Programming Task: Model Data in SQL, Implement Backend Service and Web Application

The main goal of this task is to get a picture of your proficiency in programming and the ability to deal with new assignments.Be assured that we _don't_ expect you to complete all the requirements - focus on the ones that suit you best. For example if you know a lot about backends, focus on the services and use a REST client to test them; if you know a lot about UI frameworks, show us what you can do there and e.g. mock calls and backend data.You are free to use any technology stack / framework you like (e.g. python, node.js, ...) but we expect you to implement the main parts on your own.If you think that some information / data is missing, doesn't make sense or could be organised in a better way, substitute with whatever you see fit.

Please create a source code repository on a platform of your choice and use it during the development of your software.Take all the time (within reason) and resources you need to complete. Once you are finished, let us know and send us the link to your repository.

1) Model and structure the given data in SQL

2) Implement a backend service that provides the given endpoints / handlers

3) Create a simple website/webpage/application

Please read the following descriptions very carefully. Then create a list of tasks in a tool of your choice (e.g. Excel, Textfile, ...), estimate them in hours and also keep track of how long it actually took you to implement them.

1. Model and structure the following data in a "database" of your choice

2. User - should consist of at least the following fields

- Identifier

- Name (max length is 512 characters)

- Description (max length is 1k characters)

- E-Mail (max length is 1k characters)

- Bitcoin Wallet Id (max length of Bitcoin Wallet Id)

- Bitcoin Wallet balance (max value 1 bln)

- Ethereum Wallet Id (max length of Ethereum Wallet Id)

- Ethereum Wallet balance (max value 1 bln)

- Max amount that is allowed per transaction

3. Transaction

- Identifier

- Currency Amount

- Currency Type

- Source user id

- Target user id

- Timestamp created

- Timestamp processed

- State

4. Implement a backend service that provides the following endpoints / handlers

5. Create user (with basic user details)

- Validate and store details in the database

6. Add currency account for currency (Bitcoin, Ethereum)

- Validate and set account details

7. Submit transaction to system

- Put the transaction into the transaction processor queue and return its transaction id

8. Retrieve transaction history for user id

- Retrieve list of all the processed transactions and their state, each entry consisting of amount, source user id, target user id and currency type

9. Retrieve transaction status

10. Implement a transaction processor that can run in parallel to the backend service and processes transactions (e.g. worker, job system, script, ...)

11. Users will submit transactions, specifying how much of a certain currency they want to send to another user. The processor needs to make sure that:

- Transactions must happen in the order that they were submitted

- Each transaction should only be executed once

- No transactions should be missed

- Transactions should be processed as soon as possible, but there is no hard requirement

12. The processor should implement at least the following steps for each transaction in the queue

- Validate that the transaction can be processed (user A has enough of currency type and amount, etc. ...)

- Process the transaction:

* Amount of correct type should be subtracted from sending user

* Amount of correct type should be added to target user

* Adjust transaction state

- Transaction details should be logged

- At least the transaction (id) is saved to the transaction history of both users

13. Protect all public endpoints against unauthorised access in some way.

14. Create a simple website/webpage/application that uses the previously defined endpoints of the backend and lets the user enter the required information and/or display information according to the endpoint.