This code is a simple backend application that provides endpoints for signing up, logging in, fetching and submitting questions, and submitting code for evaluation. The application uses the Express.js framework and handles data in memory.

This endpoint is used to register new users. The endpoint requires the following fields in the request body: email and password. The optional field isAdmin can also be set to true for admin users. Upon successful registration, a 200 status code and a message indicating success is returned. If the request is invalid or a user with the given email already exists, an error is returned.

This endpoint is used to log in existing users. The endpoint requires the following fields in the request body: email and password. Upon successful login, a 200 status code, a message indicating success, and a login token is returned. If the request is invalid or the user credentials are incorrect, an error is returned.

This endpoint is used to retrieve the list of questions. The endpoint requires a valid login token in the request body to access. Upon successful retrieval, a 200 status code and the list of questions is returned. If the request is invalid or the user is not logged in, an error is returned.

This endpoint is used to retrieve the list of code submissions. The endpoint requires a valid login token in the request body to access. Upon successful retrieval, a 200 status code and the list of code submissions is returned. If the request is invalid or the user is not logged in, an error is returned.

This endpoint is used to submit code for evaluation. The endpoint requires the following field in the request body: code. Upon successful submission, a 200 status code and a message indicating success or failure is returned. Submissions are randomly accepted or rejected for demonstration purposes.

This endpoint is used to submit new questions. The endpoint requires the following fields in the request body: token and question. The token field is a valid login token of an admin user, and the question field is an object that contains the fields title, description, and testCases. Upon successful submission, a 200 status code and a message indicating success is returned. If the request is invalid, the user is not logged in, or the user is not an admin, an error is returned.

The application uses two middleware functions, express.json() and express.urlencoded(), to parse incoming requests that have a JSON or URL-encoded body. This middleware is applied to all endpoints.

The application stores three arrays in memory: USERS, SUBMISSIONS, and QUESTIONS. The USERS array contains registered users, the SUBMISSIONS array contains submitted code, and the QUESTIONS array contains submitted questions. The application also stores a map of TOKENS to keep track of login tokens and the associated email of the user.