Checkers (terminal)

Checkers against the computer, in a terminal. The second version of the game beside web/, on the magmacrunch engine's terminal backend: a cabinet in the magmacrunch arcade and its own command, the same either way.

pipx install magmacrunch-checkers
checkers

For working on it, from this folder:

pip install -e ".[dev]"
python -m checkers

Keys

You play cyan, from the bottom, and move first. Marked squares are where the piece you picked up may go: green for a step, yellow for a jump. The cursor is bracketed as well as shaded, so it shows under NO_COLOR. The computer answers after half a second, as it does on the page.

Playing a person online (a prototype)

PLAY ONLINE on the title, or checkers --online, connects to the arcade's own multiplayer server, the one behind the page's PLAY ONLINE button, so a terminal and a browser can share a room. Type a name, then press C to create a room and read its four-letter code to your opponent, or J to join one by its code. The host plays red and moves first. Your own pieces are always cyan, and black sees the board turned round, arrows included. X then Y resigns.

pip install "magmacrunch-checkers[online]"     # websockets, only for this
checkers --online
checkers --online --server ws://127.0.0.1:8770  # a web/server.py on this machine

The server keeps the rules. This client sends a move and draws the board the server sends back, so it cannot disagree with the browser about a capture. The two are clients of one referee. checkers/online.py holds the protocol, split into Table (the server's state, with no I/O) and Connection (the WebSocket, on its own thread, polled once a frame).

tests/test_online.py runs web/server.py in-process on a free port and plays it over real sockets. It covers:

• a random game checked move for move against rules.py, double jumps included;
• out-of-turn and illegal moves, which the server ignores;
• a wrong room code;
• an opponent leaving;
• two complete terminal sessions, through the lobby to a resignation, using keys alone.

It never contacts the live server. By hand, the real page in headless Chromium has played a terminal client 40 moves deep, kings included, and the two boards still matched.

What a prototype has not done yet:

• Nobody has played the live server from a terminal, only a copy of it run locally. The default address is wss://magmacrunch.duckdns.org/checkers, which is what mpServerFor('checkers', 8770) gives the public site.
• No reconnect. A dropped connection says so, and the game is lost.
• No chat, which the browser has.
• Moves the server drops are dropped silently. It allows ten game actions per address every three seconds, so two players behind one address can go over that, and it ignores an illegal move without replying. This client draws a move only once the server takes it, so a dropped one just doesn't happen, and you play it again. (The page used to draw it anyway and then wait forever. It now resends an unanswered move, and after six seconds goes back to the server's board and says so.)

It is the browser's game, and the browser's opponent

checkers/rules.py is web/js/board.js, ai.js and game.js, ported function for function. tests/test_oracle.py holds it to them: tools/js_oracle.mjs loads those files unmodified, plays 120 games through Game's own API (half against a random player, half against a careful one who wins some), and the test replays every move through the port and requires the same board, state, turn and result after each. About 20,000 moves.

Double jumps, and no draws

• A jump may carry on. After jumping, a piece that can jump again may, over as many pieces as the chain allows; each stop along the way is also a move, so you may stop early. This is the multiplayer server's rule, and it became the single-player rule too when getMultiJumps in board.js was fixed (it looked for the piece on the square the first jump landed on, where the piece had not moved, so no second jump was ever offered). tests/test_server_parity.py holds this port to web/server.py's moves on 3,000 random positions, so single-player and online cannot drift apart again unnoticed.
• No draws. There is no move limit and no repetition rule, so two sides with kings can chase each other for ever. In the oracle's careful-player games that is most of them.

There is no score table: the page keeps none for checkers.

Needs a 66x19 terminal.

Licence

PolyForm Noncommercial 1.0.0, as the rest of this repository. See NOTICE.