AzureKn1ght / switcheo-code-challenge

Switcheo Code Challenge

Switcheo Code Challenge #1

Note that if you fork this repository, your responses may be publicly linked to this repo.
Please submit your application along with the solutions attached or linked.

It is important that you minimally attempt the problems, even if you do not arrive at a working solution.

Submission

You can either provide a link to an online repository, attach the solution in your application, or whichever method you prefer. We're cool as long as we can view your solution without any pain.

Problem 1: Three ways to sum to n

Question

⏰ Duration: You should not spend more than 2 hours on this problem.

Task

Provide 3 unique implementations of the following function.

Input: n - any integer

Assuming this input will always produce a result lesser than Number.MAX_SAFE_INTEGER.

Output: return - summation to n, i.e. sum_to_n(5) === 1 + 2 + 3 + 4 + 5 === 15.

var sum_to_n_a = function(n) {
    // your code here
};

var sum_to_n_b = function(n) {
    // your code here
};

var sum_to_n_c = function(n) {
    // your code here
};

> Solution

Problem 2: Fancy Form

Question

⏰ Duration: You should not spend more than 16 hours on this problem.

Task

Create a transaction form based on the template provided in this folder.

You may use any third party plugin, library, and/or framework for this problem.

1. You may add input validation/error messages to make the form interactive.
2. Your submission will be rated on its usage intuitiveness and visual attractiveness.
3. Show us your frontend development and design skills, feel free to totally disregard the provided files for this problem.

Please submit your solution using the files provided in the skeletal repo, including any additional files your solution may use.

> Solution

Problem 4: Interacting with Chain

Question

⏰ Duration: You should not spend more than 8 hours on this problem.
⚠️ TypeScript Only - you are to complete this problem using TypeScript.

Task

Implement a script to retrieve the specified holders of $SWTH token on the Binance Smart Chain network.

BSC Block Explorer: https://bscscan.com/

$SWTH Token Contract: 0xc0ecb8499d8da2771abcbf4091db7f65158f1468

Addresses to look up:

0xb5d4f343412dc8efb6ff599d790074d0f1e8d430
0x0020c5222a24e4a96b720c06b803fb8d34adc0af
0xd1d8b2aae2ebb2acf013b803bc3c24ca1303a392

How your script will be tested:

ts-node ./retrieve-holders.ts

Expected Output:

The output should be organized as one address amount per line.

Note, as this is live production contract, the amount you retrieve will be different from the sample below.

0xb5d4f343412dc8efb6ff599d790074d0f1e8d430 99,888,874.62734227
0x0020c5222a24e4a96b720c06b803fb8d34adc0af 7,970,573.69197209
0xd1d8b2aae2ebb2acf013b803bc3c24ca1303a392 2,894,918.96152958
…

💡 Hint: You may need to use the NPM module ethers.js to complete this task.

Phil's Notes

The addresses provided have zero balance

I've use the following addresses instead because it didn't make sense to test all zeroes. https://bscscan.com/token/0x250b211ee44459dad5cd3bca803dd6a7ecb5d46c#balances

0x9f264339157e0b44fbc2e56f16de68b23ef2efb3
0xdffd77664ed6e57bb3b5846d5b3e96466413fb6f
0xee0be17d50632dd13d5d2233b74392291188293e

How to test:

npm install 
npm test 

# Alternatively, install typescript and ts-node globally
# npm install -g typescript
# npm install -g ts-node
# ts-node retrieve-holders.ts

> Solution

Problem 5: Utility Contract

Question

⏰ Duration: You should not spend more than 12 hours on this problem.

⚠️ Solidity Only - you are to complete this problem using Solidity.

Task

Deploy a utility EVM contract with a function to retrieve all token balances given a wallet address and the token contract addresses.

