/// TETRIG 코어 엔진 (Dart 이식) — Phase 1.
/// 순수 로직만: Flutter/렌더/타이머 의존 없음. UI 위젯이 타이밍을 구동한다.
///
/// 좌표 규약 (명세서 §4.1):
///  - 보드 (x, y): x 오른쪽 증가, y 위쪽 증가. y=0 이 맨 아래.
///  - 킥 오프셋 (dx, dy): dy 양수 = 위쪽. 그대로 py += dy 로 적용.
///  - 회전 상태: 0=스폰, 1=CW, 2=180, 3=CCW.
///
/// (웹 레퍼런스 src/engine.js, Kotlin 이식판과 동일 알고리즘·데이터)
library;

/// 튜닝 상수 (조정 대상은 여기 한 곳).
class Config {
  static const int boardW = 10;
  static const int boardH = 40; // 내부 높이 (하단 20행만 표시)
  static const int visibleH = 20;
  static const int nextCount = 5;
  static const int lockDelayMs = 500;
  static const int maxLockResets = 15;
  static const int defaultGravityMs = 800; // Phase 1 기본 (SPRINT)
  static const int dasMs = 133;
  static const int arrMs = 10;
  static const int sdf = 20;
}

const List<String> pieceTypes = ['I', 'O', 'T', 'S', 'Z', 'J', 'L'];

/// 피스 색 (명세서 §13 v2 확정). 'G' = 가비지.
const Map<String, String> pieceColors = {
  'I': '#3EC1B6', 'O': '#F5C531', 'T': '#A76BF2', 'S': '#7FCC4C',
  'Z': '#F25C4C', 'J': '#4C7DF2', 'L': '#F2913D', 'G': '#46464F',
};

// ── 피스 스폰 셀 (박스-로컬, y 위쪽 증가) + 박스 크기 ──
class _Spawn {
  final int box;
  final List<List<int>> cells;
  const _Spawn(this.box, this.cells);
}

const Map<String, _Spawn> _spawn = {
  'I': _Spawn(4, [[0, 2], [1, 2], [2, 2], [3, 2]]),
  'O': _Spawn(2, [[0, 0], [1, 0], [0, 1], [1, 1]]),
  'T': _Spawn(3, [[0, 1], [1, 1], [2, 1], [1, 2]]),
  'S': _Spawn(3, [[0, 1], [1, 1], [1, 2], [2, 2]]),
  'Z': _Spawn(3, [[0, 2], [1, 2], [1, 1], [2, 1]]),
  'J': _Spawn(3, [[0, 2], [0, 1], [1, 1], [2, 1]]),
  'L': _Spawn(3, [[2, 2], [0, 1], [1, 1], [2, 1]]),
};

/// 스폰 시 박스 원점의 보드 위치 (px, py).
const Map<String, List<int>> _spawnPos = {
  'I': [3, 19], 'O': [4, 21], 'T': [3, 20],
  'S': [3, 20], 'Z': [3, 20], 'J': [3, 20], 'L': [3, 20],
};

/// CW 회전: 박스 b 에서 (x,y) -> (y, (b-1)-x).
List<List<int>> _rotateCW(List<List<int>> cells, int b) =>
    cells.map((c) => [c[1], (b - 1) - c[0]]).toList();

List<List<List<int>>> _buildStates(String type) {
  final sp = _spawn[type]!;
  if (type == 'O') return [sp.cells, sp.cells, sp.cells, sp.cells];
  final s0 = sp.cells;
  final s1 = _rotateCW(s0, sp.box);
  final s2 = _rotateCW(s1, sp.box);
  final s3 = _rotateCW(s2, sp.box);
  return [s0, s1, s2, s3];
}

/// STATES[type][state] = 셀 목록.
final Map<String, List<List<List<int>>>> states = {
  for (final t in pieceTypes) t: _buildStates(t),
};

