* Merels

** Quick Start

[[https://classic.yarnpkg.com/lang/en/][Yarn]], [[https://vitejs.dev/][Vite]], [[https://www.cypress.io/][Cypress]].

#+begin_src sh
yarn
yarn start # localhost:5137
yarn cy:run

yarn build
yarn preview # localhost:4137 to check build
#+end_src

Auto-prettier with [[https://github.com/toplenboren/simple-git-hooks][simple-git-hooks]] + [[https://github.com/okonet/lint-staged][lint-staged]].

** Dependencies

*** APL

[[http://archive.vector.org.uk/art10501160][Nick Nickolov's APL]] is copied into ~lib/apl~, with a few helper functions in ~lib/aplLibraryHelpers.ts~. See ~lib/apl/license~ and ~lib/apl/readme.md~. The merels application calls the APL library and helpers from ~src/aplGameFunctions.ts~ to translate between the "grid index" and "apl index" (see diagrams below), and update the pieces on the boards.

*** XState

[[https://stately.ai/docs/xstate-v5/][XState]] manages the game's context (what is often thought of as application state), as well as the game's states (ex. Placing, Moving) and actions (ex. ~place~, ~move~). A visualization can be seen in [[https://stately.ai/docs/xstate-v5/studio][Stately Studio]] [[https://stately.ai/registry/editor/57155ae7-528b-48d2-8860-55f8719a5458?machineId=e1201a57-1ff8-4634-8466-c922d56533d9&mode=Design][here]].

*** Umbrella

Once the XState actor is created by interpreting the machine, Umbrella's [[https://github.com/thi-ng/umbrella/tree/develop/packages/rstream][rstream]] subscribes to the ongoing changes of the actor's context. [[https://github.com/thi-ng/umbrella/tree/develop/packages/rdom][rdom]] is used to compile a [[https://github.com/thi-ng/umbrella/tree/develop/packages/hiccup][hiccup]] tree, along with the streaming state, into the DOM.

** Rules

- White starts, white & black alternate turns.
- Phase 1: place one piece on the board in an open point.
- If a mill is formed (three of your pieces in a row), remove an opponent piece. An opponent's piece that is locked in a mill cannot be removed unless no others are available.
- After all pieces have been placed, phase 2 begins: move one piece to an adjacent unoccupied point. Same form-a-mill-and-remove-an-opponent-piece rule applies.
- When a player has only 3 pieces remaining, their pieces are now "flying" and can move to any open point instead of only adjacent points.
- The player reduced to two pieces or trapped with no legal moves loses.

** Board

Possible piece positions:

#+begin_src
1  0  0  1  0  0  1
0  1  0  1  0  1  0
0  0  1  1  1  0  0
1  1  1  0  1  1  1
0  0  1  1  1  0  0
0  1  0  1  0  1  0
1  0  0  1  0  0  1
#+end_src

#+begin_src
1        1        1
   1     1     1
      1  1  1
1  1  1     1  1  1
      1  1  1
   1     1     1
1        1        1
#+end_src

Grid index:

#+begin_src
0  1  2  3  4  5  6
7  8  9  10 11 12 13
14 15 16 17 18 19 20
21 22 23 24 25 26 27
28 29 30 31 32 33 34
35 36 37 38 39 40 41
42 43 44 45 46 47 48
#+end_src

Grid index with non-positions omitted:

#+begin_src
0        3        6
   8     10    12
      16 17 18
21 22 23    25 26 27
      30 31 32
   36    38    40
42       45       48
#+end_src

Apl index shown on the board:

#+begin_src
0       1        2
  9     10    11
     18 19 20
3 12 21    23 14 5
     24 25 26
  15    16    17
6       7        8
#+end_src

#+begin_src
0     1     2    -       -       -    -      -       -
  -   -   -        9     10   11        -    -     -
    - - -             -  -  -             18 19 20
3 - -   - - 5    - 12 -     - 14 -    - - 21    23 - -
    - - -             -  -  -             24 25 26
  -   -   -        15    16   17        -    -     -
6     7     8    -       -       -    -      -       -
#+end_src

Apl index:

#+begin_src
0 1 2    9 10 11   18 19 20
3   5   12    14   21    23
6 7 8   15 16 17   24 25 26
#+end_src

Apl positions using the grid indices (translation with utility.ts ~gridIndexToAplIndex~):

#+begin_src
 0  3  6    8 10 12   16 17 18
21    27   22    26   23    25
42 45 48   36 38 40   30 31 32
#+end_src