Playdate list item selector that unifies d-pad and crank input

listSelector.lua

-- listSelector.lua
-- by potch
-- MIT License

-- Playdate item selector that unifies d-pad and crank input
-- useful for menus where you want to allow either crank or arrow input.
-- First argument `count` is the number of items.
-- second argument `options` is a table with the following optional fields:
-- `initSelected`: the position of the item selected at start. default is 0.
-- `crankScale`: # of crank degrees for each  item. default is 90.
-- `orientation`: either "horizontal" or "vertical" (default)- chooses which
--                d-pad inputs change the selected item.
-- returns interface with the following methods:
-- `update()`: call this each frame to re-calculate the selected item.
-- `getSelected()`: returns the current selected item. value in the range 0..count-1
-- `setSelected(n)`: sets the current selected item.

function listSelector(count, options)
  options = options or {}
  local initSelected = options.initSelected or 0
  local selected = 0
  local crankScale = options.crankScale or 90
  local arrowPos = 0
  local crankPos = 0
  local orientation = options.orientation or "vertical"
  if orientation ~= "horizontal" then
    orientation = "vertical"
  end

  local function update()
    if orientation == "horizontal" then
      if playdate.buttonJustPressed(playdate.kButtonLeft) then
        arrowPos = arrowPos - 1
      end
      if playdate.buttonJustPressed(playdate.kButtonRight) then
        arrowPos = arrowPos + 1
      end      
    else
      if playdate.buttonJustPressed(playdate.kButtonUp) then
        arrowPos = arrowPos - 1
      end
      if playdate.buttonJustPressed(playdate.kButtonDown) then
        arrowPos = arrowPos + 1
      end
    end
    arrowPos = arrowPos % count
    crankPos = (crankPos + playdate.getCrankChange()) % 360

    selected = math.floor(initSelected + arrowPos + crankPos / crankScale) % count
  end

  return {
    update = update,
    getSelected = function() return selected end,
    setSelected = function(n)
      initSelected = n
      crankPos = 0
      arrowPos = 0
    end
  }
end