var List = Immutable.List;
var Map = Immutable.Map;

function partition(size, coll) {
  var res = [];
  for (var i = 0, l = coll.size || coll.length; i < l; i += size) {
    res.push(coll.slice(i, i + size));
  }
  return Immutable.fromJS(res);
}

function identity(v) {
  return v;
}

function prop(n) {
  return function (object) {
    return object instanceof Map ? object.get(n) : object[n];
  };
}

function keep(list, pred) {
  return list.map(pred).filter(identity);
}

function repeat(n, val) {
  const res = [];
  while (n--) {
    res.push(val);
  }
  return List(res);
}

function shuffle(list) {
  return list.sort(function () { return Math.random() - 0.5; });
}

function initTiles(rows, cols, mines) {
  return shuffle(repeat(mines, Map({isMine: true, isRevealed: false})).
                 concat(repeat(rows * cols - mines, Map({isRevealed: false})))).
    map(function (tile, idx) {
      return tile.set('id', idx);
    });
}

function onWEdge(game, tile) {
  return tile % game.get('cols') === 0;
}

function onEEdge(game, tile) {
  return tile % game.get('cols') === game.get('cols') - 1;
}

function idx(game, tile) {
  if (tile < 0) { return null; }
  return game.getIn(['tiles', tile]) ? tile : null;
}

function nw(game, tile) {
  return onWEdge(game, tile) ? null : idx(game, tile - game.get('cols') - 1);
}

function n(game, tile) {
  return idx(game, tile - game.get('cols'));
}

function ne(game, tile) {
  return onEEdge(game, tile) ? null : idx(game, tile - game.get('cols') + 1);
}

function e(game, tile) {
  return onEEdge(game, tile) ? null : idx(game, tile + 1);
}

function se(game, tile) {
  return onEEdge(game, tile) ? null : idx(game, tile + game.get('cols') + 1);
}

function s(game, tile) {
  return idx(game, tile + game.get('cols'));
}

function sw(game, tile) {
  return onWEdge(game, tile) ? null : idx(game, tile + game.get('cols') - 1);
}

function w(game, tile) {
  return onWEdge(game, tile) ? null : idx(game, tile - 1);
}

const directions = [nw, n, ne, e, se, s, sw, w];

function neighbours(game, tile) {
  return keep(directions, function (dir) {
    return game.getIn(['tiles', dir(game, tile)]);
  });
}

function getMineCount(game, tile) {
  var nbs = neighbours(game, tile);
  return nbs.filter(prop('isMine')).length;
}

function isMine(game, tile) {
  return game.getIn(['tiles', tile, 'isMine']);
}

function isSafe(game) {
  const tiles = game.get('tiles');
  const mines = tiles.filter(prop('isMine'));
  return mines.filter(prop('isRevealed')) === 0 &&
    tiles.length - mines.length === tiles.filter(prop('isRevealed')).length;
}

function isGameOver(game) {
  return isSafe(game) || game.get('isDead');
}

function addThreatCount(game, tile) {
  return game.setIn(['tiles', tile, 'threatCount'], getMineCount(game, tile));
}

function revealAdjacentSafeTiles(game, tile) {
  if (isMine(game, tile)) {
    return game;
  }
  game = addThreatCount(game, tile).setIn(['tiles', tile, 'isRevealed'], true);
  if (game.getIn(['tiles', tile, 'threatCount']) === 0) {
    return keep(directions, function (dir) {
      return dir(game, tile);
    }).reduce(function (game, pos) {
      return !game.getIn(['tiles', pos, 'isRevealed']) ?
        revealAdjacentSafeTiles(game, pos) : game;
    }, game);
  }
  return game;
}

function attemptWinning(game) {
  return isSafe(game) ? game.set('isSafe', true) : game;
}

function revealMine(tile) {
  return tile.get('isMine') ? tile.set('isRevealed', true) : tile;
}

function revealMines(game) {
  return game.updateIn(['tiles'], function (tiles) {
    return tiles.map(revealMine);
  });
}

function revealTile(game, tile) {
  const updated = !game.getIn(['tiles', tile]) ?
          game : game.setIn(['tiles', tile, 'isRevealed'], true);
  return isMine(updated, tile) ?
    revealMines(updated.set('isDead', true)) :
    attemptWinning(revealAdjacentSafeTiles(updated, tile));
}

function createGame(options) {
  return Immutable.fromJS({cols: options.cols,
    rows: options.rows,
    tiles: initTiles(options.rows, options.cols, options.mines)
  });
}

function log(data) {
  document.querySelector('#output').innerHTML += JSON.stringify(data.toJS()) + '\n';
}

// Example usage
var game = createGame({cols: 3, rows: 3, mines: 2});
log(game);
var updated = revealTile(game, 0);
log(updated);