', got '{"input":{"date_of_birth":"","insurance_group":0,"license_held_since":""},"is-eligible":false,"message":"DateOfBirth cannot be empty","pricing":null}'0xc0000927e0
=== RUN   TestServiceEndpointsIntegrationTestWithActualConfigs/TestRESTAPIEndpointToGetValidGeneratedPriceList-FailureScenario-2
[74/80]0xc00010c0f0
Want 'some', got '{"input":{"date_of_birth":"2006-01-02","insurance_group":0,"license_held_since":""},"is-eligible":false,"message":"InsuranceGroup should be a Positive number","pricing":null}'0xc000092c60
=== RUN   TestServiceEndpointsIntegrationTestWithActualConfigs/TestRESTAPIEndpointToGetValidGeneratedPriceList-FailureScenario-3
[75/80]0xc00010c230
Want 'some', got '{"input":{"date_of_birth":"2006-01-02","insurance_group":20,"license_held_since":""},"is-eligible":false,"message":"LicenseHeldSince Date cannot be empty","pricing":null}'0xc0000930e0
=== RUN   TestServiceEndpointsIntegrationTestWithActualConfigs/TestRESTAPIEndpointToGetValidGeneratedPriceList-FailureScenario-4
[85/96]0xc000096720
Want 'some', got '{"input":{"date_of_birth":"2001-01-02","insurance_group":20,"license_held_since":"2006-01-02"},"is-eligible":false,"message":"Declined due to :Insurance Group:8","pricing":null}'0xc000093560
=== RUN   TestServiceEndpointsIntegrationTestWithActualConfigs/TestRESTAPIEndpointToGetValidGeneratedPriceList-FailureScenario-5
[85/96]0xc000096900
Want 'some', got '{"input":{"date_of_birth":"2006-08-02","insurance_group":20,"license_held_since":"2006-01-02"},"is-eligible":false,"message":"Declined due to :Driver Age:0-16","pricing":null}'0xc0000939e0
=== RUN   TestServiceEndpointsIntegrationTestWithActualConfigs/TestRESTAPIEndpointToGetValidGeneratedPriceList-SuccessScenario-1
[84/96]0xc000096ae0
Want 'some', got '{"input":{"date_of_birth":"2001-08-02","insurance_group":7,"license_held_since":"2014-08-02"},"is-eligible":true,"message":"Success","pricing":[{"premium":259.349,"currency":"£","fare_group":"0.5 hours, Driver Age:16-26, Insurance Group:1-8, Licence Validity:6"},{"premium":4943.8,"currency":"£","fare_group":"96 hours / 4 days, Driver Age:16-26, Insurance Group:1-8, Licence Validity:6"}]}'0xc000093e60
=== RUN   TestServiceEndpointsIntegrationTestWithActualConfigs/TestRESTAPIEndpointToGetValidGeneratedPriceList-SuccessScenario-2
[84/96]0xc000096d80
Want 'some', got '{"input":{"date_of_birth":"2001-08-02","insurance_group":7,"license_held_since":"2016-08-02"},"is-eligible":true,"message":"Success","pricing":[{"premium":300.3,"currency":"£","fare_group":"0.5 hours, Driver Age:16-26, Insurance Group:1-8, Licence Validity:0-6"},{"premium":5724.4,"currency":"£","fare_group":"96 hours / 4 days, Driver Age:16-26, Insurance Group:1-8, Licence Validity:0-6"}]}'0xc000144300
--- PASS: TestServiceEndpointsIntegrationTestWithActualConfigs (0.03s)
   --- PASS: TestServiceEndpointsIntegrationTestWithActualConfigs/TestRESTAPIEndpointToGetValidGeneratedPriceList-FailureScenario-1 (0.02s)
   --- PASS: TestServiceEndpointsIntegrationTestWithActualConfigs/TestRESTAPIEndpointToGetValidGeneratedPriceList-FailureScenario-2 (0.00s)
   --- PASS: TestServiceEndpointsIntegrationTestWithActualConfigs/TestRESTAPIEndpointToGetValidGeneratedPriceList-FailureScenario-3 (0.00s)
   --- PASS: TestServiceEndpointsIntegrationTestWithActualConfigs/TestRESTAPIEndpointToGetValidGeneratedPriceList-FailureScenario-4 (0.00s)
   --- PASS: TestServiceEndpointsIntegrationTestWithActualConfigs/TestRESTAPIEndpointToGetValidGeneratedPriceList-FailureScenario-5 (0.00s)
   --- PASS: TestServiceEndpointsIntegrationTestWithActualConfigs/TestRESTAPIEndpointToGetValidGeneratedPriceList-SuccessScenario-1 (0.00s)
   --- PASS: TestServiceEndpointsIntegrationTestWithActualConfigs/TestRESTAPIEndpointToGetValidGeneratedPriceList-SuccessScenario-2 (0.00s)
PASS
ok      pricingengine/test/service  0.463s
=== RUN   TestPricingStrategyVariedConfigs
=== RUN   TestPricingStrategyVariedConfigs/TestPricingStrategyVariedConfigsToApplyBaseStrategyWithChainStrategy
2021/08/02 17:04:23 Found a chain function, Passing on the result for further computation
=== RUN   TestPricingStrategyVariedConfigs/TestPricingStrategyVariedConfigsToApplyBaseStrategyWithoutChainStrategy
=== RUN   TestPricingStrategyVariedConfigs/TestPricingStrategyVariedConfigsToApplySubsecuentFactorsToPricingWithChainStrategy
2021/08/02 17:04:23 Found a chain function, Passing on the result for further computation