// ── 킥테이블 (명세서 §4.1) ──
const Map<String, List<List<int>>> _kicksJlstz = {
  '0>1': [[0, 0], [-1, 0], [-1, 1], [0, -2], [-1, -2]],
  '1>0': [[0, 0], [1, 0], [1, -1], [0, 2], [1, 2]],
  '1>2': [[0, 0], [1, 0], [1, -1], [0, 2], [1, 2]],
  '2>1': [[0, 0], [-1, 0], [-1, 1], [0, -2], [-1, -2]],
  '2>3': [[0, 0], [1, 0], [1, 1], [0, -2], [1, -2]],
  '3>2': [[0, 0], [-1, 0], [-1, -1], [0, 2], [-1, 2]],
  '3>0': [[0, 0], [-1, 0], [-1, -1], [0, 2], [-1, 2]],
  '0>3': [[0, 0], [1, 0], [1, 1], [0, -2], [1, -2]],
  // 180° (SRS+)
  '0>2': [[0, 0], [0, 1], [1, 1], [-1, 1], [1, 0], [-1, 0]],
  '2>0': [[0, 0], [0, -1], [-1, -1], [1, -1], [-1, 0], [1, 0]],
  '1>3': [[0, 0], [1, 0], [1, 2], [1, 1], [0, 2], [0, 1]],
  '3>1': [[0, 0], [-1, 0], [-1, 2], [-1, 1], [0, 2], [0, 1]],
};

const Map<String, List<List<int>>> _kicksI = {
  '0>1': [[0, 0], [-2, 0], [1, 0], [-2, -1], [1, 2]],
  '1>0': [[0, 0], [2, 0], [-1, 0], [2, 1], [-1, -2]],
  '1>2': [[0, 0], [-1, 0], [2, 0], [-1, 2], [2, -1]],
  '2>1': [[0, 0], [1, 0], [-2, 0], [1, -2], [-2, 1]],
  '2>3': [[0, 0], [2, 0], [-1, 0], [2, 1], [-1, -2]],
  '3>2': [[0, 0], [-2, 0], [1, 0], [-2, -1], [1, 2]],
  '3>0': [[0, 0], [1, 0], [-2, 0], [1, -2], [-2, 1]],
  '0>3': [[0, 0], [-1, 0], [2, 0], [-1, 2], [2, -1]],
  // I 180°는 (0,0)만
  '0>2': [[0, 0]], '2>0': [[0, 0]], '1>3': [[0, 0]], '3>1': [[0, 0]],
};

const List<List<int>> _origin = [[0, 0]];

List<List<int>> kickTable(String type, int from, int to) {
  final key = '$from>$to';
  if (type == 'O') return _origin;
  if (type == 'I') return _kicksI[key] ?? _origin;
  return _kicksJlstz[key] ?? _origin;
}

/// 시드 가능 난수 (mulberry32).
double Function() makeRng(int seed) {
  int a = seed & 0xFFFFFFFF;
  return () {
    a = (a + 0x6D2B79F5) & 0xFFFFFFFF;
    final x = (a ^ (a >>> 15)) & 0xFFFFFFFF;
    int t = (x * ((1 | a) & 0xFFFFFFFF)) & 0xFFFFFFFF;
    final y = (t ^ (t >>> 7)) & 0xFFFFFFFF;
    final m = (y * ((61 | t) & 0xFFFFFFFF)) & 0xFFFFFFFF;
    t = ((t + m) & 0xFFFFFFFF) ^ t;
    t &= 0xFFFFFFFF;
    return ((t ^ (t >>> 14)) & 0xFFFFFFFF) / 4294967296.0;
  };
}

/// 7-bag.
class SevenBag {
  final double Function() rng;
  final List<String> _q = [];
  SevenBag([double Function()? rng]) : rng = rng ?? (() => 0.0) {
    _refill();
    _refill();
  }
  void _refill() {
    final bag = List<String>.from(pieceTypes);
    for (int i = bag.length - 1; i > 0; i--) {
      final j = (rng() * (i + 1)).floor();
      final tmp = bag[i];
      bag[i] = bag[j];
      bag[j] = tmp;
    }
    _q.addAll(bag);
  }

