Riichi Mahjong

A complete Japanese Riichi Mahjong game built with Flutter. Play against 3 AI opponents with full rules, classic 2D top-down table view, and accurate scoring.

Features

Gameplay

• Single-player vs 3 AI — Play locally against computer opponents
• Hanchan (East + South) or Tonpuusen (East only) game modes
• All calls — Chi, Pon, open/closed/added Kan
• Riichi declaration with ippatsu tracking
• Tsumo and Ron wins with full yaku evaluation

Rules Coverage

• ~25 standard yaku — Riichi, Menzen Tsumo, Pinfu, Tanyao, Iipeiko, Yakuhai, Chanta, Sanshoku Doujun, Ittsu, Toitoi, San Ankou, Chiitoitsu, Honitsu, Chinitsu, Ryanpeikou, and more
• ~12 yakuman — Kokushi Musou, Suuankou, Daisangen, Shousuushii, Daisuushii, Tsuuiisou, Chinroutou, Ryuuiisou, Chuuren Poutou, Suukantsu, Tenhou, Chiihou
• Accurate scoring — Han + Fu calculation with standard lookup tables (Mangan, Haneman, Baiman, Sanbaiman, Yakuman)
• Dora — Regular dora, ura-dora (on riichi win), red dora (one each of 5m, 5p, 5s)
• Furiten — Permanent, temporary, and riichi furiten
• Exhaustive draw with tenpai/noten payments
• Abortive draws — Kyuushu Kyuuhai, Suufon Renda, Suucha Riichi, Suukaikan, Sanchahou
• Special wins — Rinshan Kaihou, Chankan, Haitei, Houtei
• Dealer rotation with honba counting and riichi stick collection

AI

• Shanten-reduction discard strategy
• Safety play against riichi declarers (genbutsu)
• Automatic riichi declaration when tenpai
• Call evaluation based on shanten improvement

Architecture

lib/
├── engine/          Pure Dart game engine (no Flutter imports)
│   ├── tile/        Tile model (136 tiles, 34 kinds)
│   ├── state/       Immutable game/round/player state
│   ├── win/         Win detection, shanten, tenpai, furiten
│   ├── yaku/        All yaku checks and evaluation
│   ├── scoring/     Han/fu calculation, payment tables
│   ├── game/        Game controller, round flow, action validation
│   └── ai/          AI player implementation
├── ui/              Flutter widgets
│   ├── theme/       Colors and styling
│   ├── tiles/       Tile rendering widgets
│   ├── table/       Table layout and player areas
│   ├── hud/         Action bar, scores, round info
│   ├── screens/     Title, game, game over screens
│   └── dialogs/     Round result and game over dialogs
├── providers/       Riverpod state management
└── utils/           Shared extensions

The engine layer is pure Dart with zero Flutter dependencies, making it portable for server-side use or future multiplayer.

Getting Started

flutter pub get
flutter run

Tech Stack

• Flutter — Cross-platform UI
• Riverpod — State management
• Dart — Pure game engine logic

Tile Encoding

136 physical tiles with unique IDs 0-135. Each group of 4 consecutive IDs shares a tile kind (0-33):

Kinds	Tiles
0-8	1m-9m (Man / Characters)
9-17	1p-9p (Pin / Circles)
18-26	1s-9s (Sou / Bamboo)
27-30	East, South, West, North
31-33	Haku, Hatsu, Chun

Red dora: ID 16 (5m), 52 (5p), 88 (5s).