-- sensor on the floor
-- computer above the sensor
-- monitor above the computer
-- monitor can be any size

-- make sure the whole setup is FACING north.
-- the monitor must be facing north!

os.loadAPI("ocs/apis/sensor")

local sonic = sensor.wrap("bottom")

local monitor = peripheral.wrap("top")

local centerY = 0
local centerZ = 0
local width = 0
local height = 0


-- draw a block on the screen
function drawBlock(block)

  local c = colors.white

  if block.Type == "SOLID" then
    c = colors.yellow
  elseif block.Type == "LIQUID" then
    c = colors.lightBlue
  end

  monitor.setBackgroundColor(c)
  monitor.setCursorPos(centerX - block.Position.X, centerY - block.Position.Z)
  monitor.write(" ")

end


-- forever...
while true do

  -- get the monitor width and height (in case it changes, we'll do this every loop)
  width, height = monitor.getSize()

  -- find the center point
  centerX = width / 2;
  centerY = height / 2;

  -- get all the targets available
  local targets = sonic.getTargets()

  -- clear the monitor (to black)
  monitor.setBackgroundColor(colors.black)
  monitor.clear()

  -- draw the sensor block
  drawBlock({
    Position =  {
      X = 0,
      Z = 0
    },
    Type = "SENSOR"
  });

  -- loop through all the data from the sensor
  for key, data in pairs(targets) do

    -- if the Y position is the same as the sensor
    if data.Position.Y == 0 then

      -- draw the block
      drawBlock(data)

    end

  end

  -- wait a second before doing it again
  sleep(1)

end