  String next() {
    if (_q.length <= Config.nextCount + 1) _refill();
    return _q.removeAt(0);
  }

  List<String> peek([int n = Config.nextCount]) {
    while (_q.length < n) {
      _refill();
    }
    return _q.sublist(0, n);
  }
}

// ── 보드 유틸 ──
List<List<String?>> createBoard([int w = Config.boardW, int h = Config.boardH]) =>
    List.generate(h, (_) => List<String?>.filled(w, null));

List<List<int>> pieceCells(String type, int state, int px, int py) =>
    states[type]![state].map((c) => [px + c[0], py + c[1]]).toList();

/// x 범위 밖 / 바닥 아래(y<0) / 점유 = 충돌. y >= H (버퍼 위)는 허용.
bool collides(List<List<String?>> board, List<List<int>> cells) {
  final w = board[0].length, h = board.length;
  for (final c in cells) {
    final x = c[0], y = c[1];
    if (x < 0 || x >= w || y < 0) return true;
    if (y < h && board[y][x] != null) return true;
  }
  return false;
}

/// 가득 찬 행 제거 후 위에서 빈 행 보충. 제거된 행 수 반환.
int clearLines(List<List<String?>> board) {
  final w = board[0].length, h = board.length;
  final rows = <int>[];
  for (int y = 0; y < h; y++) {
    if (board[y].every((c) => c != null)) rows.add(y);
  }
  if (rows.isEmpty) return 0;
  final rowSet = rows.toSet();
  final kept = <List<String?>>[
    for (int y = 0; y < h; y++)
      if (!rowSet.contains(y)) board[y]
  ];
  while (kept.length < h) {
    kept.add(List<String?>.filled(w, null));
  }
  for (int y = 0; y < h; y++) {
    board[y] = kept[y];
  }
  return rows.length;
}

bool isBoardEmpty(List<List<String?>> board) =>
    board.every((row) => row.every((c) => c == null));

/// T-spin 판정 (명세서 §4.2). 'none' | 'mini' | 'tspin'.
String detectTSpin(List<List<String?>> board, String type, int state, int px,
    int py, bool lastMoveRotation) {
  if (type != 'T' || !lastMoveRotation) return 'none';
  final w = board[0].length, h = board.length;
  final cx = px + 1, cy = py + 1;
  bool filled(int dx, int dy) {
    final x = cx + dx, y = cy + dy;
    if (x < 0 || x >= w || y < 0) return true; // 벽/바닥 = 채움
    if (y >= h) return false; // 버퍼 위 = 빔
    return board[y][x] != null;
  }

  final tl = filled(-1, 1), tr = filled(1, 1), bl = filled(-1, -1), br = filled(1, -1);
  final count = [tl, tr, bl, br].where((v) => v).length;
  if (count < 3) return 'none';
  late List<bool> front;
  switch (state) {
    case 0:
      front = [tl, tr];
      break;
    case 1:
      front = [tr, br];
      break;
    case 2:
      front = [bl, br];
      break;
    default:
      front = [tl, bl];
  }
  return (front[0] && front[1]) ? 'tspin' : 'mini';
}

/// B2B 대상("어려운" 클리어): Quad 또는 라인 동반 T-spin 계열.
bool isDifficult(int lines, String tspin) =>
    lines == 4 || (tspin != 'none' && lines >= 1);

class LockResult {
  final String type;
  final int lines;
  final String tspin;
  final bool allClear;
  final int combo;
  final int b2b;
  final bool difficult;
  const LockResult(this.type, this.lines, this.tspin, this.allClear, this.combo,
      this.b2b, this.difficult);
}

class Active {
  String type;
  int state;
  int x;
  int y;
  Active(this.type, this.state, this.x, this.y);
}

