Building a Simple Pay-Later Service
As a pay later service we allow our users to buy goods from a merchant now, and then allow them to pay for those goods at a later date.
The service works inside the boundary of following simple constraints -
- Let's say that for every transaction paid through us, merchants offer us a discount.
- For example, if the transaction amount is Rs.100, and merchant discount offered to us is 10%, we pay Rs. 90 back to the merchant.
- The discount varies from merchant to merchant.
- A merchant can decide to change the discount it offers to us, at any point in time.
- All users get onboarded with a credit limit, beyond which they can't transact.
- If a transaction value crosses this credit limit, we reject the transaction.
Use Cases
There are various use cases our service is intended to fulfil -
- Allow merchants to be onboarded with the amount of discounts they offer
- Allow merchants to change the discount they offer
- Allow users to be onboarded (name, email-id and credit-limit)
- Allow a user to carry out a transaction of some amount with a merchant.
- Allow a user to pay back their dues (full or partial)
- Reporting:
- How much discount we received from a merchant till date
- Dues for a user so far
- Which users have reached their credit limit
- Total dues from all users together
Goal
The goal of this coding challenge will be to build a system for satisfying above use cases.
- IO will be via a command line interface.
- The input can be given in any order as a command, and the system should respond accordingly.
- For inputs like merchant discount rate changes or credit limit changes for a user, the system adapts itself.
CLI
Here is how the command line interface, corresponding to the use-cases mentioned above, can look like
new user u1 u1@email.in 1000 # name, email, credit-limit
new merchant m1 2% # name, discount-percentage
new txn u1 m2 400 # user, merchant, txn-amount
update merchant m1 1% # merchant, new-discount-rate
payback u1 300 # user, payback-amount
report discount m1
report dues u1
report users-at-credit-limit
report total-dues
Example Flow
> new user user1 u1@users.com 300
user1(300)
> new user user2 u2@users.com 400
user2(400)
> new user user3 u3@users.com 500
user3(500)
> new merchant m1 m1@merchants.com 0.5%
m1(0.5%)
> new merchant m2 m2@merchants.com 1.5%
m2(1.5%)
> new merchant m3 m3@merchants.com 1.25%
m3(1.25%)
> set interest 1.25%
interest-rate: 1.25%
> new txn user2 m1 500
rejected! (reason: credit limit)
> new txn user1 m2 300
success!
> new txn user1 m3 10
rejected! (reason: credit limit)
> report users-at-credit-limit
user1
> new txn user3 m3 200
success!
> new txn user3 m3 300
success!
> report users-at-credit-limit
user1
user3
> report discount m3
6.25
> payback user3 400
user3(dues: 100)
> report total-dues
user1: 300
user3: 100
total: 400
brew install openssl readline sqlite3 xz zlib
export LIBRARY_PATH=$LIBRARY_PATH:/usr/local/opt/openssl/lib/
curl https://pyenv.run | bash
Add the following code to your ~/.bash_profile file
export PATH="$HOME/.pyenv/bin:$PATH"
eval "$(pyenv init -)"
eval "$(pyenv virtualenv-init -)"
This will load pyenv when a terminal is started
pyenv install -v 3.7.9
Here -v represents the python version. In our case it is 3.7.9.
You could install different versions using the -v option.
pyenv virtualenv 3.7.9 simpl-3.7.9
The above command creates a virtual environment with name simpl-3.7.9 using python version 3.7.9. You can choose a name that is preferable to you.
pyenv activate simpl-3.7.9
Once the virtual environment that you created is activated, you can install the requirements and run the server. Once the work is completed you could deactivate your virtual environment using pyenv deactivate# Setup Instructions
Using sqlite3 for this project to keep things simple.
brew install sqlite3
- Forked and cloned this repository.
- Navigate into cloned location.
- An activated virtual environment with python version 3.7.9
pip install -r requirements.txt
python manage.py migrate
python manage.py createsuperuser
python manage.py runserver 0:8000
http://localhost:8000/admin/
From the project directory Simpl-CreditCardApplication/PayLater, management commands can be executed in the following format:
python manage.py <command_name> --<option_name_1> <option_value_1> --<option_name_2> <option_value_2> ...
Available Commands
-
Command:
create_new_userOptions: username, email, credit_limit
Example:
python manage.py create_new_user --username anewuser --email anemail@mail.com --credit_limit 12000 -
Command:
create_new_merchantOptions: merchant_name, email, discount_rate
Example:
python manage.py create_new_merchant --merchant_name anewmerchant --email amerchantemail@mail.com --discount_rate 1.5 -
Command:
make_purchaseOptions: username, merchant_name, amount
Example:
python manage.py make_purchase --username anewuser --merchant_name anewmerchant --amount 12000 -
Command:
make_paymentOptions: username, amount
Example:
python manage.py make_payment --username anewuser --amount 1000 -
Command:
report_duesOptions: username(optional)
Example:
python manage.py report_dues --username anewuser -
Command:
report_discountsOptions: merchant_name(optional)
Example:
python manage.py report_discounts --merchant_name anewmerchant -
Command:
report_users_at_limitOptions:
Example:
python manage.py report_users_at_limit -
Command:
set_credit_limitOptions: username, new_limit
Example:
python manage.py set_credit_limit --username anewuser --new_limit 1000 -
Command:
set_discount_rateOptions: merchant_name, discount_rate
Example:
python manage.py set_discount_rate --merchant_name anewmerchant --discount_rate 10