capitalbr / legolas

Robinhood clone

Legolas

See it live

Legolas, a Robinhood clone, is an investing app where you can try out a crazy investing strategy without putting real money on the line. Rails and Postgres power the backend, while React and Rails handle the frontend.

This project was designed and built in under two weeks.

Features

• Authentication using BCrypt
• Users can search for stock and see its performance
• Users can buy and sell stocks
• The dashboard shows the performance of the user's own portfolio
• Users can watch stocks
• Watched stocks are listed in the dashboard sidebar

Portfolio Graph

The main feature of the app is showing a graph of the user's portfolio. It's easy enough to pull a single stock's performance from an API, but the user's portfolio combines multiple stocks together. Not only that, but the user's portfolio may change over time. Because of this it's necessary to not only be able to fetch the shares the user owns now, but also the shares the user owned at any given point of time.

This was accomplished using a transactions table. Each transaction stores a user_id, a stock symbol, the number of shares bought or sold, and the time the transaction was made. Shares are positive if the user bought shares, and negative if the user sold shares.

For example, if user 1 bought 100 shares of Apple on October 19th, 2018 at 10:34 AM, the transaction would look like this:

user_id	symbol	shares	time
1	AAPL	100	2018-10-19 10:35:26 -0400

If user 1 sold 50 shares of Facebook on October 20th, 2018 at 2:13 PM, the transaction would look like this

user_id	symbol	shares	time
1	FB	-50	2018-10-10 14:13:34 -0400

Given these transactions, we can find out how many shares the user owned of any given stock, at any given time. This is accomplished with the following query:

def shares_of(symbol, at_time: Time.now)
  transactions
    .where(symbol: symbol.upcase)
    .where("time <= ?", at_time)
    .sum(:shares)
end

(The context here is the user so transactions here refers to only that user's transactions)