How your contract will be tested:

./test.js

const { ethers } = require("ethers");

const ADDR = "…";   // your contract address
const ABI = […];    // your contract ABI

const ADDRESS = "…"; // some wallet address with token balance
const TOKENS = [    // token contract addresses
	"…",
	"…",
];

// you can use your own RPC provider url (no need to deploy to mainnet)
const provider = ethers.providers.getDefaultProvider();

const test = async () => {
	const contract = new ethers.Contract(ADDR, ABI, provider);

  const balances = await contract.getBalances(ADDRESS, tokens);
	
	return balances;
};

test().then(console.log);

Expected Output:

The output should be organized as one token amount per object.

[
  {
    token: "0x123d475e13aa54a43a7421d94caa4459da021c77",
    balance: "9988887462734227" // its okay if this is typed ethers.BigNumber
  },
  {
    token: "0x55f6823de9642f47e80ed4845a55aa8430cb4ec6",
    balance: "899998285714286"
  },
  …
]

💡 Hint: You may need to use the NPM module truffle to complete this task.

> Solution

Problem 6: Transaction Broadcaster Service

Question

⏰ Duration: You should not spend more than 6 hours on this problem.

Task

This is a system design question. Describe in detail (~500-1000 words) the specifications on how you would design a transaction broadcaster service. You may additionally attach a drawings/diagrams/illustrations if you wish.

1. There is an internal api that is used by our services. It returns HTTP 200, or HTTP 400-500 .

   POST /broadcast_transaction 
   
   {"message_type": "add_weight(address _addr, uint256 _weight)", "data": "0xd71363280000000000000000000000005eb715d601c2f27f83cb554b6b36e047822fb70a00000000000000000000000000000000000000000000000000000000000000fa"}

2. Using the post request parameters, the broadcaster service signs the data and the output returns a signed transaction. Next, it broadcasts the signed transaction to an evm-compatible blockchain network.

   1. A broadcasted transaction might fail and if it fails, it should be retried automatically.
   2. To broadcast a signed transaction, you make a RPC request to a blockchain node.
      1. 1% of the time, it does not respond earlier than 30 seconds.
      2. 95% of the time it responds with a success code within 20-30 seconds.
      3. The rest of the time it returns a failure code.
   3. There should also be a page that shows the list of transactions that passed or failed.

Additional Requirements

1. If POST /broadcast_transction returns HTTP 200 OK, it is assumed that the transaction will eventually be broadcasted successfully. If the broadcaster service restarts unexpectedly, it should still fulfil them.
2. An admin is able to, at any point in time, retry a failed broadcast.

> Solution

Problem 7: SQL Query

Question

⏰ Duration: You should not spend more than 3 hours on this problem.

Task

Tables:

balances

id	address	denom	amount	block_height
1	0xabab..	usdc	50000000000000	733755
2	0x99cc..	swth	-20000000	733757
3	0xabab..	usdc	-50000000000	733855
...	...	...	...	...

Each row in the balance table records the balance change. e.g. if address 0x99cc.. account is being deducted by 20000000swth, it will be represented as row id=2.

A denom is akin to currency.

trades

id	address	denom	amount	block_height
1	0xabab..	swth	400000000000	733756
2	0x99cc..	usdc	3500000000000	733757
3	0x67f3..	swth	72000000000000	733758
...	...	...	...	...

Each row in the trades table records the trade information. e.g. if address 0x99cc.. made a trade of 3500000000000usdc, it will be represented as row id=2.

Write an sql query that returns the the list of addresses which has recently made a trade, and wallet has at least $500 (total balance) in it.

Constraints:

1. Recently made a trade means block_height strictly greater than 730000.
2. There is a total of 3 denoms.
   1. usdc is worth $0.000001
   2. swth is worth $0.00000005
   3. tmz is worth $0.003
3. Note that the usd values of the denoms changes frequently and we want to compute the usd value of the wallet on the fly without storing them into a table.

Note:

1. You are recommended to use PostgreSQL because that is what we are using. However, feel free to use a language you are more familiar with.

> Solution