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-# 021-snake-game
+# Snake Game (Day 21)
 
+The classic Snake game, built object-oriented with Python's `turtle` module. It is
+the day-21 assignment of Udemy's *100 Days of Code: The Complete Python Pro
+Bootcamp*: a snake moves across a black 600 by 600 screen by itself and is steered
+with the arrow keys; it eats food, grows, and a score is shown at the top; the game
+is over when the head passes the wall or touches its own tail. Day 21 teaches class
+inheritance (`Food` and `Scoreboard` inherit from `Turtle`) and slicing (the tail is
+`segments[1:]`).
+
+The game has no runtime dependencies. The code keeps the names of the lectures
+(`Snake`, `create_snake`, `move`, `up`, `down`, `left`, `right`, `segments`,
+`head`, `game_is_on`, `Food`, `Scoreboard`, `refresh`, `extend`, `increase_score`,
+`game_over`) so that you can compare it with your own solution.
+
+This repository continues
+[020-snake-game](https://git.tirsystem.com/Tirsvad-Udemy-100-days-of-code/020-snake-game)
+and starts from its finished game; `docs/project-plan.md` tells how the work is split.
+
+> **Status:** the project foundation is in place (environment, constants, tests,
+> source documentation, continuous integration). The game itself, `python -m
+> snake_game`, is added by the next milestone, `MIL-002`.
+
+## Requirements
+
+- Python 3.13 or newer, with `tkinter` (the `turtle` module needs it).
+- `git`, to clone the repository.
+- Optional: [Doxygen](https://www.doxygen.nl/) to build the source documentation.
+- No runtime dependencies. The development tools (`pytest`, `ruff`, `mypy`) are
+  installed into the virtual environment by the `dev` extra.
+
+## Set up
+
+Clone the repository, then create a local virtual environment `.venv` in its
+root, upgrade `pip` and install the project with its development tools. The
+`.venv` folder is ignored by git.
+
+```bash
+git clone https://git.tirsystem.com/Tirsvad-Udemy-100-days-of-code/021-snake-game.git
+cd 021-snake-game
+```
+
+### Windows powershell
+
+```powershell
+python -m venv .venv
+.\.venv\Scripts\Activate.ps1
+python -m pip install --upgrade pip
+python -m pip install -e ".[dev]"
+```
+
+If PowerShell refuses to run the activation script, allow scripts for this
+window only with `Set-ExecutionPolicy -Scope Process -ExecutionPolicy RemoteSigned`
+and activate again. Python from python.org includes `tkinter`.
+
+### Linux debian
+
+Debian 13 or newer ships Python 3.13. On older releases install Python 3.13
+separately.
+
+```bash
+sudo apt install python3 python3-venv python3-tk
+python3 -m venv .venv
+source .venv/bin/activate
+python -m pip install --upgrade pip
+python -m pip install -e ".[dev]"
+```
+
+### MacOS
+
+```bash
+brew install python@3.13 python-tk@3.13
+python3.13 -m venv .venv
+source .venv/bin/activate
+python -m pip install --upgrade pip
+python -m pip install -e ".[dev]"
+```
+
+## Run
+
+With the virtual environment active:
+
+```bash
+python -m snake_game
+```
+
+The game is not in the repository yet: `python -m snake_game` works once `MIL-002`
+is merged, and this section is then completed with the keys, the food, the score
+and the game-over rules.
+
+## Run the tests
+
+The tests need no display: they use fakes instead of real turtles.
+
+```bash
+pytest
+```
+
+The same checks that continuous integration runs:
+
+```bash
+python -m pytest
+python -m ruff check src tests
+python -m ruff format --check src tests
+python -m mypy
+```
+
+## Continuous integration
+
+`.gitea/workflows/ci.yml` runs on Gitea Actions on every push and on every pull
+request. It sets up Python 3.13, upgrades `pip`, installs `.[dev]`, then runs
+`pytest`, `ruff` (lint and format check) and `mypy`. It does not build the source
+documentation: run `doxygen Doxyfile` yourself, as the next section shows. No
+step opens a turtle window.
+
+The workflow lives in `.gitea/workflows` and not in `.github/workflows`, so
+GitHub does not run it and pushing to the GitHub mirror needs no workflow
+permission.
+
+## Build the source documentation
+
+The source is documented with Doxygen comments and the `Doxyfile` in the root.
+Install Doxygen (`winget install DimitriVanHeesch.Doxygen` on Windows,
+`sudo apt install doxygen` on Debian, `brew install doxygen` on macOS), then:
+
+```bash
+doxygen Doxyfile
+```
+
+The HTML is written to `build/doxygen/index.html`. A warning fails the build.
+
+## Project layout
+
+```text
+.
+├── .gitea/workflows/ci.yml    continuous integration (Gitea Actions)
+├── docs/                      business case, plan, milestones, reviews
+├── src/snake_game/            the game
+│   ├── __init__.py
+│   └── constants.py           every constant of the game
+├── tests/                     pytest tests
+│   └── test_constants.py
+├── Doxyfile                   source documentation settings
+├── LICENSE
+├── pyproject.toml             project configuration
+└── README.md
+```
+
+The game modules (`snake.py`, `food.py`, `scoreboard.py`, `main.py`,
+`__main__.py`) and their tests are added by `MIL-002`.
+
+## License
+
+GNU Affero General Public License v3.0 only. See [LICENSE](LICENSE).