2021/08/02 17:04:23 Found a chain function, Passing on the result for further computation
=== RUN   TestPricingStrategyVariedConfigs/TestPricingStrategyVariedConfigsToApplySubsecuentFactorsToPricingWithoutChainStrategy
2021/08/02 17:04:23 Found a chain function, Passing on the result for further computation
=== RUN   TestPricingStrategyVariedConfigs/TestPricingStrategyVariedConfigsToFindMatchingLicenceValidityFactor-Success-Senario
=== RUN   TestPricingStrategyVariedConfigs/TestPricingStrategyVariedConfigsToFindMatchingLicenceValidityFactor-NotFound-Senario
=== RUN   TestPricingStrategyVariedConfigs/TestPricingStrategyVariedConfigsToFindMatchingLicenceValidityFactor-InvalidDate-Senario
=== RUN   TestPricingStrategyVariedConfigs/TestPricingStrategyVariedConfigsToFindMatchingInsuranceGroupFactor-Success-Senario
=== RUN   TestPricingStrategyVariedConfigs/TestPricingStrategyVariedConfigsToFindMatchingInsuranceGroupFactor-NotFound-Senario
=== RUN   TestPricingStrategyVariedConfigs/TestPricingStrategyVariedConfigsToFindMatchingDriverAgeFactor-Success-Senario
2021/08/02 17:04:23 Checking the driver factor for date_of_birth= 2018-08-02  parse_dob_t= 2018-08-02 00:00:00 +0000 UTC  age= 3
=== RUN   TestPricingStrategyVariedConfigs/TestPricingStrategyVariedConfigsToFindMatchingDriverAgeFactor-NotFound-Senario
=== RUN   TestPricingStrategyVariedConfigs/TestPricingStrategyVariedConfigsToFindMatchingDriverAgeFactor-InvalidDate-Senario
--- PASS: TestPricingStrategyVariedConfigs (0.02s)
   --- PASS: TestPricingStrategyVariedConfigs/TestPricingStrategyVariedConfigsToApplyBaseStrategyWithChainStrategy (0.02s)
   --- PASS: TestPricingStrategyVariedConfigs/TestPricingStrategyVariedConfigsToApplyBaseStrategyWithoutChainStrategy (0.00s)
   --- PASS: TestPricingStrategyVariedConfigs/TestPricingStrategyVariedConfigsToApplySubsecuentFactorsToPricingWithChainStrategy (0.00s)
   --- PASS: TestPricingStrategyVariedConfigs/TestPricingStrategyVariedConfigsToApplySubsecuentFactorsToPricingWithoutChainStrategy (0.00s)
   --- PASS: TestPricingStrategyVariedConfigs/TestPricingStrategyVariedConfigsToFindMatchingLicenceValidityFactor-Success-Senario (0.00s)
   --- PASS: TestPricingStrategyVariedConfigs/TestPricingStrategyVariedConfigsToFindMatchingLicenceValidityFactor-NotFound-Senario (0.00s)
   --- PASS: TestPricingStrategyVariedConfigs/TestPricingStrategyVariedConfigsToFindMatchingLicenceValidityFactor-InvalidDate-Senario (0.00s)
   --- PASS: TestPricingStrategyVariedConfigs/TestPricingStrategyVariedConfigsToFindMatchingInsuranceGroupFactor-Success-Senario (0.00s)
   --- PASS: TestPricingStrategyVariedConfigs/TestPricingStrategyVariedConfigsToFindMatchingInsuranceGroupFactor-NotFound-Senario (0.00s)
   --- PASS: TestPricingStrategyVariedConfigs/TestPricingStrategyVariedConfigsToFindMatchingDriverAgeFactor-Success-Senario (0.00s)
   --- PASS: TestPricingStrategyVariedConfigs/TestPricingStrategyVariedConfigsToFindMatchingDriverAgeFactor-NotFound-Senario (0.00s)
   --- PASS: TestPricingStrategyVariedConfigs/TestPricingStrategyVariedConfigsToFindMatchingDriverAgeFactor-InvalidDate-Senario (0.00s)
PASS
ok      pricingengine/test/strategy 0.383s
=== RUN   TestAssert
--- PASS: TestAssert (0.00s)
=== RUN   TestFactorMapperFeaturesWithMockConfigs
=== RUN   TestFactorMapperFeaturesWithMockConfigs/TestFactorMapperBaseRateToRangeConfig-SuccessScenario
=== RUN   TestFactorMapperFeaturesWithMockConfigs/TestFactorMapperDriverAgeFactorToRangeConfig-SuccessScenario
=== RUN   TestFactorMapperFeaturesWithMockConfigs/TestFactorMapperInsuranceGroupFactorToRangeConfig-SuccessScenario
=== RUN   TestFactorMapperFeaturesWithMockConfigs/TestFactorMapperLicenceValidityFactorToRangeConfig-SuccessScenario
--- PASS: TestFactorMapperFeaturesWithMockConfigs (0.00s)
   --- PASS: TestFactorMapperFeaturesWithMockConfigs/TestFactorMapperBaseRateToRangeConfig-SuccessScenario (0.00s)
   --- PASS: TestFactorMapperFeaturesWithMockConfigs/TestFactorMapperDriverAgeFactorToRangeConfig-SuccessScenario (0.00s)
   --- PASS: TestFactorMapperFeaturesWithMockConfigs/TestFactorMapperInsuranceGroupFactorToRangeConfig-SuccessScenario (0.00s)
   --- PASS: TestFactorMapperFeaturesWithMockConfigs/TestFactorMapperLicenceValidityFactorToRangeConfig-SuccessScenario (0.00s)
PASS
ok      pricingengine/test/util 0.449s
➜  pricing-engine-go git:(master)

