local state = runtime.import("state")
local board = runtime.import("board")

local rules = {}

function rules.next_player()
  if state.current_player == "red" then
    return "blue"
  end
  return "red"
end

function rules.next_dice()
  state.dice_index = state.dice_index + 1
  if state.dice_index > #state.dice_values then
    state.dice_index = 1
  end
  return state.dice_values[state.dice_index]
end

function rules.piece_home_position(piece)
  if piece.owner == "red" then
    if piece.id == "red_1" then return board.red_home[1] end
    return board.red_home[2]
  end
  if piece.id == "blue_1" then return board.blue_home[1] end
  return board.blue_home[2]
end

function rules.can_move(piece, dice)
  if piece.status == "home" then
    return dice == 6
  end
  return true
end

function rules.movable_pieces()
  local result = {}
  for id, piece in pairs(state.pieces) do
    if piece.owner == state.current_player and rules.can_move(piece, state.dice) then
      table.insert(result, id)
    end
  end
  return result
end

function rules.all_piece_ids()
  local result = {}
  for id, _ in pairs(state.pieces) do
    table.insert(result, id)
  end
  return result
end

function rules.calculate_path(piece, dice)
  local path = {}
  if piece.status == "home" then
    local start_index = board.start[piece.owner]
    local pos = board.path[start_index]
    table.insert(path, {x = pos.x, y = pos.y})
    return path
  end

  for i = 1, dice do
    local index = piece.path_index + i
    while index > #board.path do
      index = index - #board.path
    end
    local pos = board.path[index]
    table.insert(path, {x = pos.x, y = pos.y})
  end
  return path
end

function rules.apply_move(piece, dice)
  if piece.status == "home" then
    piece.status = "path"
    piece.path_index = board.start[piece.owner]
    return
  end

  piece.path_index = piece.path_index + dice
  while piece.path_index > #board.path do
    piece.path_index = piece.path_index - #board.path
  end
end

return rules