-- robot api

local api = {}

local ROBOT_DEFAULT_STATE_FILE = '/.robotstate'

local DEFAULT_CONFIG = {
  autosave = false,
  autoload = false,
  stateFilePath = ROBOT_DEFAULT_STATE_FILE
}

local function identity(x)
  return x
end

local function getConfig(givenConfig)
  if givenConfig.onSave and not givenConfig.onLoad then
    error('robot.getConfig: custom "onSave" passed in config but no "onLoad"')
  end

  if givenConfig.onLoad and not givenConfig.onSave then
    error('robot.getConfig: custom "onLoad" passed in config but no "onSave"')
  end

  return {
    autosave = givenConfig.autosave or DEFAULT_CONFIG.autosave,
    autoload = givenConfig.autoload or DEFAULT_CONFIG.autoload,
    stateFilePath = givenConfig.stateFilePath or DEFAULT_CONFIG.stateFilePath,
    onSave = givenConfig.onSave or identity,
    onLoad = givenConfig.onLoad or identity
  }
end

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

local saveRobotState = function(stateFile, onSave, state)
  state = state or createDefaultState()
  local file = fs.open(stateFile, 'w')

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

  local transformedState = onSave(state)

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

  return transformedState
end

local loadRobotState = function(stateFile, onLoad, onSave)
  local file = fs.open(stateFile, 'r')

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

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

  local parsedResult = textutils.unserializeJSON(serializedRobotState)

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

  return onLoad(parsedResult)
end

local getAutoSave = function(config, state)
  local autoSave = function() end

  if config.autosave then
    autoSave = function()
      saveRobotState(config.stateFilePath, config.onSave, state)
    end
  end

  return autoSave
end

api.create = function(state, givenConfig)
  state = state or createDefaultState()
  local config = getConfig(givenConfig)

  if config.autoload then
    state = loadRobotState(config.stateFilePath, config.onLoad, config.onSave)
  end

  local autoSave = getAutoSave(config, state)

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

    return ok, err
  end

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

    if ok then
      mutateRobotPosition(true)
      autoSave()
    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
      autoSave()
    end

    return ok, err
  end

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

    if ok then
      state.y = state.y - 1
      autoSave()
    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

      autoSave()
    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

      autoSave()
    end

    return ok, err
  end

  robot.turnBack = function()
    local ok, errorMessage = robot.turnLeft()

    if not ok then
      error('turnBack: cannot turn left because ' .. tostring(errorMessage))
    end

    return robot.turnLeft()
  end

  robot.getState = function()
    return state
  end

  robot.saveState = function()
    return saveRobotState(config.stateFilePath, config.onSave, state)
  end

  robot.loadState = function()
    return loadRobotState(config.stateFilePath, config.onLoad, config.onSave)
  end

  return robot
end

return api