Enhancements and Potential Improvements:

• Improving performance using concurrency. I am a fan of multi-threading and concurrency. However, given that the expected time to complete this task is 4-5 hours and I am totally new to the functional programming aspects of GoLang I was not able to wrap my head around few of the concurrency concepts like defer, wait-group and go coroutine execution all together.
• Better error handling at some of the places can be done to have better user response. Aspects like fail fast or Circuit Breakers can be applied to quickly break the chained flow and give defined error messages to the end user.

Time taken to implement the solution:

• This solution has been completely implemented within 4-5 hours of time on top of +2 hours to understand the basics of the GoLang syntaxes and other programming nuances.

Learning

• I have mostly worked on OO programming languages like Java and C++, working on a pure functional language like GoLang is really a fun challenge. I learned a lot from the functional perspective and some minute data handling and code structuring that enabled proper control of data flow.
• Generalisation and Specialisation of certain aspects like ConfigFetcher and FactoMapper was really interesting learning as well. Applying delegated single responsibility helped a lot with a granular scoped testing and also helped in plugging in and toggle for tests such that the behaviour can be changed at different layers according, kind of similar to DependencyInjection and InversionOfControl aspects in pure Object Oriented languages
• It was really exciting to use OO patterns in a functional programming language like Go. The code looked really clean on brining in the Chain of Commands approach in combination with Strategy pattern that typically revolved around the Function as a datatype concept.

Setting up the environment

This application is purely build on goLang. To run this application in your local you need to follow the below steps

Build:

go build ./cmd/.

Run

go run ./cmd/.

Test

go test ./test/... -p 1

References:

Since this is a beginner/learning project based on GoLang I had to go through a lot of documentations and references related to syntaxes and approaches in arriving at the actual problem solution. All the references that were really useful during the project working can be found here: References