architecture.md

Architecture

This contains all the higher-level explanations of the different parts of this project. All the single-function documentation is already in the docstrings of the funcs so therefore I don't "crosspost" those here.

Structure

Chess

The chess takes care of the rating calculations of players. It can calculate new ratings of two players after a played game depending on the result.

 classDiagram
      class ChessRating{
          white
          black
      }

Here is an example use if you need to calculate new ratings for two players after having played a game.

from src.chess import ChessRating

# create a ChessRating object with the old ratings and add a game result
ratings = ChessRating(white_initial_rating, black_initial_rating)
ratings.game_result(1, 0)

# new ratings can be accessed with class properties black and white
white_new_rating = ratings.white
black_new_rating = ratings.black

ChessRating uses few helper functions to calculate the final rating.

• expected_scores()
• calculate_chess_rating(white_adjustment, black_adjustment)

These functions are called by the game_result() method.

• expected_scores() calculates the likelihood of each player winning that is needed for the final formula to calculate the ratings. The expected score is based on the rating difference.

"It then follows that for each 400 rating points of advantage over the opponent, the expected score is magnified ten times in comparison to the opponent's expected score." ~Elo rating system

• calculate_chess_rating(white_adjustment, black_adjustment) calculates the rating with the expected score. More information about the formula can be found from wikipedia. The adjustment values mentioned in the parameters are the amount the rating is wanted to change per one game. In this project at the moment the value is 24 when according to the formula $K=16$ is for masters and $K=32$ is for weaker players.

Config

The config takes care of the environment variables. It reads the .env file in the root of the project for POSTGRES_URL, TEST_POSTGRES_URL and ENV. These can be used by invoking the functions

• db_url()
• env()

The TEST_POSTGRES_URL is reserved for tests. The environment variables can be used by importing and calling the correct function.

from src import config

env = config.env()
db_url = config.db_url()

Database

The database is accessed with functions in the database folder. All database functions utilize a sqlalchemy engine to create connection to the database. This engine is created in the src/__init__.py file, but alternative engines can be provided.

Game

This folder contains all query-functions that interact with the sql table Games

• get_all_games() returns all played games
• create_game(white_id, black_id, result, rated) used to insert a new game to the database

Ratings

This folder contains all query-functions that interact with users' ratings.

• get_user_rating(user_id) returns user's rating with the user's id
• get_ratings() returns all users' ratings
• update_user_rating(user_id, new_rating) updates user's rating to the database
• update_ratings_with_game_result(white_id, black_id, result) updates both users' ratings to the database with the given game result. Used by the api when creating a new game.

User

This folder contains all query-functions that interact with users in general.

• check_username(username) queries the database for user id with the user's username and returns a boolean if the id exists.
• get_username(user_id) returns the username with the corresponding id.
• get_user_id(username) returns the user's id with the corresponding username.
• get_user_data(user_id) returns all fields (columns in sql) of an user.
• get_all_users() returns all users in the database.
• create_user(username, rating) inserts a new user with an unique username to the database.

Helper

Contains (a single) universal helper function that can be used by all of the previous modules.

• check_user_exists(user_id) checks if there is an user with the id given. The functionality is rather close with other functions in the user file and the function could be removed later due to repeated code.

API

Project uses fastapi to serve the data as an api over http for easy access. With this implementation the api can be used as a backend to a frontend app.

Paths

This is an exhaustive list of all api paths.

/api/users

• GET localhost:8000/api/users returns all users in the database with their id, username and rating.
• POST localhost:8000/api/users adds user given in the request body, ex. {"username": "<wanted_name>", "rating": }.
• GET localhost:8000/api/users/<user_id> returns same data but of one user (selected by id).
• PUT localhost:8000/api/users/<user_id> updates the user's rating with a value given in the request body. For ex. {"rating": <new_rating: int>}

/api/rating

• GET localhost:8000/api/rating returns all users in the database with their id, username and rating sorted by their rating.
• GET localhost:8000/api/rating/<user_id> returns the rating of the user with corresponding id.

/api/games

• GET localhost:8000/api/games returns all games in the database.
• POST localhost:8000/api/games creates a new game with the values given in the request body. {"white_id": <user_id>, "black_id: <ohter_user_id>, "result": <one of "1-0", "0-1" or "0.5-0.5">, "rated": <boolean (defaults to True)>}