-- robot api

local api = {}

local ROBOT_DEFAULT_STATE_FILE = '/.robotstate'

local function createDefaultState()
  return {
    y = 0,
    x = 0,
    z = 0,
    -- | BACKWARD | LEFT | RIGHT
    dir = 'FORWARD'
  }
end

api.create = function(state, defaultStateFile)
  defaultStateFile = defaultStateFile or ROBOT_DEFAULT_STATE_FILE
  state = state or createDefaultState()

  local mutateRobotPosition = function(isBackward)
    local incValue = 1
    if isBackward then invValue = -1 end

    if state.dir == 'FORWARD' then
      state.z = state.z + incValue
    elseif state.dir == 'BACKWARD' then
      state.z = state.z - incValue
    elseif state.dir == 'LEFT' then
      state.x = state.x - incValue
    elseif state.dir == 'RIGHT' then
      state.x = state.x + incValue
    end
  end

  local robot = {}

  robot.forward = function()
    local ok, err = turtle.forward()

    if ok then
      mutateRobotPosition(false)
    end

    return ok, err
  end

  robot.back = function()
    local ok, err = turtle.back()

    if ok then
      mutateRobotPosition(true)
    end

    return ok, err
  end
  robot.backward = robot.back

  robot.up = function()
    local ok, err = turtle.up()

    if ok then
      state.y = state.y + 1
    end

    return ok, err
  end

  robot.down = function()
    local ok, err = turtle.down()

    if ok then
     state.y = state.y - 1
    end

    return ok, err
  end

  robot.turnLeft = function()
    local ok, err = turtle.turnLeft()

    if ok then
      if state.dir == 'FORWARD' then
        state.dir = 'LEFT'
      elseif state.dir == 'LEFT' then
        state.dir = 'BACKWARD'
      elseif state.dir == 'RIGHT' then
        state.dir = 'FORWARD'
      elseif state.dir == 'BACKWARD' then
        state.dir = 'RIGHT'
      end
    end

    return ok, err
  end

  robot.turnRight = function()
    local ok, err = turtle.turnRight()

    if ok then
      if state.dir == 'FORWARD' then
        state.dir = 'RIGHT'
      elseif state.dir == 'LEFT' then
        state.dir = 'FORWARD'
      elseif state.dir == 'RIGHT' then
        state.dir = 'BACKWARD'
      elseif state.dir == 'BACKWARD' then
        state.dir = 'LEFT'
      end
    end

    return ok, err
  end

  robot.getState = function()
    return state
  end

  robot.saveRobotState = function(stateFile)
    stateFile = stateFile or defaultStateFile
    local file = fs.open(stateFile, 'w')

    if not file then
      error('saveRobotState: cannot open ' .. stateFile ..  ' file!')
    end

    file.write(textutils.serializeJSON(state))
    file.close()

    return state
  end

  robot.loadRobotState = function(stateFile)
    stateFile = stateFile or defaultStateFile
    local file = fs.open(stateFile, 'r')

    if not file then
      return robot.saveRobotState(stateFile)
    end

    local serializedRobotState = file.readAll()
    file.close()

    local parsedResult = textutils.unserializeJSON(serializedRobotState)

    if not parsedResult then
      return robot.saveRobotState(stateFile)
    end

    return parsedResult
  end

  return robot
end

return api