Beyond the Basics of JavaScript

Intermediate level JavaScript course

Daniel Shijakovski - Web Developer

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Introduction

This is the Final task required to complete the course on Intermediate level JavaScript.
When implementing the task, try to use the latest ES6 features we talked about throughout the course. Try to make your code clean and easy to read. Also, try to avoid duplication of code as much as you can.

Deadline

The deadline to complete the task will be 2 weeks from the day this is uploaded to Moodle.

Start Date: 18.12.2023, 09:00
End Date: 01.01.2024, 09:00

Points System

The total amount of points you can receive is 50 points + an optional bonus task of 5 points.
In order to pass, you will need to receive at least 70% of the total points i.e. 35 points or more.

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ATM Machine with API endpoints

This application represents a simplified version of an ATM. You need to build an Express server that listens to various endpoints, to mimic the behavior of an ATM.
To start off, the ATM machine is empty. The user needs to initialize it first, after which they can either deposit or withdraw money to/from it.

ATM data model

The ATM will be represented by an object with the following properties:

• total - representing the total amount of TDL dollars currently stored in the ATM
• dynamic keys representing the banknotes that the ATM can support

Banknotes that CAN be supported: 1, 5, 10, 20, 100, 500, 1000

Important: The 1 banknote should ALWAYS be supported

The user initializes the ATM at the beginning of the app, providing the supported banknotes - they can either choose to support some of the banknotes, or support all of the banknotes provided above.

Initializing the ATM - 10 points

At the beginning of the app, the ATM object is not initialized.
To initialize the ATM, the user must send a POST request to the ATM API endpoint / with the body

{ 
    "banknotes": number[] | null
}

Notice the banknotes field can be null - the user can pass in null or an empty array for the ATM to support all the default banknotes.
Alternatively, they can pass in an array of numbers, containing a subset of the supported banknotes.

Example

{
    "banknotes": [10, 100, 1000]
}

If the user chooses the above configuration - the ATM object (initially) would look like this:

    const ATM = {
        1: 0, // The '1' banknote is here because it should ALWAYS be supported
        10: 0,
        100: 0,
        1000: 0,
        total: 0
    };

Note: Is a regular object the best approach for representing the ATM? Is there maybe another data structure better fit to handle this type of data?

 

Important: If the list of banknotes provided by the user, contains a banknote that isn't supported - the entire list is considered invalid and an error should be returned.

{
    "error": "Invalid list of banknotes!"
}

If the initialization is a success, the API returns a success message:

Example

{
    "message": "ATM is up and running!"
}

 

Important: If the user makes a request to deposit or withdraw money, and the ATM hasn't been initialized, an error should be returned.

{
    "error": "Cannot make transaction. ATM is not initialized!"
}

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Deposit - 20 points

To deposit money into the ATM, the user can send a POST request to the ATM API endpoint /deposit with the body

{
    "amount": number
}

Withdraw - 20 points

To withdraw money, the user can send a GET request to the ATM API endpoint /withdraw with the query parameter amount={number}

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Task

Your task is to program the ATM to deposit and withdraw banknotes, in the most efficient way possible.
What this means is that both when depositing (inserting) and withdrawing (returning) money - the ATM should do that using the least amount of banknotes as possible - with the banknotes that it supports.

Example

Let's say the ATM is empty and looks like this:

const ATM = {
    1: 0, // Again, supported by default
    10: 0,
    20: 0,
    100: 0,
    total: 0
}

If we then choose to store 390 TDL dollars into it, the most efficient way to do that would be to store it with:

• 3 x 100 banknotes => 300
• 4 x 20 banknotes => 80
• 1 x 10 banknote => 10
• Total: 390

So, after that operation the ATM should look like this:

const ATM = {
    1: 0,
    10: 1,
    20: 4,
    100: 3,
    total: 390
}

If we then choose to take out 70 TDL dollars, the most efficient way to do that would be to return them using:

• 3 x 20 banknotes => 60
• 1 x 10 banknote => 10
• Total: 70

So after that operation the ATM should look like this:

const ATM = {
    1: 0,
    10: 0,
    20: 1,
    100: 3,
    total: 320
}

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What is your job?

Your job will be to figure out the algorithm to do this efficient deposit and withdraw operation. In addition, when a transaction is successful, you will need to return an message to the user, saying that the transaction was successful and return some kind of text representation of what the transaction looked like.
Below are some examples of how that might look like.

Note: You can use the provided examples are your template or choose your own way of representing the transaction

Example - Successfully depositing 390 TDL dollars

{
    "message": "Successful DEPOSIT of 390 TDL dollars!",
    "transaction": {
        "100": 3, // Used 3 banknotes of 100 TDL dollars
        "20": 4, // Used 4 banknotes of 20 TDL dollars
        "10": 1, // Used 1 banknote of 10 TDL dollars

        "total": 390 // The total amount of money DEPOSITED
        // NOT the total amount of money in the ATM
    }
}

Example - Successfully withdrawing 70 TDL dollars

{
    "message": "Successful WITHDRAWAL of 70 TDL dollars!",
    "transaction": {
        "20": 3, // Used 3 banknotes of 20 TDL dollars
        "10": 1, // Used 1 banknote of 10 TDL dollars

        "total": 70 // The total amount of money WITHDRAWN
        // NOT the total amount of money in the ATM
    }
}

Important components of the returned response

However you choose to structure your response for a successful transaction, you must include these 3 pieces of information inside of your response:

• The type of the transaction (deposit/withdraw)
• The type and number of banknotes used in the transaction
• The total amount of money deposited/withdrawn

Again, your response doesn't need to look like the ones above, it just needs to contain the above mentioned information in any shape you choose.

What if there isn't enough money in the ATM?

If there isn't enough money in the ATM, an error should be returned.

{
    "error": "Not enough money in the ATM!"
}

What if there IS enough money but NOT ENOUGH banknotes?

In the case that there are not enough banknotes to complete a withdrawal, an error should be returned.

{
    "error": "Not enough banknotes to complete the transaction!"
}

Example:
The ATM only has 2 banknotes of 20 TDL dollars - this means it has a total of 40 TDL dollars
The user asks for 30 TDL dollars
In this case, while the total IS technically larger than the requested amount - the ATM doesn't have the APPROPRIATE BANKNOTES to perform this transaction (1x10 + 1x20), since it only has 2x20 banknotes
This should then be considered an error with an response like the one above.

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Bonus Task - 5 extra points

Add a feature for the user to check the ATM's balance.
Create an endpoint /balance which the user can hit to check the state of the ATM.

What type of request should this be?

Example response

{
    "balance": number // The total amount of money in the ATM
}

If the ATM has not been initialized, return an error

{
    "error": "Cannot check balance. ATM is not initialized!"
}

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Submitting the task

In order to submit the Final task, you can just zip/compress the entire directory and upload it to the Final Task section.

Important: DO NOT include the node_modules folder or the package-lock.json file in your uploaded file. This will just make the size of the submitted file bigger.

Final Remarks

Feel free to message me in private, or in the #help channel if any part of this task is confusing, or you just need clarification on something.

If for any reason you might need an extension to your deadline, please PM me on Discord and we will sort it out.

 

Good luck, have fun and crush it! 💪