# scrabble-solver — project guide

A Go library that, given a dictionary, a board position and a rack, returns every legal
play ranked by score, and scores/validates arbitrary plays. The move generator is the
**DAWG** algorithm (Appel & Jacobson) over `github.com/iliadenisov/dafsa` — a bit-packed,
minimised DAWG with a compact ≤63-symbol alphabet. A GADDAG generator was also built,
measured by self-play, and **removed**: DAWG won for this scoring-solver workload
(~7× smaller, comparable speed) — see `RESULTS.md`.

Module `scrabble-solver`, Go 1.26. Rulesets: English Scrabble, Russian Scrabble, and
Russian **Эрудит** (`rules` package); Эрудит has no Ё tile and folds Ё→Е in its dictionary.

## Layout

- `scrabble/` — the public API: `Solver` (`NewSolver`, `GenerateMoves`, `ScorePlay`,
  `ValidatePlay`), the `Move`/`Placement`/`Word` types, the DAWG generator and scoring.
- `board/`, `rack/`, `rules/` — board grid (+ transpose), rack as per-letter counts,
  and rulesets (geometry, premium layout, tile values/counts, alphabet, bonus):
  `rules.English()`, `rules.RussianScrabble()`, `rules.Erudit()`.
- `dictdawg/`, `wordlist/` — **public** helpers: `dictdawg` (build/load/serialise DAWGs
  over dafsa), `wordlist` (encode/filter/sort/dedupe + `FoldYo`). Imported by the separate
  `scrabble-dictionary` repo that builds and publishes the DAWG set.
- `internal/` — `encoding`, `graph`, `dict` (loads the committed `dawg/en_sowpods.dawg`
  for `cmd/stress`).
- `cmd/stress`, `selfplay/` — the self-play stress harness behind `RESULTS.md`.
- `dawg/` — **committed** dictionaries: `en_sowpods.dawg`, `ru_scrabble.dawg`,
  `ru_erudit.dawg` (Ё→Е folded). The word-list sources and build pipeline live in the
  separate [`scrabble-dictionary`](https://gitea.iliadenisov.ru/developer/scrabble-dictionary)
  repo (which publishes the DAWG set as a release artifact); these committed copies are
  test fixtures.

## Build & test

    go test ./...            # all packages green; also run go vet ./... and gofmt

Scoring and move generation are validated against **real tournament games** in GCG format
(`scrabble/gcg_test.go` + `scrabble/testdata/*.gcg`, including the 700+ club): for every
move the test checks the score, the running total, and that the generator actually
produces the played move with that score — canonical play, not invented cases.

## Key facts

- Compact byte encoding: low 6 bits = alphabet index; `0x80` = blank/wildcard (board, rack
  and output bytes only — never inside the graph). The public API is byte-indexed.
- DAWG is the production generator; the GADDAG was removed after measurement.
- Detailed docs: `ALGORITHM.md` (the algorithm — single source of truth), `PLAN.md`
  (design and decisions), `RESULTS.md` (DAWG-vs-GADDAG). The RU word-list pipeline and the
  DAWG build now live in the `scrabble-dictionary` repo.