/// 게임 상태 (UI 가 타이밍을 구동).
class TetrigGame {
  List<List<String?>> board = createBoard();
  final SevenBag _bag;
  String? hold;
  bool holdUsed = false;
  bool over = false;
  bool lastMoveRotation = false;
  int lockResets = 0;
  int combo = -1;
  int b2b = -1;
  LockResult? lastClear;
  late Active active;

  TetrigGame({int seed = 1}) : _bag = SevenBag(makeRng(seed)) {
    spawn();
  }

  List<List<int>> cells([Active? a]) {
    a ??= active;
    return pieceCells(a.type, a.state, a.x, a.y);
  }

  bool spawn([String? type]) {
    type ??= _bag.next();
    final pos = _spawnPos[type]!;
    active = Active(type, 0, pos[0], pos[1]);
    lastMoveRotation = false;
    lockResets = 0;
    if (collides(board, cells())) {
      over = true;
      return false;
    }
    return true;
  }

  List<String> peekNext([int n = Config.nextCount]) => _bag.peek(n);

  bool canFall() {
    final c = cells().map((p) => [p[0], p[1] - 1]).toList();
    return !collides(board, c);
  }

  bool resetLockDelay() {
    if (lockResets >= Config.maxLockResets) return false;
    lockResets++;
    return true;
  }

  bool move(int dx) {
    if (over) return false;
    final c = pieceCells(active.type, active.state, active.x + dx, active.y);
    if (collides(board, c)) return false;
    active.x += dx;
    lastMoveRotation = false;
    return true;
  }

  bool softDrop() {
    if (over) return false;
    final c = pieceCells(active.type, active.state, active.x, active.y - 1);
    if (collides(board, c)) return false;
    active.y -= 1;
    lastMoveRotation = false;
    return true;
  }

  /// dir: 'cw' | 'ccw' | '180'.
  bool rotate(String dir) {
    if (over) return false;
    final a = active;
    final to = dir == 'cw'
        ? (a.state + 1) % 4
        : dir == 'ccw'
            ? (a.state + 3) % 4
            : (a.state + 2) % 4;
    for (final k in kickTable(a.type, a.state, to)) {
      final nx = a.x + k[0], ny = a.y + k[1];
      if (!collides(board, pieceCells(a.type, to, nx, ny))) {
        a.state = to;
        a.x = nx;
        a.y = ny;
        lastMoveRotation = true;
        return true;
      }
    }
    return false;
  }

  List<List<int>> ghostCells() {
    final a = active;
    int dy = 0;
    while (!collides(board, pieceCells(a.type, a.state, a.x, a.y - dy - 1))) {
      dy++;
    }
    return pieceCells(a.type, a.state, a.x, a.y - dy);
  }

  LockResult? hardDrop() {
    if (over) return null;
    final a = active;
    int d = 0;
    while (!collides(board, pieceCells(a.type, a.state, a.x, a.y - d - 1))) {
      d++;
    }
    a.y -= d;
    return lock();
  }

  bool holdSwap() {
    if (over || holdUsed) return false;
    final cur = active.type;
    if (hold == null) {
      hold = cur;
      spawn();
    } else {
      final swap = hold!;
      hold = cur;
      spawn(swap);
    }
    holdUsed = true;
    return true;
  }

  LockResult lock() {
    final a = active;
    final tspin = detectTSpin(board, a.type, a.state, a.x, a.y, lastMoveRotation);
    for (final c in cells()) {
      if (c[1] >= 0 && c[1] < board.length) board[c[1]][c[0]] = a.type;
    }
    final cleared = clearLines(board);
    final allClear = cleared > 0 && isBoardEmpty(board);
    combo = cleared > 0 ? combo + 1 : -1;
    final diff = isDifficult(cleared, tspin);
    if (cleared > 0) b2b = diff ? b2b + 1 : -1;
    final result = LockResult(a.type, cleared, tspin, allClear, combo, b2b, diff);
    lastClear = result;
    holdUsed = false;
    spawn();
    return result;
  }
}